CFX 5.7 Heating Coil Simulation Workshop 12 ANSYS CFX 5.7.

CFX 5.7

Heating Coil Simulation

Workshop 12

ANSYS CFX 5.7

Workshop

CFX - 5.7

October 1, 2004Inventory #002157

WS12-2CFX 5.7© 2004 ANSYS, Inc.

Introduction

The objective is to set up, solve and post-process a simplified CFD problem which

illustrates fluid flow and conjugate heat transfer.

The mesh resolution used in this workshop will not necessarily obtain accurate results,

but will enable the participants to work through test cases in the limited time available.

Workshop

CFX - 5.7



Workshop Outline

Analysis of a heating coil surrounded by moving fluid

Open an existing workbench project containing the Design Modeler geometry

Open CFX Mesh: Set mesh parameters and create mesh

Preprocess: set fluid domain physics, boundary conditions, initial conditions, solver

parameters

Solution: monitor residuals, review out files

Post-process

Workshop

CFX - 5.7



Heating Coil Workshop

Double click on to start the CFX5.7 launcher ...

Workshop

CFX - 5.7



Getting Started

Ensure that the Working Directory

is set

Copy the following files to your

working directory

HeatCoil.wbdb & HeatCoil.agdb

Click on the CAD2Mesh icon to

start the ANSYS Workbench

environment

Workshop

CFX - 5.7



Starting CFX Mesh

Select Open Project and

open the HeatCoil.wbdb

database.

On the project page, select

on the Design Modeler

database HeatCoil.agdb

With the Design Modeler

database selected, click

on Generate CFX Mesh.

Workshop

CFX - 5.7



Mesher Environment

Mesher window appears

as tab on the Project Page

Layout is similar to Design

Modeler with parts tree on

left

Meshing Progress from

top to bottom of Tree

Feedback from mesher

appears at bottom left

Workshop

CFX - 5.7



Mesher Environment

Perform tree

functions by right-

clicking on objects

Suppress or

unsuppress geometry

parts/bodies for

easier viewing

Mouse Usage:

to rotate (default)

+ shift to zoom

+ ctrl to translate

Workshop

CFX - 5.7



Mesher Environment

Left clicking on selected

objects in the tree allows you

to change attributes of that

object

To change the geometry view

from solid (opaque) to

transparent mode, left click on

Geometry

Set % Transparency to 67

using the slider bar or by

typing in a number.

Experiment with different

transparencies and shine

Workshop

CFX - 5.7



2D Region Creation 1

Define 2D regions for

placement of CFD

boundary conditions

Right-click on

Regions to Insert a

new Composite 2D

Region

Composite regions

can consist of one or

more surfaces

Workshop

CFX - 5.7




Create the 2D Region

“cinlet” to define the

nearest end of the

cylinder

To select a location

on the geometry,

click None under

Composite 2D Region

at bottom left

Pick the nearest end

of the cylinder

Workshop

CFX - 5.7



Save Often

Save your work often !

Save after each

significant change to

the mesh definition

Click Save As … and

save in your working

directory

For subsequent

saves, simply click

Save

Workshop

CFX - 5.7




Surfaces selected for

2D regions will

appear as green in

the viewer window

Unfinished region

definitions appear

with a red-circled

exclamation mark

Click Apply to finish

defining the new 2D

region. Marks should

disappear

Workshop

CFX - 5.7




Create 3 more 2D

regions:

coutlet for the far end

of the cylinder

hinlet for the end of

the coil nearest to the

inlet

houtlet for far end of

the coil

Workshop

CFX - 5.7




We will now create a region coil

that defines the surfaces of the

coil which will be in contact with

the fluid.

Set the display to transparent so

that the interior structures of the

geometry become visible

Left click the Geometry object in

the tree

Use the slider bar to adjust the

transparency

Workshop

CFX - 5.7




Orient the geometry so

that you are viewing the

side of the cylinder

Insert a new 2D Region “coil”

Click on None to set the Location

Box select the coil to

include all the coil

surfaces. Note that the

ends of the coil have

already been assigned to

hinlet and houtlet

Workshop

CFX - 5.7




All the selected coil surfaces

should turn green.

Holding down the control key

select the two end surfaces of

the coil (previously defined as

hinlet and houtlet) to deselect

them

Click on apply to assign the

selected surfaces

Workshop

CFX - 5.7



Mesh Controls 1

Some parameters are required to

control the density of the

tetrahedral mesh produced by

CFX-Mesh

Under Mesh in the Object Tree,

click on Default body spacing

and set to 0.12 mm.

Click on Default Face Spacing.

Set Angular resolution to 30

Degrees, Minimum and Maximum

Edge Lengths to 0.006 and 0.12

mm respectively

Workshop

CFX - 5.7



Mesh Controls 2

Click on Inflation. Set

the number of Inflated

Layers to 3. Set the

Expansion Factor to

1.7.

Inflation controls the

mesh near the walls of

the geometry (more

later …)

Click on Options. Set

Overwrite Existing GTM

file to Yes.

Workshop

CFX - 5.7



Mesh Controls 3

Click on Preview. This section of

the tree controls mesh

visualization. Set Mesh Render

Mode to Wireframe

Set the mesh Face Colour Mode to

Uniform and choose a color by

clicking on the colored bar

Next, we will select the surfaces

on which to display the finished

mesh.

Workshop

CFX - 5.7



Mesh Preview 1

Mesh Preview allows the definition

of surfaces on which to view the

mesh before exporting to CFD

Right click on Preview and Insert a

Preview Group. Label the group

“coilsurface”.

Click on None under Preview

Group to select surfaces and box

select the entire Coil

Click Apply to accept the selection

Workshop

CFX - 5.7



Mesh Preview 2

Create a second Preview

Group called “all”

Click on None to select the

defining surfaces

Box Select the entire

geometry

Click Apply to accept the

selection

Workshop

CFX - 5.7



Mesh Generation 1

CFX Mesh generates surface

meshes first, then makes the

volume mesh

To generate a surface mesh for the

coil, left-click on the coilsurface

Preview region and select Generate

This Surface Mesh

A progress bar appears at the

bottom of the window.

When the coil surface mesh is

complete, it appears in the viewer

Workshop

CFX - 5.7



Mesh Generation 2

To generate a surface mesh

for the coil, left-click on the all

Preview region and select

Generate This Surface Mesh

A progress bar appears at the

bottom of the window.

When the surface mesh is

complete, it appears in the

viewer

Workshop

CFX - 5.7



Mesh Generation 3

Next we will define the characteristics of the

mesh near the walls of the geometry

Insert Inflated Boundary “cylinder” and set

the maximum thickness to 0.12 mm

Click on None next to Location box and

select, the inner and outer cylinders. (Note:

Use the control key for multiple selections)

Click on Apply to accept

Workshop

CFX - 5.7



Mesh Generation 4

Now we will view the changes produced by

defining inflation.

Click on Preview and Set Mesh Render

Mode to Solid Face

Right-click on Preview region all and

generate the surface mesh

Mesh appears as solid and shaded. The

meshed surfaces shown represent the

interface between the inflation layer and

the tetrahedral mesh

Workshop

CFX - 5.7



Mesh Generation 5

Generate the volume mesh (this step

writes out a mesh *.gtm file)

Use the icon at the top right corner of

the meshing window,

Or right click on the Mesh object in

the tree

Volume meshing uses the constraints

created during surface meshing

A progress bar will appear at the

bottom left of the mesher window

Workshop

CFX - 5.7



Saving the Mesh file

Save the CFX Mesh

database.

Return to the Project

Page by clicking the

Project Tab

Save the project and exit

Workbench

Workshop

CFX - 5.7



Starting CFX-5 Pre

Click on CFX-Pre 5.7

The CFX-Pre Splash Screen should appear

Workshop

CFX - 5.7



Starting CFX-5 Pre

Click on Open Simulation

Set the file type to be GTM Database

Select the GTM file written out by CFX Mesh (HeatCoil.gtm)

Click on Open to start CFX Pre.

Workshop

CFX - 5.7



Preprocessing 1

Click on the Physics Tab to start defining the problem parameters

Click Create, Flow Objects and select Simulation Type.

Set the Simulation Type to Steady State.

Click Ok

Workshop

CFX - 5.7



Preprocessing 2

Next we will define the working fluid around the coil

Click Create, Flow Objects and select Domain.

Call the Domain “fluid”

Click Ok to Edit the Domain

Workshop

CFX - 5.7



Preprocessing 3

The Edit Domains Form has three sections

Under General Options set the location to B2.P3, the fluid to Water and the reference Pressure to 1 atm

Under Fluid Models, set the Heat Transfer Model to Thermal energy and the Turbulence Model to k-Epsilon

Workshop

CFX - 5.7



Preprocessing 4

Under Initialization, set the fluid Relative Pressure to 0 Pa. This is the pressure relative to the reference pressure set for the domain

Click on the checkbox next to Turbulence Eddy Dissipation to set it

Leave the initialization as automatic

Click OK to save all the Domain settings and close the form

Click on initialconditions checkboxto activate initialization

Workshop

CFX - 5.7



Preprocessing 5

Note that the Tree at the left now has a new object called fluid

This is the domain created in the last few steps

Create a second domain and call it coil

Click OK to edit the coil domain

Workshop

CFX - 5.7



Preprocessing 6

Set the Location to B1.P3. This should highlight the coil mesh in the viewer window

Set the Domain Type to Solid and select Copper from the Solids List

Under the Solid Models tab, note the the Heat Transfer Option is already set to Thermal Energy

Leave the Radiation Model as None

Workshop

CFX - 5.7



Preprocessing 7

Click on Initial Conditions to Activate initialization

Set the Temperature Option to Automatic (this is default if the Initialization is not activated)

Click OK to save the domain settings and exit the form

Workshop

CFX - 5.7



Preprocessing 8

Next we will specify a heat source in the coil location

Create a Subdomain

Label it “heatsource”

Make sure the Domain is set to coil

Click OK to accept the selection

Workshop

CFX - 5.7



Preprocessing 9

Set the location to B1.P3 (Note: the heat source will be specified for the entire volume of the coil)

Under The Sources Tab, set the Energy Sources Option to Total Source

Specify a total heat source of 50 kg m^2 s^-3 (50 W)

Click OK to save the subdomain setting and exit the form

Workshop

CFX - 5.7



Preprocessing 10

Next, we will create inlet and outlet boundary conditions to the fluid domain

Create a boundary condition called “inlet”

Make sure that the domain is set to fluid

Click OK to accept and specify the inlet conditions

Workshop

CFX - 5.7



Preprocessing 11

Edit the inlet boundary conditions

Under Basic Settings, set the Boundary Type to Inlet and the Location to cinlet

Under Boundary Details, set the Normal Speed to 0.1 m/s and the Temperature to 300 K

Click OK to save the boundary settings and exit the form

Workshop

CFX - 5.7



Preprocessing 12

Note that creating objects automatically adds them to the tree at left

To make changes to any object, simply double click to bring up the appropriate form

The inlet boundary is shown as flow arrows in the viewer

Create a second boundary condition called “outlet” for the domain fluid and click OK to edit it

Workshop

CFX - 5.7



Preprocessing 13

Edit the outlet boundary conditions

Under Basic Settings, set the Boundary Type to Outlet and the Location to coutlet

Under Boundary Details, set the Mass and Momentum Option to Average Static Pressure

Set the Relative Pressure to 0 Pa

Click OK to save the boundary settings and exit the form

Workshop

CFX - 5.7



Preprocessing 14

We are now ready to set the CFD Solver Specifications

Create a Solver Control Flow Object

This will bring up a form on which the discretization scheme and fluid/solid time scales can be set

Workshop

CFX - 5.7



Preprocessing 15

For most problems, only the Basic Settings Tab is used

The default discretization is High Resolution and is also most accurate and robust.

The fluid will have a much shorter timescale than the solid

Use a physical timescale of 0.01 s for the fluid and 5 s for the solid

Set the Conservation target for equation balances to 0.01

Click OK to save and exit the form

Workshop

CFX - 5.7



Preprocessing 16 (optional)

Click on File -- Export ccl to save the problem setup

Turn off ‘Save All Objects’ and select the Flow & Library objects.

Save the setup as coil.ccl

Saving setup files will allow the boundary conditions to be read in quickly if the grid is changed

The .ccl file is a text file that can be edited using any text editor

Workshop

CFX - 5.7



Preprocessing 17

Click on File -- Write Solver (.def) file to write a file to the solver

Save the setup as HeatCoil.def

Set the Operation to Start Solver Manager and turn ON the Report Summary Interface Connections option.

Click OK to save and exit the form

Workshop

CFX - 5.7



Preprocessing 18

Minimize the Solver Manager window.

Notice that a domain interface has been automatically created by PRE, to connect the fluid and solid domains.

Click OK on the information window.

Save the CFX Pre database and exit.

Restore the Solver Manager window.

Workshop

CFX - 5.7



Starting the Solver

On the Define Run form click on Start Run to start the solver

Workshop

CFX - 5.7



The Solver Manager Workspace

All the functions available from the icons at the top of the Solver Manager window are also available from the Workspace menu

Use the Workspace menu or the icon tool tips to see what various icons do

Note that once a workspace has been changed, this custom setting can be saved and recalled when needed

Workshop

CFX - 5.7



Viewing the residual plots

Click on the Heat Transfer tab to see the solution residuals for the solid (coil) and fluid energy equations

Workshop

CFX - 5.7



RMS Residual Diagnostics

Click on the Turbulence Quantities tab to see the solution residuals for the fluid turbulence

The text window at the right shows the solution progress and the numerical values of the solution residuals

As the solution progresses, the Rate of convergence should fall below 1.0

Values from 0.4 - 0.8 are indicative of a well chosen timestep

Workshop

CFX - 5.7



Changing the Layout

The Solver Manager can be reconfigured to view all diagnostics simultaneously.

Click on the Toggle Layout Type icon at the top of the Solver Manager Window

Click on the Arrange Workspace icon afterward to organize the extra windows that appear, or use the Workspace Menu

Workshop

CFX - 5.7



Multiple Residual Plots

Seeing all the solution residual plots simultaneously makes it easier to diagnose the trends in a run

Workshop

CFX - 5.7



Changing the plot windows

The RMS (root mean square) residuals are the default plot for the Solver Manager

To see the maximum residuals, click on the View Max Residuals icon at the top of the Solver Manager window

Workshop

CFX - 5.7



Interpreting Residual Plots

All the plots should change to show the maximum residuals

Maximum residuals will generally be a one or more orders of magnitude higher than RMS residuals

Note that the convergence rates on the right are now between 0.5 and 0.9

Flat residual plots indicate that the timestep should be increased

Workshop

CFX - 5.7



Changing individual plot formats

Right clicking on the residual plots allows the plot format to be changed

Right click on the Momentum and Mass Max residuals plot and select Monitor Properties

The Monitor Properties form for Momentum and Mass Balances should appear

Change the Window Label to Momentum and Mass Balances

Workshop

CFX - 5.7



Changing individual plot formats

The Range Settings tab allows the axes ranges of the residual plots to be changed

Click the Plot Lines tab and remove the checks from the checkboxes beside Max P-Mass, MAX U-Mom, MAX V-Mom and MAX W-Mom

Click Apply to update the plot title and remove the Max residual plotlines

Workshop

CFX - 5.7



Plotting Mass Imbalances

The Plot Lines window allows a number of diagnostic variables to be plotted. These are shown in a tree structure

Collapse the RESIDUAL tree (by clicking the minus sign) to view the entire list

Since the equation imbalances are not shown in the text window, we will plot these

Expand the IMBALANCE tree so that the required plots can be selected

Workshop

CFX - 5.7



Plotting Mass Imbalances

The IMBALANCE tree shows all equations for which an imbalance can be computed

Note that the solid energy balance is shown separately

Check off P-Mass, U-Mom, V-Mom and W-Mom under fluid

Click on Ok to update the plot settings and exit the form

Workshop

CFX - 5.7



Plotting Energy Imbalances

The Momentum and Mass window now shows all the changes

Note that the balances show a different trend from the residuals.

Create a new Monitor to plot energy imbalances. (Workspace >New Monitor)

Workshop

CFX - 5.7



The completed run

The run should stop after about 30 iterations

Diagnostics will be generated by the solver in the text window at right.

Workshop

CFX - 5.7



Final momentum balances

Maximize the view of the text window

The Boundary Flow and Total Source Term Summary shows the convergence level of the equations

Click on the Post Processing button to launch CFX-Post with the current results file.

Workshop

CFX - 5.7



Post Processing

CFX Post starts with a wireframe view of the geometry

The boundary condition and interfaces created in CFX-Pre appear in the tree to the left

Test Mouse Usage:

to rotate

to translate

to zoom

Workshop

CFX - 5.7



Creating a Locator Plane 1

Start the Post Processing session by creating a YZ locator plane.

This plane will be used to locate plots of solution variables on a cross section of the geometry

Leave the name as Plane1

Click OK to set the plane attributes

Workshop

CFX - 5.7



Creating a Locator Plane 2

Note that Plane 1 has been added to the tree on the left under User Locations and Plots

The plane attributes can be set in the form that appears under the tree.

Leave all the default settings as they are and click Apply

Workshop

CFX - 5.7



Creating a Contour Plot 1

Hide Plane 1 by clicking the checkbox to the left

Create a contour plot using the Create Menu or the icons across the top of the viewer

Leave the name as Contour 1 and click OK

This contour plot will be associated with Plane 1 to view temperature and velocity

Workshop

CFX - 5.7



Creating a Contour Plot 2

Set the attributes of the Contour plot by changing the properties in the form below the tree

Set the location to Plane 1

Change the Variable to Temperature

Change the Range to Local

Click Apply to save

Workshop

CFX - 5.7



Customizing the Legend 1

The contour plot of temperature should appear

Next, we will change the format of the legend to increase the view area

Expand the View Control object in the tree at left

The Default Legend object should be listed

Double click to edit the legend

Workshop

CFX - 5.7



Customizing the Legend 2

The Default Legend form should appear under the tree

Change the Title Mode to Variable and Location

Click the Appearance tab to change the legend text

Set the Precision to 0 and change Scientific to Fixed

Click Apply to update the legend in the viewer window

Workshop

CFX - 5.7



Coil Temperature

Note that the coil temperature changes from inlet to outlet

The coil creates turbulence, which improves heat transfer from the downstream portion of the coil

Downstream sections are therefore slightly cooler

Workshop

CFX - 5.7



Fluid Temperature 1

Change the range of the contour plot to see what is happening to the fluid temperature

Double click on Contour1 under User Locations and Plots

Change the Range from Local to User Specified

Set the Min and Max to 300 K and 400 K respectively

Click Apply to update

Workshop

CFX - 5.7



Fluid Temperature 2

The fluid gets progressively hotter as it moves along the coil

The largest temperature increases in the fluid corresponds to areas where the cooling water has stagnated

The smallest temperature increases in the fluid correspond to areas where the flow velocity is higher

Create a contour plot of fluid velocity on Plane 1

Create a tangential vector plot of fluid velocity on Plane 1.

Workshop

CFX - 5.7



Streamline Plots 1

Streamline plots give the best visualization of flow around the coil

Under User Locations and Plots, hide the Vector and Contour plots by clicking on the checkboxes

Use the Create Menu or icons to create a Streamline plot

Leave the name as Streamline 1 and click OK

Workshop

CFX - 5.7



Streamline Plots 2

In the Streamline 1 form, set Start From to inlet

Set Reduction to 2 (streamline for every second node on inlet)

Under the Color tab, set Mode to Variable

Set Variable to Temperature and Range to User Specified

Set Min and Max to 300 and 400 K as before

Workshop

CFX - 5.7



Streamline Plots 3

Click on the Symbol tab, to set the appearance of streamlines

Change the Stream Type to Tube

Set the Tube Width to 2.5

Leave the # sides as 8

Click Apply to update the plot in the viewer window

Workshop

CFX - 5.7



Streamline Plots 4

The streamline plot shows the flow path of a fluid “parcel”

Streamlines can be coloured by pressure, velocity, turbulence variables

Experiment with different types of streamline colouring

Date post:	17-Jan-2016
Category:	Documents
Upload:	duane-morgan
View:	322 times
Download:	15 times

CFX 5.7 Heating Coil Simulation Workshop 12 ANSYS CFX 5.7.

Documents