ME 566 Computational Fluid Dynamics for Fluids Engineering
Contents
1. 1When NEXUS network traffic is high it is better to make the working directory on your local machine i e C Temp Ductbend 4 COMMANDS FOR DUCT BEND EXAMPLE ses i i i i i H i i i i i i Fig 2 1 Wireframe of the final sketch of the duct bend flow path Click OK to save the options and close the window e Under Create DesignModeler Geometry choose New Geometry e Check that the desired length unit is Meter is selected and click Ok in the units window that appears e Inthe Tree View select the XYPlane entity and then click the New Sketch icon to create the Sketch1 entity as a component of the XYPlane e To start the sketching select the Sketching tab e To draw in the 2D sketch of the duct flow path Figure 2 1 1 Select the Sketching tab and GEOMETRY MODEL 5 2 Click on the Z coordinate of the triad in the lower right corner of the Model View e Select the Draw toolbox and 1 With the Arc by Center tool sketch the inner wall bend shape a Place the cursor over the origin watch for the P constraint symbol and left mouse button click b Move the cursor to the left along the X axis With the C constraint visible click the left mouse button to put the start point of the arc on the X axis c Sweep the cursor clockwise until the C constraint appears at the Y axis Clic2. Apply This creates a line that follows the inner wall You can follow the steps for export along a line to export the values of the pressure total pressure and wall shear stress along this line into the data file wall csv e Choose Insert Location Point accept Name Point 1 and click OK to define a point object Use Method VW XYZ and initialize the point to 0 10 0 04 0 before clicking Apply Choose Tools Function Calculator to open the Function Calculator panel Use Function V probe Location V Point 1 Variable Y Velocity u Gradient X Note Use the m7 to get a list of all possible variables before clicking on the Calculate button The re sult with units appears in the Result box Move the point around to probe other regions in the flow e Choose File Save State and enter tutorial1 cst for the file name to save all of the information associated with the visualization and post processing objects you have created in this session You can load this state file File Load State to recreate these objects and images in later sessions This facility allows easy comparison of results between simulations e Return to the Project page and choose File Exit Select Yes to save high lighted files 2 6 Clean Up The last step is to remove unnecessary files created by CFX 5 This step is necessary to en
3. ii Select the upper end of the entrance inner wall with a left mouse button click The square end marker should be yellow iii Select the square end marker of the arc that lies on the X axis with a left mouse button click The inner entrance wall should join the inner wall bend 2Notice that the drawing instruction steps are provided in the lower left corner 6 COMMANDS FOR DUCT BEND EXAMPLE 4 To draw a line across the inflow entrance a b Use the Line tool in the Draw toolbox Place the cursor over the bottom end point of the entrance inner wall and notice that a P constraint symbol appears Left mouse button click to select this point and then move the cursor to the left and click while the H constraint symbol is visible Use the General tool in the Dimensions toolbox Select a point near the centre of the line Click and drag the cursor to the bottom to form the dimension lines Release the mouse button where the label H3 is to be placed e In the Details View change the value of H3 to 0 075 m Repeat the procedure used for the entrance inner wall to draw the exit inner wall a Draw a horizontal line in the upper right XY quadrant near the end point of the inner wall bend b Set the length of the line to 0 20 m with the General tool from the Dimensions toolbox c Join the exit inner wall to
4. Preview entity and select Generate Surface Meshes Progress is shown in the lower left corner After a short time you should see a mesh of triangles and rectangles on the surfaces of the solid e Click the Generate the volume mesh for the current problem icon on the top row of icons buttons Again progress is shown in the lower left corner When this process is completed go to the Tree View and select Errors to ensure that no errors are reported in the Details View e To close this phase select File Save As and set File name Ductbend cmdb PRE PROCESSING 9 Return to the Project page by clicking on the Ductbend Project tab at the top left corner of the window 2 3 Pre processing The first CFD phase is preprocessing In this phase the complete CFD model mesh fluids flow processes boundary conditions etc is defined and saved in a hierarchical database After opening CFX Pre the commands listed below will accomplish the following steps link the mesh file to a CFX flow project set simulation type to steady state establish a fluid with nominal properties of water specify the region through which the fluid will flow the fluid nominally water and the physical models fluid flow no heat transfer turbulence standard k model with scalable wall functions set up and attach the rough wall boundary condition the inlet boundary condition the outlet bound
5. the inner wall bend with the Coincident toolbox tool from the Constraints Draw the outer entrance wall with the Line tool Start at the outer left end point of the inflow edge look for the P constraint symbol and draw a vertical line that is coincident C with the X axis Draw the outer bend wall with the Arc by Center tool Put the centre at the origin make the start point at approximately 20 above the X axis in the upper left quadrant and make the end point coincident C with the Y axis Use the Coincident constraint tool to join the start point of the arc to the end point of the outer entrance wall Draw the outer exit wall with the Line tool Draw a horizontal H line coincident C with the Y axis above its final desired location Use the Coincident constraint tool to join this line to the end of the outer bend wall Use the Equal Length constraint tool to make the outer exit wall the same length as the inner exit wall and Draw a line from the end of the outer exit wall to the end of the inner exit wall to form the outflow edge Make sure that the end points are coincident P The sketch should now be an enclosed contour on the XYPlane e To create the three dimensional solid body 1 Switch to the Tree View by selecting the 2 Click on the Extrude Details View Check Base O
6. to define a line object and open an edit panel Use Method Two Points set Point 1 to 0 0 0 1 0 01 set Point 2 to 0 0 0 025 0 01 set the number of samples to 25 and click Apply to see the line make sure that the visibility of the contour plot etc is turned off e Choose File Export to open the Export panel where you can set File velocity csv select Line 1 from the Locations list set O Export Geometry Information on select Ctrl key plus click Velocity u and Velocity v from the Select Variable s list and click Save to write the data to a file in a comma separated format that can be imported into a conventional spreadsheet program for plotting or further analysis Notice that this file includes x y and z values e Choose Insert Location Plane accept Name Plane 1 and click OK to define a plane object and open an edit panel Use Method Y XY Plane CLEAN UP 15 with Z Ofm and click Apply turn highlighting off to avoid clutter in the view e Choose Insert Location Polyline accept Name Polyline 1 and click OK to define a polyline object In the edit panel use Method V Boundary Intersection with Boundary List V inner wall and Intersect With Vv Plane 1 and then click
7. under the o Boundary Type V o Location x and under the o Flow Regime Option O O O o Value O and then click Basic Settings tab set Normal Speed Y Inlet and E inflow surface Boundary Details tab set Mass and Momentum Option 3 Subsonic Normal Speed Vims 1 A Turbulence Option V 0 05 Eddy Length Scale Right mouse click front surface and select Insert Boundary to open the Right mouse click inflow surface and select Insert Boundary to open the gt Intensity and Length Scale 9 0 0075 v m 9 Ok to close the panel and create the new boundary object e Right mouse click inner wall and select Insert Boundary to open the bound ary details panel In this panel x under the o Boundary Type V o Location Y x and under the O Basic Settings tab set Wall and inner wall Boundary Details tab set o Wall Influence on Flow Option Y No Slip Wall Velocity off o Wall Roughness Option Y Rough Wall 0 0001 W m o Roughness Height and then click k Ok to close the panel e Right mouse click outer wall and select Insert Boundary to open the bound ary det
8. D EXAMPLE x Option V x Density expand Transport Properties and then click Value 2 1000 Ok V kgm 3 9 Dynamic Viscosity on and Dynamic Viscosity 0 001 Pa S e In the Outline view right mouse click the Simulation Type entity and select Edit to open the Simulation Type panel Check that Option Y is set and then click e In the Outline view double left mouse click the Default Domain entity to open the Domain Default Domain panel which will have several tabbed sub panels On the Ok General Options o Location V green in the Viewer window o Domain Motion Option YV Domain Type V Fluids List V Particle Tracking off Reference Pressure Buoyancy Option B28 sub panel set Fluid Domain Water nominal 1 y atm z Non Buoyant and Stationary on the Fluid M odels sub panel o Heat Transfer Model Option Y o Turbulence Model Option YV o Turbulent Wall Functions Option V o Reaction or Combustion Model Option Y o Thermal Radiation Model Option Y on the Initialization off and then click Ok sub panel ensure that set None k Epsilon
9. ME 566 Computational Fluid Dynamics for Fluids Engineering Design ANSYS CFX STUDENT USER MANUAL Version 11 Upgrade Gordon D Stubley Department of Mechanical Engineering University of Waterloo G D Stubley 2007 2007 Contents 1 Introduction 2 Commands for Duct Bend Example 2 1 2 2 2 3 2 4 2 5 2 6 Geometry Model Mesh Generation Pre processing Solver Manager Post processing Clean Up 1 Introduction In these notes the basic steps in a CFD solution will be illustrated using the professional software ANSYS Workbench Version 11 Upgradewhich includes the components DesignModeler Meshing and Advanced CFD all trademarks of ANSYS These notes are designed for students who have had some exposure to ANSYS Workbench 10 There are four significant differences between Versions 10 and 11 Meshing Besides the CFX Mesh tool Version 11 provides a range of meshing tools for generating hexahedral and tetrahedral meshes The emphasis in these notes is on tetrahedral meshing with inflation as implemented in CFX Mesh By setting the ANSYS Workbench options the default meshing tool is set to CFX Mesh CFX GUI Mouse The CFX Pre and Post GUI s and mouse actions have been changed to make them compatible with the actions used in Design Modeler and CFX Mesh In particular the rotation actions in CFX Pre and CFX Post are now context sensitive The coordinate system triad in CFX Pre and Post remains inactive To set standard di
10. Scalable ba None None 9 to close the panel Steady State and notice that the geometry is highlighted in and Domain Initialization is e To prepare for implementing the boundary conditions expand the expand Ductbend cmdb mesh model to see the Principal 2D Regions of the ge ometry Check that all 2D regions are highlighted e Right mouse click back surface and select Insert Boundary to open the boundary details panel In this panel under the o Boundary Type YV Basic Settings o Location V and then click Ok tab set Symmetry and back surface to close the panel and create the new boundary object PRE PROCESSING 11 Notice that perpendicular red arrows appear on the back surface in the Viewer window and the boundary object is listed in the Default Domain entity Clicking on back surface object in the Default Domain database causes the back surface mesh to be outlined with green in the Viewer window A double mouse click will re open the boundary details panel boundary details panel In this panel x under the o Boundary Type Y o Location V and then click Basic Settings tab set Symmetry and front surface Ok to close the panel boundary details panel In this panel x
11. ails panel In this panel 12 COMMANDS FOR DUCT BEND EXAMPLE x under the Basic Settings tab s o Boundary Type VY Wall an o Location Y outer wall et d x and under the Boundary Detail s tab set o Wall Influence on Flow Option Y 0 Wall Velocity off No Slip 9 o Wall Roughness Option Y Rough Wall 7 0 0001 o Roughness Height Yim p and then click Ok to close the panel e Right mouse click outflow surface and select Insert Boundary to open the boundary details panel In this panel tab s under the Basic Settings Outlet outflow surface o Boundary Type YV d o Location V et and and under the Boundary Detail tab set S o Flow Regime Option Subsonic pi o Mass and Momentum Option Average Static Pressure d o Relative Pressure 0 v Pa ps and then click Ok to close the panel e Right mouse click on Solver Control entity and select Edit to open the Details of Solver Control panel Under the Basic Settings x Advection Scheme Option V Upwind Timescale Control v Physical Timescale 0 04 x Physical Timescale Vis a flui
12. ary condition and the symmetry boundary con ditions set the global initial conditions set the solver controls for discretization scheme time step type and conver gence criteria set the output variable list and write the complete CFD model definition to a def file To accomplish these steps execute the following commands Highlight the Mesh Model Ductbend cmdb in the Project page and select Create CFD Simulation with Mesh under Advanced CFD Tasks After a short wait the CFX Pre page will open This page is similar to the CFX Post page There are three main areas the menus and command buttons at the top the Viewer window at the right and the Outline view of the database trees at the left Right mouse click on the Materials entity in the Outline tree and select Insert Material to create a new material with the required water properties In the Insert Material panel fill in Name Water nominal and click OK to open a panel with two tabs Click the Basic Settings tab and set x Option V Pure Substance x Material Group Y Constant Property Liquids x O Material Description off x O Thermodynamic State on and Thermodynamic State Y Liquid Click the Material Properties tab and set Option Y General Material in the Equation of State area set 10 COMMANDS FOR DUCT BEN
13. bject Modeling tab bi button to create the Extrudel feature Sketch1 In the MESH GENERATION 7 Select Operation V Add Material Select Direction Vector Y None Normal Set FD1 Depth gt 0 0 02 Select As Thin Surface Y No and Select Merge Topology Y Yes 3 Click on the Generate button to create a Solid Use the isometric view in the Model View to check that you have a three dimensional solid grey body Choose File Save As and set File name Ductbend agdb in the Save As window Click Save to close window Return to the Project page by clicking on the Ductbend Project tab at the top left corner of the window 2 2 Mesh Generation The second phase uses CFX Mesh The commands listed below will generate a discrete mesh in the flow domain name the surfaces faces of the solid geometry to ease boundary condition specification specify the properties of the mesh in the interior of the flow domain and close to solid walls preview the surface mesh to check for anomalies and create the geometry file with volume mesh information Choose the New Mesh DesignModeler Tasks Notice the three primary areas Graphics View Tree View and Details View in the CFX Mesh window The surfaces faces of the solid are labeled as regions f
14. d e Lastly create a region called back surface Notice that when this region is created the Default 2D Region disappears e In the Tree View select Options to see the mesh options in the Details View Set Surface Meshing Y Advancing Front Set Meshing Strategy V Extruded 2D Mesh Set 2D Extrusion Option Y Full and Set Number of Layers V 1 3 e In the Tree View expand the Spacing entity e Select the Default Body Spacing entity to open the Body Spacing Details View Set Maximum Spacing m 0 0075 e Left mouse click on the Extruded Periodic Pair entity x In the Graphics View select the front surface and then click Location 1 Apply in the Details View x In the Graphics View select the back surface remember to use the location planes in the lower left corner of the Graphics View and then click Location 2 Apply in the Details View and Set Periodic Type Translational e In the Tree View right mouse click on Inflation and select Insert Inflated Boundary to create an Inflated Boundary entity Select the three surfaces of the inner wall in the Graphics View for the Location and set Maximum Thickness m 0 0075 e Repeat to create an Inflated Boundary of Maximum Thickness m 0 0075 on the outer wall e In the Tree View right mouse click on
15. d parcel inside the flow domain Max No Iterations 50 MAX 1 0e 3 Fd x Residual Type V Residual Target Ok 4 and then click tab set 30 of the average residence time of e Right mouse click on Output Control entity and select Edit to open the Detail x Option V Standard Output Variable Operators o gt x and then click Ok s of Output Control panel Under the Output Boundary Flows on and choose Results tab set n and choose V All and 3 All SOLVER MANAGER 13 e On the row of buttons below the menu bar above the Viewer window click Write Solver File icon last one in the row to open the panel Accept the the default filename Ductbend def and Operation VW Start Solver Manager 2 4 Solver Manager The CFX Solver window will open after CFX Pre closes In the Define Run panel set e Definition File run you would enter the name of the most current results file e Type of Run Y Full e Run Mode Y and then click Finished Normally window click Process Results Now ductbend def NOTE If restarting a partially converged Serial and 2 Start Run After a few minutes execution should begin Diagnostics will scroll on the te
16. k the left mouse button 2 Switch to the toolbox to size the inner wall bend radius a Select the Radius tool b Select a point on the arc Then move the cursor to the inside of the arc near the origin Click to complete a dimension which is labelled R1 c In the Details View notice that R1 is shown under the Dimensions title d Change the value of R1 to 0 025 m Notice the arc radius changes automatically If the dimension is poorly placed on your sketch you can use the Move tool to correct the placement 3 Switch back to the Draw toolbox to sketch the inner entrance wall a With the Line tool selected place the cursor in the lower left quadrant of the XY plane near the arc Click the left mouse button Move the mouse cursor down to create a vertical line Look for the V constraint symbol and click the left mouse button b Switch to the Dimensions toolbox to size the inner entrance wall length i Select the General tool ii Select a point near the centre of the line Click and drag the cursor to the right to form the dimension lines Release the mouse button where the label V2 is to be placed iii In the Details View change the value of V2 to 0 10 m c To join the inner entrance wall and the inner wall bend switch to the Constraints toolbox i Select the Coincident tool
17. or ease of attach ing the boundary conditions To attach a region entity at the inflow see Figure 2 1 1 Orient the model so that the inflow surface can be easily picked with the mouse cursor 2 Right mouse click over Regions in the Tree View and select Insert V Composite 2D Region to create a new region entity 3 Left click over the new entity s name Composite 2D Region 1 and edit the region name to inflow surface 4 In the Graphics View put the mouse cursor over the inlet surface area and left mouse click The inlet surface area should turn green and 5 In the Details View click on Location V Apply and the surface will now turn red Repeat to create a region entity called outflow surface Notice that if you left mouse button click on inflow surface or the outflow surface in the Tree View that the resulting region in the Graphics View turns green 8 COMMANDS FOR DUCT BEND EXAMPLE e Create a region entity called inner wall This region is composed of three primitive surfaces To select a set of surfaces or faces hold the Ctrl key down while clicking on the component surfaces in the Graphics View e Repeat to create an entity called outer wall e For a region called front surface use the Z view of the Graphics View when selecting the surface Notice that there are two parallel planes in the lower left corner of the Graphics View The front most of these planes should be outlined in re
18. ose the selection s from the named list Name Panel or window name Name On off switch box and Name On off switch circle radio button 2 Commands for Duct Bend Example 2 1 Geometry Model The first phase uses DesignModeler The commands listed below will create a solid body geometry that will represent the flow domain e set up the project directory and page e set up a plane for sketching on e sketch in the flow path through the duct Figure 2 1 e generate the solid body geometry To begin e Create a new folder N Ductbend to be the working directory for the project files e Open ANSYS Workbench from Start Programs Engineering ANSYS 10 0 ANSYS Workbench To open a new project 1 In the Start window select Empty Project in the New panel 2 From the menu bar choose File Save As to create a project file in your working directory and 3 In the Save As window fill in File name Ductbend wbdb and click the Save button e From the menu bar choose Tools Options to change the length units and meshing tool options In the Options window expand the DesignModeler entity and select Grid Defaults Meters in the tree view on the left Set Minimum Axes Length 0 5 and Major Grid Spacing 0 1 x In the Options window expand the Meshing entity and select Meshing Set Default Physics Preference CFD and Default Method CFX Mesh
19. r minal output panel and the equation RMS residuals will be plotted as a function of time step After the first few time steps the residuals should fall monotoni cally Execution should stop within 40 time steps In the ANSYS CFX Solver 2 5 Post processing The most interesting step is the analysis of the results To illustrate this step the commands listed in the next paragraph step through the following tasks create a vector plot on one of the symmetry boundary planes save an image of the plot create a vorticity variable create a fringe plot of the vorticity field create a line and export the velocity data along the line export the inner wall pressure and wall shear stress distribution probe the velocity field and save the visualization state To accomplish these tasks click the CFX Post tab in bottom left corner and then e Choose Insert Vector accept Name Vector 1 and click OK to define a vector object and open an edit panel In the panel set x Locations V Reduction front surface Reduction Factor Factor 1 Variable V Hybrid Projection plots vector at every mesh point Velocity on Vv None 14 COMMANDS FOR DUCT BEND EXAMPLE and click Apply The vector plot should appear in the 3D Viewer window and the vecto
20. r object is listed in the User Locations and Plots database tree Turn O Default Legend View 1 off and back on to remove and then replace the scale legend Turn O Wireframe off and on Orthographic projection will work best for two dimensional views Notice that if you double click on an object in the database tree then a details panel opens up for that object e Choose File Print and in the Print panel set x File vectorplot png and x Format v PNG followed by Print The plot will printed to the file vectorplot png in your working directory You can import this file into other documents e Choose Insert Variable and in the New Variable definition window set Name Vorticity and click OK In Vorticity edit panel lower left x set Method Expression set O Scalar on fill in Expression Velocity v Gradient X Velocity u Gradient Y and click Apply e Choose Insert Contour accept Name Contour 1 and click OK to define a fringe contour plot object and open an edit panel In the panel set x Locations W front surface x Variable Y Vorticity and click Apply The fringe plot should appear in the 3D Viewer window e Choose Insert Location Line accept Name Line 1 and click OK
21. rectional views type x y or z while the Viewer window is active to get views in the positive axis direc tions and type X Y or Y to get views in the negative axis directions Other standard key mappings can be seen by clicking on the Show Help Dialog icon at the right of the lower row of icon buttons Tree View CFX Pre and CFX Post now make use of the tree view of object databases similar to that of DesignModeler and CFX Mesh In particular commands for modifying the database can be directly accessed from the tree view The implementation of boundary conditions for boundary surfaces is an application of this new capability Default Settings CFX Pre uses more default settings to reduce the number of details that the user must directly set to establish a solver definition file To illustrate these differences the notes only provide the steps required to complete the ductbend example program provided in the Version 10 Student User Manual The following font format conventions are used to indicate the various com mands that should be invoked 2 INTRODUCTION Menu Sub Menu Sub Sub Menu Item chosen from the menu hierarchy at the top of a main panel or window Button Tab Command Option activated by clicking on a button or tab Link description Click on the description to move by a link to the next step page Name value Enter the value in the named box Name Y selection Cho
22. sure that you do not exceed your disk quota At the end of each session delete all files except e agdb cmdat cmdb wbdb def and _ res files If you no longer need your results but would like to be able to replicate them then you should delete all files except e def files After removing all unnecessary files use the WinZip utility to compress the contents of your directory 3If you have used a local temp drive remember to copy your work to your N drive
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