# interpolation scheme?

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 September 6, 2005, 04:39 interpolation scheme? #1 HADD Guest   Posts: n/a Sponsored Links Good day I'm very interested in what manner STAR-CD interpolates the pressure values at the cell faces Any suggestions or references will be highly appreciated Daria

 September 6, 2005, 07:46 Re: interpolation scheme? #2 4xF Guest   Posts: n/a As far as I remember, 2nd order central differencing is used.

 September 14, 2005, 10:34 Re: interpolation scheme? #3 HADD Guest   Posts: n/a Thanks And for interpolating face velocity in continuity equation - a face momentum equation is used? Or I`m not right?

 September 15, 2005, 08:06 Re: interpolation scheme? #4 4xF Guest   Posts: n/a Actually, there is no such thing. As far as I reckon (please anybody corrects me), the face velocities are not used in the continuity (or in this case the "pressure" equation) but rather the mass fluxes. These are evaluated in the same way as in the momentum equation in order to have a consistent discretization practice.

 September 15, 2005, 08:37 Re: interpolation scheme? #5 HADD Guest   Posts: n/a As I understand, if mass fluxes in "pressure equation" is interpolated in usual way (linear interpolation of cell-centered velocities to the face), then so called checker-boarding of pressure may occur (in other words - oscillations)

 September 15, 2005, 13:20 Re: interpolation scheme? #6 4xF Guest   Posts: n/a Of course, but there is a special procedure implemented (also known as Rhie & Chow correction) to get rid of this problem

 September 15, 2005, 14:03 Re: interpolation scheme? #7 HADD Guest   Posts: n/a Thanks But I wonder, if for interpolating mass fluxes Rhie and Chow procedure is used, why for interpolating pressure in momentum equation the 2nd order central differencing scheme (as you wrote) is implemented? What is in this case with checker-boarding ?

 September 16, 2005, 07:13 Re: interpolation scheme? #8 4xF Guest   Posts: n/a I think there is some kind of misunderstanding here. In the mass conservation equation which degenerates in the case of incompressible flow into a Laplace equation on pressure, the pressure stencil uses second-order differencing. For consistency, the mass fluxes are evaluated in the same way they are evaluated in the momentum equations. Then, for avoiding the checkerboard patterns on pressure, you have an additional term based on the Rhie&Chow procedure. This is mandatory when you use a colocated arrangement of variables. I hope this is clearer now. For more details, I would suggest to read the book by Ferziger & Peric: "Computational Methods for Fluid Dynamics".

 September 16, 2005, 07:42 Re: interpolation scheme? #9 HADD Guest   Posts: n/a Thanks a lot! I understand, that for Laplace equation the second-order differencing is used. But what scheme is used for pressure in momentum equation in STAR-CD? Thank you for the book recommended!

 September 16, 2005, 13:08 Re: interpolation scheme? #10 4xF Guest   Posts: n/a Gauss' theorem with pressure at the face centers, hence second-order interpolation as in the mass conservation equation (for consistency).

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