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Old   June 2, 2010, 14:51
Default Air flow on a pipe
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I am working on the simulation of a modified melt blowing process in which air flowing through a channel expands forming fibers from a polymer source.

At this moment I want to simulate the velocity flow field from the air flowing on the pipe. I have air coming from a compressor source at 80 psi. The air coming from this source is passed through a 2 mm channel (5 cm length) and then it is expanded to a 3 mm channel (1 cm length) before expanded completely to atmospheric pressure. I use k-e turbulence model and pressure inlet=80psi, and pressure outlet 0 psi boundary conditions. The problem that I have found is that the air speed is too high at the beginning. Usually I have supersonic speeds on the channel and I can get even M=2 on the expansion. These values are very unrealistic compared to what I can see on the lab. Any ideas for what I am doing wrong?. Any help is highly appreciated.

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Old   June 8, 2010, 07:31
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check your ambient pressure if it zero? should be 1 bar or equivqlent...
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