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Boundary Layer Across the Inlet of Nozzle

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Old   December 2, 2011, 06:46
Default Boundary Layer Across the Inlet of Nozzle
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I have a converging-diverging nozzle with 'pressure-inlet' and a 'pressure-outlet' and are using a no slip condition at the wall.

At my inlet, I have a velocity profile across it, indicating that I have some sory of boundary layer as I have a velocity profile across the inlet. But, as it is the inlet, I should not have a boundary layer because there has not been any boundary layer growth or anything.

Does any one know why this would be the case? The image shows what I mean. The x axis represents the y distance away from the centreline. There is a velocity profile when there shouldn't be one. I have also attached the velocity vectors at the inlet.

Thanks in advance!
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File Type: jpg inletvelocityprofile.jpg (45.6 KB, 13 views)
File Type: jpg Inletvelocityvectors.jpg (47.4 KB, 10 views)
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Old   December 2, 2011, 07:02
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shoeb khan
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Hi
Just try to use a very very fine mesh at the corners if you want a boundary layer at that place.

Thanks
SHK
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Old   December 2, 2011, 07:07
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I meant there should not be a boundary layer at the inlet, but my case shows there is a boundary layer there because of the velocity profile. I want to find out why there is a velocity profile there, when there shouldn't be one.

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Old   December 2, 2011, 23:43
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The problem is that at inlet the flow is developing and it requires some time to come under the state of fully developed state.
Hence during that transaction period there has to increase of velocity .

There is no slip condition at the walls. Hence the velocity there is 0.But at the center of the pipe velocity has to maximum. Hence there should be a velocity profile.

I hope this may help you.

SHK
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