Simulation of flow at very low Reynolds number using Reynolds number

SimoY · February 11, 2024, 21:40

Edit: I realized that there is a typo in the title. It should be: Simulation of flow at very low Reynolds number using RANS
__________________________________________________ __________________________________________________ __

Hi

I need to run a simulation of the flow around an airfoil (Reynolds number based on the airfoil chord is only about 890). But the inlet of the domain has a turublence intensity of 0.6%.

I have limited computing power, so I can afford only relatively small simulations. I have some questions.

- Can I use a RANS turbulence model for this case?

- If I use laminar flow (without a turbulence model) how can I include the effects of inlet turbulence intensity?

Thank you for your help.

SimoY · February 15, 2024, 18:53

Could someone please provide some comments.

Thank you

andy_ · February 16, 2024, 07:14

Turbulence is dissipated by viscosity in low Reynolds number regions. The PhD project in the 70s that first introduced the k-e turbulence model was on the subject of relaminarization of turbulent shear layers. It is doable.

Almost all general 2 equation (or more) RANS turbulence models assume the Reynolds number is high. Models that are intended to be used in low Reynolds number regions are almost always tuned to be valid for only one specific type of flow.

No general RANS model is going to be valid for the low Reynolds number flow over your aerofoil. Whether the free stream unsteadiness is significant is likely to depend on the information you want from the simulation and/or the form of the unsteadiness (wakes?).

A reasonably accurate unsteady simulation of the flow over your aerofoil is likely to be viable on a modern desktop (subject to the relevant physics). It might take a few days for the statistics to settle down. I suspect the biggest problem is likely to be how to impose representative unsteady inlet conditions.

February 11, 2024, 21:40	Simulation of flow at very low Reynolds number using Reynolds number	#1
SimoY New Member Simo Med Join Date: Jan 2024 Posts: 6 Rep Power: 2	Edit: I realized that there is a typo in the title. It should be: Simulation of flow at very low Reynolds number using RANS __________________________________________________ __________________________________________________ __ Hi I need to run a simulation of the flow around an airfoil (Reynolds number based on the airfoil chord is only about 890). But the inlet of the domain has a turublence intensity of 0.6%. I have limited computing power, so I can afford only relatively small simulations. I have some questions. - Can I use a RANS turbulence model for this case? - If I use laminar flow (without a turbulence model) how can I include the effects of inlet turbulence intensity? Thank you for your help. Last edited by SimoY; February 12, 2024 at 10:38.

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February 15, 2024, 18:53		#2
SimoY New Member Simo Med Join Date: Jan 2024 Posts: 6 Rep Power: 2	Could someone please provide some comments. Thank you

February 16, 2024, 07:14		#3
andy_ Senior Member andy Join Date: May 2009 Posts: 276 Rep Power: 18	Turbulence is dissipated by viscosity in low Reynolds number regions. The PhD project in the 70s that first introduced the k-e turbulence model was on the subject of relaminarization of turbulent shear layers. It is doable. Almost all general 2 equation (or more) RANS turbulence models assume the Reynolds number is high. Models that are intended to be used in low Reynolds number regions are almost always tuned to be valid for only one specific type of flow. No general RANS model is going to be valid for the low Reynolds number flow over your aerofoil. Whether the free stream unsteadiness is significant is likely to depend on the information you want from the simulation and/or the form of the unsteadiness (wakes?). A reasonably accurate unsteady simulation of the flow over your aerofoil is likely to be viable on a modern desktop (subject to the relevant physics). It might take a few days for the statistics to settle down. I suspect the biggest problem is likely to be how to impose representative unsteady inlet conditions.