Lec STARCCM FoundationTrainingV2.0

7/23/2019 Lec STARCCM FoundationTrainingV2.0

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CD-adapco, Americas Agency Training Document CFD Basics - 1

CFD Basics - Outline

CFD Basics Introduction

CAD to Solution overview Governing Equations

Initial and Boundary Conditions Turbulence Modeling Solution of Governing Equations

Convergence Monitoring Errors in CFD Analysis Non-Dimensional Numbers Mesh Generation

Post-Processing Divergence

Ensuring Quality of a CFD analysis CD-adapco solvers

Which Solver Do I Choose for my Application


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CFD Basics

Introduction to CFD

Governing equations of fluid flow and heat transfer

Boundary Conditions

Meshing Guidelines

Solution best practices

STAR Workflow overview


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CFD Basics

What is CFD?

CFD is Computational Fluid Dynamics

Computational numerical methods

PC, workstation, cluster

Fluid

gas or liquid: Material that deforms continuously underapplication of a shear stress

Dynamics

Moving (as opposed to static)


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CFD Basics Need For CFD

Why do we need CFD?

Very few fluid mechanics problems have analytical

solutions (e.g. Laminar flow between parallel plates,laminar flow between rotating cylinders).

Most real world problems do not have a closed formsolution, and require a numerical solution.


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CFD Basics Applications where CFD is used

What are some of the areas in which CFD is used?

- Aerospace

- Automotive- Biomedical

- Building

- Civil Engineering

- Chemical Process- Environmental

- Marine

- Power Generation

- Sport Equipment

- Turbomachinery


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CFD Basics - ELEMENTS OF 3D CFD SIMULATION

conservationequations

turbulence

model

spray model

combustion

model

wall film

model

mathematicalmodel

(differential)

finite volume

discretisation

solution

algorithm

finite volumemodel

initial/boundary

conditions*

movingmesh*

CFD cpdeSTAR-CD

operating

conditions*

solutioncontrols*

RESULTScomputer

post-processing*

optimisation

CADgeometry*

*via STAR-CD or STAR-CCM+


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CFD Basics CAD to Solution Overview

1. CAD Modeler

2. CAD Importer

3. Pre-Processor

4. Solver

5. Post-Processor

CADCAD

CFDCFD

Meshing

Pre/Post

/Solution

COMPONENTFUNCTION

Geometry Building

Geometry Import and Mesh Generation

Physics and Boundary Conditions

Run Analysis

Solution Revealed to User

Discipline CFDSOFTWARE


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CFD Basics CAD to Solution

1 h

4 h

2 h

8 h

CAD Geometry

Surface Clean-up

Surface Meshing

Volume Meshing

CFD Solution

Post-processing

1 h


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CFD Basics Governing Equations Conservation Laws

The following equations are fundamental to CFD:

Conservation of Mass(continuity)

Conservation of Momentum(F=ma)

Conservation of Energy(1st Law of Thermodynamics)

In addition, depending on complexity of the problem (e.g. ifturbulent), additional transport equations are solved.


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CFD Basics Governing Equations ConstitutiveRelationships

In order to close the system of equations (laws of conservation), we need the responseof materials to external effects (i.e. surface forces, heat or mass fluxes). These aredescribed by constitutive relationships.

Stokes LawExpresses relationship between stresses and rate of deformation for fluids:

is the dynamic viscosity, P is the pressure, V is the velocity vector and I is the identitytensor.

Fouriers LawExpresses relationship between heat flux and temperature gradient

Where k is the thermal conductivity

Tk-q =

( ) IPIV.2D2rrr

= ( )[ ]T

VV2

1D

rr

+=


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CFD Basics Governing Equations Equation of State

Additional requirement for closure of governing equations.

The equation of state links density and internal energy tothe basic thermodynamic variables p (pressure) and T(temperature)

= (p,T); e = e(p,T)


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CFD Basics Governing Equations General Form

=1 mass =u,v,w momentum = e energy A is the surface area V is the volume S is the source term

V VS S

dVSAdAdudVt VSSV +=+

r

CONSERVATION:


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CFD Basics Governing Equations

/t dV + u dA = dA + S dV

Rate of change of

quantity in ControlVolume

Convective Flux

Diffusion Flux

Volumetric Source

V VS S


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CFD Basics Convection and Diffusion

u dA

CONVECTION

dA

DIFFUSION

u


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CFD Basics Initial and Boundary Conditions

To complete our mathematical model, conditions on thesolution domain boundaries have to be specified.

Conditions related to start time are called InitialConditions.

Conditions related to space are called BoundaryConditions.


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CFD Basics Boundary Conditions - Types

Dirichlet Boundary Conditionsare BCs where value ofthe dependent variable at the boundary is given (e.g. inlet

velocity of fluid).

Neumann Boundary Conditionsare BCs where gradientof the dependent variable at the boundary is specified.

It is possible that for the same boundary, Dirichlet BCs areapplied for some dependent variables, and Neumann BCs

are applied for other dependent variables.


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CFD Basics Boundary Conditions (External flow)


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CFD Basics Boundary Conditions External FlowExamples

- Flow over an aircraft or automobile

- Flow over a cylinder

- Flow around buildings


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CFD Basics Boundary Conditions (External Flow)

FreeStreamFreeStreamFreeStreamFreeStream

InletInletInletInlet OutletOutletOutletOutlet

NoslipWallNoslipWallNoslipWallNoslipWall


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CFD Basics Boundary Conditions Free Stream


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CFD Basics Boundary Conditions

Inlet Boundaries can be specified at portions of boundary where thefluid enters the solution domain, and where the velocity and scalar(temperature, species concentration, turbulence quantities)

distributions is known.

Outlet Boundaries can be specified at that portion of the solutiondomain, where flow leaves the domain. It assumes zero gradient of all

dependent variables in the flow direction.

No-Slip Wall requires prescription of velocity at the wall (e.g. zerovelocity for a stationary wall).

Free Stream boundary represents the conditions at a far-field location(i.e. At the periphery of a bubble of fluid surrounding a moving object)


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CFD Basics Boundary Conditions PressureBoundaries

Pressure boundary conditions can be specified at boundarieswhere the pressure distribution is known.

Boundary velocities are obtained from Neumann Boundary conditionfor velocity.

All dependent variables are either specified or extrapolated from theinside using zero gradient assumption. At outflow, all variables areextrapolated.

Note: The velocity at the pressure boundary where the flow comes inhas to be sub-sonic, or else the upstream velocity needs to bespecified, thus violating the Neumann boundary condition.


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Day 1 : CFD Basics Boundary Conditions - InternalFlow


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CFD Basics Boundary Conditions Internal Flow -Examples

- Flow inside ducts

- Flow inside Intake/Exhaust manifolds

- Flow inside coolant jackets

- Flow inside human blood vessels

- In-Cylinder flow of IC engines


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CFD Basics Boundary Conditions Internal Flow

InletInletInletInletOutletOutletOutletOutlet

Noslipwall(u=0)Noslipwall(u=0)Noslipwall(u=0)Noslipwall(u=0)

Adiabatic,fixedAdiabatic,fixedAdiabatic,fixedAdiabatic,fixedtemperature,ortemperature,ortemperature,ortemperature,or

fixedheatflux.fixedheatflux.fixedheatflux.fixedheatflux.


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CFD Basics Boundary Conditions - Inlets

Velocity and Scalars can be specified for an inlet.

u v

w

x

y

x

y


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CFD Basics Boundary Conditions - Outlet

n is the unit normal.

Gradients of all variablesalong flow direction is takento be zero.

Mass flow is fixed fromoverall continuity.

n

FLOW SPLITorMASS FLOW RATE


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CFD Basics - Outlet Boundary Conditions

10L

L

Zone ofZone of

Recirculation:Recirculation:Area is

inaccurate

DevelopingDeveloping

Zone:Zone:

Area has littleaccuracy

DevelopedDeveloped

Zone:Zone:

Area isaccurate

3L-8L

Flowdirection


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CFD Basics Boundary Conditions - Symmetry

n

SymmetryplaneindicatesasurfacewherenormalvelocityandnorSymmetryplaneindicatesasurfacewherenormalvelocityandnorSymmetryplaneindicatesasurfacewherenormalvelocityandnorSymmetryplaneindicatesasurfacewherenormalvelocityandnormalmalmalmal

velocitygradientsareallzero.(nindicatestheunitnormal)velocitygradientsareallzero.(nindicatestheunitnormal)velocitygradientsareallzero.(nindicatestheunitnormal)velocitygradientsareallzero.(nindicatestheunitnormal)


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CFD Basics Boundary Conditions - Periodic

AperiodicboundaryconditionreferstoapairAperiodicboundaryconditionreferstoapairAperiodicboundaryconditionreferstoapairAperiodicboundaryconditionreferstoapair

ofboundarieswheretheflowrepeatsitself.ofboundarieswheretheflowrepeatsitself.ofboundarieswheretheflowrepeatsitself.ofboundarieswheretheflowrepeatsitself.


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CFD Basics Gallery of Turbulence


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CFD Basics - Turbulence

Most of the commonly occurring flows are turbulent innature (e.g. Jet streams, combustion, boundary layers onwings of aircraft etc.). Turbulence by itself is difficult todefine, but typically has the following characteristics:

- Irregular(hence requires statistical methods)

- Diffusive(causes rapid mixing)- Large Reynolds numbers

- Three dimensional vorticity fluctuations

- Dissipative(exhibits viscous losses, and needs acontinuous supply of energy to make up for losses)


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CFD Basics - Why do we need turbulence models?

Turbulence is influenced by structures having large lengthscales, and small length scales (down to the molecular

level). To resolve all scales, the number of computationalcells is approximately (Re3), which is beyond thecomputing resources currently available.

In order to model scales smaller than the computationalcell size, turbulence models are required.


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CFD Basics - Turbulence

= = (t) dt

(t)=+ (t)

t

t1

0

High Reynolds Number u(t) = U + u(t)

t

u

u(t) U u'(t)


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CFD Basics - TURBULENCE MODELLING OPTIONS

Eddy Viscosity Models

1. Linear k- models: standard, RNG, Chen low- and high-Re variants of k-

2. V2F model3. Non-linear models: quadratic and cubic k-, several variants low- and high-Re Suga Speziale quadratic

4. Other k-: standard and SST, low- and high-Re Spalart-Almaras

ReynoldsStressTransportmodelsReynoldsStressTransportmodelsReynoldsStressTransportmodelsReynoldsStressTransportmodels

1. GibsonandLaunder

2. Craft

3. Speziale,Sarker andGatski


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CFD Basics - TURBULENCE MODELING OPTIONS

Detached Eddy Simulation

- In regions of irrotational flow, RANS is used

- In regions of detached eddies, LES is used

- Accurate for capturing eddies created by bluff bodies

- Excellent compromise between RANS and LES

Large Eddy Simulation

- Resolves the large scale eddies- Uses a sub-grid scale model for small eddies

- Requires very fine mesh

DNS

- Models all eddies from large scale to small scale- Not practical for industrial applications


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CFD Basics Inlet Turbulence

Turbulence conditions at inlet are seldom known.

If inlet is sufficiently upstream of region of interest, results

are insensitive to inlet turbulence. If inlet is close to region of interest, need to perform a

sensitivity study of inlet turbulence on results.


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CFD Basics Inlet Turbulence

Estimation of Inlet Turbulence:

Intensity of turbulence I Length of turbulence scale L

Common Practice

I 0.03 - 0.10 L Dh/10Dh is hydraulic diameterC = 0.09 L

kC

VI2

3k

3/23/4

22

=

=


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CFD Basics Turbulence Wall Treatment

Near wall treatment for turbulence models is typically chosenbased on the local non-dimensional distance of the cell centroidof the near wall cell from the wall (y+).

Whereyisthedistanceofthenearwallcellcentroid fromthewall,kis

thelocalturbulencekineticenergy,andC isaconstanthavingavalueof

0.09.

y/kCy1/21/4=+


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CFD Basics Turbulence Wall Treatment

Wall Functions

Computationally efficient

Uses logarithmic law of the wall

Requires y+ to be in the 30 200 range

Applies only to attached flows and fails in recirculating flows

Low Reynolds number approach

Computationally expensive

Integrates down to the wall and uses no-slip Requires near wall y+ less than 5

Hybrid Treatment

If y+ < 5, use Low Re approach

If y+ > 30 use Wall Function approach If 5 < y+ < 30 blend smoothly between two approaches


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CFD Basics - Estimation of Near Wall Cell Thickness

How can I get an approximate estimate of the nearwall cell thickness?

y+ = C1/4 k1/2 y /

1. Estimate k from free stream velocity and an assumedturbulence intensity (1.5 * I2 U2)

2. Substitute the required y+ value in the equation, and getan estimate of y.

Note: C=0.09


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CFD Basics - Choosing a turbulence Model

Spallart Almaras Turbulence Model

Recommended when flow is primarily attached with no separation, ormild separation. e.g. For flow over a wing or a fueslage.

k- or k- Turbulence Model

Common industrial applications, with flow separation and recirculation.

Reynolds Stress Model

When the turbulence is highly anisotropic. e.g. In a Cyclone separator.

Detached Eddy SimulationRecommended for aeroacoustic applications


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CFD Basics - Choosing a Turbulence Model


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CFD Basics - Choosing a Turbulence Model

What is our recommendation on choosing a turbulence model?

Choose the simplest model which gives acceptable engineering resultsfor your application. Typically start with the k- turbulence model. If wall

effects are important, use either the hybrid wall functions, or a lowReynolds number turbulence model, making sure to have a fine meshresolution in the wall region. If anisotropic effects are important, thenuse Reynolds Stress Models.

What factors other than a turbulence model affect accuracy of asimulation?

- Inlet values of turbulence chosen

- Size and quality of the computational grid


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CFD Basics - Discretization

In order to obtain a solution for the governing equations, themathematical model (equations and constitutive relationships) istransformed into a system of algebraic equations.

Special techniques are used for the transient, convection,diffusion and source terms in this process.

The discretized equations have the form expressed in theequation below. C denotes cell center value, and k denotesvalues in neighboring cells.

=+k

ckkcc QAA


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CFD Basics Solution of Discretized Equations

The discretized equations are coupled and non-linear. Thediscretized equations are then solved using iterative

methods.

Steady State problems typically use the SIMPLE algorithm,and transient problems either use SIMPLE or PISO

algorithms.


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CFD Basics SIMPLE Algorithm

What does SIMPLE stand for?

Semi-Implicit Method for Pressure Linked Equations

A variation of the SIMPLE algorithm is used in all CD-adapco solvers for solving the equations of fluid flow andheat transfer. (Note that STAR V3.26 uses the PISOalgorithm (Pressure Implicit Split Operator) for transientanalysis)


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CFD Basics SIMPLE Algorithm

Main Steps in SIMPLE:

1. Variables are assigned initial values at startup, and time is advanced by dt(time step).

2. With the initially guessed pressure field, the momentum equations are solved,to obtain an approximate velocity field.

3. The velocity field computed in step 2 along with the prevailing density is usedto compute new mass fluxes, and then solve the mass conservation (pressurecorrection equation). This results in corrections for velocities, density andpressure being computed and applied.

4. If applicable, additional transport equations (turbulence, energy, speciesconcentration) are solved.

5. If necessary, fluid properties (e.g. density, viscosity, Prandtl number areupdated).

6. Steps 2 through 5 constitute an outer iteration. These steps are repeated until

the residual level before the first inner iteration in each equation becomessufficiently small.

7. When the non-linear coupled equations are satisfied to a desired tolerance,time is advanced by dt, and the process is repeated.


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CFD Basics Under-relaxation

In order to promote stability of the solution method, an under-relaxation is done for all variables (other than the pressurecorrection).

In the equations below, k+1 refers to the most recent iteration ortime step, and k refers to the prior iteration or time step. Omega isthe under-relaxation factor, having a value between 0 and 1.

CFD B i C M i i


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CFD Basics Convergence Monitoring

There are two main criteria for convergence monitoring:

1. Make sure that the global residuals reduce by 2-3 orders

of magnitude (applies only if starting with a zero solutionin the domain, or a simple initial guess).

2. Monitor of engineering quantities of interest (e.g. dragcoefficient, pressure rise across a fan, pressure drop

across a heat exchanger) and make sure that they do notchange with iteration.

We need to make sure that both of the above criteria aremet before we declare our solution to be converged.

CFD B i C M it i


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CFD Basics Convergence Monitoring

ResidualsResidualsResidualsResiduals OutletTemperatureOutletTemperatureOutletTemperatureOutletTemperature

CFD B i E i CFD


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CFD Basics Errors in CFD

The following are the main types of errors in a CFD analysis:

Modeling Errors This is the difference between the actual flow and

the exact solution of the model equations (Navier stokes or RANSequations)

Discretization Errors This is the difference between the exact

solution of the differential equation, and the exact solution of thealgebraic system of equations obtained by discretizing them.

Iteration Errors This is the difference between the iterative and

exact solution of the algebraic equation systems.

CFD B i M d li g E


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CFD Basics Modeling Errors

In case of turbulent flows in complex geometries, modelingerrors are mainly due to imperfections in the turbulencemodel and to simplifications in the geometry or boundaryconditions.

How can modeling errors be estimated?

Compare solutions in which discretization and iterationerrors are negligible, with accurate experimental data, ordata obtained by more accurate models (e.g. Direct

Numerical Simulation).

CFD Basics Discretization Errors


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CFD Basics Discretization Errors

Discretization errors can be estimated by performing asystematic grid refinement and comparing the solutionsobtained on a sequence of grids. The errors areproportional to the difference in solution obtained onconsecutive grids.

CFD Basics Iterative Errors


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CFD Basics Iterative Errors

The level of iterative errors can be reliably controlled bymonitoring the residual norms (either sum of absolutevalues, or the square root of the sum of squares ofresiduals in all Control Volumes).

It is not the level of the residual itself, but the amount of

reduction compared to initial levels that is important.

CFD Basics Non Dimensional Numbers


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CFD Basics Non Dimensional Numbers

Next we briefly overview some important non-dimensionalnumbers that are used in CFD.

CFD Basics Laminar vs Turbulent


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CFD Basics Laminar vs Turbulent

Reynolds Number = Inertia Force / Viscous force

Reynolds Number = ( * U * L)/

( is the density, U is a characteristic velocity, L is a characteristiclength scale, and is the laminar viscosity)

If Reynolds number is low, flow is laminar (viscous forces dominate)

If Reynolds number is high, flow is turbulent

e.g.For pipe flows: Re > 2300 implies turbulent flow

For flat plate: Re > 5e5 implies turbulent flow

CFD Basics Compressible vs Incompressible


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CFD Basics Compressible vs Incompressible

Mach Number = speed of flow / speed of sound

If Mach Number is above 0.3, need to model ascompressible.

In low speed flows, if temperature change causes achange in density, then flow should be modeled ascompressible.

CFD Basics Natural vs Force Convection


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CFD Basics Natural vs Force Convection

Gr/Re2 = Buoyancy Force / Inertia Force

Grashof Number / Reynolds Number

2

= g *

*

T / (U

2

)

Where g is gravity, is the coefficient of volumeexpansion, T is the difference in temperature between

the surface and the free stream, U is the free streamvelocity.

If Gr/Re2 >> 1, then effect of buoyancy is important

If Gr/Re2


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CFD Basics Conduction vs Convection

Biot Number = Resistance of conduction / Resistanceof convection

Biot Number = (L/k) / (1/h)

Where L is the thickness of the body, k is the thermalconductivity, and h is the heat transfer coefficient.

If Bi >> 1, wall side resistance is large, and wall conductionshould be included

If Bi


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CFD Basics Mesh Generation

Solid Fluid

Meshing: ......of the Surface

...of the Volume

(calculation)

CAD MESHER



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The quality of a CFD solution is dependent on the quality ofthe underlying volume mesh.

Hence it is important to ensure a good quality volumemesh (which requires a good quality surface mesh)

CFD Basics - Elements of Surface Meshing


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C as cs e e ts o Su ace es g

Arbitrary Polygonquad

triangle

CFD Basics - Surface Mesh Quality


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y

LOW QUALITY HIGH QUALITYEquilateraltrianglesimplygoodqualityEquilateraltrianglesimplygoodqualityEquilateraltrianglesimplygoodqualityEquilateraltrianglesimplygoodquality.

CFD Basics - Surface Mesh Quality


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y

LOW QUALITY HIGH QUALITYIftheanglebetweenthefacenormalandthevectorjoiningadjaIftheanglebetweenthefacenormalandthevectorjoiningadjaIftheanglebetweenthefacenormalandthevectorjoiningadjaIftheanglebetweenthefacenormalandthevectorjoiningadjacentcellcentcellcentcellcentcell

centroidscentroidscentroidscentroids issmall,thetrianglequalityishigh.issmall,thetrianglequalityishigh.issmall,thetrianglequalityishigh.issmall,thetrianglequalityishigh.

CFD Basics Surface Mesh


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What are the requirements of a surface mesh, in orderto get a valid volume mesh using CD-adapco automesh tools?

- Surface is closed (water tight)

- Triangles are connected one to one

- Surface is manifold (Only two cells connected to an edge)

CFD Basics Basic Volume Mesh Elements


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ArbitraryPolyhedral

Prismatic

Pyramid

Hexahedral

Tetrahedral

Day 1 CFD Basics Volume Mesh Types


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Generally mesh generation is done either using manualtechniques (e.g. in pro-STAR) or using an auto-mesher(e.g. ammbatch)

When do we need manual meshing?

- If we need a structured mesh (for cell layer addition and

deletion)

- If we have very tight gaps (e.g. nominal cell size is 2mm,but gaps are of the order of 0.05 mm)

CFD Basics Volume Mesh Types


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What are the mesh types that can be generated by CD-adapco auto meshers?

Trim Mesh Least demanding on surface quality

Polyhedral Mesh

As automated as a tetrahedral mesher

Numerically more stable, less diffusive, and more accurate

than an equivalent tetrahedral mesh

Hybrid Mesh

Tetrahedral mesh



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Trim Mesh



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When is a trim mesh recommended?

1. If an underlying custom mesh needs to be used (e.g. forturbo machinery applications, a basic bodyfittedstructured mesh can be used as a template for creating avolume mesh with additional details.)

2. If surface quality is not good enough for a polyhedralmesh.



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Polyhedral Mesh



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When is a polyhedral mesh recommended?

1. If the quality of surface mesh is excellent.2. If process of mesh generation needs to be highly

automated (as automated as a tetrahedral mesh).



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Tetrahedral Mesh



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When is a tetrahedral mesh recommended?

The only scenario where a tetrahedral mesh isrecommended is when comparisons have to be made withlegacy tetrahedral models.

CFD Basics Advantages of Polyhedral Mesh overTetrahedral Mesh


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Mesh dependency performedby successively halvingsurface triangulation size from

20mm to 0.625mm Convergence judged from

pressure drop across jacket

CFD Basics Advantages of Polyhedral Meshover Tetrahedral Mesh


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21,87221,87221,87221,872

POLYSPOLYSPOLYSPOLYS

39,58739,58739,58739,587

TETSTETSTETSTETS

593,888593,888593,888593,888

POLYSPOLYSPOLYSPOLYS

2,322,1062,322,1062,322,1062,322,106

TETSTETSTETSTETS

CFD Basics Advantages of Polyhedral Mesh

over Tetrahedral Mesh


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ContoursofStaticContoursofStaticContoursofStaticContoursofStatic

PressurePressurePressurePressure

593,888593,888593,888593,888

POLYSPOLYSPOLYSPOLYS2,322,1062,322,1062,322,1062,322,106

TETSTETSTETSTETS

CFD Basics Advantages of Polyhedral Meshover Tetrahedral Mesh


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3

4

5

6

7

10000 100000 1000000 10000000

Number of Cells

Delta

P(

kPa)

POLYPOLYPOLYPOLYTETTETTETTET

MESHDEPENDENCYMESHDEPENDENCYMESHDEPENDENCYMESHDEPENDENCY

43.25hours43.25hours43.25hours43.25hours

10hours10hours10hours10hours1.6hours1.6hours1.6hours1.6hours

5%error

Run on a 3GhzDual Processorworkstation with2GB RAM

CFD Basics Volume Mesh Quality


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High QualityLow Quality

Diffusion

Conve

ction

CFD Basics Volume Mesh Quality


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Accuracy of Convection

- When using linear interpolation for convective fluxes, thelines connecting neighboring faces should pass throughthe center of the common face.

Accuracy of Diffusion

- Maximum accuracy of diffusive fluxes is achieved when theline connecting neighbor cell centers is orthogonal to thecell face, and also passes through the center of the

common face.

CFD Basics Grid Generation Guidelines


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General Guidelines on Grid Generation

~5 control volumes across a shear layer ~5 control volumes across a separated region

At Least 4 control volumes across a flow passage

Vary grid spacing gradually

Keep aspect ratio reasonable (Less than 1:10 wheneverpossible)

CFD Basics Grid Generation Guidelines


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InsufficientmeshInsufficientmeshInsufficientmeshInsufficientmesh

resolutiontoresolveresolutiontoresolveresolutiontoresolveresolutiontoresolve

flow.flow.flow.flow.

RefinementenablesbetterRefinementenablesbetterRefinementenablesbetterRefinementenablesbetter

resolutionoftheflow.resolutionoftheflow.resolutionoftheflow.resolutionoftheflow.

CFD Basics - Post-Processing


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Reporting

Drag / Lift Coefficients

Heat Rejection by heat exchanger

Pressure rise across a fan or compressor Pressure drop in a duct

Swirl, tumble, burn rate in an IC engine

Flow Visualization Visualization of Fields

Scalar Quantities

Vector Quantities

Streamlines

Iso-Surfaces

Animation

CFD Basics Reporting and Monitoring


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ResidualConvergenceResidualConvergenceResidualConvergenceResidualConvergence

FieldValuesFieldValuesFieldValuesFieldValuesDrag/LiftMonitoringDrag/LiftMonitoringDrag/LiftMonitoringDrag/LiftMonitoring

CenterlineCpCenterlineCpCenterlineCpCenterlineCp

CFD Basics Post Processing Scalars and Vectors


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CFD Basics Post-processing Surface Plot Coefficient of Pressure


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CFD Basics : Post-Processing Capabilities: Streamlines


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CFD Basics : Post-Processing - Isosurfaces


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TotalPressure=0,Isosurface

plot.

CFD Basics - Divergence


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What do I do if my solution diverges?

- Check physical models chosen, and boundary conditionsapplied.

- Check and make sure dimensions of the problem are setupcorrectly.

- Check and make sure mesh quality is good, and sufficient

mesh density is available for resolving the flow features.- Reduce under-relaxation factors.

- Simplify the physics

CFD Basics Ensuring Quality in CFD Analysis


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Ensuring quality of CFD analysis is an important process.The next few slides briefly outline practices used withinCD-adapco.

CFD Basics Ensuring Quality in CFD Analysis


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Main Phases:

1. Initial Project Review

2. Pre-Analysis Review

3. Final Analysis Review

CFD Basics Ensuring Quality of CFD Analysis


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Initial Project Review

- Define scope of project and cross check with customer

- Define time frame and resources for project

- Check with customer and make sure all cad data isavailable and consistent



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Pre Analysis Review

- Does the generated mesh match CAD supplied?

- Have the boundary conditions been correctly applied?

- Is the mesh density sufficient to answer objectives ofanalysis?

- Have correct material properties been defined?

- Have the correct physics models been applied?

- What post processing is required?

- Do results from running a few iterations / time steps look

reasonable?



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Final Analysis Review

- Has the solution fully converged?

- Double check, initial and boundary conditions

- Double check material properties

- Do results make physical sense? (compare with prioranalysis if possible)

- Have all the questions of the customer been answered?

CFD Basics: CD-adapco Solvers


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CD-adapco offers two CFD Solvers:

STAR-CD

- V3.2x- 20 Years of Development

- V4.x

- Rewrite of STAR V3.2x as a face based solver.

- Uses an upgraded pre/post Processor of V3.2x

STAR-CCM+

- New Integrated Meshing / Pre-Processor / Solver / Post Processor, allunder one GUI.

- Developed with novel concepts, keeping in mind of very large models.

CFD Basics Comparison of CD-adapco Solvers


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The next few slides compare the available features (formesh generation, physics, and coupling) in STAR V3.26,STAR V4.06 and STAR-CCM+ V3.02

CFD Basics Comparison of Solvers Mesh Topology


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YesYesNoArbirtraryPolyhedra

YesYesYesHex / Tet (Hybrid)

YesYesYesHexahedral / Trim

YesYesYesHexahedral

STAR-CCM+

V3.02

STAR-CD V4.06STAR-CD V3.26Mesh Type

CFD Basics Comparison of Solvers Mesh Motion


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NoYesYesCell layer addition /removal

NoYesYesConditional Cellattachment / detachment

NoYesYesGeneral Mesh Motion

YesNoNoParallel Partition across

interfaces

YesYesYesArbitrary Sliding Meshes

YesYesYesRotating ReferenceFrames

STAR-CCM+V3.02

STAR-CDV4.06

STAR-CDV3.26

Mesh Motion

CFD Basics Comparison of Solvers SolutionAlgorithms


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YesNoNoCoupled Solver

NoYesYesPISO

YesYesYesAMG

YesYesYes*SIMPLE

STAR-CCM+

V3.02

STAR-CD V4.06STAR-CD V3.26Algorithm

Note:Note:Note:Note: STARV3.26hasSIMPLEforSteadyStateOnly.

CFD Basics Comparison of Solvers Heat Transfer


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YesYesYesSolar Radiation

YesYesYesTransparent Solids

YesYesYesParticipating Media

Radiation

YesYesYesSurface ExchangeRadiation

YesYesYesConjugate Heat Transfer

STAR-CCM+V3.02

STAR-CDV4.06

STAR-CDV3.26

Heat Transfer

CFD Basics Comparison of Solvers GeneralCombustion Models

STAR-CCM+STAR-CDSTAR-CDMesh Type


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NoYesYesNOx and SOOT Models

NoYesYesHybrid (kinetic / EBU)

YesYesYesPPDF

YesYesYesIgnition

NoYesYesComplex Chemistry

YesYesYesEBU

YesYesYesCFM

YesYesYesGaseous

NoYesYesLiquid

NoYesYesSolid (e.g. Coal)V3.02V4.06V3.26

yp

CFD Basics Comparison of Solvers IC EngineCombustion Models


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NoYesYesNOx

NoYesYesSOOT

NoYesYesDiesel Ignition Models

NoYesYesEGR

NoYesYesDiesel Combustion Models

NoYesYesPartially Premixed SI

NoYesYesPremixed SI

STAR-CCM+V3.02

STAR-CDV4.06

STAR-CDV3.26

IC Engine Combustion

CFD Basics Comparison of Solvers Multi-PhaseFlows


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NoYesYesInterpenetratingPhases (Eulerian)

NoYesYesLiquid Film

Yes*YesYesDispersed Multiphase(Lagrangian)

YesYesYesCavitation

YesYesYesFree Surface

STAR-CCM+

V3.02

STAR-CD V4.06STAR-CD V3.26Feature

Note:* Currently L2P in STAR-CCM+ does not include evaporation.

CFD Basics Comparison of Solvers Multiphysics


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NoYes* (Beta)NoMelting andSolidification

NoYes* (Beta)NoElectromagnetics

NoYes* (Beta)NoStress

NoNoYesFluid StructureInteraction

YesYesYesAeroacoustics

STAR-CCM+

V3.02

STAR-CD V4.06STAR-CD V3.26Feature

CFD Basics Comparison of Solvers Coupling to OtherCodes

STAR CCMSTAR CD V4 06STAR CD V3 26CODE


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NoNoYesCHEMKIN

NoYesYesSYSNOISE andACTRAN

YesYesYes* (V3.27)DARS

NoYesYesFlowMaster

NoYesYesWave

NoYesYesGT-Power

STAR-CCM+V3.02

STAR-CD V4.06STAR-CD V3.26CODE


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Lecture STAR-CCM+ - Basics

This lecture introduces the basics of STAR-CCM+ to a new user.


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CD-adapco, Americas Agency Training Document STAR-CCM+ Basics -1

Topics Covered

1. Introduction to the client server architecture2. Unique features

3. Meshing capabilities

4. Physics Models

5. Boundary conditions and Post-Processing

6. GUI layout

7. Simulation File

8. Workflow

9. Accessing Help

Lecture - STAR-CCM+ Basics - Introduction


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STAR-CCM+ is a state-of-the-art CFD solver from CD-adapco that uses a Client Server approach.

- Java front end(light on memory) and a C++ server

ClientClientClientClient

ServerServerServerServer

Lecture - STAR-CCM+ Basics - Introduction

What is a client?


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Client is the part through which you launch a simulationand work with, typically through the STAR-CCM+

workspace.

What is a server?

Server is the part of the architecture that implementscommands in a simulation (e.g. import data, run the solver)

Lecture - STAR-CCM+ - Basics Unique Environment

What is unique about the STAR CCM+ environment?


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What is unique about the STAR-CCM+ environment? State of the art object-based GUI

Simulation database:

Fast, loaded on demand Binary Platform and Parallel independent

User Programming

Java language scripting

User defined boundary conditions, source terms and post-processing Scalable, seamless parallel operation

Client Server Architecture Operable on Windows, LINUX, and several UNIX platforms

Documentation

Via online browser Context Sensitive help with F1 Key pdf document

Lecture - STAR-CCM+ Basics Novel Concepts

1. Multi-Physics, continuum based modeling.


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2. Separation of Physics and Mesh.

3. Generalized interfaces (allow communication between

different regions in the solution domain).

Lecture - STAR-CCM+ Basics Ports Supported

STAR-CCM+ is currently ported to:


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Windows 2000 / XP (32 bit and 64 bit)

Linux 32 bit

Linux 64 bit

IBM AIX

HPUX PaRisc

HP Itanium

SGI Altix

Sun Solaris

Lecture - STAR-CCM+ Basics Mesh


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Surface Mesh Formats

.dbs pro-STAR surface database

.inp pro-STAR cell / vertex shell input file

.nas NASTRAN shell file

.pat PATRAN shell file

.stl Stereolithography file .fro FELISA front surface file

Jt JT Open Surface file

Lecture STAR-CCM+ Basics - Mesh

CAD Import Formats


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- x_t, x_b Parasolid Transmit File

- .stp, .step Standardized Exchange of Product File

- .igs, .iges International Graphics Exchange Standard File

Lecture - STAR-CCM+ - Basics - Mesh

Surface Meshing

Surface Remesher


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Surface Remesher

Surface Wrapper (automated method for closing surfaces)

Hole Filling

Rough Patcher

Edge Zipper

Edge split, swap (techniques for improving triangle quality)

Automatic repair of surface errors

Automatic / Manual extraction of feature curves

Surface Creation and Manipulation

- Creation of simple shapes

- Boolean Unite, Subtract and Intersect

Lecture STAR-CCM+ Basics - Mesh

Volume Meshing

Core Mesh


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Core Mesh

Tetrahedral mesh

Polyhedral mesh

Advanced Hexahedral (Trim) mesh

Boundary Layer mesh with prism layer

Local / global parameter setting for mesh generation

Volume sources (shapes like box, cone, cylinder, sphere fordeclaring regions in the cfd domain that need refinement)

Extruder (For extending domains, building a solid layer)

Lecture - STAR-CCM+ Basics - Mesh

Mesh Manipulation

T f l l d fl h


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Transform scale, translate, rotate, and reflect meshes

Split and combine boundaries and regions

Create, delete and fuse interfaces

Convert 3D mesh to 2D mesh

Create Cell Sets

Lecture - STAR-CCM+ - Basics - Mesh

Import of Volume Mesh

STAR


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pro-STAR

Gridgen (via .cas file)

Fluent (.cas, .msh)

Gambit

ICEM

Lecture - STAR-CCM+ Basics - Physics

Basic Models


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Space

Two-Dimensional Axisymmetric

Three-Dimensional

Time

Steady

Explicit / Implicit Unsteady

Motion

Moving Reference Frames, Rotational, Translational Frozen Rotor (multiple reference frame)


Flow and Energy


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Inviscid, Laminar and Turbulent flow regimes

Gas, Liquid, Solid, and Porous Media Total Energy Formulation

Conjugate Heat Transfer

Free-surface (VOF) Cavitation

Lagrangian Multi-phase (no evaporation)

Radiator Type Heat Exchanger

Fan Curve Adjusted Momentum Source Fan


Turbulence Models


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3 Variants of Spallart-Allmaras

7 Variants of k-

3 Variants of k-

3 Variants of Reynolds Stress Transport

Large Eddy Simulation

Detached Eddy Simulation Wall Treatment

Low y+

High y+

All y+


Radiation


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Thermal

Solar

View Factors including support for baffles and symmetric boundaries

Surface-to-Surface

Participating Media

Multiphase Flow

VOF

Cavitation

Homogeneous Boiling Model

Lagrangian Multi-Phase


Combustion


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Eddy Break Up (EBU)

Coherent Flame (CFM)

Partially-Premixed Coherent Flame (PCFM)

Presumed Probability Density Function (PPDF), adiabatic

and non-adiabatic Ignitors

Lecture - STAR-CCM+ Basics Boundary Conditions

Boundary Conditions


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Wall

No-slip, slip, specified temperature, adiabatic, specified heat flux,

thermally convective wall (Tamb and heat transfer coefficient specified)

Pressure Outlet

Specified pressure, radial equilibrium

Flow Split Outlet

Specified outlet mass flow for incompressible flows Mass Flow Inlet

Specified mass flow for compressible flows

Stagnation Inlet

Total Temperature, Total Pressure and Flow Direction

Lecture - STAR-CCM+ Basics Boundary Conditions

Non-Reflecting

Average total pressure, temperature and flow angle at inlet, static


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g p p gpressure at outlet.

Velocity Inlet

Specified velocity components, or specified magnitude anddirection

Free Stream

Specified Mach number and flow angle, static temperature andstatic pressure

Symmetry Plane

Axis

For Axisymmetric simulations

Lecture - STAR-CCM+ Basics - Numerics

Numerics in STAR-CCM+


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1. Segregated Implicit Uses AMG SIMPLE solver

2. Coupled Explicit Uses multi-stage Runge-Kutta solver

3. Coupled Implicit Uses block AMG solver

Lecture - STAR-CCM+ Basics Tools for Interacting withthe Solution

What are the tools available for interacting with thesolution?


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- User defined properties and conditions

- Local coordinate systems

- Engineering Units for Input and Output (SI, USCS, User

defined)- Full interactivity between user and solution

- Field Functions

- Reports and Monitors- Derived Parts (iso-surfaces, planes, lines, points, etc.)

Lecture - STAR-CCM+ Basics Tools For Interacting withthe Solution

- Visualization

- Mesh, scalar and vector display


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, p y

- Streamlines

- Animated streamlines and vectors- Transforms (for symmetric or periodic models)

- Annotations with text or images

- Scene Legend- Save Restore Views

- High Resolution hard copy for plots

- X-Y plotting capability

Lecture - STAR-CCM+ Basics - Terminology

STAR-CCM+ uses thefollowing terminology:

R i


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1. Regions

2. Boundaries

3. Interfaces

4. Continuum

Using the example shown onthe right, the next few slidesexplain the terminology used.

Lecture - STAR-CCM+ Basics - Region

A Region is a volume domain in space. Could be conformal (nodes

connected one to one) or non-conformal (nodes not connected one to one).


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Lecture - STAR-CCM+ Basics - Boundaries

Boundariesare the exterior surface of regions. They could be aphysical boundary (e.g. wall, inlet, outlet) or a connectionbetween different regions


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between different regions.

Lecture - STAR-CCM+ Basics - Interfaces

Interfacespermit transfer of mass and (or) energy between differentregions, or non-conformal parts of the same region.

Internal interface permits transfer of mass and energy


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Internal interface permits transfer of mass and energy.

Contact interface permits transfer of energy only.

Lecture - STAR-CCM+ Basics - Continuum

A continuumrepresents a collection of models that represent eitherthe physics or the mesh of a given region.


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Lecture - STAR-CCM+ Basics Mouse Controls

Left Rotate

Middle Zoom

Right P


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Right Pan

Shift + Left Zoom box

Lecture - STAR-CCM+ Basics Launching STAR-CCM+

In Windows:

Double click on the STAR-CCM+ Icon


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In UNIX/LINUX

Issue the command starccm+

Note: Need to make sure that the location of the starccm+

executable is defined in the path environmental variable.

Lecture - STAR-CCM+ Basics - Startup

At startup, user can either:

1. Start a new simulation.

2 Load an existing simulation


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2. Load an existing simulation(after browsing files).

3. Select a simulation fromrecently opened simulations.

Lecture - STAR-CCM+ Basics - Workspace


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Lecture STAR-CCM+ Basics - Toolbars

Toolbars in STAR-CCM+ provide easy access to commontasks executed while preparing and running a simulation.The next slide shows standard toolbars in STAR CCM+


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The next slide shows standard toolbars in STAR-CCM+.

STAR-CCM+ provides methods for controlling theappearance of toolbars.

Lecture - STAR-CCM+ Basics - Toolbars

EditToolbar

SystemToolbar


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MeshToolbar

DataToolbar

DisplayToolbar

BuildToolbar

PlotToolbar

AnimateToolbar

Lecture - STAR-CCM+ - Objects


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Lecture - STAR-CCM+ Basics - GeneralInformation

STAR-CCM+ has one file: (.sim)that contains the mesh, analysissetup and results.


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How do I save the simulation?

File -> Save

Lecture - STAR-CCM+ Basics: GeneralInformation

How do I run a simulation?

Either:

1. Solution -> Run


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2. Toolbar, pick run icon

Lecture - STAR-CCM+ Basics SettingPreferences


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Lecture - STAR-CCM+ Basics SettingPreferences


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Lecture - STAR-CCM+ - General Information Work Flow

Work Flow in STAR-CCM+

Import CAD


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Check Surface

Do manual repair if required.

Setup Meshing Models and properties

Setup Physics Models and properties

Setup Boundary Conditions Generate Mesh

Setup solver parameters and stopping criteria

Setup post-processing (optional)

Run analysis

Lecture - STAR-CCM+ - General Information - Workflow


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Lecture - STAR-CCM+ - Getting Help

If you need help, you can clickon the help button.


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The online documentation can be accessed with a browser


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Lecture STAR-CCM+ - Basics - Help

Help contains:

Model description and formulation.


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Model description and formulation.

Meshing, Solving, and Post-Processing techniques

GUI panel descriptions.

Training Guide that has several tutorials


In addition the F1 Key providescontext sensitive help.

e g If you need help on


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e.g. If you need help on

stopping criteria, then selectStopping Criteria, and hit the F1key.


The browser will display help on Stopping Criteria


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Lecture - STAR-CCM+ - Post-Processing

This section covers basic post-processing techniques instarccm+. For this case, we will use a pre-existingsimulation file (lock30.sim).


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CD-adapco, Americas Agency Training Document Post-Processing - 1

Main topics covered

1. Scene Properties

2.

Working with Views3. Creation of Iso-surface

4. Creation of tables to extract boundary values

5. XY Plotting

Lecture - STAR-CCM+ - Post-Processing Location offile

File for the exercise (lock30.sim) is located in:


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Foundation/STARCCM+/PostProcessing

Lecture - STAR-CCM+ - Post-Processing - Basics

STAR-CCM+ provides a powerful set of tools to visualizeyour solution.


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Post-Processing can be setup before, or after a CFDsolution is obtained.

Setting up of post-processing before start of the CFDsolution, offers the advantage of watching the solutiondevelop (as the CFD analysis is running in serial or parallelmode)

Lecture - Post-Processing - Basics

What is a Scene?A scene encapsulates a complete representation ofcomponents required to create an image or animation. Itincludes lights, cameras, actors, properties,


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includes lights, cameras, actors, properties,

transformations and geometry.

What are the various types of Scenes?

GeometrySceneMeshScene

ScalarScene

VectorScene

EmptyScene

Lecture - Post-Processing - Displayers

What is a displayer?

It is the basic building block of a scene. Displayers providea flexible way of controlling graphics entities in a scene.


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What are the types of displayers available?

Geometrydisplayer (controls geometric appearance)

Outlinedisplayer (controls appearance of sharp edges)Scalardisplayer (controls appearance of scalar contours)

Vectordisplayer (controls appearance of vectors)

Streamlinedisplayer (controls appearance of streamlines)


The next few slides show the layout of a typical scene inSTAR-CCM+ (taken from our lock-valve tutorial) that has ageometryand scalardisplayer.


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The properties associated with these displayers areexplained.


WhataretheAttributesofaScene?WhataretheAttributesofaScene?WhataretheAttributesofaScene?WhataretheAttributesofaScene?

-Backgroundcolor

-View(Projectionmode)


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-Update(Isplotupdatedperiteration,timestep?Whereisit

output(screenorfile))

-Axes(Istriaddisplayed?)

-Lights


Geometry displayercontrols

-Color Mode


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-Opacity

- Representation shown

-Display of outline, mesh

-Lighting

-Transforms


Properties of Outlinedisplayer are similar to thegeometry displayer, but itcontrols the appearance of


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outlines (edges) in the plot.


Properties of a contourplot are controlled bythe Scalar Displayer.


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Lecture Post-Processing - Displayers


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Lecture Post-Processing - Displayers

Main properties vector displayercontrols:

-Vector appearance and style


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-Projection mode-Opacity

-Lighting


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Lecture Post-Processing - Views

Views control the appearance of a plot in STAR-CCM+.

What are the three attributes of a view?


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- Position- Focal Point

- View up

- Projection Mode

Where can I access views?

Via Tools Folder



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What is the Projection Mode?Property that controls how the camera maps worldcoordinates to view coordinates.


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Perspective Mapping of world coordinates into viewcoordinates that roughly approximates a camera lens.

Parallel Mapping of world coordinates into viewcoordinates that preserves all parallel lines.


How can I access standard views?


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Lecture Post-Processing Iso-surfaces

Iso-surfaces can be created via the Derived Parts folder inSTAR-CCM+.

O t d i f b di l d i g m t


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Once created, iso-surfaces can be displayed in geometry,scalar and vector scenes, by including it in the parts folderof the appropriate geometry.

Exercise: Create an iso-surface of turbulent viscosity ratio= 20 for the lock valve 30 deg Configuration.

Lecture Post-Processing Iso-surface


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Lecture Post-Processing Iso-Surfaces


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Lecture Post-Processing Iso-Surface


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Lecture Post-Processing - Tables


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Lecture Post-Processing XY Plots

The next few slides outline a procedure for creation of aline probe along a plane section, and plotting pressure onthis line probe in the form of an XY plot.


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Lecture Post-Processing XY plot


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Lecture Post-Processing XY plot


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Lecture Post-Processing XY Plot


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Lecture - STAR-CCM+ - Meshing

This Lecture outlines the Mesh Generation capabilitiesthat are currently available in STAR-CCM+.

Topics1. Surface Mesh Import and Checks


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CD-adapco, Americas Agency Training Document Meshing -1

1. Surface Mesh Import and Checks

2. Surface Mesh fixing tools

3. Mesh generation Models

4. Mesh Model Parameters

5. Volume mesh generation

6. Cell Quality Metrics

Lecture - STAR-CCM+ - Meshing SurfaceImport

What are the surface mesh formats allowed by STAR-CCM+?

.dbs proSTAR/amm database file

.inp proSTAR/amm cell, vertex file

NASTRAN h ll fil


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.nas NASTRAN shell file

.pat PATRAN shell file

.stl Stereolithography file

.fro- FELISA front surface file

.jt JT Open Surface file

Lecture - STAR-CCM+ - Meshing SurfaceImport Format Summary


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Lecture STAR-CCM+ Meshing CAD Import FormatSummary


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Lecture - STAR-CCM+ - Meshing Surface Requirement

What are the requirements for a surface mesh?

Closed No free edges or mismatches

Manifold Edges shared by no more than two trianglesNon-Intersecting surface does not self intersect


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g

Good triangle quality- Nearly equal sized triangles

- Gradual variation in triangle size

- No sharp angles/ surface folds

Lecture - STAR-CCM+ - Meshing SurfaceFixing

What are the errors that can be fixed in STAR-CCM+?Holes

Mismatchesin surface (shells not connected one to one)

Double surfaces, overlapsand unwanted internalfeatures(via surface wrap)


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Pierced edges(self intersections)

Details of surface repair in STAR-CCM+ will be coveredwith a tutorial.

Lecture - STAR-CCM+ - Meshing Surface Checking

How can I check the imported surface for errors?

1. Open RepresentationsFolder.

2. Right click on Import, and select Repair Surface.


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Lecture STAR-CCM+ Meshing Surface Fixing


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Lecture STAR-CCM+ Meshing Surface Checks


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Lecture STAR-CCM+ Meshing Surface Repair

- After running surface checks, review the errors in surface.- If there are too may errors to fix, you may need to run

surface wrapper to fix errors.

- If there are a few errors in the surface, the followingprocedure is recommended:


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1. Fix non-manifold errors and free edges.

2. Run Auto-repair to fix remaining errors

Lecture STAR-CCM+ Meshing Surface Repair -Options


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Lecture STAR-CCM+ Meshing Surface Repair -Options


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Lecture STAR-CCM+ Meshing Surface Repair Selection Controls


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Lecture STAR-CCM+ Meshing Surface Repair Display Controls


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Lecture - STAR-CCM+ - Meshing - Continuum

What is a mesh continuum?A mesh continuum is a collection of models that are usedto generate a mesh.

What are the models that are available?Surface Wrapper


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pp

Remesher

Volume Mesher (tetrahedral, trimmed, polyhedral)Prism Layer Mesher

Extruder

Lecture STAR-CCM+ Meshing Surface MesherSelection

When should the surface remesherbe used?

- When a high accuracy of surface resolution is required.

- When imported surface is closed, but has poor qualitytriangulation (e.g. STL import)

When triangulation quality of import surface has to be


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- When triangulation quality of import surface has to beimproved.

- When surface wrapper has been used.

Lecture STAR-CCM+ Meshing - Surface Mesher Choice

When should the Surface Wrapperbe used?- When a high level of surface accuracy is not critical

- When imported surface contains large gaps, holes andoverlaps that cannot be fixed easily using manual repair.

- When import surface is made up of intersecting volumesthat have to be combined


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that have to be combined.

Lecture - STAR-CCM+ - Meshing ModelSelection

To select models, right click onMesh Continuum

Pick Select Meshing Models


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Lecture - STAR-CCM+ - Meshing Reference Values

The properties of the Meshingmodels can be specified viathe Reference ValuesFolder


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Reference values allowed, depend on meshing models selected.


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Reference values can be specified at 4 levels:1. Continuum

2. Region

3.

Boundary4. Interface


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Values specified at the boundary and interface levelsupercede values specified at region level, which in turnsupercedes values specified at a continuum level.

Lecture - STAR-CCM+ - Meshing Reference ValueSpecification

What is the base size?Base size refers to a characteristic size used in meshgeneration.

What is a target size?

Desired edge length


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es ed edge e gt

What do we mean by min-max size?

When proximity / curvature refinements are turned on, thisparameter controls the lower and upper bounds of the cell

size.

Lecture - STAR-CCM+ - Meshing Reference ValueSpecification

Methods for specifying surface size:

Min and Target

-Try to achieve target size in absence of refinement from

curvature / proximity-Refinements from curvature will not cause surface size togo below minimum


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go below minimum

Min and Max

- Try to maintain current triangle size

- If triangle size is larger than max, surface is refined

- If triangle size is smaller than min, surface is coarsened

Lecture - STAR-CCM+ - Meshing Reference valuespecification

Min only- Models will try and maintain current local triangle size

- When local triangle size is below minimum, it will becoarsened


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Lecture - STAR-CCM+ - Meshing Surface Wrapper -Example


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Lecture - STAR-CCM+ - Meshing Surface Wrapper -Example


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Lecture - STAR-CCM+ - Meshing - Remesher

What does the Remesher do?The remesher re-triangulates and improves the overallquality of the surface and optimizes it for generation of avolume mesh.


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Lecture - STAR-CCM+ - Meshing - Remesher

The remesher improves triangulation quality as shown below.


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Lecture - STAR-CCM+ - Meshing VolumeMeshing

What are the types of volume meshes that can begenerated by STAR-CCM+?

TetrahedralMesh

PolyhedralMesh

Trimmed Mesh(Advanced Hexahedral)


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TetrahedralMeshTetrahedralMeshTetrahedralMeshTetrahedralMesh


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PolyhedralMeshPolyhedralMeshPolyhedralMeshPolyhedralMesh


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Lecture - STAR-CCM+ Meshing VolumeMeshing


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