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Need help with analysis of a small compressor/diffuser system

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Old   September 27, 2009, 15:40
Default Need help with analysis of a small compressor/diffuser system
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James Berlin
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Hello, I am doing my senior design capstone project on the optimization of the diffuser in a small turbojet engine that we are building. The compressor is 66mm diameter.

Because the diffuser is so small, lots of the diffusion takes place in the case rather than in the diffuser, so the case volume needs to be incorperated.

I am trying to start using some CFD on the current diffuser design and subsequently some new designs, but don't have the method correct yet.

I have gotten some results using an external flow with the rotating region around the compressor at 10,000rad/s, but I don't know how to add "backpressure" due to the combustion/turbine; I can only get results with the case open to atmospheric pressure. This, I think is leading to excessively high mach numbers and unuseable results.

When I try to use an internal flow analysis, I cannot select the lid at the exit because it is "not on the fluid boundary" and Im not sure why.

If anyone has advice or can suggest an alternative way of obtaining results I would appreciate it.
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File Type: jpg Vel cut and vector.jpg (50.6 KB, 12 views)
File Type: jpg Combustion Chamber Trajectory Rear.jpg (77.9 KB, 12 views)
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Old   September 27, 2009, 15:50
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James Berlin
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For reference, this is a cut away of our turbojet design and a rendering of the compressor and diffuser.
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File Type: jpg cut away rear iso.jpg (44.0 KB, 6 views)
File Type: jpg DiffuserCompressor.jpg (43.5 KB, 8 views)
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Old   October 1, 2009, 09:59
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Could you load a picture of your model with all parts visible and the computational domain. I don't quite understand where your lid is positioned. I had similar problems from changing an external calculation to an internal. Mostly I had to redesign the model and create a complete new file.
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Old   October 3, 2009, 06:44
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murat
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Quote:
Originally Posted by jkbg38 View Post
Hello, I am doing my senior design capstone project on the optimization of the diffuser in a small turbojet engine that we are building. The compressor is 66mm diameter.

Because the diffuser is so small, lots of the diffusion takes place in the case rather than in the diffuser, so the case volume needs to be incorperated.

I am trying to start using some CFD on the current diffuser design and subsequently some new designs, but don't have the method correct yet.

I have gotten some results using an external flow with the rotating region around the compressor at 10,000rad/s, but I don't know how to add "backpressure" due to the combustion/turbine; I can only get results with the case open to atmospheric pressure. This, I think is leading to excessively high mach numbers and unuseable results.

When I try to use an internal flow analysis, I cannot select the lid at the exit because it is "not on the fluid boundary" and Im not sure why.

If anyone has advice or can suggest an alternative way of obtaining results I would appreciate it.

I suggest a code to redesign the project

http://www.softinway.com/

Axstream turbomachinery software has experimental solver and has CFD solver too

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