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Old   April 16, 2008, 08:01
Default Pressure drop measurement
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Ananta
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Hi

I am trying to compute the local pressure drop due to flow area changes. I have first tried with simple geometry, a sudden enlargement in flow area in fluid flow through pipe. But the pressure difference across the area change I got is 40% less than the calculated by standard handbook formula. I have taken care of the entrance effect etc.

Please help!

Bye

Ananta
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Old   April 22, 2008, 11:23
Default Re: Pressure drop measurement
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Mike
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Are you comparing like with like? Engineering handbooks usually give the total pressure loss. If yes, then maybe there is insufficient grid resolution in the vicinity of the sudden expansion.
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Old   April 30, 2008, 05:18
Default Re: Pressure drop measurement
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hervé
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Additionnally, I would recommend to make sure:

- that your numerical model matches with the test rigg from which the handbook derives its results. (for instance, that you calculate the pressure drop on the very same sections, with sufficient length upstream and downstream the domain of interest, etc ..., etc ...)

- that you calculate (as implied by Mike) the pressure drop in the same way as the handbook does. It is usually based on the total pressure. Experimently, the static pressure is an average of locally measured static pressures whilst the dynamic pressure is constructed on the surface-averaged velocity (given by overall flowrate divided by the area of the surface).It is recommended to derive the dynamic pressure in the same way in the CFD model. The static pressure on a given surface can be obtained by calculating the mass-averaged static pressure on this surface.

- that you bear in mind that 40% difference can even exist between two handbooks. I have the experience of differences that were higher than 30% for a simple T-junction (3 channels), between the "Idel'cick" and the "D.S Miller" handbooks.

Hope it helps.
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