Turbulence length scale

MissCFD · August 7, 2014, 16:44

Hello,

I don’t understand very well the notion of turbulence length scale. Is anybody can help me on this?

I must set the turbulence length scale for my inlet boundary condition in a circular pipe just after an elbow. I have a turbulent flow. I ask me if the turbulence length scale that I indicate for my inlet boundary condition will be the maximum length scale of eddies in the whole domain or just in the inlet of pipe ? I tend to say that it is just valid at the inlet of pipe because the thickness of the boundary layer increase and so it will generate larger structure, no ?

Also, can I say that more the turbulent velocity profil is full and more the maximum turbulence length scale is small because shear is only very important on a short height of my boundary layer relative to turbulent velocity profil less full, no ?

Thank you for your help

ghorrocks · August 7, 2014, 18:32

http://www.lmgtfy.com/?q=turbulence+length+scale

Turbulence length scale is a field variable just like velocity, pressure or temperature. This means it can take different values at different locations or times. So the inlet will have its own value of length scale determined by the flow at that location.

Length scale versus wall height: I recommend you read a turbulence modelling textbook to answer this. "Turbulence modelling for CFD" by Wilcox is a good textbook on the area.

August 7, 2014, 16:44	Turbulence length scale	#1
MissCFD Senior Member Join Date: Aug 2014 Posts: 160 Rep Power: 11	Hello, I don’t understand very well the notion of turbulence length scale. Is anybody can help me on this? I must set the turbulence length scale for my inlet boundary condition in a circular pipe just after an elbow. I have a turbulent flow. I ask me if the turbulence length scale that I indicate for my inlet boundary condition will be the maximum length scale of eddies in the whole domain or just in the inlet of pipe ? I tend to say that it is just valid at the inlet of pipe because the thickness of the boundary layer increase and so it will generate larger structure, no ? Also, can I say that more the turbulent velocity profil is full and more the maximum turbulence length scale is small because shear is only very important on a short height of my boundary layer relative to turbulent velocity profil less full, no ? Thank you for your help

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August 7, 2014, 18:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	http://www.lmgtfy.com/?q=turbulence+length+scale Turbulence length scale is a field variable just like velocity, pressure or temperature. This means it can take different values at different locations or times. So the inlet will have its own value of length scale determined by the flow at that location. Length scale versus wall height: I recommend you read a turbulence modelling textbook to answer this. "Turbulence modelling for CFD" by Wilcox is a good textbook on the area.