Rotated Airfoil with horizontal Velocity Vs. Horizontal Airfoil with inclined veloci

KarimSayed · November 6, 2020, 12:27

Greetings,

I am carrying out a CFD analysis of SD7032 Airfoil at Re=60000. I am encountering a weird problem. I tried two methods. First, keeping the airfoil in a horizontal position and defining the velocity direction to satisfy the angle of attack, and second, rotating the airfoil with the specified angle of attack and Keeping the velocity in a horizontal direction. The results of drag coefficient are different in both cases. I am using rectangular domain surrounding the airfoil with the following boundary conditions: first case, Velocity inlet from the front, upper and lower sides, and pressure outlet at the rear side, while in the second case, velocity inlet from the front side, walls for the upper and lower sides, and pressure outlet for the rear side. I also tried symmetry, and pressure outlet instead of the upper and lower walls in the second case and they yield almost the same weird result.

LoGaL · November 8, 2020, 05:23

Are you calculating it in the same direction with respect to the airfoil? I bet that when the flow is inclined and the airfoil is horizontal, you calculated the drag on the X direction rather than the one parallel to the inflow condition

KarimSayed · November 8, 2020, 07:51

Quote:

Originally Posted by LoGaL

Are you calculating it in the same direction with respect to the airfoil? I bet that when the flow is inclined and the airfoil is horizontal, you calculated the drag on the X direction rather than the one parallel to the inflow condition

Yes I calculated the drag in the same flow direction by setting up the x & y components of the drag monitor.

LoGaL · November 10, 2020, 17:07

So in the inclined Airfoil you are taking the x component of the drag and in the inclined flow the X component divided by the cosine of the angle of attack?

KarimSayed · November 10, 2020, 19:11

Quote:

Originally Posted by LoGaL

So in the inclined Airfoil you are taking the x component of the drag and in the inclined flow the X component divided by the cosine of the angle of attack?

In the inclined flow: Inlet velocity x=cos (AoA) Inlet velocity y=sin (AoA) drag x=cos(AoA) drag y=sin(AoA)

In the inclined Airfoil: Inlet velocity x=1 Inlet velocity y=0 drag x=1 drag y=0

LoGaL · November 11, 2020, 04:24

Ok I believe you. Can you post two velocity contours, one for the inclined airfoil and one for the inclined flow? Please use the same scale and try to make the airfoil size more or less equal

November 6, 2020, 12:27	Rotated Airfoil with horizontal Velocity Vs. Horizontal Airfoil with inclined veloci	#1
KarimSayed New Member Karim Sayed Join Date: May 2020 Posts: 7 Rep Power: 6	Greetings, I am carrying out a CFD analysis of SD7032 Airfoil at Re=60000. I am encountering a weird problem. I tried two methods. First, keeping the airfoil in a horizontal position and defining the velocity direction to satisfy the angle of attack, and second, rotating the airfoil with the specified angle of attack and Keeping the velocity in a horizontal direction. The results of drag coefficient are different in both cases. I am using rectangular domain surrounding the airfoil with the following boundary conditions: first case, Velocity inlet from the front, upper and lower sides, and pressure outlet at the rear side, while in the second case, velocity inlet from the front side, walls for the upper and lower sides, and pressure outlet for the rear side. I also tried symmetry, and pressure outlet instead of the upper and lower walls in the second case and they yield almost the same weird result.

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November 8, 2020, 05:23		#2
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	Are you calculating it in the same direction with respect to the airfoil? I bet that when the flow is inclined and the airfoil is horizontal, you calculated the drag on the X direction rather than the one parallel to the inflow condition

November 10, 2020, 17:07		#4
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	So in the inclined Airfoil you are taking the x component of the drag and in the inclined flow the X component divided by the cosine of the angle of attack?

November 11, 2020, 04:24		#6
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	Ok I believe you. Can you post two velocity contours, one for the inclined airfoil and one for the inclined flow? Please use the same scale and try to make the airfoil size more or less equal