2D Axisymmetric vs. 3D

aloesch · July 31, 2009, 21:12

I am running a drag study on a shape that is essentially a revolved airfoil. As a test, I ran this shape in a 3D case then to cut down on computational time, I ran it in an antisymmetric 2D case. Problem is that the antisymmetric 2D case yields a drag which is nearly three times that of the 3D case (0.06lbf as compared to 0.18lbf). My tests are being performed at low velocities (30fps). I realize that with this little amount of information it is impossible for anyone to give me a definitive cause, but I was curious if this much variation is to be expected with such a low velocity, Reynolds Number, and drag, and if so, which calculation is more likely to be closer to the actual physical case. Thank you for any insight you can provide.

-mAx- · August 3, 2009, 00:51

axisymmetric gives you results as it should be in 3d.
* Is your 3d-model a full one, or did you use symmetric planes?
* Did you give same BC in 2d as in 3d?
compare the massflow-rates between 3d and 2d-axi

July 31, 2009, 21:12	2D Axisymmetric vs. 3D	#1
aloesch New Member Adam Loesch Join Date: May 2009 Posts: 8 Rep Power: 16	I am running a drag study on a shape that is essentially a revolved airfoil. As a test, I ran this shape in a 3D case then to cut down on computational time, I ran it in an antisymmetric 2D case. Problem is that the antisymmetric 2D case yields a drag which is nearly three times that of the 3D case (0.06lbf as compared to 0.18lbf). My tests are being performed at low velocities (30fps). I realize that with this little amount of information it is impossible for anyone to give me a definitive cause, but I was curious if this much variation is to be expected with such a low velocity, Reynolds Number, and drag, and if so, which calculation is more likely to be closer to the actual physical case. Thank you for any insight you can provide.

August 3, 2009, 00:51		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	axisymmetric gives you results as it should be in 3d. * Is your 3d-model a full one, or did you use symmetric planes? * Did you give same BC in 2d as in 3d? compare the massflow-rates between 3d and 2d-axi __________________ In memory of my friend Hervé: CFD engineer & freerider

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