Pro­peller Design: Com­par­i­son of Blade Sections

If you need to compare one pro­peller design with another one — e.g. a new design can­di­date that is derived from the baseline — it helps a lot to have the 2D section infor­ma­tion at hand. When you set up a para­met­ric blade model in CAESES®, you can typ­i­cally access the 2D curve directly so that it is easy to compare a baseline with a new design. However, if you have the baseline design given as an imported NURBS surface or as simple point data, then you need other ways to bring back the 3D infor­ma­tion into the 2D space. 

The Reverse Transformation

Let’s say we have an imported baseline design i.e. a blade surface, and we addi­tion­ally created a new para­met­ric model in order to optimize the blade shape. So how can we now compare the section changes at a specific radius? Here is a possible quick solution:

1. As a first step, inter­sect the blade surface with a cylinder to receive an inter­sec­tion curve in the 3D space.
2. Cal­cu­late a set of posi­tions on this curve by using the ​“getPos()” command.
3. For each position, cal­cu­late the rota­tional angle ​‘theta’ — (oh no, trigonometry …)
4. Having the radius plus the angle ​‘theta’, unroll the infor­ma­tion into the xy-plane

You can put such a sequence in a small feature which should take you not more than 3 minutes (ok, I mean, it is easy once you’ve under­stood the maths and the idea behind it…). The fol­low­ing screen­shot shows the pro­ce­dure from above, wrapped into a CAESES® feature def­i­n­i­tion (click on the image to enlarge it):

Com­par­i­son of Baseline Design and a Variant

Now you create 2 instances of this feature def­i­n­i­tion, one for the baseline blade (red color) and another one for the new design (blue color). The input for these features are only the cor­re­spond­ing blade surface, and the radius where you want to compare the sections. Here is another screen­shot that shows the 2D com­par­i­son in the xy-plane:

Since we have the 3D inter­sec­tion avail­able from the feature above, we can of course also compare the 3D sections, together with the trans­par­ent new blade surface: 

Finally, here is an ani­ma­tion which shows the com­par­i­son of the baseline design with can­di­dates that have been gen­er­ated in an auto­mated design study: 

BTW: This also works for other blade appli­ca­tions such as fans, where you also design based on cylin­dri­cal surfaces. 

More Infor­ma­tion

Short and sweet.… You can find the project file of this post in our com­mu­nity forum. Let us know your thoughts about this post, and feel free to get in touch with us. Here is also another post about auto­matic blade gen­er­a­tion from imported data.

If you are inter­ested in trying out CAESES® for your appli­ca­tion then check out our product pages for more amazing details. Note that we also offer a powerful & free edition of CAESES®, which can be down­loaded from our website. There are no annoying or hidden lim­i­ta­tions, and you can directly start to set up your own intel­li­gent model today! 

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