# [DesignModeler] Shroud of centrifugal compressor

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August 17, 2014, 07:26
Shroud of centrifugal compressor
#1
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Sijal Ahmed Memon (turboenginner@gmail.com)
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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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 August 17, 2014, 11:53 #2 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 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...

 August 18, 2014, 05:14 #3 Senior Member   Josef Runsten Join Date: Jul 2010 Location: Gothenburg, Sweden Posts: 174 Rep Power: 13 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

 August 18, 2014, 09:24 #4 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 Is it normal to to tip locally? it is mixed flow impeller how would you extend the surface at outlet...

 August 18, 2014, 09:35 #5 Senior Member   Josef Runsten Join Date: Jul 2010 Location: Gothenburg, Sweden Posts: 174 Rep Power: 13 I don't understand your question

 August 18, 2014, 12:23 #6 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 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 ?

 August 19, 2014, 11:46 #7 Senior Member   Josef Runsten Join Date: Jul 2010 Location: Gothenburg, Sweden Posts: 174 Rep Power: 13 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

August 19, 2014, 15:12
#8
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Sijal Ahmed Memon (turboenginner@gmail.com)
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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.
Attached Images
 1.jpg (53.0 KB, 3 views) 2.jpg (67.0 KB, 6 views) 3.jpg (59.4 KB, 5 views) 4.jpg (73.2 KB, 6 views) 5.jpg (44.7 KB, 4 views)

August 19, 2014, 15:16
#9
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Sijal Ahmed Memon (turboenginner@gmail.com)
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As CFD-Online allow max 5 images per post as attachment. Remaining are here...
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 6.jpg (86.5 KB, 8 views) 7.jpg (45.0 KB, 6 views) 8.jpg (59.0 KB, 5 views) 9.jpg (56.0 KB, 7 views)

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