[TouZ]

I'm doing my thesis on plain flapped NACA 0012 airfoil. I ran some simulations where flap angle was varied from 10-50 degrees. But when I plot the curve of Cd Vs mach number, for 40 and 50 degrees of flap angle maximum Cd occurs at Mach 0.5 instead of Mach 1. And with increasing mach number Cd decreases afterwards . But, for 10, 20 and 30 degrees of flap angle it conforms to the standard curve somewhat. Way is this happening?? If this is the real case, can anyone explain the physical mechanism occurring there??

[Aeronautics El. K.]

Can you give more information please?
I don't know which equations you're solving or the freestream conditions but I think that at some point the local Mach number exceeds the local speed of sound and you have a shock wave.

[TouZ]

Originally Posted by Aeronautics El. K.

Can you give more information please?
I don't know which equations you're solving or the freestream conditions but I think that at some point the local Mach number exceeds the local speed of sound and you have a shock wave.

Sir,
I'm doing my simulation in ansys fluent. Used k-omega SST model. Mach no was varied from 0.1 to 1.0 for each flap angles (i.e. 10, 20, 30, 40, 50). I also tried these simulations on Slidworks flow simulation. But at higher flap angles (30, 40, 50) solution does not even converge (Fluent also). I took the avg. of highest and lowest values for computing Cl and Cd. I used conventional equations of Cl and Cd.

Temp: 300k, rho: 1.225, viscosity: 1.749E-5

Anything wrong with the flap angles?? In internet I could not find any results for such high AoA. I would be very nice if you help me to understand this phenomenon. Any academic reading material will also do.

Thank you for your reply.

[Aeronautics El. K.]

For M>0.3 the assumption that the flow is incompressible does not hold. The flow must be considered compressible. Did you account for compressibility in your calculations?

[TouZ]

oh... Actually I did not assume compressible flow for Mach no.>0.3. Should I select density based solver in Fluent for Mach > 0.3? What should I do for simulating compressible flow in SolidWorks Flow simulatuion??

Thank you.