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Question about inviscid model in CFD software
Hi, hello everyone，I have a strange question.
When can the inviscid model (not potential model) be applied in CFD software? In other words, how to judge the inviscid model and turbulent model has little influence on the numerical results? Thank you everyone! |
When the simulation you're trying to do, doesn't need viscosity to give accurate results.
For example: Hypersonic flows can ignore viscosity. Don't worry too much. Learn how to solve with viscosity. The problem you're trying to solve will most likely state if you need viscosity or not. |
If you are doing RANS, the turbulent stress tensor is there because of the fluctuating velocities in the advection term. Should we neglect as well the turbulence modelling?
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Quote:
Inviscid fluid model (Euler equations) is used prevalently for potential flows and shock-waves dominated problems. Few applications can be found for LES. |
If you non-dimensionalize the Navier-Stokes equations (https://en.wikipedia.org/wiki/Non-di...okes_equations) you will see that the coefficient in front of the viscous can be written as 1/Re . (The article shows the incompressible NS, but this is true for compressible NS as well).
Therefore in order to ignore the effects of viscosity the Reynolds number should be quite large, probably a million at the very least. |
Just to address some further comments.
Assuming ideal flows (no viscosity, no conducibility) you disregard any type of dissipation of kinetic energy. That means you have a model for the turbulence where the energy cascate is never terminated by dissipation. In no way that can be simulated on a finite grid since the theoretical Kolmogorov lenght is exactly zero and you can never approach a DNS. Therefore, in any simulation you have to terminate numerically the energy cascate. Furthermore, since you have no dissipation, you cannot suppose a statistical energy equilibrium between production and dissipation of kinetic energy to introduce a turbulence model for the closure of the equations. In this sense, RANS is not suitable as formulation. The Euler equations are mainly solved for flows with shock by disregarding the turbulence effects. https://link.springer.com/chapter/10.1007/11545989_1 |
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