Spalart allmaras

jesumi · May 4, 2017, 12:26

Hello everyone,

I am trying to run a simulation on starting and stopping vortices of a given airfoil. I chose the Spalart-Allmaras method in the simpleFoam algorithm. These are my question.

1. Meaning of nut and nuTilda.

2. Do I have to type unsteadyState in order to take the temporal term of the equation into account? (I have the answer, thanks in advance to everyone)

3. How do I make the velocity to accelerate suddenly and then stops just for me to prove that those vortices exist and, therefore, the net circulation value is 0.

thank you for your help guys.

random_ran · May 11, 2017, 18:08

Greeting jesumi:

1. nut is the eddy viscosity. It describes the transfer of the momentum in the flow. nuTilda is the modified eddy viscosity. It can be calcuated from turbulent intensity and turbulent length scale. "A convenient option is set nuTilda = 5*nut".

2. Can you share your answer?

3. I am not understand what you want simulate. A fixed valued inlet velocity can not meet your standard? I mean why velocity need to accelerate suddenly to generate votices? And what is your net circulation ?

May 4, 2017, 12:26	Spalart allmaras	#1
jesumi New Member Jesús Miguel Join Date: Dec 2016 Posts: 8 Rep Power: 10	Hello everyone, I am trying to run a simulation on starting and stopping vortices of a given airfoil. I chose the Spalart-Allmaras method in the simpleFoam algorithm. These are my question. 1. Meaning of nut and nuTilda. 2. Do I have to type unsteadyState in order to take the temporal term of the equation into account? (I have the answer, thanks in advance to everyone) 3. How do I make the velocity to accelerate suddenly and then stops just for me to prove that those vortices exist and, therefore, the net circulation value is 0. thank you for your help guys. Last edited by jesumi; May 4, 2017 at 12:39. Reason: Found one doubt

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May 11, 2017, 18:08		#2
random_ran Member Ran Join Date: Aug 2016 Posts: 69 Rep Power: 10	Greeting jesumi: 1. nut is the eddy viscosity. It describes the transfer of the momentum in the flow. nuTilda is the modified eddy viscosity. It can be calcuated from turbulent intensity and turbulent length scale. "A convenient option is set nuTilda = 5*nut". 2. Can you share your answer? 3. I am not understand what you want simulate. A fixed valued inlet velocity can not meet your standard? I mean why velocity need to accelerate suddenly to generate votices? And what is your net circulation ?