Hi,everyone Simple question. Why can't we solve the low mach number flow by compressible navier-stokes code.

Someone say, bacause range of eigen value of flux jacobian (eg. U+C>>U>>U-C) is broaden. And preconditioning method adjusts magnitude of eigenvalue.

I can't understand above reason.

Give me a advice please.

thanks kei-tee

You can if you solve for the pressure as a primitive variable and use the the proper adimensional quantity to scale it (rho*u*u or (p-pinf)/(rho*u*u) ).

A good reference on this subject is:

Principles of Computational Fluid Dynamics. Author: Wesseling

(Very good book).

A low Mach number flow (weakly compressible) is hard to solve when you use a code which solves for density (as a lot of high speed Euler codes do). For low Mach numbers the density doesn't change (much) so this is the wrong variable to solve for. pressure based codes will not have a problem with these flows as the pressure does change. There is no point in solving for density in an incompressible case (density is constant anyway). Low Mach number flows tend to go to this limit.