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Tutorial:Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENTIntroductionThis tutorial demonstrates how to model2D turbulentflow across a circular cylinder using large eddy simulation(LES)and computeflow-induced(aeroacoustic)noise using FLUENT’s acoustics model.You will learn how to:•Perform a2D large eddy simulation.•Set parameters for an aeroacoustic calculation.•Save acoustic source data for an acoustic calculation.•Postprocess aeroacoustic results.PrerequisitesThis tutorial assumes that you are familiar with the FLUENT interface and that you have a good understanding of basic setup and solution procedures.Some steps will not be shown explicitly.In this tutorial you will use the acoustics model.If you have not used this feature before,first read Chapter21,Predicting Aerodynamically Generated Noise,of the FLUENT6.2 User’s GuideModeling Flow-Induced (Aeroacoustic)Noise Problems Using FLUENT Problem DescriptionThe problem considers turbulent air flow over a 2D circular cylinder at a free stream ve-locity (U)of 69.2m/s.The cylinder diameter (D)is 1.9cm.The Reynolds number based on the diameter is 90,000.The computational domain (Figure 1)extends 5D upstream and 20D downstream of the cylinder.U = 69.2 m/s D = 1.9 cmFigure 1:Computational DomainPreparation1.Copy the file cylinder2d.msh to your working directory.2.Start the 2D version of FLUENT .Approximately 2.5hours of CPU time is required to complete this tutorial.If you are interested exclusively in learning how to set up the acoustics model,you can reduce the computing time requirements considerably by starting at Step 7and using the provided case and data files.福昕软件（Ｃ）２００５－２０１０，版权所有，仅供试用。

Modeling Flow-Induced (Aeroacoustic)Noise Problems Using FLUENTStep 1:Grid1.Read the grid file cylinder2d.msh .File −→Read −→Case...As FLUENT reads the grid file,it will report itsprogress in the console window.Since the grid for this tutorial was created in meters,there is no need to rescale the grid.Check that the domain extends in the x-direction from -0.095m to 0.38m.2.Check the grid.Grid −→CheckFLUENT will perform various checks on the mesh and will report the progress in the console window.Pay particular attention to the reported minimum volume.Make sure this is a positive number.3.Reorder the grid.Grid −→Reorder −→DomainTo speed up the solution procedure,the mesh should be reordered,which will substan-tially reduce the bandwidth and make the code run faster.FLUENT will report its progress in the console window:>>Reordering domain using Reverse Cuthill-McKee method:zones,cells,faces,done.Bandwidth reduction =32634/253=128.99Done.福昕软件（Ｃ）２００５－２０１０，版权所有，仅供试用。

Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT4.Display the grid.Display−→Grid...(a)Display the grid with the default settings(Figure2).Use the middle mouse button to zoom in on the image so you can see the meshnear the cylinder(Figure3).Figure2:Grid DisplayModeling Flow-Induced (Aeroacoustic)Noise Problems UsingFLUENTFigure 3:The Grid Around the Cylinder Quadrilateral cells are used for this LES simulation because theygenerate lessnumericaldiffusion than triangular cells.The cell size should be small enough to capture the relevant turbulence length scales,and to make the numerical diffusion smaller than the subgrid-scale turbulence viscosity.The mesh for this tutorial has been kept coarse in order to speed up the calculations.福昕软件（Ｃ）２００５－２０１０，版权所有，仅供试用。

Modeling Flow-Induced (Aeroacoustic)Noise Problems Using FLUENT Step 2:Models1.Select thesegregated solver with second-order implicit unsteady formulation.Define −→Models −→Solver...(a)Retain the default selection of Segregated under Solver .(b)Under Time ,select Unsteady .(c)Under Transient Controls ,select Non-Iterative Time Advancement .(d)Under Unsteady Formulation ,select 2nd-Order Implicit .(e)Under Gradient Option ,select Node-Based .(f)Click OK .福昕软件（Ｃ）２００５－２０１０，版权所有，仅供试用。

Modeling Flow-Induced (Aeroacoustic)Noise ProblemsUsing FLUENT2.Select the LES turbulence model.The LES turbulence model is not available by default for 2D calculations.You can make it available in the GUI by typing the following command in the FLUENT console window:(rpsetvar ’les-2d?#t)Define −→Models −→Viscous...(a)Under Model ,select Large Eddy Simulation .(b)Retain the default option of Smagorinsky-Lilly under Subgrid-Scale Model .(c)Retain the default value of 0.1for the model constant Cs .(d)Click OK .You will see a Warning dialog box,stating that Bounded Central-Differencing is default for momentum with LES/DES .Click OK .The LES turbulence model is recommended for aeroacoustic simulations because LES resolves all eddies with scales larger than the grid scale.Therefore,wide band aeroa-coustic noise can be predicted using LES simulations.福昕软件（Ｃ）２００５－２０１０，版权所有，仅供试用。