Verification of Laminar and Validation of Turbulent Pipe Flows 58 160 Intermediate Mechanics of Fluids CFD LAB 1 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 1 is to simulate steady laminar and turbulent pipe flow following the CFD Process by an interactive step by step approach Students will have hands on experiences using FlowLab to compute axial velocity profile centerline velocity centerline pressure and friction factor Students will conduct verification studies for friction factor and axial velocity profile of laminar pipe flows including iterative error and grid uncertainties and effect of refinement ratio on verification Students will validate turbulent pipe flow simulation using EFD data analyze the differences between laminar and turbulent flows and present results in CFD Lab report Geometry Physics Heat Transfer Incompress ible Flow Properties Viscous Models Boundary Conditions Unstructured Automatic Coarse Structured Manual Medium Fine Density and viscosity Laminar Turbulen Inviscid One Eq Two Eq Report Steady Unsteady Iterations Steps Convergent Limit SA k e k w Initial Conditions Pipe Solve Mesh Single Precisions Post processing Total pressure drop Wall friction force XY plot Verification Contours Validation Vectors Double Streamlines Numerical Schemes 1st order upwind 2nd order upwind Residual Quick Centerline Velocity Pipe Radius Centerline Pressure Pipe Length Profiles of Axial Velocity Flow Chart for ISTUE Teaching Module for Pipe Flow red color illustrates the options you will use in CFD Lab 1 1 2 Simulation Design In CFD Lab 1 simulation will be conducted for laminar and turbulent pipe flows Iterative error and grid uncertainties will be studied Comparison between CFD and AFD for laminar flow and CFD and EFD for turbulent flow will be performed The problem to be solved is that of laminar turbulent flows through a circular pipe Reynolds number is 655 for laminar flow and 111 569 for turbulent pipe flow based on pipe diameter Symmetry Axis Inlet Outlet Pipe Wall Since the flow is axisymmetric we only need to solve the flow in a single plane from the centerline to the pipe wall Boundary conditions need to be specified include inlet outlet wall and axis as will be described details later Uniform flow was specified at inlet the flow will reach the fully developed regions after a certain distance downstream No slip boundary condition will be used on the wall and constant pressure for outlet Symmetric boundary condition will be applied on the pipe axis All analytical data AFD for Laminar Pipe Flow and EFD data for turbulent pipe flow can be downloaded from the class website http css engineering uiowa edu me 160 3 CFD Educational Interface Right after you launch FlowLab 1 2 10 the following interface will be shown The top right corner illustrates the CFD processes Geometry Physics Mesh Solve Reports Post processing There is also a sketch window that shows the definition of all boundary conditions and coordinates 2 If you close the sketch window and want to see it again you can click File Problem Overview You MUST save your work regularly to avoid any possible lost of your data and jobs File Save As Then use the Browse button to locate the directory where you want to save It is recommended that you created your own folder in the FlowLab working directory C Documents and Settings Fluidslab myflowlab YOURNAME 4 CFD Process Step 1 Geometry 1 Radius of pipe 0 02619 m 2 Length of pipe 7 62 m Click Create after you see the pipe geometry created click Next Step 2 Physics 3 The Reynolds number shown in the above figure is for laminar pipe flow case for turbulent pipe flow the Reynolds number will be different based on the inlet velocity you specified 1 With or without Heat Transfer Thermal effects are not considered in CFD Lab 1 turn OFF Heat Transfer button 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 In CFD Lab 1 both laminar model and turbulent model k e will be used follow exercise notes for specifications and click OK Note For each simulation you can only choose one model either laminar model OR turbulent k e model 4 5 Boundary Conditions At Inlet FlowLab use zero gradient for pressure and fix the velocity to be 0 2 m s and 34 08 m s for laminar and turbulent pipe flows respectively Use default values for intensity and length scale Laminar Turbulent At Axis FlowLab use zero gradient for axial velocity and Pressure and specify the magnitude for radial velocity to be zero Read all the values and click OK Laminar Turbulent At Outlet FlowLab uses magnitude for pressure and zero gradients for axial and radial velocities and turbulent quantities For pressure magnitude use 0 for laminar flow and 400 Pa for turbulent flow click OK 5 Laminar Turbulent At Wall no slip boundary conditions are fixed for both axial and radial velocity gradients for other variables are zero For turbulent pipe flow pipe roughness also needs to be specified which is 2 5e 5 m in this lab Read the panel input pipe roughness and click OK Laminar Turbulent 6 Initial Conditions Use the default setup for initial conditions Laminar 6 Turbulent After specifying all the above parameters click Compute button and FlowLab will automatically calculate the Reynolds number based on the inlet velocity and pipe diameter you input Note For turbulent pipe flow the outlet pressure is 400 Pa you may specify pressure magnitude in initial condition to be 400 Pa to speed up convergence Click the Next this takes you to the next step Mesh Step 3 Mesh For CFD Lab 1 Structured meshes will be generated using either Automatic or Manual generations see exercises at the end of this document for details NR and NX is the number of intervals in axial and radial directions For Automatic generation just choose the mesh density coarse medium or fine and click Create FlowLab will automatically create the mesh you required and display the grid information NR NX For manually generating mesh you should first choose the Manual button and then the following panel will be shown 7 Choose Uniform distribution for both axial and radial directions and use the appropriate numbers required in the exercise notes click Create buttons in NR NX and Mesh windows then the mesh will be
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