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-   -   Speed Limitations of CFD Codes (https://www.cfd-online.com/Forums/main/4222-speed-limitations-cfd-codes.html)

 Aldrin Wong December 19, 2001 01:43

Speed Limitations of CFD Codes

Hi,

The present day CFD codes using say a variety of flux vector or flux difference splitting etc have been amply demonstrated for fluid flows from Mach 0.6 to say Mach 2.0

What about other speeds. Can I use the same codes for same Mach 0.01 ? What about Mach 4 ? What are the issues (CFD wise) involved ?

Would appreciate if anyone can shed some light on this.

Cheers Aldrin

 sylvain December 19, 2001 07:08

Re: Speed Limitations of CFD Codes

Limitations are from :

- the validity of the Navier-Stokes equations (ratio mean free path / fluid particules size);

- the numerical scheme you use (ex : FEM for incompressible flows (Mach number <= 0.6); FVM with Roe or ... for compressible flows (converge faster without preconditionning for Mach number greater than 0.3)).

- the turbulence model you use : for Mach number lower than 2 the turbulence is suppose to be nearly incompressibe (Turbulent Mach Number = sqrt(turbulent kinetic energy) / sound speed lower than 0.6). For higher Mach number, the turbulent Mach number rise and the usual turbulence models are no more satisfactory.

I probably forget other aspects, but hope thats help.

Sylvain

 Aldrin Wong December 19, 2001 21:40

Re: Speed Limitations of CFD Codes

if i do solve everything using the Euler equations, will that help ?

If I can recall correctly, the farfield should be bigger for very high speed flows (Mach > 2) ??

Whereas convergence is more of an issue at very low speeds.

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