I am trying to simulate the turbulent, transient flow of water over a vertically oriented flat plate that has finite length and depth in ANSYS Fluent. This simulation aims to focus on what is happening within the boundary layer, so after using ANSYS Mesher to make the mesh, I think I should be using the k-epsilon model. Since I think k-epsilon is the way to go, I used this y+ calculator for a y+=30 at x=15 m and Re = 1.98e+9 I was given a first cell height of 1.133e-5 m which I used in the last ratio boundary layer method 15 layers. I tried running this simulation, slowly ramping up the velocity after some time steps, and changing the time step size to maintain a CFL between 0.7 and 0.9.
Here are my boundary conditions:
- The flat plate with dimensions L x D on the x/y plane is a normal no-slip wall. (yellow green surface)
- The top and bottom surfaces are L x H parallel to the x/z plane I've set as a wall but with an applied shear stress of zero. (gray surfaces)
- I have a velocity inlet Vx and a pressure outlet at zero gage pressure since I am not including body forces currently. (blue and red arrows)
- Finally the far wall is also treated as a wall with an applied shear stress of zero, where H >= 5L.
After running the simulation, ramping up the inlet velocity as I described prior, I was able to achieve residuals for all values between 1e-4 and 1e-12. However, when I looked at my results I was alarmed to see 1) Cf near 240 (using the area average of the definition in ANSYS) and 2) a y+ contour in the xz plane where y+ decreased moving away from the wall instead of increasing. I can include the images of the residuals and Cf plot if anyone asks.
One thing to note is I could not get the flow to converge at all unless I enabled pseudotime, however, I'm worried this is a leading source of the errors I am seeing.
I am pretty lost at what else I might try, since the problem could be a combination of a bad choice of geometry, boundary conditions, boundary layer mesh, or turbulence model. Is it possible to get some recommendations from others who are more experienced? I was expecting this to be a pretty simple case to run.
Please let me know if you have any questions.