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 zwdi June 20, 2004 20:37

turbulent intensity

Hello,

I am wonderring how to get intensity values from kinetic energy and dissipation values in Fluent 6.1. Because I got unreasonable turbulent intensity at some points, even though correct turbulent kinetic energy and dissipation values at these points. Could anybody help me and give me some hightlights? Thank you very much.

Best regards,

Zwdi

 Christian June 23, 2004 07:07

Re: turbulent intensity

You might want to check what the reference value that the calculation of the intensity is based upon is.

 Karl June 23, 2004 09:46

Re: turbulent intensity

Turbulent Intensity is the ratio of the magnitude of the RMS turbulent fluctuations to the reference velocity:

I = (SQR(2/3*k))/vref

where k is the turbulence kinetic energy and vref is the reference velocity specified in the Reference Values panel. The reference value specified should be the mean velocity magnitude for the flow.

 zwdi June 23, 2004 19:44

Re: turbulent intensity

Thank you vey much, guys. I didn't realize this is relative with the reference values. Thank you for your hightlights.

I have another question related with kinetic energy and disspation rate at the boundaries. I set UDF function of dissipation rate and kinetic energy at inlet boundary. After I initialize the calculation from inlet boundary(only initialize,0 iteration), I check my boundary condition to see if they are defined correcly. But from report of the value of one specified point at the inlet boundary, I found disspation rate(epsilon value) changed a lot. The value is largely different from what I set in UDF(20 times), while kinetic energy,intensity and velocity are resonable. I checked a lot and could not image what is the reason. For calculating epsilon, Fluent must use length scale at specified cell. Do you know how Fluent deal with length scale to get the epsilon values?

Could you please give me a little bit highlights on this? Thank you very much.

Best regards, Zwdi

 Wu Jiankang June 24, 2004 04:57

Re: turbulent intensity

Hello, In some complex flow problems it is impossible to distiguish where is layer flow, where is turbulant flow. Can we always use turbulance model to calculate layer flow problems ? In theorey, it sounds reasonable, but I am wondering if it works or not.

In FLUENT, I simulated flows in micropump, using layer flow model and K-e model, respectively, I got different results. The flow patterns are similar, the velocity is smaller using K-e model than using layer model. Do you have any ideal ???

Thanks

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