turbulent kinetic energy and turbulent dissipation rate

D_L · February 23, 2010, 18:02

Hi all, I am a Star CCM+ user and currently doing a project on wind turbine wakes. In the Star CCM+, I have to assign a value to both turbulent kinetic energy (TKE) and turbulent dissipation rate (TDR) for simulation, but I have no ideas what values should they be.
Could anyone suggest me on how to define these values? If these values are chosen incorrectly, how will it affect the results?

Thank you.

harishg · February 24, 2010, 17:43

If the values are not chosen to represent the flow conditions approximately, the wind turbine wake predictions will be different. In outflow zerogradient is usually used. At walls you have k=0 and dissipation has to be calculated from asymptotic expressions to avoid singularity. At the inflow you need to know the precise value of k/epsilon/L.

D_L · March 2, 2010, 17:41

Quote:

Originally Posted by harishg

If the values are not chosen to represent the flow conditions approximately, the wind turbine wake predictions will be different. In outflow zerogradient is usually used. At walls you have k=0 and dissipation has to be calculated from asymptotic expressions to avoid singularity. At the inflow you need to know the precise value of k/epsilon/L.

Than you for answering. How can I get a precise value of the TKE and TDR at the inflow?
I looked at some technical reports but they did not mention the values of TKE and TDR used in their CFD simulations.

harishg · March 3, 2010, 20:39

Look for the NREL reports. They did extensive measurements. I am not sure of the exact details of the experiment but you should be able to find some useful information. Another option will be to look into the atmospheric rough boundary layer equations and check in the literature on ways people have used these equations for problem definition.

nvtrieu · July 14, 2010, 00:55

Hello,

I've been working with Star-CCM+ for several months. I also have the same question with D_L. How do I calculate the value for k,w,epsilon for the boundaries? could any one give me the answer?
Thanks in advance!

Trieu
email: trieuckgt@gmail.com

CCTech_Pune · July 17, 2010, 02:35

Hi

Please refer to "Development and Validation of WECC Variable Speed Wind Turbine Dynamic Models for Grid Integration Studies". This give good insight.

For length scales, you should consider using a length scale which is based on the size of the object over which flow is moving.

Thanks

February 23, 2010, 18:02	turbulent kinetic energy and turbulent dissipation rate	#1
D_L New Member Join Date: Feb 2010 Posts: 2 Rep Power: 0	Hi all, I am a Star CCM+ user and currently doing a project on wind turbine wakes. In the Star CCM+, I have to assign a value to both turbulent kinetic energy (TKE) and turbulent dissipation rate (TDR) for simulation, but I have no ideas what values should they be. Could anyone suggest me on how to define these values? If these values are chosen incorrectly, how will it affect the results? Thank you.

July 17, 2010, 02:35	Turbulence Intensity	#6
CCTech_Pune New Member CCTech Join Date: Jul 2010 Posts: 20 Rep Power: 15	Hi Please refer to "Development and Validation of WECC Variable Speed Wind Turbine Dynamic Models for Grid Integration Studies". This give good insight. For length scales, you should consider using a length scale which is based on the size of the object over which flow is moving. Thanks

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February 24, 2010, 17:43		#2
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	If the values are not chosen to represent the flow conditions approximately, the wind turbine wake predictions will be different. In outflow zerogradient is usually used. At walls you have k=0 and dissipation has to be calculated from asymptotic expressions to avoid singularity. At the inflow you need to know the precise value of k/epsilon/L.

March 3, 2010, 20:39		#4
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	Look for the NREL reports. They did extensive measurements. I am not sure of the exact details of the experiment but you should be able to find some useful information. Another option will be to look into the atmospheric rough boundary layer equations and check in the literature on ways people have used these equations for problem definition.

July 14, 2010, 00:55		#5
nvtrieu Member Join Date: Jul 2009 Posts: 70 Rep Power: 16	Hello, I've been working with Star-CCM+ for several months. I also have the same question with D_L. How do I calculate the value for k,w,epsilon for the boundaries? could any one give me the answer? Thanks in advance! Trieu email: trieuckgt@gmail.com