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Old   July 3, 2005, 12:50
Default BC for oscillating airfoil
  #1
ganesh
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Dear Friends,

I am working on a Euler solver for oscillating airfoils, but I have a few problems.

1. What are the BCs on the wall of the airfoil. I have the following as of now

Mass flux = 0

Mom. flux in x = pressure * nx

Mom. flux in y = pressure * ny

Energy flux = pressure * Vel of grid motion normal to the body

Are these right ?

2. I am using a modified version of Roe scheme for interfacial flux computations. The modifications are the following

a. The eigen values have been modified to incorporate the grid velocity b. The fluxes are modified to incorporate grid velocity.

I am using Geometric Conservation Law while computing the grid motion velocities.

3. Is there any difference in the way Cl,Cd or Cp is calculated for such moving cases. I do not think the basic equations to compute these coefficients vary only that the quantities affecting them are modified as a result of grid motion through the flux computations.

Am I right in this context too ?

Looking forward to any possible suggestions and help in this regard,

Thanks in advance,

Ganesh
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Old   July 5, 2005, 14:05
Default Re: BC for oscillating airfoil
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Mani
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You didn't write your equations in detail, so I just want to make sure that you understand that the grid velocity enters all governing equations, not just the energy equation.

Definitions of force coefficients are no different from the steady case.

If you have any trouble, just try to reduce your case to the simplest possible configuration to single out the problem. For example: For an oscillating airfoil the geometric conservation law is not necessary, because you can let the grid move rigidly without cell deformation. Furthermore, if you solve the unsteady flow over a grid at prescribed rigid oscillation, you know the exact analytical expressions for the grid velocities. No need to do this numerically, until you actually consider a case with deformation.

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Old   July 6, 2005, 05:14
Default Re: BC for oscillating airfoil
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ganesh
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Dear Mani,

Thankyou for your suggestions. In any case, I understand that the grid velocities do appear in all the equations, affecting the convective part, but I am specifically interested as to what exact BCs will be applied on the surface. Is the mass flux essentially zero, and the momentum and energy flux have contribution only from pressure, in which case the wal bcs are similar to a static problem, except in the energy flux case?

Thanks in advance,

Ganesh
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Old   July 6, 2005, 15:12
Default Re: BC for oscillating airfoil
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Mani
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Ganesh,

you know how the grid velocity is taken into account in the fluxes. This is done the same way on the boundary of the flow domain as in the interior flow domain. Your boundary conditions are similar to the static ones, the only difference being the influence of the grid velocity. Essentially, all fluxes are expressed in terms of the relative velocity = flow velocity minus grid velocity.
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Old   July 7, 2005, 12:29
Default Re: BC for oscillating airfoil
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ganesh
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Dear Mani,

Thankyou for the information.

Ganesh
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