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-   -   Oscillating airfoil problem (https://www.cfd-online.com/Forums/main/9388-oscillating-airfoil-problem.html)

 ganesh June 25, 2005 03:25

Oscillating airfoil problem

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

Ganesh

 asue June 27, 2005 08:32

Re: Oscillating airfoil problem

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.

 ganesh June 27, 2005 13:57

Re: Oscillating airfoil problem

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

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