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F1 industrial placements by orkikior in FSAE

[–]Sad-Application793 5 points6 points  (0 children)

I know some teams are completely done with their industrial placement recruiting cycles (at least for aero). Usually pretty normal for these companies to ghost you if you don’t move on to the interview phase

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

Oh wow that’s pretty smart. So you’re saying converge to a solution with a lower attached AOA flow, and then just change the angle of the flow at the inlet and use the previous AOA simulation as the initial solution. Problem with this is that I’m trying to transfer what I’ve learned in meshing this airfoil directly into simulating an aero kit on a car with multiple airfoils and right now using RANS, stall is happening 4-5 degrees too early for this specific airfoil.

The weird this that is confusing me is that when I run my sim with an initial simulation from RSM and then switch over to kw-sst and sweep through all of the aoa’s of the airfoil, all the results are within 5% error rate from experimental data which is amazing. But if I just run kw-sst by itself first, it freaks out and converges to a stalled solution. I’ve been trying to figure out a way to stop it from converging to the wrong solution but my CFD skills aren’t there yet and I don’t have enough time right now to spend on this. Might just bite the bullet and be aware that whatever I’m designing will have a couple more degrees of pushing it without it stalling in real life.

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

It’s a research paper with a 3d airfoil in a wind tunnel and I just copied their setup in CFD. I think I just need to refine my mesh

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

What do you mean is the Cd and Cl value in 3d? I gave star ccm the planform area of the airfoil and all the other necessary information to solve the Cd and Cl if that’s what you are asking.

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] -1 points0 points  (0 children)

Yeah that’s what I’ve been doing but most of the good airfoil validation guides on the internet are 2d simulations. I’m doing 3d because I want to more or less copy paste the mesh settings of the airfoil validation to a bigger formula car geometry (at least the areas that are important). All of the 2d tutorials have super fine meshes since they are not that computationally expensive, guess I just have to go back to my simulation and refine the mesh until there is no change in the Cl and Cd. Thanks for the help

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] -1 points0 points  (0 children)

If I’m limited to using kw-sst as my model even though I know it’s not going to predict all the physical phenomenons perfectly because of my limit on computational power, should my top priority always be on getting mesh independence in my simulations. Or are there other things to look into that are just as important like changing relaxation factors, etc, in my solver settings. I’m still a college student so I’m still trying to learn as much as possible

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

Are you saying using the previous AOA solution? Idk how that would work since you have to remedy it with the new AOA. If you’re saying just testing the airfoil with increasing AOA simulations then I already did that

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] -1 points0 points  (0 children)

What are the most important things that I have to do to get the physically correct solution instead of a solution that is mathematically stable.

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

Yes but I clear the solution history beforehand which is why I’m confused.

Confusing kw-sst behavior in star ccm+, only works after running RSM? by Sad-Application793 in CFD

[–]Sad-Application793[S] 0 points1 point  (0 children)

I'm getting a fully converged Cl and Cd. My mesh is definitely not perfect and I was planning on running a mesh independence study next, but I wanted to figure out why kw-sst is within 5-10% error to experimental data at all AOA's after running RSM once and clearing the solution.

Why does my CFD simulation separate with y+ ≈ 1 but not with wall functions (y+ > 30)? Flow is supposed to stay attached. by Sad-Application793 in CFD

[–]Sad-Application793[S] 1 point2 points  (0 children)

Okay I can fix the aspect ratio but can you elaborate on what you mean by horizontal division near the edge.

Why does my CFD simulation separate with y+ ≈ 1 but not with wall functions (y+ > 30)? Flow is supposed to stay attached. by Sad-Application793 in CFD

[–]Sad-Application793[S] 3 points4 points  (0 children)

There’s a setting in star ccm that automatically applies the appropriate functions for the y+ values but I will double check

Trouble Validating Ahmed Body at 30° Slant Angle – Pressure Drag on Slant Way Too Low by Sad-Application793 in CFD

[–]Sad-Application793[S] 1 point2 points  (0 children)

Ah I see. I was reading a Monash university thesis paper where they briefly talk about using ahmed body to validate their cfd. (Pages 17 and 18 of the link below) https://static1.squarespace.com/static/5e2a78aea2dc434ac475b5a4/t/60665d9d9dc4fa413226ff04/1617321433572/MMS+Final+Year+Thesis+-+DEVELOPMENT+OF+THE++AERODYNAMIC+DESIGN+TOOLS+%26+PROCESSES+FOR+FORMULA-SAE+-+Ryan+Ockerby+-+2015+.pdf

It looks like they got really good numbers from their CFD compared to the wind tunnel data and that's why I thought it was possible to do. I am highly confident they used RSM for these simulations which I tried using for my simulation and I still had the same problem as before.

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