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Old   April 13, 2011, 14:47
Smile Help.. Boundary conditions for external flow...
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Suresh
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Hi,
I am solving 3D euler equation on aircraft wing, I am using FVM in unstructured grid with cell centred method. I use Lax-Friedrich scheme to discretize the equation. My results are not correct, temperatures, pressure and density are higher than the stag. values at wall boundaries. I think my boundary conditions are wrong.

I am using a circular domain of 15 times of root chord as diameter, my BC are as follows,

Far field: Free stream values. (since the domain is circular, no seperate BC for inlet and exit)

Wall boundary: reflective velocity method is used for velocity, and pressure and temperature are extrapolated from boundary cell to ghost cell.

Can any one suggest me for solution?
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Old   April 13, 2011, 21:12
Default what is reflective velocity? Does that refer to slipping?
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what is reflective velocity? Does that refer to slipping?
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Old   April 14, 2011, 03:00
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I am reflecting normal component of velocity from the boundary cell to the ghost cell to make the velocity normal to the surface zero. (i.e) I implemented v.n = 0, by this method. I have used the expression
vg=vb-2(vb.n)n, where g refers to ghost cell and b refers to boundary cell. Above expression is from the book Blazek
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Old   April 14, 2011, 10:19
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This method should work, actually it is exactly what I use. How is your convergence? I use Roe, but should not make much difference.
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Old   April 14, 2011, 11:11
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I am calculating norms by taking residual per time step. (i.e) Residual / t, I a using local time step. My norm converges in the order of 10-4, not increasing more than that.
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Old   April 14, 2011, 11:26
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If residual does not drop to machine zero, 10e-14, there is bug in your code, especially for Euler problem.
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