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May 6, 2010, 08:54 

#41  
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Attesz
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Quote:
yes you are right, the "real" surge is a totally transient phenomenon. But I found in every paper, that the operational point is easily attainable with steady simulations. My compressor works at 70000RPM and PR1.65, but we reach "surge" at PR1.4. This "surge" means, that there is a very low mass flow in and out of the domain. The separation mentioned above closes the whole blade passage. 

May 6, 2010, 08:59 

#42 
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Susann
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And how big is the distance between instability/surgelimit and this operational point? Do you have measurements? Often big separations already occur at the design point of a compressor, so that there are strong transient effects even at design point.


May 6, 2010, 09:05 

#43  
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Attesz
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Quote:
I have measurements only on operating point, because this is a gas turbine engine. We have not enough equipment to measure the compressor stage separately. Thanks for your advices! 

May 12, 2010, 04:10 

#44 
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Attesz
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Hi,
can I use Frozen Rotor fluid interface, when my geometry is periodic, and the Pitch Ratio isnt equals 1? There is nothing about it in the help. I have a 60deg impeller, and a 72deg stator, so the Pitch Ratio is about 1.2. I want to take into account the blade interferences...and I think, I cannot use TRS only when I have the same periodicity angles.. Regards, Attesz 

May 12, 2010, 09:51 

#45 
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Susann
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Hey,
when you use FrozenRotorModel and the pitch changes, the fluxes are scaled by the pitch change. 

May 13, 2010, 05:53 

#46 
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Attesz
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Hi Susann,
I know that, but can it cause high numerical errors? In some papers, I read that in Transient Rotor Stator, or Transient Frozen Rotor simulations, I can use only Pitch Ratio 1. Of course, with Stage option, it is not a problem. What do you think? Thanks, Attila 

May 15, 2010, 09:44 

#47 
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Susann
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Could you maybe give me a link to this papers? I`ve never heard about this before...I would follow the recommendation of CFXhelp and I found nothing about a pitch change of 1 for frozen rotor or transient simulations...would be very bad because there is seldom a pitch change of 1 for a compressor with vaned diffusor. Just give it a try with the frozen rotormodel, its even faster than stage model...than you will see whats better in your case after comparing it to the experimental results...


May 15, 2010, 10:07 

#48 
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Attesz
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http://www.ansys.com/events/proceedi...PAPERS/252.pdf
There is really nothing in help about this, but in this paper, it is described. Have a nice weekend! 

May 17, 2010, 03:43 

#49 
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Susann
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I know this paper...but i find the same description of the interfacemodels as in CFXhelp...i cannot find something about pitch change 1...sorry but can you give me a hit where in the text you find that?


May 17, 2010, 05:01 

#50  
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Attesz
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Hi Susann,
Quote:
So I correct myself, you can use not only pitch ratio 1, but using frozen rotor, it can cause as big numerical error as big the area difference is. 

March 17, 2014, 01:17 
Turbulence model in Rotor 37

#51 
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Manpreet
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Hello Guys,
I am working on project Flow field analysis through rotor 37. Cd anyone please let me know about which turbulence model is better to get results and why ? I really appreciate . Thanks Manpreet Singh manpreet_singh_er@yahoo.co.in 

March 21, 2014, 04:45 

#52 
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Song Weimin
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what u mean by "increase"is continuing to calculate the original results by larger time step?


March 23, 2014, 16:26 

#53 
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Manpreet
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Hello Guys,
Cd anyone please let me know detail about Timescale factor and Convergence RMS. What's significance of these two? In addition, Which solver method is responsible for solving Nstokes equations in CFX. I really appreciate . Thanks With regard Manpreet Singh manpreet_singh_er@yahoo.co.in 

March 23, 2014, 17:49 

#54 
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Glenn Horrocks
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Time scale factor is used by the solver to march towards a solution. It is part of the numerical method. The residual is a measure of the accuracy of the solution of the equations.


March 24, 2014, 00:06 

#55 
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Manpreet
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Thanks..ghorrocks.
Cd u please tell me in detail which numerical method CFX used for soling NS equations such as time marching or anything else. Where can I find detail about this. Thanks Manpreet Singh 

March 24, 2014, 00:07 

#56 
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Glenn Horrocks
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It is all in the documentation  see the theory manual.


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