Capturing stall on airfoil
 

Hi Guys,

I am hoping somebody out there can give me a bit of insight into my problem.

I am trying to capture the stall position and conditions of the naca4415 airfoil to compare to experimental results.

I have previously ran the simulation in steady state and achieved fair results for most angles of attack, but it failed to pick up the point of where the airfoil stalls and only picks this up 6 degrees further out than what it should be.

I am now in the process of trying to redo the simulation but in transient flow, i have no experience using this. The solver i am running a density based model with the solver being Transition SST with the DES function being switched on and the shield left as the default DDES.

The solution methods screen shot is attached. My reynolds number is 3E6.
I have been performing standard initialization from the inlet.

I used a time step size of 0.001 and 200 steps (not actually sure on how i am meant to calculate what i actually need?).

I have attached a picture of my mesh if that helps.

When i check the plot of my x and y forces they are much lower than they should be for any given AOA (from 10 upwards) and I am not sure what i am doing wrong?

It may be that i am a complete beginner in CFD but i have a very close deadline so would really appreciate any help even if it does not directly answer my question but points out things i am doing wrong.

If any further information is required please do not hesitate to ask for it.

sorry for such a long message
Anthony

Just an update, i started to get very good answers for this simulation but i am unsure why and how changing the time step is making such an effect on my convergence and answer, would really appreciate any help or hints as to where i should go and read about such a subject .

Anthony

having a small timestep is conceptually the same as having a small element size, one is discretizing in the spatial domain the other in the temporal domain. As always by refining both these you are trying to achieve accuracy and stability. you can read about this in detail the fluent theory guide - temporal discretization