Uniform flow test case

Hooman · January 11, 2016, 18:56

Hi, a few quick questions:

1) what is mean by calculation of the uniform flow. I know it means that properties of a flow are the same from one point to the next and that they can change with time, but then I've come across papers which state that uniform flow on a fixed grid is essentially steady. Is that right?

2) what is meant by solving the uniform flow test case? (in particular in 1D)

Thank you.

davidwilcox · January 14, 2016, 05:49

If the flow is uniform, what that means is that it is devoid of shear which gives the flow a profile. think of it this way, a boundary layer is NOT a uniform flow.

if the flow is subjected to perturbations, it will of course no longer be steady. In other words, it will encounter turbulence. Normally high wind speeds come with high turbulence. So it depends on the Reynolds number.

if it is purely a uniform flow, then it is generally pure convection. I'm not sure why anybody would want to simulate this though.
Viscous effects are negligible.

I'm not sure if you meant uniform flow at the inlet. If you have uniform flow everywhere then why do CFD at all?

agd · January 14, 2016, 08:56

An additional consideration is that a uniform flow calculation is a good first test case for a new CFD solver. If the flowfield is uniform and the boundary conditions are turned off, then the solver should return uniform flow. Deviation from uniform behavior then indicates problems with the flow solver.

January 11, 2016, 18:56	Uniform flow test case	#1
Hooman Senior Member Join Date: Jun 2010 Posts: 111 Rep Power: 15	Hi, a few quick questions: 1) what is mean by calculation of the uniform flow. I know it means that properties of a flow are the same from one point to the next and that they can change with time, but then I've come across papers which state that uniform flow on a fixed grid is essentially steady. Is that right? 2) what is meant by solving the uniform flow test case? (in particular in 1D) Thank you.

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January 14, 2016, 05:49		#2
davidwilcox Senior Member david Join Date: Oct 2012 Posts: 142 Rep Power: 13	If the flow is uniform, what that means is that it is devoid of shear which gives the flow a profile. think of it this way, a boundary layer is NOT a uniform flow. if the flow is subjected to perturbations, it will of course no longer be steady. In other words, it will encounter turbulence. Normally high wind speeds come with high turbulence. So it depends on the Reynolds number. if it is purely a uniform flow, then it is generally pure convection. I'm not sure why anybody would want to simulate this though. Viscous effects are negligible. I'm not sure if you meant uniform flow at the inlet. If you have uniform flow everywhere then why do CFD at all?

January 14, 2016, 08:56		#3
agd Senior Member Join Date: Jul 2009 Posts: 353 Rep Power: 18	An additional consideration is that a uniform flow calculation is a good first test case for a new CFD solver. If the flowfield is uniform and the boundary conditions are turned off, then the solver should return uniform flow. Deviation from uniform behavior then indicates problems with the flow solver.