External flow with rotating propellors MRF domain size
 

Hi,

In my external flow studies of an aircraft with rotating rotors I am running simpleFoam with MRF defined in constant/MRFProperties. I have run the case twice, once with the MRF bounding box modelled very snug around the rotor (which is roughly 70cm diameter and 3cm height), the second one with 5cm ahead and 15cm behind the rotor. The results are vastly different, both visually in streamlines as in the magnitude of forces, with the first case being the most realistic in order of magnitude.

Does anyone know where I can find some good practice rules about which size this domain should be?

Also, I find it very hard to predict, but some of the streamlines are moving all over the place. Does anyone have any good rotor wake analysis and modelling papers I should read? I can't seem to find any decent papers, and the little images I find show a near perfect corkscrew wake, while mine veers of to the side, depending on rotation direction and geometry.

Cheers,

Bruno

Hi Bruno, I am also confused about the size of MRF region. With all the parameters constant, each time I change my MRF region size I get different results. I have made several simulations in this regard and found out that, whenever MRF domain is very close to upper part of the propeller, It usually gives wrong results and wrong representation of flow. A domain size of around 1.1D width and 0.3-0.5D height have given good results, which are closer to the experimental values. Very small MRF regions have given poor results. It would be great if you can share your experience with MRF domain size.

Thank you
Krao

It seems that the issue is being studied...Maybe the following paper can help.


https://www.tandfonline.com/doi/abs/...nalCode=tish20


Best,


CRI