Different Propeller RPMs Effect

[Maryam Alkhateri]

Hello

I tried to do an AERO analysis using the new version of OpneVSP (3.46- python 3.11). So my project is a Quadplane and I need to do an aerodynamic and stability analysis considering the effect of the propeller. To do this I used the Disk. The analysis worked, but now I need to repeat it for different scenarios (different RPMs all uniform & different RPMs not all uniform) but the thing is whenever I’m trying to do this the results do not change and are exactly the same!! Even I tried to do this using the propellers (Pseudo Steady Rotating) where the analysis will only show a single point (at a certain AoA) but still same result!!

Please I need your guidance on what to change for this analysis to make it work.
Find attached the file I’m working on.

Thank you

[Brandon Litherland]

You attached the Blades version of your propellers so I have no idea what actuator disk settings you were trying to use. Please attach a working version of your problem exactly as you modeled it.

I also suspect that you may be using the Shown set with your propellers instead of a named set.  Other posts here have pointed out that the new mesher will hide the disks and exclude them from the analysis unless you are using Sets.

[Maryam Alkhateri]

Please find attached the file with the disks, the following photos show what I have selected for the analysis.

[Maryam Alkhateri]

Hello again,

I want to double check if it’s working with you or if there’s any more information needed from my side. 

[Brandon Litherland]

All of your actuator disks have the default values of 2000 RPM, CT=0.4, CP=0.6. Let's do a quick test.  I pushed your wing NumU up to 41 and ran a comparison and set the Vinf to 15 as in your screenshot. You don't need both Vinf and Vref except for hover or very near hover. I also placed the wing and all props to Set 0 and ran Thin as described in other posts.  Your file still had Shown selected and did not reflect the images you posted above.

Using the default disk settings I get the following:

Now with 4000 RPM, keeping CT and CP fixed. Note that this is greatly increasing your thrust and power per  11.7 Performance of Propellers (MIT Propeller Performance page for easy reference).

Propeller RPM is clearly having a significant effect, as expected.  It seems like you're working in meters.  Have you determined what settings would be appropriate for this aircraft?  How heavy is it? You can directly set the thrust, torque, and RPM rather than using CT and CP or CQ. In order for us to be able to help you with your problem, we need to have enough information to understand exactly what you are doing.  There are things that we will know to do as part of the normal setup for an analysis that some may miss simply because they didn't fully understand the software or the problem being solved.  If you need to use actuator disks in your analysis, make sure you're modeling them properly with reasonable settings. Otherwise, the solution will be meaningless and often confusing.

[Maryam Alkhateri]

Appreciate your time and help, thank you.

We are working on a Quadplane project that is being designed without a tail, and part of our objective is to prove that the propeller effects can contribute to stabilizing the aircraft.

The total weight of the aircraft is 5 kg without payload, and 7 kg including a 2 kg payload. It’s designed to fly at 10–15 m/s at an altitude of 150 m.

We’re using five 860 kv motors with 14×7 propellers.

The goal of our analysis is to study the moment versus angle of attack under different rotational speeds of the propellers, considering several scenarios for the front and rear propeller speeds. For each case, we aim to determine the static margin to evaluate the aircraft’s longitudinal stability.

Please let me know what additional parameters you need for the analysis. If you make any changes, kindly share the updated file.

Thank you again for your support.

[Brandon Litherland]

It sounds like you have everything you need to do this study.

[Maryam Alkhateri]

Hi Brandon,

I tried running the analysis the same way you did, but my results came out different — the graphs don’t match yours. Could you please send me your file or share the parameters you used?

Also, have you had a chance to check the Cl vs AoA graph if it changes because this is the graph I need.

Thanks!

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[Brandon Litherland]

Although you will find extensive support for fundamental problems regarding OpenVSP, and often a great deal of additional explanation into specific problems, the community does not typically go so far as to solve your research problems for you.  It sounds to me like you have everything that you need to run your analysis including the proper disk settings.  If your results came out different than mine, that's completely fine.  I was using the default values as a demonstration and you shouldn't expect that to reflect the right answer.  It's been stated many times on this forum that there is no such thing as a CFD "easy button."  VSPAERO is deceptively simple to set up and run a problem but you still have to know _why_ you are setting the inputs to the solver how you are.  This includes performing a grid resolution study to compare trends, building up your model from an isolated wing to more complex simulations to ensure everything is trending as expected, and then checking your results against prior research to see if the simulation is giving you reasonable results.  All of this is part of learning how to solve these kinds of problems and we won't rob you of that experience.  Spend a week or so working on this, run your simulations, check your work, and then post some example results here if you still question the data.  We can and will help you with that when you've put the work in.

If this is for an academic project, I very strongly advise you to talk to your professor or research assistant to better understand the different requirements for this aircraft and how to set up the problem.  If this is for work, talk to some of the senior engineers and ask for their help.

[Maryam Alkhateri]

Dear Brandon,

I hope you’re doing well. I wanted to update you on the actuator disk analysis I’ve been working on. I’ve tried running multiple analyses with the propellers included, and then again without them. However, I obtained exactly the same results in both cases, which suggests that the software might not be taking the actuator disk into consideration.

Additionally, when I use the viewer to visualize the airflow over the wing, the actuator disk does not appear at all, unlike in the example image you shared earlier, where the disks were visible. I’ve actually been facing this issue since I first started working with the actuator disk.

I also wanted to confirm something regarding your setup. You mentioned that you placed the wing and all the propellers in set 0 and then performed the analysis. Could you please clarify whether the analysis was done for set 0 only or for all the shown components, including the fuselage? We want to make sure that the fuselage is also included in the analysis.

Lastly, could you please guide me through the steps you followed for the analysis to work properly and to show different results for different actuator disk RPM values? It would really help me understand what I might be missing.

Thank you very much for your time and guidance.

Best regards,

Maryam Alkhateri 

To view this discussion visit https://groups.google.com/d/msgid/openvsp/75fb6f58-a5e8-46ca-87ad-cdc2862ec1d4n%40googlegroups.com.

[Brandon Litherland]

I think that watching Rob's VSPAERO walkthrough will solve a lot of your issues.  

https://www.youtube.com/watch?v=yn1qsW3zWZk

Watch the entire video and implement the steps as described and demonstrated.  If you still have questions after that, please follow up on this thread and we can go from there.