hydrofoil cavitation

meem · October 9, 2016, 04:16

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

me3840 · October 9, 2016, 15:00

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.

meem · October 9, 2016, 15:36

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.

meem · October 9, 2016, 15:41

I didn't get any error message for reverse flow, the velocity distribution and pressure coefficient also looks good.

October 9, 2016, 04:16	hydrofoil cavitation	#1
meem New Member Join Date: Feb 2016 Posts: 7 Rep Power: 10	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

October 9, 2016, 15:00		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	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. meem likes this.

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October 9, 2016, 15:36		#3
meem New Member Join Date: Feb 2016 Posts: 7 Rep Power: 10	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.

October 9, 2016, 15:41		#4
meem New Member Join Date: Feb 2016 Posts: 7 Rep Power: 10	I didn't get any error message for reverse flow, the velocity distribution and pressure coefficient also looks good.