wind tunnel correction
 

Does anyone know of any project or reference involving wind tunnel correction method for a CFD model? I'm using a 2-D Euler code to model a supercritical airfoil in subsonic flow then compare it to wind tunnel experimental results. And I would like to find a method that could compensate between the free-stream environment in the model and the effects of wind tunnel on the experimental result. I would appreciate any help, thanks...

Art C.

Re: wind tunnel correction
 

In 70's, researchers were interested in the transonic wall porosity control to simulate the flow without the wall ( free flight condition). In those days, CFD results without wall were used to guide the porosity setting at the transonic wall location. It was aimed at the coupled CFD and testing loop to provide better wind tunnel testing results. If you do journal search on AIAA from 1965 through 1980, you may be able to locate papers related to this type of wind tunnel. They were trying to simulate the free flight condition using CFD as guide, while you are trying to simulate wind tunnel testing results. It maybe more difficult in your case, because you don't know the exact wall boundary condition.

Re: wind tunnel correction
 

Your question brings up several important points that you should address.

1. Are inviscid (Euler) aerodynamics sufficient to model a supercritical airfoil? In most cases, I think the answer is no. Transonic airfoil flows are usually dominated by viscous and turbulent effects.

2. How much do you know about the experiment? This is a critical point. In many cases, reported experimental data includes corrections for wall and support effects. The safest route is to model the experiment (including walls and support) and then compare to the uncorrected experimental data. If this is not possible then you must trust the corrections applied to the experiment and assume they get you back to equivalent free stream conditions.

After gaining confidence in your CFD approach by doing a proper comparison with experiment, it should be easy to run a free air model. While you may be able to come up with a free air to tunnel correction method, it will not provide nearly the same confidence as a direct comparison to the experiment.

If you would like some more information on modeling transonic wind tunnel experiments (i.e porous wall boundary conditions), you should search mainly AIAA papers. J. Erickson and J. Jacocks published some papers from the 70's till the late 80's. Sickles et. al. published some information about wind tunnel wall conditions used in calculations for the Space Shuttle in the mid 80's. I don't have exact paper numbers, but they should be easy enough to find.

Hope this information helps.