Tutorial: Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT Introduction This tutorial demonstrates how to model 2D turbulent fl ow across a circular cylinder using large eddy simulation (LES) and compute fl ow-induced (aeroacoustic) noise using FLUENTs acoustics model. You will learn how to: Perform a 2D large eddy simulation. Set parameters for an aeroacoustic calculation. Save acoustic source data for an acoustic calculation. Calculate acoustic pressure signals. Postprocess aeroacoustic results. Prerequisites This 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, fi rst read Chapter 21, Predicting Aerodynamically Generated Noise, of the FLUENT 6.2 Users Guide c? Fluent Inc. May 11, 20051 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT Problem Description The problem considers turbulent air fl ow over a 2D circular cylinder at a free stream ve- locity (U) of 69.2 m/s. The cylinder diameter (D) is 1.9 cm. 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 cm Figure 1: Computational Domain Preparation 1. Copy the fi le cylinder2d.msh to your working directory. 2. Start the 2D version of FLUENT. Approximately 2.5 hours 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 7 and using the provided case and data fi les. 2c? Fluent Inc. May 11, 2005 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT Step 1: Grid 1. Read the grid fi le cylinder2d.msh. File Read Case. As FLUENT reads the grid fi le, it will report its progress 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 -0.095 m to 0.38 m. 2. Check the grid. Grid Check FLUENT 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 Domain To 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 = 128.99 Done. c? Fluent Inc. May 11, 20053 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT 4. Display the grid. Display Grid. (a) Display the grid with the default settings (Figure 2). Use the middle mouse button to zoom in on the image so you can see the mesh near the cylinder (Figure 3). Grid FLUENT 6.2 (2d, segregated, LES, unsteady) Figure 2: Grid Display 4c? Fluent Inc. May 11, 2005 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT Grid FLUENT 6.2 (2d, segregated, LES, unsteady) Figure 3: The Grid Around the Cylinder Quadrilateral cells are used for this LES simulation because they generate less numerical diff usion than triangular cells. The cell size should be small enough to capture the relevant turbulence length scales, and to make the numerical diff usion smaller than the subgrid-scale turbulence viscosity. The mesh for this tutorial has been kept coarse in order to speed up the calculations. A high quality LES simulation will require a fi ner mesh near the cylinder wall. c? Fluent Inc. May 11, 20055 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT Step 2: Models 1. Select the segregated solver with second-order implicit unsteady formulation. Defi ne 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. 6c? Fluent Inc. May 11, 2005 Modeling Flow-Induced (Aeroacoustic) Noise Problems Using FLUENT 2. 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) Defi ne 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 0.1 for the model constant Cs. (d) Click OK. You will see a Warning dialog box, stating that Bounded Central-Diff erencing is default for momentum with LES/DES. Click OK. Th