
Re: Kutta Joukowski theorem for flow over a rotating cylinder
Amit Katz Aug 22, 2016 9:44 AM (in response to Theo Linders)I haven't looked at your model yet, but I'm not sure about your math. When I calculate the theoretical lift according to the simplified theorem, I only get 711 N/m, this is the equation I used: WolframAlpha: Computational Knowledge Engine
Your calculate force from the model is .485 N / 10cm = 4.85 N/m. So still pretty far off, but different numbers from what you have.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Theo Linders Aug 22, 2016 11:06 AM (in response to Amit Katz)your result is equal to mine.
My total lift for a 5 meter long beam is 3552 N, yours 711*5 = 3555 N. (manually calculated using the NASA site)
So our results differ 3 N.
the result from the flow software is 0.485 N per 10 cms computational domain
So.485*50 = 24.3 total lift


Re: Kutta Joukowski theorem for flow over a rotating cylinder
Amit Katz Aug 22, 2016 12:27 PM (in response to Theo Linders)There are some errors in your setup I can see.
Where you are setting your real wall condition, you are giving a translation and a rotation about the wrong axis.
First of all you don't need to translate the wall, because you already set the fluid to be moving at 40m/s in the project settings. So in the real wall settings the translation value should be 0 m/s.
Your rotation should be set around the zaxis, which is the longitudinal axis of your cylinder, it's currently set about the xaxis.
I changed these settings and came up with a lift value of 160 N/m, which is not correct according to theory but at least it's going in the right direction.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Theo Linders Aug 22, 2016 1:00 PM (in response to Amit Katz)aarghh
oh my god, that was stupid. I will also change the mesh and see what i get

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Theo Linders Aug 22, 2016 1:49 PM (in response to Amit Katz)i'm starting to changing the refinement criteria in de calculation control options and the values are going up. i keep you informed

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Theo Linders Aug 25, 2016 9:57 AM (in response to Amit Katz)
Re: Kutta Joukowski theorem for flow over a rotating cylinder
Amit Katz Aug 25, 2016 1:36 PM (in response to Theo Linders)This may be due to vortex shedding in the wake, which causes alternating lift forces on your blunt body. It's possible the physics code is simply not up to the task of simulating this theorem, you may want your VAR to take this up with SolidWorks.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Bill McEachern Aug 25, 2016 1:41 PM (in response to Amit Katz)you can use the Strohal number and get the frequency, first thing would be to check if you are in the right R'number range to see if vortex shedding is a possibility. See Hoerner, Dynamic Drag.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Amit Katz Aug 25, 2016 1:49 PM (in response to Bill McEachern)The R# is ~2.5x10^6. If I remember my theory correctly the only time you don't see vortex shedding in potential flow is at extremely low R#s, up to 1050.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Bill McEachern Aug 25, 2016 2:02 PM (in response to Amit Katz)Hoerner says max R'number ~80k for the upper limit if recollection serves. This is not, structly speaking, potential flow.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Amit Katz Aug 25, 2016 2:51 PM (in response to Bill McEachern)You're right, that wasn't the right term to use. I should have wrote "incompressible flow", that's the flow regime I meant.

Re: Kutta Joukowski theorem for flow over a rotating cylinder
Bill McEachern Aug 25, 2016 3:29 PM (in response to Amit Katz)figured you knew that but others might not understand the difference, hence the strictly speaking bit..






