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Mr. Simone Bigalli

Parametric volute - transition between circular and overhung section

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Hi,

 

I’m currently working on the creation of a parametric volute with an overhung section.

 

Recently I’ve encountered many problems in the creation of the loft connecting the initial section of the volute with the one of the outlet duct, since I’m not able to obtain a smooth transition from a circular shape to an overhung one (of which I attached a picture).

 

In the last CAESES webinar I attended (Volute Optimization by CAESES + GRIDPRO + TCFD, 5.03.2019), a volute similar to the one I’m working on is shown, where such transition is obtained in a smooth and robust way, and I was wondering how did you manage to achieve it.

Did you connect the two sections by mean of a pseudo-circular section, extrapolated from the overhung one? Or did you use a special loft function embedded in CAESES, capable of automatically excluding the diffuser region from the loft? 

 

Thank you very much.

 

Cheers.

Simone

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Hi Simone,

 

Please find attached a simple example that shows the basics. In most cases, you can use a fillet surface which can be nicely controlled (varied during studies) by means of its tangent factors. In order to build it up, you need auxiliary adjacent surfaces (e.g. ruled surfaces) that provide the tangent information.

 

Some additional things to keep in mind:

 

The start locations of the start and end profile needs to be aligned, otherwise the surface gets twisted. You can control this by rotating the circle profile to a suitable location, for instance.

 

The fillet surface has 3 different creation methods. The sampling method in the attached example creates a set of points (number can be controlled) which are interpolated. NURBS-based creation matches the profile exactly. Difficult to tell which one is more suitable, this depends on your application. In the example, sampling with a sufficiently high number of points is ok, the resulting brep geometry seems to be closed. Just play around with it and check the brep or surface results.

 

Let me know whether this helps.

 

Cheers

Jörg

post-8-0-42049700-1552978043_thumb.png

volute_outlet.fdb

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Hi Joerg,

 

thank you very much for your reply, the methodology you described will be very useful for my work. Do you know if there's also the possibility, like in the webinar, to exclude the diffuser from the loft, generating a transition from a circular shape to a pseudo-circular one?

 

Cheers.

 

Simone

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Hi Simone,

 

I'm not exactly sure what you need, but if you want to use only a part of the cross section profile, you can use image curves and change the domain to create a sub curve. In order to close the open section, simply use a fillet curve, for instance. Then put everything into a polycurve again (take care of curve orientations, e.g. use auto-orientation of polycurves).

 

Hope this helps,

Jörg

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