Now the convergence criteria need to be set.Later on, however, we will try turbulent flow calculations this is where the turbulence models are specified in Fluent. Laminar flow is the default, so we really don't need to do anything here. Back in Fluent, Define- Models- Viscous.So, it is wise to enter the x and y components of the freestream velocity here (these will depend on your assigned angle of attack). In our problem, the velocity will be that of the uniform stream over most of the flowfield. The convergence can be sped up slightly be giving more realistic values of the initial velocity distribution. The default initial values of velocity and gage pressure are all zero. In Fluent, Solve- Initialize- Initialize.Finally, Close the Boundary Conditions window.Likewise, top-and-bottom, and verify that the top and bottom edges are periodic.It is a good idea to verify them, however. The default boundary conditions for the airfoil (wall) and the outlet (pressure outlet) are okay, so nothing needs done to those. Alternately, from Fluent, Define- Boundary Conditions to re-show the window. At this point it may be hidden under the Fluent window, so some moving around may be required. Return to the Boundary Conditions window.Write down the density and viscosity on a piece of paper (these will be needed later on). From the main Fluent window, Define- Materials.Select air as the Material Name in the Fluid window, and OK. The default fluid is air, which is the fluid we desire in this problem. In Boundary Conditions, select fluid, and Set. Set Y-component of Flow Direction to the sine of your angle of attack. Change X-component of Flow Direction to the cosine of your angle of attack. In Velocity Inlet, change Velocity Specification Method to Magnitude and Direction.In Boundary Conditions, select inlet, which is the left side of the computational domain.In Fluent, Define- Boundary Conditions, and a new Boundary Conditions window will pop up. wall, velocity inlet, etc., but actual values for inlet velocity, etc. In Gambit, the boundary conditions were declared, i.e. Now the boundary conditions need to be specified.Close the Grid Display window the display itself will remain. Play with this feature until your domain is shown nicely in the window. from the lower right to the upper left, it will zoom out. If you draw a rectangle backwards with the middle mouse button, i.e. Meanwhile, the left mouse button can be used to drag the image to a new location. If you start on the upper left and draw a rectangle with the middle mouse button towards the lower right, the display will zoom in on what is included in the rectangle. The graphical display can be zoomed-in or zoomed-out with the middle mouse button.The Fluent window and/or the graphical display window may need to be moved to accomplish this. It is best if the graphical display window is small enough that both it and the Fluent window are both visible simultaneously. If this window is too big, rescale it by dragging the edges of the window. Look at the grid: Display- Grid- Display.If the grid is not valid, you will have to return to Gambit and regenerate the grid. Look for any error messages that indicate a problem with the grid. Verify the integrity of the grid: Grid- Check.If all went well, it should give no errors, and the word Done should appear. Some information is displayed on the main screen. Fluent will read in the grid geometry and mesh that was previously created by Gambit. In Select File, select airfoil.msh from the lisitng of available files shown on the right side. Read the grid points and geometry of the airfoil flow domain: After a few seconds, the main Fluent window should appear on your screen. (Note: It is assumed that the grid file resides in the Fluent subdirectory.) From your main directory, enter "cd Fluent" to change the working directory to Fluent.cshrc file so that you won't have to add it manually every time you log in. Enter "set path = (/disk03/local/Fluent.Inc/bin $path)" to give you access to the Fluent programs.Create a Unix shell: Desktop- Unix shell.If you have just completed the Gambit learning module for generating the grid, you should already be logged in, and your working directory should be Fluent. Log onto one of the SGI cluster computers.(See the learning module, Gambit - Generation of Grid for a 2-D Airfoil.) The file airfoil.msh is assumed to exist on the student's Fluent directory on the SGI cluster. Note: This set of instructions assumes that the student has already run the Gambit program, and has generated a grid for the airfoil. Readers should already be familiar with the notation used in this module, as described in the learning module, Fluent and Gambit - Introduction and General Information. In this document is a procedure that enables students to solve a 2-D airfoil flow problem with the CFD program, Fluent.
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