Tut 08 Supersonic Wing

Master Contents

Master Index

Help On Help

CFX-5 Tutorials

Tutorial 8

Supersonic Flow Over a Wing Sample files used in this tutorial can be copied to your working directory from /examples. See Working Directory (p. 2) and Sample Files (p. 3) for more information. Sample files referenced by this tutorial include:

CFX-5 Tutorials

•

WingSPS.pre

•

WingSPSMesh.out

Page 187

Master Contents Master Index Supersonic Flow Over a Wing—Introduction

Help On Help

8.A:

Introduction

8.A.1:

Features explored in this tutorial Introduction: This tutorial addresses the following features of CFX-5. Component CFX-Pre

Feature User Mode

Details Quick Setup Wizard

Simulation Type Fluid Type

Steady State Ideal Gas

Domain Type Turbulence Model Heat Transfer

Single Domain Shear Stress Transport Total Energy

Boundary Conditions

Inlet (Supersonic) Outlet (Supersonic) Symmetry Plane Wall: No-Slip Wall: Adiabatic

Domain Interfaces

CFX-Solver Manager

Timestep n/a

CFX-Post

Plots

Other

Wall: Free-Slip Fluid-Fluid (No Frame Change) Auto Timescale n/a Contour Default Locator Vector Variable Editor

You learn about:

Page 188

•

setting up a supersonic flow simulation

•

using the Shear Stress Transport turbulence model to accurately resolve flow around the wing surface

•

defining custom vector variables for use in visualising pressure distribution

CFX-5 Tutorials

Master Contents

8.A.2:

Master Index

Help On Help Supersonic Flow Over a Wing—Introduction

Before beginning this tutorial Introduction: It is necessary that you have a working directory and that sample files have been copied to that directory. This procedure is detailed in "Introduction to the CFX-5 Tutorials" on page 1. Unless you review the introductory materials and perform required steps including setting up a working directory and copying related sample files, the rest of this tutorial may not work correctly. It is recommended that you perform the tasks in Tutorial 1, Tutorial 2 and Tutorial 3 before working with other tutorials as these three tutorials detail specific procedures that are simplified in subsequent tutorials.

8.A.3:

Overview of the problem to solve This example demonstrates the use of CFX-5 in simulating supersonic flow over a symmetric NACA0012 airfoil at 0o angle of attack. A 2D section of the wing is modelled. A 2D hexahedral mesh is provided that is imported into CFX-Pre. air speed u= 600 m/s 1.25 [m]

outlet 30 [m]

wing surface

70 [m]

CFX-5 Tutorials

Page 189

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

8.B:

Defining the Simulation in CFX-Pre This section describes the step-by-step definition of the flow physics in CFX-Pre. If you wish, you can use the session file Wing.pre to complete this section for you and continue from Obtaining a Solution (p. 196). This session file sets up the model to produce an initial guess. See one of the first four tutorials for instructions on how to do this.

8.B.1:

Creating a New Simulation 1. Start CFX-Pre and create a new simulation named Wing using the General Mode.

8.B.2:

Importing the Mesh Tip: While we provide a mesh to use with this tutorial, you may want to develop your own in the future. Instructions on how to create this mesh in CFX-Mesh are available from the CFX Community Site. Please see "Mesh Generation" on page 3 for details. 1. Copy the mesh file WingSPSMesh.out, located in the examples directory (/examples), to your working directory. 2. Click the Mesh tab to access the Mesh workspace. 3. Right-click in the Mesh Selector and select Import. 4. In the Mesh Workspace, on the Definition panel, set: a. Mesh Format to PATRAN Neutral b. File to WingSPSMesh.out 5. Click OK to import the mesh. The mesh will appear in the viewer. 6. Click Isometric View (Y up)

8.B.3:

Creating the Domain

Creating a new domain

1. Click Domain

Page 190

from the Viewer toolbar.

.

2. Enter Wing in the Name box and click OK.

CFX-5 Tutorials

Master Contents

Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

3. On the General Options panel: a. Set Location to Assembly, Assembly 2 and Assembly 3. (Use the key to select more than one region.) b. Leave Domain Type set to Fluid Domain. c. Set Fluids List to Air Ideal Gas. d. Leave Coord Frame set to Coord 0. e. Set Ref. Pressure to 1 [atm]. When using an Ideal Gas, it is important to set an appropriate reference pressure since some properties depend on the absolute pressure level. See "Setting a Reference Pressure" on page 10 in the document "CFX-5 Solver Modelling" for details. f.

Under Buoyancy, leave Option set to Non Buoyant.

g. Under Domain Motion leave Option set to Stationary. 4. Click the Fluid Models tab. a. Under Heat Transfer Model, set Option to Total Energy. The Total Energy model is appropriate for high speed flows since it includes kinetic energy effects. b. Under Turbulence Model, set Option to Shear Stress Transport. c. Set Turbulent Wall Functions to Automatic. d. Leave Reaction or Combustion Model and Thermal Radiation Model set to None. The Initialisation panel sets domain specific initial conditions, which are not used in this tutorial. Global initialisation will be set later in the tutorial. 5. Click OK to create the domain.

8.B.4:

Creating the Boundary Conditions

Creating the Inlet Boundary Condition

1. Create a boundary condition named Inlet. 2. On the Basic Settings panel, set: a. Boundary Type to Inlet b. Location to INLET

CFX-5 Tutorials

Page 191

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

3. Click the Boundary Details tab, then: a. Under Flow Regime set Option to Supersonic. b. Under Mass and Momentum set: •

Option to Cart. Vel. & Pressure

•

U = 600 [m/s]

•

V = 0 [m/s]

•

W = 0 [m/s]

•

Relative Static Pressure to 0 [Pa]

c. Under Turbulence, set Option to Intensity and Length Scale, Fractional Intensity to 0.01, and Eddy Len. Scale to 0.02 [m]. d. Under Heat Transfer, set Option to Static Temperature and Static Temperature to 300 [K]. 4. Click OK to create the boundary condition. Creating the Outlet Boundary Condition

1. Create a boundary condition named Outlet. 2. On the Basic Settings panel, set: a. Boundary Type to Outlet b. Location to OUTLET 3. Click the Boundary Details tab, then, under Flow Regime set Option to Supersonic. 4. Click OK to create the boundary condition.

Creating the Required Symmetry Plane Boundary Conditions

1. Create a boundary condition named SymP1. 2. On the Basic Settings panel, set: a. Boundary Type to Symmetry b. Location to SIDE1 3. Click OK to create the boundary condition. 4. Create two more symmetry planes in the same way, using the names and locations given below: a. SymP2, at the location SIDE2. b. Bottom, at the location BOTTOM.

Creating a Free Slip Boundary Condition for the Top of the Domain Page 192

Create a free slip wall at the location TOP.

CFX-5 Tutorials

Master Contents Creating a Wall Boundary Condition for the Wing

Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

1. Create a boundary condition named WingSurface. 2. On the Basic Settings panel, set: a. Boundary Type to Wall b. Location to WING 3. Click the Boundary Details tab, then: a. Under Wall Influence On Flow, leave Option set to No Slip. b. Under Heat Transfer, leave Option set to Adiabatic. 4. Click OK to create the boundary condition.

8.B.5:

Creating Domain Interfaces The imported mesh contains three regions which will be connected with domain interfaces. To ensure a one-to-one connection between the three regions, a translational periodic interface (with a zero translation in this case) will be created. See "One-to-one Connections" on page 127 in the document "CFX-5 Solver Modelling" for details. 1. Click Domain Interface

.

2. Accept the default name by clicking OK. 3. Set Interface Type to Periodic. 4. Set Connection Type to Automatic. 5. Set Periodic Type to Translational. 6. For Side 1, leave Domain (Filter) set to -- All Domains --. 7. Set Region List 1 to Assembly 3D A External. 8. For Side 2, leave Domain (Filter) set to -- All Domains --. 9. Set Region List 2 to Assembly 3D B External A. 10. Click OK to create the domain interface. The second domain interface is set up in a similar way: 1. Click Domain Interface

.

2. Accept the default name by clicking OK. 3. Set Interface Type to Periodic. 4. Set Connection Type to Automatic. 5. Set Periodic Type to Translational. 6. For Side 1, leave Domain (Filter) set to -- All Domains --. CFX-5 Tutorials

Page 193

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

7. Set Region List 1 to Assembly 3D B External B. 8. For Side 2, leave Domain (Filter) set to -- All Domains --. 9. Set Region List 2 to Assembly 3D C External. 10. Click OK to create the domain interface.

8.B.6:

Setting Initial Values For high speed compressible flow, the CFX-Solver usually requires sensible initial conditions to be set for the velocity field. 1. Click Global Initialisation

from the main toolbar.

2. Leave Velocity Type set to Cartesian. 3. Under Cartesian Velocity Components, set: a. Option to Automatic with Value b. U = 600 [m/s] c. V = 0 [m/s] d. W = 0 [m/s] 4. Under Temperature, set Option to Automatic with Value and Temperature to 300 [K]. 5. Use Automatic for all other variables. 6. Turn on Turbulence Eddy Dissipation and leave Option set to Automatic 7. Click OK to set the initialisation details.

8.B.7:

Setting Solver Control 1. Click Solver Control

.

2. Under Advection Scheme, set Option to High Resolution. The residence time for the fluid is approximately: 70 [m] / 600 [m s^-1] = 0.117 [s] In the next step, you will start with a conservative timescale that gradually increases towards the fluid residence time as the residuals decrease. A user specified maximum timescale can be combined with an Auto Timescale in CFX-Pre.

Page 194

CFX-5 Tutorials

Master Contents

Master Index Help On Help Supersonic Flow Over a Wing—Defining the Simulation in CFX-Pre

3. Under Convergence Control: a. Set Timescale Control to Auto Timescale. b. Set Max. No. Iterations to 100. c. Set Length Scale Option to Conservative. d. Turn on Maximum Timescale and set Maximum Timescale to 0.1 [s]. 4. Under Convergence Criteria, set: a. Residual Type to RMS b. Residual Target to 1.0e-05 5. Click OK to set the solver control parameters.

8.B.8:

Writing the Solver (.def) File 1. Click Write Solver (.def) File

.

2. Leave Operation set to Start Solver Manager. 3. Turn on Report Summary of Interface Connections. 4. Click OK. Since this tutorial uses domain interfaces and the Report Summary of Interface Connections toggle was enabled, an information window is displayed that informs you of the connection type used for each domain interface; see "Connection Types" on page 127 in the document "CFX-5 Solver Modelling" for details. 5. Click OK in the information window. 6. Select File > Quit. 7. Click Yes when asked if you want to save the CFX file.

CFX-5 Tutorials

Page 195

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Obtaining a Solution

8.C:

Obtaining a Solution When CFX-Pre has shut down, and the CFX-Solver Manager has started, obtain a solution to the CFD problem by following the instructions below. 1. Click Start Run. When it has finished: 2. Click OK. 3. When the CFX-Solver has finished, click OK in the message window. 4. Click Post-Process Results

.

5. When Start CFX-Post appears, turn on Shut down Solver Manager then click OK.

Page 196

CFX-5 Tutorials

Master Contents

8.D:

Master Index

Help On Help Supersonic Flow Over a Wing—Viewing the Results

Viewing the Results The following Plots are recommended: 1. Create a Contour plot on the SymP2 boundary. a. Set the Variable to Mach Number. b. Use a User Specified Range with a Min of 1 and Max of 2. c. Set the # of Contours to 21. You will see that the bulk of the flow has a Mach number which is very close to the maximum. The velocity goes to zero on the wing surface.

Figure 1: Mach Number on SymP2

CFX-5 Tutorials

Page 197

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Viewing the Results

2. Another recommended view of the results is a plot of Pressure on SymP2, with a global range. You will be able to see that a bow wave has formed, and the highest value of pressure is at the leading edge.

Figure 2: Pressure on SymP2

3. You can confirm that a significant energy loss occurs around the wing leading edge by plotting Temperature on SymP2. The temperature at the wing tip is approximately 180 K higher than the inlet temperature.

Figure 3: Temperature on SymP2

Page 198

CFX-5 Tutorials

Master Contents

Master Index

Help On Help Supersonic Flow Over a Wing—Viewing the Results

You can also try creating a user vector variable to show the pressure magnitude and direction acting on points along the airfoil: 1. Select Create > Variable. 2. Accept the default name and click OK. 3. Turn on the Vector toggle, then enter the following expressions: •

X Expression: (Pressure+101325[Pa])*Normal X

•

Y Expression: (Pressure+101325[Pa])*Normal Y

•

Z Expression: (Pressure+101325[Pa])*Normal Z

4. Click Apply. 5. Click Create Vector Plot

and accept the default name.

6. Set Locations to WingSurface and Variable to Variable 1. 7. Click the Symbol tab and set: a. Symbol to Line Arrow b. Symbol Size to 0.04 8. Click Apply. The resulting vector plot shows the pressure acting against the surface of the wing.

Figure 4: Pressure acting on the Wing

When you have finished, quit CFX-Post.

CFX-5 Tutorials

Page 199

Master Contents Master Index Help On Help Supersonic Flow Over a Wing—Viewing the Results

Previous Tutorial Page 200

Next Tutorial CFX-5 Tutorials