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-   -   Question on the freestream boundary conditions for airfoil computations (https://www.cfd-online.com/Forums/main/73522-question-freestream-boundary-conditions-airfoil-computations.html)

 mbt March 10, 2010 11:55

Question on the freestream boundary conditions for airfoil computations

Hi all. In the airfoil computations, freestream variables are always needed for the treatment of boundary conditions. While in some cases, only freestream Mach number, Reynolds number and AoA are provided (such as the AIAA Drag Predition Workshop cases). Maybe an additional quatity, such as temperature, or pressure is needed to fix the freestream conditions ($\rho, u, v, w, p$). I am confusing a reasonable temperature/pressure is acceptable or there is always widely-used values. Many thanks.

Maybe a silly question because I am new to this area.

 thanos March 11, 2010 05:32

Hi!

If you are trying to simulate subsonic flow, temperature is not needed. You only have to know density and viscosity which are constant values. When compressibility emerges T is essential.

My question is:

-What happen with the turbulence parameters such as modifed viscosity ratio, turbulence intensity etc? In experiments there are no data about them.

 mbt March 11, 2010 08:43

Many thanks. Even for incompressible fluids, such as water, the molecular viscosity is function of temperature. I have checked the AIAA DPW series, only in the DPW-4 cases, the reference temperature is supplied. Really a big problem for me, for my code is originally developed for turbomachinery computations in which total temperature, total pressure and velocity angle at inlet boundary are widely used.

I think the Reynolds number maybe defined with only molecular viscosity, while, just a guess. Anyone experienced in this area could please explain them? Many thanks.

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