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fatb0y December 8, 2010 00:08

Dynamic simulation for unknown variables?
Hi all,

This is jsut a quick question. I hope that theres a Yes/No answer, and If its yes then pointing me to the right terminology to look for in help/other threads should be enough!

Basically, I am looking to simulate a gliding bird. But the specifics of the simulation isnt all that important... My qestion is, can you with CFX, set say airspeed and a desired lift force and have angle of attack parametric so that it settles on a value that satisfies both conditions above?

I am simulating something for which I have no way of knowing the exact angle of attack and airspeed combination to achieve a desired lift force.

I understand that this would require an adaptive mesh.

I have another project running simultaneously to this one in which I am plotting Cl, Cd and Cm vs Angle of attack for an aircraft at constant Reynolds numbers. And I wouldn't say Im a beginner with CFD/CFX (far from expert, very far) but I've been trying to think about how to plot a glide polar which is done at 1G (const Lift force), and I dont really want to trial and error my way through setting an airspeed and varying angle of attack to achieve 1G over a range of airspeeds.

Using thin airfoil theory to approximate Cl as = 2pi * alpha crossed my mind, but I thought I'd see if it is possible to set it up within the simulation so that this isn't needed any more than to perhaps estimate where it may be.

Sorry if this is an obvious or stupid question, never know perhaps I'd realise Im thinking about this the wrong way around if I leave it for a couple days, but I've been racking my brain and thought I'd throw it out there.


ghorrocks December 8, 2010 07:02

Rather than use a adaptive mesh this would be better done as a parametric study using WB. Then the simulations would be standard steady simulations with a fixed mesh, but the parametric stuff can take care of homing in on the correct AOA.

fatb0y December 8, 2010 18:43

OK thanks ghorrocks. Im yet to do anyting parametric in CFX but I'll look into it. Am I right in assuming then that because the mesh is fixed the angle of attack is then altered by changing the angle at which the flow enteres the doamin?

Thanks again, I'll see if I can dig up a tutorial.


ghorrocks December 8, 2010 19:24

No, you misunderstand. The parametric control will be on the AOA of the solid model, so it will automatically generate a range of solid models with different AOA. This then goes through the meshing, setup and solver stages to give the lift. You can either just plot lift vs AOA or use the parametric feature to home in on a lift value.

But each individual solution is done on a static mesh.

fatb0y December 8, 2010 20:26

Ah ok, thanks i understand now. Sounds like It may be a simple solution after all.


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