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Problem comparing CFD results with experiment.

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Old   April 13, 2015, 23:34
Default Problem comparing CFD results with experiment.
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Sogol
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I am using STARCCM+ to simulate tubes with internally helical grooved (the ratio of tube length to pitch size is over 100 )with Re ranged between (4000-10000). Fluid model is solved with K-epsilon turbulent model in steady state. The mesh independence study have been done and the wall y+ is around 1. I calculated the Nu and F value for different Re which there are huge errors between experimental and CFD values especially in large Re. Since the groove is too small and generate swirl, I am thinking the realizable K-Epsilon two layer model ( I used all y+ wall treatment) cannot capture swirl effect inside the tube. Do you have any suggestion?

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Old   April 18, 2015, 06:55
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Tim Meier
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First of all, you have to be absolutely sure that you are comparing apples with apples and not something else. The Nu number can be automatically calculated in STAR-CCM+ (be careful with the inputs). You are comparing the experimental and numerical results at the same location? The boundary conditions are correct?

I think a two equation turbulence model is not suitable for such an application. Give it a try with V2F or an eliptic blending version of the k-epsilon.
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Old   April 18, 2015, 12:59
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Thanks Tim,
I tried to be as accurate as possible to match the boundary condition of simulation to study. Also, I am using the exact formula of the study to calculate Nu and friction factor. In Tubes with groove that has a larger pitch sizes, the results is acceptable but for smaller pitch the results is far off from the study. Again thanks, I 'll try with these two version to see if it is going to change.
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