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Speed Limitations of CFD Codes

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Old   December 19, 2001, 01:43
Default Speed Limitations of CFD Codes
Aldrin Wong
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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
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Old   December 19, 2001, 07:08
Default Re: Speed Limitations of CFD Codes
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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.


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Old   December 19, 2001, 21:40
Default Re: Speed Limitations of CFD Codes
Aldrin Wong
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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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