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Mr. Chien Nguyen

Fitting a mathematic functions to set of blade sections

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Hello,

My problem is that I am having a set of blade section from 0.2R to 0.95R with data points for each sections. Basically, I can model the propeller from those sections by lofting a surface through all the sections.

But now, I would like to fit a mathematic function to all the blade sections to create a parametric profile then put it in a curve engine for propeller modelling. 

For example, fitting a mathematic function to the Wageningen propeller sections. Is there anyway in Caeses that can do this ?

I am thinking to start with the Naca profile then using optimization algorithm to find the value of c, m and p that creates the sets of sections which are best match with the sections from data points (for example the maximum distance is less than a define limit)

 

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Dear Chien,

it is indeed possible to use CAESES' optimization algorithms to perform geometric optimizations such as the fitting of parametric profile to a set of points. The main difficulty usually is the definition of an appropriate objective function -- you will want to put "weight" onto the leading and trailing edge region, otherwise they will be matched poorly as they take up only a small fraction of the overall chord length.

Depending on the quality of your data and how well the parametric profile matches the point data you will have to adjust things to your specific case. 

Attached is an example where I created a NACA profile and a set of discrete points from it. I then use a simple TSearch to fit another NACA to the point data -- looks like this:

profileFitting.thumb.gif.422b879d171d16237a02207a3a6de964.gif

Like I mentioned, I expect that you will have to play around a bit with how the error (which is minimized by the optimization algorithm) is calculated. Right now, it's a simple least squares approach...

Best regards,

Heinrich

testCase.fdb

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Dear Heinrich,

Thanks so much for your reply.

I have managed to import my data points and got the result as a picture below. The red curve is the Naca4ds after 100 iteration and the black one is the original profile from data points.

However as you said, I did not get good result at leading and trailing edge. I realized that at x = 0 and x = profile length, the y value of the Naca4Ds profile is also 0. But for the original profile, those y values are not 0.So that, it is impossible to get a good approximation Naca4ds curve to the original profile.

I am thinking to apply a deformation(or a deformation function, or something similar) to the Naca4Ds at leading and trailing edge to get the shape of original profile. How do you think ?

Thank you

image.png.d38817a1eee9577c6f25c4b15e73b06d.png

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