How does FLUENT caculate velocity profile at wall when shear is specified?

Faizan89 · June 4, 2021, 08:54

Dear all,

I am doing simulations for laminar flow in a 2D rectangular channel where a wall is modelled with specified shear (against the flow direction using a udf prescribed profile (for example using linear or sinusoidal functions.) Although, the udf profile works fine and the wall shear stress remains as specified, I am not able to understand how does Fluent calculates the corresponding velocity profile at the wall. I have tried comparing velocity profile from Fluent with that calculated using integration of tau=mu *du/dy but the velocity is significantly smaller in FLUENT.

Does anybody know how does velocity profiles is implemented in FLuent when shear stress is specified?

Regards,
Faizan

LoGaL · June 4, 2021, 19:13

Which viscosity did you use? Are you perhaps running a turbulence model?

Faizan89 · June 5, 2021, 12:04

Hi Lorenzo,

I have tried constant viscosity as well as temperature dependent viscosity using udf (not needed for base case with only flow) for this case. I am not using any turbulence model. My flow strain calculation is correct given as du/dy=stress/viscosity but apparantly Fluent is calculating velocity in some different way. Any ideas?

Regards,
Faizan

June 4, 2021, 08:54	How does FLUENT caculate velocity profile at wall when shear is specified?	#1
Faizan89 New Member Faizan Join Date: Apr 2020 Location: Netherlands Posts: 6 Rep Power: 6	Dear all, I am doing simulations for laminar flow in a 2D rectangular channel where a wall is modelled with specified shear (against the flow direction using a udf prescribed profile (for example using linear or sinusoidal functions.) Although, the udf profile works fine and the wall shear stress remains as specified, I am not able to understand how does Fluent calculates the corresponding velocity profile at the wall. I have tried comparing velocity profile from Fluent with that calculated using integration of tau=mu *du/dy but the velocity is significantly smaller in FLUENT. Does anybody know how does velocity profiles is implemented in FLuent when shear stress is specified? Regards, Faizan

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June 4, 2021, 19:13		#2
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	Which viscosity did you use? Are you perhaps running a turbulence model?

June 5, 2021, 12:04		#3
Faizan89 New Member Faizan Join Date: Apr 2020 Location: Netherlands Posts: 6 Rep Power: 6	Hi Lorenzo, I have tried constant viscosity as well as temperature dependent viscosity using udf (not needed for base case with only flow) for this case. I am not using any turbulence model. My flow strain calculation is correct given as du/dy=stress/viscosity but apparantly Fluent is calculating velocity in some different way. Any ideas? Regards, Faizan