Prediction of the critical Reynolds number

Mehrez · May 13, 2014, 12:45

Hi every one,
I'm using OpenFoam for simulating fluid flow in periodic media.
Do you have an idea on how can I predict the laminar/turbulent transitional Reynolds ?
Thank you in advance

Mehrez

kalle · May 15, 2014, 02:36

Well, in theory it should be possible using a DNS solver and sweep the Re-number, while assuring there is some small disturbances present. If you are below the critical number, the disturbance should decay, while if you are above, it should grow (into turbulence).

In practise it is tricky because you need to assure that your numerical viscosity is small enough (to be accurate in Re), and things like wall roughness may play significant role.

For an academic case (smooth wall), this is possible with OpenFOAM, (dnsFoam solver), but you would need massive computational resources (i.e. hyper-fine mesh)

K

Mehrez · May 15, 2014, 12:21

Hi dear Kalle,

Thank you for your answer.
Concerning my geometry, I have smooth walls. I have proceeded like you said by DNS (using IcoFoam solver with dimensionless NS equations).
I have got results but I want to verify if it is OK. I thought about the linear stability theory but OpenFoam doesn't have a such solver, so to validate my DNS results I need to adopt another method...
Best regards,

Mehrez

May 13, 2014, 12:45	Prediction of the critical Reynolds number	#1
Mehrez Member Sami Join Date: Nov 2012 Location: Cap Town, South Africa Posts: 87 Rep Power: 14	Hi every one, I'm using OpenFoam for simulating fluid flow in periodic media. Do you have an idea on how can I predict the laminar/turbulent transitional Reynolds ? Thank you in advance Mehrez

May 15, 2014, 02:36		#2
kalle Senior Member Karl-Johan Nogenmyr Join Date: Mar 2009 Location: Linköping Posts: 279 Rep Power: 21	Well, in theory it should be possible using a DNS solver and sweep the Re-number, while assuring there is some small disturbances present. If you are below the critical number, the disturbance should decay, while if you are above, it should grow (into turbulence). In practise it is tricky because you need to assure that your numerical viscosity is small enough (to be accurate in Re), and things like wall roughness may play significant role. For an academic case (smooth wall), this is possible with OpenFOAM, (dnsFoam solver), but you would need massive computational resources (i.e. hyper-fine mesh) K Mehrez likes this.

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May 15, 2014, 12:21		#3
Mehrez Member Sami Join Date: Nov 2012 Location: Cap Town, South Africa Posts: 87 Rep Power: 14	Hi dear Kalle, Thank you for your answer. Concerning my geometry, I have smooth walls. I have proceeded like you said by DNS (using IcoFoam solver with dimensionless NS equations). I have got results but I want to verify if it is OK. I thought about the linear stability theory but OpenFoam doesn't have a such solver, so to validate my DNS results I need to adopt another method... Best regards, Mehrez