Dear Friends,

I am working on an oscillating airfoil problem at present and I have a few doubts in this regards. I am trying to solve AGARD CT5 test case which is inviscid flow past harmonically oscillating NACA0012 airfoil. The variation of AOA is given as alpha(t) = alp_mean + alpha_o*sin(wt) where alp_mean = 0.016deg, alpha_o= 2.51 deg. Instead of w, what is reported commonly is the reduced frequency, k = w*chord/ 2*U_infty. For this case at hand, k = 0.0814.

The NACA airfoil has a chord of unity and my freestream Mach is 0.755. Since I need my w for calculations, I need U_infty. I plan to calculate U_infty as U_infty = Mach * a_infty

My question is what reference temperature must be used to calculate a_infty ? And what would be the corressponding w ? I calculated w as around 41 rad/s, but my results show reasonable disagreement with experiments, eventhough the 'hysterisis oval' I am supposed to get is seen in my computations.

Can anyone in this field give me a reply, I have been stuck for nearly two weeks on this problem

Thanks in advance,

Ganesh

hi,

Actually, the temperature doesn't matter much as long as it is around experimental temperature condition (say 20 degree). you have no problem to calculate U-infty by using U_infty = Mach * a_infty. Once you have U_infty, you can easily work out w(Omiga). The most important issue is that you should define your k consistent with that in the experiment. Some studies use k = w*chord/ 2*U_infty and other use k = w*chord/U_infty. So check with the expemental document to make sure you have used the same difinition.

Dear Asue,

Thanks for your reply. I did use a temperature of around 25 C and calculated w. I have checked out k and its definition is consistent with the experiment. I think my code has a bug somewhere else, not possibly on this account. Thankyou for your suggestion.

Regards,

Ganesh