Calculating Lift/Drag for a boat

bart_weisser · August 18, 2013, 08:09

Hi people:

I am wondering if someone might be able to point me in the right direction.

I am simulating two-phase flow (air / water) over a (partially submerged) boat. The goal is to calculate the lift and drag forces over the surface.

If I simulated this as single phase (either totally water, or totally air), I get something that I consider as "reasonable".

However, when I combined the two phases, and extracted the lift and drag force, they are (1) not bounded by the corresponding single phase solution and (2) they are off by about two to three orders of magnitude.

I am thinking there might be something with the to the two-phase flow case setup, but I am not sure what that was. Any insights into this problem would be greatly appreciated.

Thanks in advance, Bart.

ghorrocks · August 18, 2013, 19:18

For a general question I can only give a general answer: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

You have not even told us whether the inaccuracy is in lift, drag or both - or if it is too high or low. You need to look at the model closely in the post processor and try to find things which do not appear realistic - they would be the focus of what to do next to improve accuracy.

August 18, 2013, 08:09	Calculating Lift/Drag for a boat	#1
bart_weisser New Member Bart Weisser Join Date: Feb 2010 Posts: 4 Rep Power: 16	Hi people: I am wondering if someone might be able to point me in the right direction. I am simulating two-phase flow (air / water) over a (partially submerged) boat. The goal is to calculate the lift and drag forces over the surface. If I simulated this as single phase (either totally water, or totally air), I get something that I consider as "reasonable". However, when I combined the two phases, and extracted the lift and drag force, they are (1) not bounded by the corresponding single phase solution and (2) they are off by about two to three orders of magnitude. I am thinking there might be something with the to the two-phase flow case setup, but I am not sure what that was. Any insights into this problem would be greatly appreciated. Thanks in advance, Bart.

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August 18, 2013, 19:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	For a general question I can only give a general answer: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F You have not even told us whether the inaccuracy is in lift, drag or both - or if it is too high or low. You need to look at the model closely in the post processor and try to find things which do not appear realistic - they would be the focus of what to do next to improve accuracy.