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[DesignModeler] Shroud of centrifugal compressor

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Old   August 17, 2014, 06:26
Lightbulb Shroud of centrifugal compressor
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Hi

I am trying to draw a surface body i.e. shroud or casing around centrifugal compressor.

First i tried to project a line on the one of the blades in y direction with no success. My plan was to offset that curve by constant distance (equal to tip clearance gap).

As second attempt i have created a spline by choosing arbitrary location and then used revolve command to get the surface body. But I am not clear how to maintain the constant distance from blade tip (equal to tip clearance).

Any idea ?







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Old   August 17, 2014, 10:53
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Found some partial workaround...

Projected one the nearest blade on ZX plane (in fact made new exactly overlapping ZX as per requirement) and from there I have spline type curve. Moved that curve using offset command and then used revolve command to get the surface of shroud.





But I am not sure if this method is technically sound and would be produce shroud which would had been produced if we have drawn the curve for shroud in first instance when design of centrifugal compressor is carried out.



To check this method I have used one of the available geometry in Ansys DM workshops. These blade are straight and casing is linear and parallel to axis of rotation. This time i have two blades to make projection on two sketches and to my surprise (may be obvious) they are different.





Any idea how to move forward...
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Old   August 18, 2014, 04:14
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I can't see your pictures, but I have an idea of something that might work. What if you do a Solid Extension on the surface below. I think it extends in the surface normal direction.



Then revolve an edge of that extended surface. Would that be something to work from?



Then you could perform a surface extension from the edge at the outlet, and an extrude on the inlet edge if you wanted a larger surface.



Just some ideas
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Old   August 18, 2014, 08:24
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Is it normal to to tip locally?

it is mixed flow impeller how would you extend the surface at outlet...
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Old   August 18, 2014, 08:35
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I don't understand your question
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Old   August 18, 2014, 11:23
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I am asking two questions:

1. (related to the above posts) When you extend blade tip using solid extension feature (beta feature i guess), in which direction it extends? Requirement of turbomachinery design is that it should be constant (gap between shourd and tip at each station) and should be normal to blade tip at that location .

Typically compressors are designed in 2-d (meridional view) it is very much easy to get clearance gap and hence shroud curve by just moving the blade tip section by constant value or any other method.


2. This question is related to the surface extension after solid extension you have just shown. When we extend the surface beyond leading and trailing edge, what is the direction of extension? Will it be following some curvature and by which algorithm? For mixed flow pumps or compressors shourd is not straight at trailing, so will this method work there as well ?
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Old   August 19, 2014, 10:46
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1. The one I tried on was "almost" equal distance across the gap. I don't know the details, but try on yours and measure to see if its acceptable?

2. I believe it follows the curvature. If you know the path i suppose you can extend it by creating the new outer edge as well as a curve connecting the new and old on, then revolve it.

Just suggestions, in case you're really stuck
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Old   August 19, 2014, 14:12
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jrunsten : Method is working. As far as geometry is concerned, I have obtained it from somewhere. I am also attaching it here : https://dl.dropboxusercontent.com/u/...2014-1-20.STEP

Images from the working on same geometry in turbogrid and cfx are also attached for completeness.
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Old   August 19, 2014, 14:16
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