Effect of free surface on hydrofoil lift

swaze · April 20, 2017, 12:41

hi guys,

i'm doing a project on analysing the effect of the free surface on hydrofoil lift performing on an open channel using ANSYS CFX and i'm getting some odd results for the lift coefficient as i'm using the following equations for the drag and lift forces Lift=∫Pcosθ-∫Ʈsinθ since the lift is based on pressure and shear pressure around the airfoil. i'm supposed to get a Cl value up to 1.5 but i'm getting up to 3.4

ghorrocks · April 20, 2017, 18:52

Have you looked at the usual issues to establish accuracy: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

I have attempted this exact simulation several years ago, amazingly enough. I also found it a very difficult one to get accurate results on. This is because you have both flow over an airfoil (which probably has turbulence transition as a significant contributor) in addition to the effect of the free surface disrupting the pressure field. It is a challenging model.

And by the way, just use the force() function to get forces. There is no need to integrate pressure and shear forces over a surface. Let CFX do that for you.

April 20, 2017, 12:41	Effect of free surface on hydrofoil lift	#1
swaze New Member Darlin L. V Join Date: Mar 2017 Location: London Posts: 4 Rep Power: 9	hi guys, i'm doing a project on analysing the effect of the free surface on hydrofoil lift performing on an open channel using ANSYS CFX and i'm getting some odd results for the lift coefficient as i'm using the following equations for the drag and lift forces Lift=∫Pcosθ-∫Ʈsinθ since the lift is based on pressure and shear pressure around the airfoil. i'm supposed to get a Cl value up to 1.5 but i'm getting up to 3.4

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April 20, 2017, 18:52		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	Have you looked at the usual issues to establish accuracy: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F I have attempted this exact simulation several years ago, amazingly enough. I also found it a very difficult one to get accurate results on. This is because you have both flow over an airfoil (which probably has turbulence transition as a significant contributor) in addition to the effect of the free surface disrupting the pressure field. It is a challenging model. And by the way, just use the force() function to get forces. There is no need to integrate pressure and shear forces over a surface. Let CFX do that for you.