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June 10, 2018, 04:57 

#21 
Senior Member

hm, Now I get it. I guess it would be ridiculous to use Euler to simulate turbulence.


June 10, 2018, 06:04 

#22  
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,266
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Quote:
This is an example of turbulence problem studied assuming no physical viscosity https://www.researchgate.net/profile...kmanlayer.pdf 

June 10, 2018, 06:07 

#23  
Senior Member

Quote:
Viscous drag needs a form of viscosity to be present, either real or numerical. In a direct Euler computation it is typically present in the form of numerical viscosity due to the numerical convective scheme. Thus, by nature, it cannot be actually accurate. But, imagine an aircraft at high speed with attached flow (low angle of attack). The numerical viscosity, in this case, will help you get lift and its induced drag, which is a form of pressure drag. If you know the liftdrag plot, you should know that the lift induced drag can be much higher than the base friction drag. The same, of course, won't work on a sphere or a cube. But, the idea of using Euler equations, is not much in getting an estimate of the drag, but in computing flows that, due to such feature, can return reliable evaluation of other quantities, like the lift, knowing that the neglected and/or miscomputed drag is not playing a dominant role in your computation. In a word... engineering. 

June 10, 2018, 06:11 

#24 
Senior Member

In the base Euler/NS equations with an ideal gas law (remember that we are talking about the equations, not the real flow), there is no such distinction between supersonic or hypersonic. So, what I wrote just applies to any supersonic flow with such model equations.


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euler equations, navier stokes equations, shock wave, turbulence 
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