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Drag/Lift coefficients over an airfoil.

Posted May 20, 2010, 1:47 p.m. EDT Computational Fluid Dynamics (CFD) Version 4.2a 6 Replies

Alex Capdevila
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Hi,

Anyone know how to calculate this two important parameters over an airfoil?
I mean, how to do it, with COMSOL postprocess interface?

Lift coefficient = Integration of the vertical component of the pressure field over the surface of the airfoil.
Drag coefficient = Integration of the flow direction component pressure + viscous force x component.

I don't know how to use correctly the boundary integration command, in order to obtain these parameters.

Thanks in advance.
6 Replies Last Post Nov 29, 2011, 6:26 p.m. EST
Danial Tz
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Posted: 1 decade ago May 20, 2010, 2:00 p.m. EDT
Hi Alex,

Look at the flow over a cylinder example in the modeling library.
Hi Alex, Look at the flow over a cylinder example in the modeling library.
Alex Capdevila
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Posted: 1 decade ago May 21, 2010, 6:52 a.m. EDT

Hi Alex,

Look at the flow over a cylinder example in the modeling library.


Thanks Danial. It has been very useful.

I use the turbulent k-epsilon model, so the operator react() always returned the zero value.

With the operator T_x_chns / T_y_chns seems that it works well.


In other way, I would be able to calculate theese coefficients, with the momentum balance into rectangular domain with the airfoil inside. It would not contemplate the turbulence influences in the boundary layer and it would be more accurate.

THANKS.
[QUOTE] Hi Alex, Look at the flow over a cylinder example in the modeling library. [/QUOTE] Thanks Danial. It has been very useful. I use the turbulent k-epsilon model, so the operator react() always returned the zero value. With the operator T_x_chns / T_y_chns seems that it works well. In other way, I would be able to calculate theese coefficients, with the momentum balance into rectangular domain with the airfoil inside. It would not contemplate the turbulence influences in the boundary layer and it would be more accurate. THANKS.
Danial Tz
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Posted: 1 decade ago May 21, 2010, 8:41 a.m. EDT
Great to hear it.

Also, if you enable the weak constaints in the N-S do you get lm5 lm6? they are the lagrange multipliers that are the best to calculate the forces (they are the same as reacf(u) and reacf(v))

sorry I can not help more, as I have not played with turbulence yet.
Great to hear it. Also, if you enable the weak constaints in the N-S do you get lm5 lm6? they are the lagrange multipliers that are the best to calculate the forces (they are the same as reacf(u) and reacf(v)) sorry I can not help more, as I have not played with turbulence yet.
Alex Capdevila
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Posted: 1 decade ago May 24, 2010, 1:51 p.m. EDT
I am about to modelling a fin with 3D fluid flow k-epsilon environment. I am excited.

Thanks again Danial.
I am about to modelling a fin with 3D fluid flow k-epsilon environment. I am excited. Thanks again Danial.
Xue Cao
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Posted: 1 decade ago Jul 1, 2011, 9:24 a.m. EDT
hi, have you worked out the lift and drag coeff on the airfoil?? Does that depends on the time or may be I can use the stationary model?
I am running a project related to that... Do you have any idea of how to work out the coeff with attack angle? Thanks.
hi, have you worked out the lift and drag coeff on the airfoil?? Does that depends on the time or may be I can use the stationary model? I am running a project related to that... Do you have any idea of how to work out the coeff with attack angle? Thanks.
Nader Noroozi
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Posted: 1 decade ago Nov 29, 2011, 6:26 p.m. EST
Hi Alex

I am facing the same problem with reacf() since it gives me zero at all times. i am solving a flow between two eccentric cylinders and i would like to find a load that the inner cylinder can handle by integrating over the pressure on the inner cylinder surface.

Hi Alex I am facing the same problem with reacf() since it gives me zero at all times. i am solving a flow between two eccentric cylinders and i would like to find a load that the inner cylinder can handle by integrating over the pressure on the inner cylinder surface.

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