Hi all, I was wondering if anyone could help me with this problem.I m try to show that is possible to delay the separation over a NACA 0012 using vortex genereators into the sub-boundary layer.I ve done 4 2-D simulations at 4 different a0a in CFX.Now,as the separation happen,I need to determine the distance between the leading edge and the separation point to calculate the geometric dimension of the VGs.Anyone has a clue of how this can be done? After plotting streamlines and velocity vectors,I dont know how to do.Maybe plot the velocity on the polyline and export in Excel and see where the velocity goes down....It looks too rough as definition of an exect point. If you have an idea, please let me know it.

Thanks for now.

Franny

Wall shear stress

Thanks joe,where the shear stress is zero,then the corresponding coordinate gives me the exact point right?

Hi Franny,

It sounds like an interesting analysis. Just out of curiosity: How are you modelling the vortex generators?

/CFDWorker

Hi CFD worker, could you please be a little more specific about your question?What I ve done till now is see the flow around the airfoil for 4 different AOA from 0 to 20.I ve get the separation at 15deg.Then im calulating BL thickness and I will insert into the lower sub BL co-rotating or counter rotating VGs.Still have to decide.I m considering also the trapezoidal ones.Once i ve ribuilt my wing with the VGs on it i will run another simulation and see what happen to the flow separation.I should get some improvement from the free VGs case. I m not sure i ve answer at your qstion,then email me back in this case.

Cheers

Franny

Hi Franny,

In my opinion there are several ways to deal with VG's. You could model them directly (ie. resolving the geometry), and I understand that is what you are planning. Alternatively, you could use different kind od source models, ie. you could apply imposed velocities or turbulence quantities in the areas of the location of VG's. Now, I do not have the answer how to, but it is also a computation that I am planning to try out in the future. It is a bit of a trial and error prob. What application are you using the VG's for. Airplanes or?

Best regards

CFDworker

Hi ,Im have to find a way how to delay separation over a NACA0012 and one method is use VGs.I think i will go for the geometrical approach asI new at cfx and the deadline for my project is close.And if i dont get good results i will find another way. May i ask you a question? I need to calculate the boundary layer thickness.I suppose i need to plot the velocity and see when it equals the 99% of the freestream value , let s say along a polyline.But Is that correct? Thank you for your help.

Regards.

Franny

Hi Franny,

Yes, I think that would be an ok method of estimating the approximate BL thickness.

Best regards CFDworker

[jacson]

HI Franny,

Total pressure

[Far]

what?