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December 7, 2007, 06:46 |
effekt of surface roughness very small
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Hi!
We did a simulation of heat transfer from a submerged body into a gas flow (2D, air, inkompr., Re = 10,000 based on body dimension, Tu of the upstream flow = 10%) with differnet surface roughness values and turbulence moddels. BUT: There is allmost no effect of the wall roughness hight on the Heat transfer. Even a value of 50 µm is resulting in a max. 1% decreased Nu number compared to a smooth surface (k-w sst with yplus between 1 and 5 an also k-e, std wall function yplus 30-80), What is the reason?? And even if the magnitude of the changes is ok - i would wonder about the direktion. I would expect the heat transfer to be higher for a rough wall! Any idea?? Ralf |
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