1 Simulation of Turbulent Flow around an Airfoil 57:020 Mechanics of Fluids and Transfer Processes CFD PRELAB 2 By Tao Xing and Fred Stern IIHR-Hydroscience & Engineering The University of Iowa C. Maxwell Stanley Hydraulics Laboratory Iowa City, IA 52242-1585 1. Purpose The Purpose of CFD PreLab 2 is to simulate turbulent flow around Clarky airfoil following “CFD process” by an interactive step-by-step approach. Students will have “hands-on” experiences using FlowLab to compute pressure, lift and drag coefficients using both viscous and inviscid models. Students will validate simulation results with EFD data measured at EFD Lab 3, analyze the differences and possible numerical errors, and present results in Lab report. 2. Simulation Design In EFD Lab 3, you have conducted experimental study for turbulent flow around a ClarkY airfoil (Re=300,000) for two angles of attack 0 and 16 degrees. The pressure on the foil surface you have measured Flow chart for ISTUE teaching module for airfoil flow (red color illustrates the options you will use in this CFD PreLab 2) Geometry Post-processing Report Physics Mesh Contours Vectors Streamlines Solve Iterations Conver-gent. Limit Precisions Single Double Numerical Schemes 1st order 2nd order QUICK Steady/ Unsteady? Coarse Medium Fine Automatic Manual Structured Unstruct-ured Boundary Conditions Flow Properties Viscous Models One Eq. Two Eq. Density and viscosity Laminar Turbulent Inviscid SA k-e k-w Heat Transfer? Incompress-ible? Initial Conditions Clarky NACA12 LS(1) 0417 Import Profile Chord length Angle of attack Select domain Select geometry Wall shear stress Skin friction Factor XY plots Verification and validation Coefficient of lift Coefficient of drag Residuals Pressure coef. Distri. Shear stress Distri. Airfoil Y plus2 will be used for CFD PreLab 2. In CFD PreLab 2, simulation will be conducted under the same conditions of EFD Lab 3 (geometry, Reynolds number, fluid properties) at angle of attack 0 degree using both viscous and inviscid models. Simulation results will be validated by your own EFD data. The problem to be solved is turbulent flow around the ClarkY airfoil with angle of attack () In the figure above, C is the chord length of the airfoil,  is the angle of attack, and Rc is the radius of the “O” domain. 3. CFD Process Step 1: (Geometry) Choose “ClarkY” airfoil and “O type” domain, input the chord length of the foil and angle of attack 0 degree. 1. Select Geometry (Clarky) 2. Select domain (O type) 3. Chord length (0.3048 m)3 4. Angle of attack (0) 5. Mesh type (Map) 6. Circle Radius Rc (6m) Click <<Create>><<Next>>. Step 2: (Physics) (1). With or without Heat Transfer? Since we are not dealing with the thermal aspects of the flow, like heat transfer, etc., switch the <<Heat Transfer >> button OFF, which is the default setup. (2). Incompressible Use “Incompressible”. “Compressible” option is not available for current template. (3). Flow Properties Use the air properties at the room temperature when you conducted EFD Lab3 and click <<OK>>. You can use the following website to calculate air properties from the temperature: http://www.mhtl.uwaterloo.ca/old/onlinetools/airprop/airprop.html The values in the figure above are for 24° temperature. NOTE: viscosity used in FlowLab is the dynamic viscosity (kg m s), NOT kinematic viscosity (2ms)4 (4). Viscous Model For turbulent flow simulations, choose turbulent model (k-e). For Inviscid flows, choose “inviscid” and click <<OK>>. (5). Boundary Conditions At “Inlet”, we use constant pressure and constant velocity. Inlet velocity should be computed from the EFD data reduction sheet and could be different from 15 ms. Use default values for turbulent quantities “k” and “e”. At “Outlet”, FlowLab uses magnitude for pressure and zero gradients for axial and radial velocities. Input “0” for the Gauge pressure and click <<OK>>. Turbulent Inviscid5 On “Airfoil”, if flow is turbulent, FlowLab uses no-slip boundary conditions for velocities and zero-pressure gradient. Turbulent quantities k and e are also specified to be zero. If flow is inviscid, then zero gradient is used for pressure and certain boundary conditions (not discussed in this lab due to its complexity) are used for velocities. Read all the values and click <<OK>> (6). Initial Conditions Use the default setup for initial conditions. Turbulent Inviscid Turbulent Inviscid6 After specifying all the above parameters, click <<Compute>> button and FlowLab will automatically calculate the Reynolds number based on the inlet velocity and airfoil chord you entered. Click <<Next>>. This takes you to the next step, “Mesh”. Step 3: (Mesh) For CFD PreLab 2, use “Automatic” meshing and “Medium” mesh. Click <<Create>>, The mesh generated will be displayed in the graphic window. NA and NC are the numbers of grid points on the airfoil surface and radial direction, respectively. Inviscid Turbulent7 Step 4: (Solve) Specify the iteration number and convergence limit to be 2000 and 10-5, respectively. Choose “Double Precision”, “2nd order” for numerical schemes, and “New” calculation. Click <<Iterate>>, FlowLab will fire the XY plot for residuals that is dynamically updated during the calculation. Whenever you see the window, “Solution Converged”, click <<OK>>.8 Step 5: (Reports) “Reports” first provides you the information on “wall shear stress”, “skin friction factor”, “coefficient of lift”, and “coefficient of drag”. XY plot provide plots for “residuals”, “pressure distribution”, “pressure Coefficient”, and “Shear Stress Distribution”, etc. In this Lab, only XY plots for “residuals” and “pressure coefficient” are required. “XY Plots” provides the following options: To import the EFD data on top of the above CFD results, just click <<File>> button and use the browse button to locate the data file you need and click <<Import>>. Details have been described in previous CFD PreLab 1 for laminar pipe flow.9 In this Lab: 1. EFD data for pressure coefficient distribution should be created in your folder under H: \myflowlab\SESSION-NAME\*.xy” (Example: H: \myflowlab\prelab2\pressure-EFD.xy) The