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-   -   Help.. Boundary conditions for external flow... (http://www.cfd-online.com/Forums/main/87199-help-boundary-conditions-external-flow.html)

suresh1483 April 13, 2011 14:47

Help.. Boundary conditions for external flow...
 
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?

gems April 13, 2011 21:12

what is reflective velocity? Does that refer to slipping?
 
what is reflective velocity? Does that refer to slipping?

suresh1483 April 14, 2011 03:00

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

gems April 14, 2011 10:19

This method should work, actually it is exactly what I use. How is your convergence? I use Roe, but should not make much difference.

suresh1483 April 14, 2011 11:11

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.

gems April 14, 2011 11:26

If residual does not drop to machine zero, 10e-14, there is bug in your code, especially for Euler problem.


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