# turbulent intensity

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 June 20, 2004, 20:37 turbulent intensity #1 zwdi Guest   Posts: n/a 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

 June 23, 2004, 07:07 Re: turbulent intensity #2 Christian Guest   Posts: n/a You might want to check what the reference value that the calculation of the intensity is based upon is.

 June 23, 2004, 09:46 Re: turbulent intensity #3 Karl Guest   Posts: n/a 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. villager likes this.

 June 23, 2004, 19:44 Re: turbulent intensity #4 zwdi Guest   Posts: n/a 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

 June 24, 2004, 04:57 Re: turbulent intensity #5 Wu Jiankang Guest   Posts: n/a 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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