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 anne November 26, 2008 10:20

attack angle in CFX

we all know that there are tow ways to consider attack angle in CFX simulation:

method 1: rotate geometry and remesh

method 2: modify inlet velocity components, as well as in intialization conditions.

however, in my case (I tried both of them), only method 2 works. method 1 can be run, but after I finish the running, i can't get all of the results (only part of them), i.e. i can't save the results correctly.

it doesn't make any sense, does it?

do your guys have any comments on it? a new bug? or i did sth wrong?

many thanks

anne

 CycLone November 27, 2008 10:15

Re: attack angle in CFX

Method 1 will work if you have done the geometry steps properly. Make sure you are rotating only the part of interest (presumably an airfoil or aircraft?) and if you did some kind of enclosure operation or boolean to create the fluid volume, you need to insert the rotation ahead of this operation, otherwise the fluid region will be unaffected.

There are a few other alternatives:

3. Rotate the geometry within CFX using the moving mesh capability. If you do this, you'll need to solve the mesh motion equations, so you may want to do a few iterations to move the geometry then restart with mesh motion turned off.

4. Place your body within a cylindrical or spherical domain and rotate the grid surrounding the body by using a mesh transformation in CFX-Pre.

5. Place you body with a cylindrical or spherical domain and apply a "frozen rotor" interface between the domains. The frozen rotor interface is only available if you have rotating frames of reference, but you can still use it for stationary domains. If you apply it, make sure the axis of rotation is aligned with the axis of your sphere or cylinder. The Frozen Rotor interface allows you to specify a clocking angle, which is normally used to examine the effect of grid alignment between rotors and stators. Rather than rotating the grid, the solver will offset the "virtual" alignment of faces at the interface, but the effect is the same.

6. Use the grid motion as in 2, but apply it to a cylindrical or spherical domain.

The advantage to doing this at the solver level is that you can write a CEL expression to clock the angle to achieve the desired CL on the fly.

-CycLone

 anne November 28, 2008 08:50

Re: attack angle in CFX

thanks, cyclone.

however, what about if I only rotate the geometry, and then modify the mesh a little (the mesh around the body is a cylindrical mesh), like reprojet some points, etc in order to make sure the mesh quality is still good. is that OK? actually that's what I have done, running can be started, but I can't save the results correctly. what do you think about this?

many thanks

 CycLone November 28, 2008 12:11

Re: attack angle in CFX

Where are you rotating it? In what application and how?

 anne December 2, 2008 07:42

Re: attack angle in CFX

it's nacelle application, let's assume flow direction is x-axis, so I rotate it along y or z and make it incline an angle with x-axis, which is the attack angle or side angle.

so what do you think

 CycLone December 2, 2008 11:13

Re: attack angle in CFX

Are you only rotating the nacelle?

 anne December 4, 2008 10:55

Re: attack angle in CFX

yes, then remesh around the nacelle.

 CycLone December 5, 2008 00:12

Re: attack angle in CFX

Why would you remesh around the nacelle only?

 anne December 12, 2008 13:00

Re: attack angle in CFX

because there is o-grid around nacelle. outside o-grid there is no big change because of the small attack angle

 CycLone December 16, 2008 21:33

Re: attack angle in CFX

How's the grid quality? Why just remesh locally?

 anne December 17, 2008 14:31

Re: attack angle in CFX

mesh quality is good, above 0.35, and it is a structured mesh, no need to change the far field area, anyway, many thanks for your points

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