preliminary propeller design

[jacckko]

hi guys, i'd like to make a thesis related to the preliminary propeller design, so finding the optimum circulation.. I found in internet a thesis wich use a matlab tool related to the induction factors.. could I use it for my thesis??
Any ideas of how continue the thesis??

thanks

[daiquiri]

Originally Posted by jacckko

I found in internet a thesis wich use a matlab tool related to the induction factors... could I use it for my thesis??

If you don't show us what you've found, it will be difficult to answer...

[jacckko]

these are the 2 projects..

http://dspace.mit.edu/bitstream/hand...pdf?sequence=1


www.dem.ist.utl.pt/~m_pta/pdf/30projecto.pdf


I'd like to compare the optimization method of the second project with the exact solution of the first project..
What do you think??

[jacckko]

anyone can help me??

[daiquiri]

Well, both works you have linked describe in a pretty detailed manner the mathematical formulation used. The first work is purely teoretical, no comparisons with experimental data are shown - while the second one shows some validation results.

I am not familiar with the OpenProp, don't know if it uses a lifting-line or a vortex-panel formulation. Don't have time now to investigate into the software documentation.
But, generally speaking, all lifting-line prop design software share some common accuracy issues, which become more pronounced with increased blade loading - like under-predicting Kt and Kq at low J. This is due to increased inluence of transverse flow components (which are neglected in the lifting-line formulation), but also due to methods used for the evaluation of induced velocity components, which are not very reliable at high disc loadings. A blade wake made of constant-diameter helical vortices is a mathematical hack valid for a lightly loaded propeller disc, but giving an increasing error as the loading becomes higher and the wake contracts.

Furthermore, there is a problem of the spanwise velocity of separated flows in the root (hub) region, which is induced by the centrifugal force. It is not accounted for in the 2D airfoil lift-drag curves on which lifting-line mathematical formulation relies, and significantly modifies the post-stall characteristics of the affected area of the blade. It is a well-known phenomena to aeronautical engineers which have to deal with high-rpm props and rotors, though I don't know how important it is for ship props which are revving at lower speeds (and hence centrifugal forces acting on separated boundary layers are much lower).

Vortex-panel methods have the capability of anlysis of more complex 3D-shaped propellers, like highly skewed or raked props. They can give a more detailed info about points of possible onset of cavitation. But they also tend to underpredict the coefficients at low J's, mainly due to inability to model the leading-edge flow separation at high blade loadings.

That said, if your design point is in a low or moderate-low disc loading zone, you can use the above tools for a preliminary prop design and optimization. Because of the aforementioned hydrodynamical issues, don't be too confident in the results at J < 0.4 (or even 0.5) without further validation. And also don't rely the results if the pressure distribution indicate the possibility of cavitating areas of the blade.

Cheers!