Verification and Validation of Turbulent Flow around a Clark Y Airfoil 58 160 Intermediate Mechanics of Fluids CFD LAB 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 Lab 2 is to simulate turbulent airfoil flows following CFD process by an interactive step by step approach and conduct verifications using CFD Educational Interface FlowLab 1 2 Students will have hands on experiences using FlowLab to conduct verification and validation for lift coefficient and pressure coefficient distributions including effect of numerical scheme Students will manually generate the O type and C type meshes and investigate the effect of domain size and effect of angle of attack on simulation results Students will analyze the differences between CFD and EFD analyze possible source of errors and present results in the CFD Lab report 1 Geometry Physics Heat Transfer Incompress ible Flow Properties Viscous Models Boundary Conditions Solve Mesh Unstructured Automatic Coarse Structured Manual Medium Fine Turbulent Inviscid One Eq Two Eq SA Single 1st order Wall shear stress Iterations Skin friction Factor Coefficient of lift Precisions Coefficient of drag Numerical Schemes XY plots Double k e k w Initial Conditions Steady Unsteady Convergent Limit Density and viscosity Laminar Report Post processing Contours Vectors Streamlines Verification and validation 2nd order Select geometry Clarky Select domain NACA12 Chord length LS 1 0417 Angle of attack Import Profile Residuals QUICK Pressure coef Distri Shear stress Distri Airfoil Y plus Flow Chart for ISTUE Teaching Module for Airfoil Flow red color illustrates the options you will use in CFD Lab 2 2 Simulation Design The problem to be solved is that of turbulent flows around a Clark Y airfoil Reynolds number is 143 000 based on the inlet velocity and airfoil chord length The following figures show the illustrations for C type and O type meshes Note the figures are not in the exact scale as the true size of the domain and airfoil as you will see in FlowLab 2 In CFD Lab2 Boundary conditions for C type of meshes will be inlet outlet symmetry and airfoil as described later Boundary conditions for O type of meshes will be inlet outlet and airfoil Uniform flow was specified at inlet For outlet zero gradients are fixed for all velocities and pressure is constant No slip boundary condition will be used on the airfoil Symmetric boundary condition will be applied on the symmetry All EFD data for turbulent airfoil flow in this Lab can be downloaded from class website 3 CFD Process Step 1 Geometry 1 Select Geometry Clark Y 2 Chord length 0 3048 m 3 Angle of attack 0 or 6 refer to exercises for details 4 Circle Radius 5 meters except for exercise 1 where effect of domain size is studied 5 Radius Rc for C mesh 5 meters 6 Down stream length Lo for C mesh 12 meters Click Create after you see the airfoil geometry created in the graphic window click Next Step 2 Physics 3 1 With or without Heat Transfer No thermal effects are considered in this lab switch the Heat Transfer button OFF which is the default setup 2 Incompressible or compressible Choose Incompressible which is the default setup 3 Flow Properties Use the values shown in the above figure Input the values and click OK 4 Viscous Model 4 Choose turbulent model k e 5 Boundary Conditions At Inlet we use constant pressure and fix the velocity to 7 04m s for turbulent airfoil flow Use default values for 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 On Airfoil if flow is turbulent FlowLab uses no slip boundary conditions for velocities and zeropressure gradient Turbulent quantities k and e are also specified to be zero Read all the values and click OK For C type mesh there is one additional boundary condition i e Symmetry 5 6 Initial Conditions Use the default setup for initial conditions After specifying all the above parameters click Compute button and FlowLab will automatically calculate the Reynolds number based on the inlet velocity and the airfoil chord length you specified Click Next This takes you to the next step Mesh Step 3 Mesh For CFD Lab 2 Structured meshes will be generated using either Automatic or Manual generations see exercises at the end of this document for details For Automatic generation just choose the mesh density coarse medium or fine and click Create FlowLab will automatically create the mesh you required For manually generation you should first choose the Manual button and then the following panel will be shown 6 1 O mesh generation to generate an O type mesh you need to specify the number of intervals and the first length in grid spacing for NA1 NA2 NA3 and NA4 which are the four curves that form the airfoil geometry Then choose the number of intervals and the grid spacing near airfoil for the edge NC1 which lays from the airfoil surface to the far field Finally choose Uniform distribution for NF1 NF2 NF3 and NF4 which are the four curves that form the far field circumference Click Create after you input the parameters for each edge and then click Create in the mesh step window to generate the whole mesh 2 C mesh generation to generate a C type mesh you need to specify NA1 NA2 NA3 RC Symmetry and inlet For details on setting up those parameters see exercises on C mesh generation NOTE When specifying parameters for NA1 NA2 NA3 NA4 you have to use the zoom in order to visualize the mesh distribution near the airfoil Step 4 Solve In this Lab both 1st order and 2nd order numerical schemes will be used read exercises for details 7 The flow is steady so turn ON the Steady option Specify the iteration number and convergence limit to be 10000 and 10 5 respectively Choose Double precision with 1st or 2nd order scheme based on which exercise you are working on Use New calculation for this Lab Then click Iterate and FlowLab will begin the calculation Whenever you see the window Solution Converged click OK NOTE FlowLab stops a calculation when the maximum number of iterations or the convergence limit is reached whatever happens first In the first case the Iterations complete window will be shown In the second case the Solution Converged window will be displayed The iterative history of residuals for continuity equation x and y momentum equations and k and epsilon equations for
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