New topic on same subject - Flow around race car

Tudor Miron

Hi Guys! Glenn, Neale, Bob. Many thanks for you help. Without your input it would be impossible to do much at all. I did some validation study of a two element wing for which I had wing MIRA tunnel data. Data was not very "clean" as wing was mounted on a single seater car which was tested with and without wing. So it was actually a good reliable data of how thing wing worked on THIS car. How ever as I didn't have anything better I decided that I'd try anyway. I understand that it's much better to start validating my results on something like Ahmed body – I will do it anyway but it looked much more boring that nice rear wing . I used a mesh consisting of 1800000 elements and results was within 8% for lift and 17% for drag. Used SST model. Flour, side wall and top wall set as free slip. Now I'm trying to model the flow around a (generic but fairly close) sports racer body. I started with flat bottom (no rake) and got positive lift as expected. Than I added healthy front splitter and lift was reduced and center of pressure moved forward (it was far rear) Than I added a rear diffuser only to find that it doesn't really work. At first I had more lift than with flat bottom. After some tweaking of diffuser shape and I managed to reduce lift some more but still it was lift. Now I recreated (fairly close) underbody of 92 group C Toyota sports prototype (a car that produced tons of negative lift. I'm at the closing stages of convergence (2.2e-4) and forces seem to stabilize. Still there's lift…. Not much 155N (still falling but very slowly) for a half car but I expected some down force using a proved design (which was disallowed by tech reg. for creating too much downforce!) Point is I'd like to ask for some good (ball park) guidance for how to model this kind of solution. What is suggested minimum quantity of elements for a roughly 3.5m long , 1.7m wide car body? Fluid domain is 11m long, 2.5m wide and 2.5m tall (half symmetry model). I use around 2000000 elements. If to ask this question from other end what is recommended edge length scale for background and model? I use 0.3m for background with MC of 0.02m for model. I use 5 layers for inflation, Proximity set at 5 for edge (surface not checked). I used free slip for ground plane ( think I have to change it for moving wall with same speed as "free stream" ) I use SST with 1% (low intensity) turbulence option.

So questions are – 1) recommendations for mesh. 2) recommendations for physics settings (with "ground effect" in mind) Machine I'm working on has 2Gb RAM. I had not problems to solve 2350000 elements and it was showing 1.4Gb mem usage. But when I tried to solve a problem with 2550000 elements it said that there's not enough memory…. Strange!

Thank you Ted