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hydrofoil cavitation

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Old   October 9, 2016, 04:16
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Hi, while running a DES simulation for cavitation on NACA 0015 in Star-ccm+, I observed vapours at near the outlet developing after the bubble diminished from the trailing edge. The scene in the link below shows the volume fraction of vapour at 100ms, they starting developing 10 time steps before this, would be great if someone could shed some light as I am still an amateur. This is at σ = 1, inlet velocity 6m/s and outlet pressure 20.9 kPa, could this be flashing? Thanks
http://imgur.com/a/YVo8H
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Old   October 9, 2016, 15:00
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Do you get reversed flow at the outlet during the run? Your outlet is far too close to your airfoil. Move it back 10-15 chord lengths.
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Old   October 9, 2016, 15:36
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Thank you for replying. The outlet is 4 chord lengths and I used several relevant papers to finalise the boundary conditions/domain size and ran a domain independence test. What causes reverse flow and how does it affect the residuals? The solution was converging but the X-momentum criterion was slightly above 1e-04. Cavitation and vapour shedding is observed at the hydrofoil tip and trailing edge. This happened only in DES model... it wasn't there in RANS and LES simulations.
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Old   October 9, 2016, 15:41
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I didn't get any error message for reverse flow, the velocity distribution and pressure coefficient also looks good.
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