how to normalize velocities? must we divide by kinematic viscosity or diffusivity ?

lbmagis · March 11, 2013, 09:34

Hello CFD Friends

,

i am using fluent ansys 6.3 right now and i am new ; i tried to divide by kinematci viscosity first and divide by thermal diffusivity another time in order to get the dimensioless velocities (Vx in the x-direction and Vy in the y-direction ) ;so the problem was that i got good results for values of the nusselt number but the velocities are not similar to those found in litterature(especially those found by De Vahl DAVIS 1983)
By the way , i am simulating natural convection in square cavity ,
please could you tell me where the mistakes i have?help me please
Thank you in advance

All the best

A CFD free user · March 11, 2013, 14:27

Hi
How do you want to get normalized velocity by dividing it by for example diffusivity or kinematic viscosity? Check it yourself. I guess it's totally impossible, cause velocity has a L/T dimension while for instance, dynamic viscosity has a M.L/T. I suppose that you need to divide the velocity by a reference velocity what exactly I did in my case where I divided the velocity obtained during simulation in a stirred tank by the tip velocity of impeller so as to get normalized velocity. In your case, I think you need to divide the velocity by free flow velocity which is not influenced by boundary layer, I mean V infinity. Hope it help.

March 11, 2013, 09:34	how to normalize velocities? must we divide by kinematic viscosity or diffusivity ?	#1
lbmagis Member amine Join Date: Jun 2012 Posts: 65 Rep Power: 13	Hello CFD Friends , i am using fluent ansys 6.3 right now and i am new ; i tried to divide by kinematci viscosity first and divide by thermal diffusivity another time in order to get the dimensioless velocities (Vx in the x-direction and Vy in the y-direction ) ;so the problem was that i got good results for values of the nusselt number but the velocities are not similar to those found in litterature(especially those found by De Vahl DAVIS 1983) By the way , i am simulating natural convection in square cavity , please could you tell me where the mistakes i have?help me please Thank you in advance All the best

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March 11, 2013, 14:27		#2
A CFD free user Senior Member A-A Azarafza Join Date: Jan 2013 Posts: 226 Rep Power: 14	Hi How do you want to get normalized velocity by dividing it by for example diffusivity or kinematic viscosity? Check it yourself. I guess it's totally impossible, cause velocity has a L/T dimension while for instance, dynamic viscosity has a M.L/T. I suppose that you need to divide the velocity by a reference velocity what exactly I did in my case where I divided the velocity obtained during simulation in a stirred tank by the tip velocity of impeller so as to get normalized velocity. In your case, I think you need to divide the velocity by free flow velocity which is not influenced by boundary layer, I mean V infinity. Hope it help.