# new to CFD, changing angle of attack/incidence?

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 April 22, 2012, 10:57 new to CFD, changing angle of attack/incidence? #1 New Member   Benjamin Kim Join Date: Apr 2012 Location: Philadelphia, Pennsylvania Posts: 6 Rep Power: 5 I am new to CFD and just learning how to use Star-CCM+. I was able to analyze and simulate a very simple airfoil by following tutorials. However, I do not know how to change the angle of attack. Do I just transform the geometry part by rotating it a certain amount of degrees/radians? Or is it more complex than that? Thank you.

April 22, 2012, 16:19
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Ryne Whitehill
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Quote:
 Originally Posted by bjk87 I am new to CFD and just learning how to use Star-CCM+. I was able to analyze and simulate a very simple airfoil by following tutorials. However, I do not know how to change the angle of attack. Do I just transform the geometry part by rotating it a certain amount of degrees/radians? Or is it more complex than that? Thank you.

Depending on your problem type, you do not need to rotate the geometry.... just change your farfield boundary conditions to reflect new velocity values (i.e. use the directional scalars of the velocity vector to "rotate" the flow)

April 23, 2012, 15:42
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Lucky Tran
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Quote:
 Originally Posted by bjk87 I am new to CFD and just learning how to use Star-CCM+. I was able to analyze and simulate a very simple airfoil by following tutorials. However, I do not know how to change the angle of attack. Do I just transform the geometry part by rotating it a certain amount of degrees/radians? Or is it more complex than that? Thank you.
It depends on your boundary conditions, but another way is to simply have the velocity inlet to have flow at an angle relative to the inlet instead of purely normal.

 April 23, 2012, 17:05 #4 New Member   Benjamin Kim Join Date: Apr 2012 Location: Philadelphia, Pennsylvania Posts: 6 Rep Power: 5 Oh, I see. Thanks.

 August 18, 2015, 16:13 angle of attack in STARCCM+ #5 New Member   rangel Join Date: Aug 2015 Posts: 1 Rep Power: 0 Hello all, I changed the velocity components to obtain an angle in an airfoil but I am having negative drag. Anyone knows why? The lift is ok. In other simulation, I changed the angle of attack in CAD program and imported for STARCCM+, thus I know the right values. I just would like to be able to change the angle of attack IN the STARCCM. And you know other ways to do this? I couldn't understand the ways in the tutorial.

August 19, 2015, 12:34
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Lucky Tran
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Quote:
 Originally Posted by rangelgeja Hello all, I changed the velocity components to obtain an angle in an airfoil but I am having negative drag.
Did you update the direction vector for the drag and lift?

 August 20, 2015, 15:42 #7 Senior Member   Matt Join Date: Aug 2014 Posts: 352 Rep Power: 4 1. As LuckyTran implied but did not specify, your drag vector must point in the same direction as freestream flow. Lift is perpendicular to that. So if you are changing your velocity vector then your force vectors must change too. You can also define the vectors along the chord line and normal to the chord line to get normal and axial force, then simply transform those using: L=N*cos(AOA)-A*sin(AOA), and D=N*sin(AOA)+A*cos(AOA). 2. No need to rotate in CAD if you want to move model WRT flow direction. There is a transform and rotate function if you right click the geometry under parts and select transform > rotate. Then define origin, axis and angle to get your model pointed in the right direction. You will have to remesh.

 September 2, 2015, 11:11 #8 New Member   Xiaosong Zhang Join Date: Oct 2014 Posts: 10 Rep Power: 3 There is another way to do this. Make sure you have 2 regions. One region is a disk region which has the airfoil in it and the other one is the stationary fluid domain. Simply rotate the first domain to fit your AOA. Hope that will help.

 October 2, 2015, 03:31 #9 New Member   fangwei Join Date: Sep 2015 Posts: 4 Rep Power: 2 in the inlet boundary condition if i change the angle of attack by change the directional vector.like below for example X-direction 1 Y-direction 0 which is 0 angle of attack. right? X-direction 0.97814760073 Y-direction 0.20791169081775931 which is 12 degree angle of attack. right? if i change the AOA, do i have to change the axis for the life and drag?

October 2, 2015, 03:32
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fangwei
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Quote:
 Originally Posted by MBdonCFD 1. As LuckyTran implied but did not specify, your drag vector must point in the same direction as freestream flow. Lift is perpendicular to that. So if you are changing your velocity vector then your force vectors must change too. You can also define the vectors along the chord line and normal to the chord line to get normal and axial force, then simply transform those using: L=N*cos(AOA)-A*sin(AOA), and D=N*sin(AOA)+A*cos(AOA). 2. No need to rotate in CAD if you want to move model WRT flow direction. There is a transform and rotate function if you right click the geometry under parts and select transform > rotate. Then define origin, axis and angle to get your model pointed in the right direction. You will have to remesh.

in the inlet boundary condition if i change the angle of attack by change the directional vector.like below
for example
X-direction 1
Y-direction 0
which is 0 angle of attack. right?
X-direction 0.97814760073
Y-direction 0.20791169081775931
which is 12 degree angle of attack. right?

if i change the AOA, do i have to change the axis for the life and drag?

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