High performance car simulation
Good morning everyone,
I am trying to run a simulation of a high-performance car and right now I am trying to make a mesh study. However, I have some doubts that I would really appreciate some help with. I have calculated the first prism layer height for a y+=1 (0.0103mm) and taken 20% of the total boundary layer height for my simulation (14mm). I have chosen a stretching factor of 1.2 and 12 prism layers. How do these numbers sound?? I am using an airspeed of 40m/s. Star-ccm+ doesn't allow you to insert the first prism layer height if you want to set up a stretching factor, so I have been playing with the stretching factor and the number of layers to get the first height similar to the one I calculated. Does this approach make sense?? Should I have selected a higher y+? I am expecting to have an important boundary separation, so that is why I decided to use that small value. I have then selected the K-omega SST low y+ treatment, but I am getting reversed flow on the outlet region of my block and a high number of cells with turbulent viscosity limited. what does it mean?? When should I use low y+ treatment and when all y+ treatment?? Thank you very much in advance for the help |
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2) Reverse flow at outlet and turbulent viscosity limitation might die out as your iteration increase. |
K-omega SST vs K-epsilon
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After the mesh study, I am doing a turbulent model study. I am comparing the k-epsilon all y+ treatment with K-omega SST all y+ treatment, and I am using the same mesh for both of them of course. However, I am getting very different Cl values. 0.05 with k-epsilon (totally converged) and 0.2 with k-omega, although this last one fluctuates between 0.09 and 0.25 all the time. On the other hand, I am getting mostly the same Cd in both cases without fluctuations. Does it make any sense?? I should be getting similar cl values, right?? and why the CL is not converging as good as CD? I attached a picture of the plots I got with K-omega |
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