ANALYSIS OF GEAR PUMP USING ANSYS FLUENT
SAVANI BHAVIK B.
INTRODUCTION What is CFD?CFD: A methodology for obtaining a discrete solution of real world fluid flow problems.Discrete solution: Solution is obtained at a finite collection of space points and at discrete time levels
CFD IN A NUTSHELL
Solving the governing equation of fluid by using computational methods under various physical conditions (e.g. heat transfer, radiation, electromagnetic field, nuclear reaction…etc.) to study different phenomena encountered in the numerous branches of physical science.
CFD APPLICATIONAerospace Automotive
Chemical Processing
Polymerization reactor vessel- prediction of flow separation and residence time effects.
Marine
CFD APPLICATIONTurbomachinery Semiconductor
Industry
Civil Engineering
BUILDING BLOCKS
Geometry & grid generation
module
Problem setting module
Solution Module
Visualization Module
What to: Presume• Boundary / initial
conditions • Physical models
& what to: Neglect• Physical phenomena (i.e. heat transfer,
chemical reaction…etc)• Properties (i.e. Compressibility, real gas…
etc)
& what to : Calculate • Unknowns • Relationships between field
variable
Solution methods & algorithms • Spatial / temporal discretization
schemes • Convergence criterion • Interpolation methods
METHODOLOGY During Preprocessing
The geometry of the problem is defined The volume occupied by the fluid is divided into discrete cells.
The mesh may be uniform or non-uniform The physical modelling is defined – for eg. The equation of
motion + enthalpy + radiation + species conservation Boundary conditions are defined. This involves specifying the
fluid behavior and properties at the boundaries of the problem. For transient problems, the initial conditions are also defined
The simulation is started and the equation are solved iteratively as a steady-state or transient
Finally a postprocessor is used for the analysis and visualization of the resulting solution.
FINITE VOLUME METHOD USED IN DISCRETIZATION
The finite volume method (FVM) is a common approach used in CFD codes, as it has an advantage in memory usage and solution speed, especially for large problems, high Reynolds number turbulent flows, and source term dominated flows (like combustion).
In this method the governing partial differential equations are recast in the conservative form and then solved over a discrete control volumes and thus guarantees the conservation of fluxes through a particular control volume.
Here Q is the vector of conserved variables, F is the vector of fluxes V is the volume of the control volume element, and A is the surface area of the control volume element. The finite volume equation yields governing equations in the form:
FINITE ELEMENT METHOD The finite element method (FEM) is
used in structural analysis of solids, but is also applicable to fluids.
It is much more stable than the finite volume approach. However, it can require more memory and has slower solution than the FVM.
FINITE DIFFERENCE METHOD
The finite difference method (FDM) has historical importance and is simple to program.
It is currently only used in few specialized codes, which handle complex geometry with high accuracy and efficiency by using embedded boundaries or overlapping grids (with the solution interpolated across each grid).
PURPOSE OF PRESENTATIONGEAR PUMP A gear pump uses the
meshing of gears to pump fluid by displacement.
There are two main variation: external gear pump and internal gear pump
Gear pump are positive displacement meaning they pump a constant amount of fluid for each revolution.
THEORY OF OPERATION As the gears rotate they separate on the intake
side of the pump, creating a void and suction which is filled by fluid. The fluid is carried by the gears to the discharge side of the pump, where the meshing of the gears displaces the fluid.
Mechanical clearances are small, which prevents the fluid from leaking backwards.
Rigid design of the gears and houses allow for very high pressures and the ability to pump highly viscous fluids.
Internal Gear Pump
External Gear Pump
PROCESS IN SOLVING PROBLEM Set up a problem using the 2.5D dynamic re-
meshing model. Specify dynamic mesh modeling parameters. Specify a rigid body motion zone. Specify a deforming zone. Use prescribed motion UDF macro. Perform the calculation with residual
plotting. Post process using CFD-Post.
PROBLEM STATEMENT The current setup is an external gear
pump which uses two external spur gears.
Gears rotate at constant rate of 100 rad/s.
Fluid- oil (Density- 844 kg/m3 & Viscosity – 0.02549 kg/m-s)
Mass flow rate of fluid in and out of the pump is of interest.
PROBLEM SCHEMATIC
MESH
PROBLEM SETUP General setting- Solver
1. Type- pressure-Based2. Velocity Formulation- Absolute 3. Time – Transient
Models- Viscous - Realizable k-epsilon with standard wall function
PROBLEM SETUP Material
1. Material – oil2. Density -844 kg/m33. Viscosity – 0.02549 kg /m-s
Cell Zone conditions1. Each cell zone, select material as oil
PROBLEM SETUP Boundary conditions (Inlet and outlet
conditions are set)1. Inlet- Default Pressure 2. Outlet – Gauge Pressure (101325 Pa)
Define UDF 1. UDF macro is written for the gear sets to
rotate in opposite directions at constant rate of 100 rad/s
2. UDF is loaded and compiled
PROBLEM SETUP Mesh Motion Setup
1. Dynamic mesh Mesh Method:
Smoothing Remeshing
Remeshing Method 2.5D Parameters
Min. Length Scale – Default
Max. Length Scale – Default
Size Remeshing Interval - 1
2. Motion of gear 1 Zone – Gear 1 Type – Rigid body Motion UDF/ profile –
gear1::libudf C.G (X,Y,Z)- (0, 0.085,
0.005)3. Motion of gear 2
Zone – Gear 2 Type – Rigid body Motion UDF/ profile –
gear2::libudf C.G (X,Y,Z) – (0, -0.085,
0.005)
PROBLEM SETUP4. Motion of symmetry-1
gear_fluid Zone – sym1-gear_fluid Type – Deforming Geometry Definition – Plane Point on Plane (X ,Y, Z) – (0,
0, 0.01) Plane normal (X ,Y, Z) – (0,
0, 1) Meshing Options:
Methods: Smoothing & Remeshing
Zone Parameters Min. Length Scale – 0.0005 Max. Length Scale- 0.002 Max. Skewness – 0.8
5. Motion of symmetry-2 gear_fluid
Zone – sym1-gear_fluid Type – Deforming Geometry Definition – Plane Point on Plane (X ,Y, Z) – (0,
0, 0) Plane normal (X ,Y, Z) – (0,
0, 1) Meshing Options:
Methods: Smoothing Zone Parameters
Min. Length Scale – 0.0005 Max. Length Scale- 0.002 Max. Skewness – 0.8
PROBLEM SETUP Dynamic mesh
Time step size – 5e-6 No. of steps – 1000 Integrate
Preview control Time step size – 5e-6 No. of steps – 1000
SOLUTION Solution methods
Retain defaults Solution controls
Relaxation factor of pressure- 0.4
Momentum – 0.5 Turbulent K.E – 0.7 Turbulent dissipation
rate – 0.7 Turbulent viscosity –
0.75
Solution initialization TKE – 0.1 Gauge pressure – 101325
Pa Initialize the solution
Run Solution (Run calculation for 150 time steps) Time step size- 5e-6 No. of time steps – 3000 Max iterations / time step
– 40 Calculate
POSTPROCESSING Velocity Contour
Pressure Contour
CONCLUSION The accuracy of the computed flow rate
for a given model increases as the outlet pressure decreases.
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