Spinning propeller running vspaero

[Lan Ding]

Hi Brandon, a quick question. I setup a propeller model in vsp and use the aero to run the simulation. The trust and torque results do not fit what we had in CFD. I couldn't find a proper setup for wake nodes and time step to get steady results. Could you help me with this？It's a quite simple case and it drives my nuts. I can append the model if you need. 

[cean wang]

Sure the model is needed.

On Wed, 8 Nov 2023, 2:25 pm Lan Ding, <lding...@gmail.com> wrote:

Hi Brandon, a quick question. I setup a propeller model in vsp and use the aero to run the simulation. The trust and torque results do not fit what we had in CFD. I couldn't find a proper setup for wake nodes and time step to get steady results. Could you help me with this？It's a quite simple case and it drives my nuts. I can append the model if you need. 

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[Lan Ding]

Hi Cean, here is the thing. I have a about 2.5m 2-bladed propeller spinning at 1300rpm. I am using vspaero to get the thrust and torque and the FOM. I increas the wake nodes number and decrease the time step, expecting to get a set of steady results which I couldn't accomplish. I also compared with the results we get from CFD. The thrust is high and the torque seems close to what CFD gets. So I got struct now. We are deciding if it is allowed to upload this model. Meanwhile, do you have any idea what I can do about it? Or do you have a validated case so I can try to modify to my model to test again. Many thanks!!!   

[Brandon Litherland]

We would need more information in the absence of a model.  You can also create a "dummy" model that represents your case and see if the behavior persists with different geometry.  That model can be shared.  How many wake nodes are you using?  How many degrees per step are you taking?  What is your blade tessellation like?  What makes you think that the CFD results are accurate to reality and not the potential flow methods?  Have you validated your CFD process against a similar experiment to ensure that the results agree?

[Lan Ding]

Hi Brandon, I will try to make a "dummy" model. The wake nodes I am using is 128, 5 degrees time step and we validated the model using the test results. For the tessellation, I will need to check and get back to you.  

[Lan Ding]

Also, for the tessellation, do you have any recommendation?

[Lan Ding]

Hi Brandon, attached is my simplified model and we get the results as below: 64 wake nodes, 5 deg time step, thrust 800N; 64 wakes nodes, 15 deg time step, thrust 400N.  From my understanding, we should get steady/converged results when we change the wakes nodes larger or the time step smaller. Am I missing something here? 

[Cibin Joseph]

I was just curious about this case, so I took a look.

Looks like you're trying to simulate hover for the prop. The hover case will typically have wake instabilities. You could try using the hover ramp in the Propeller tab to start from a finite velocity and ramp down to zero; I've never been able to get it to work properly.

Perhaps inspect the wake in the viewer and check if the wake is converging.

Cibin

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[Lan Ding]

Thanks! I will give it a try.