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-   -   BladeGen and CFX - basic question (http://www.cfd-online.com/Forums/cfx/24265-bladegen-cfx-basic-question.html)

Dip July 12, 2007 21:18

BladeGen and CFX - basic question
 
I have created the impeller and diffuser(simple axial) in Bladegen, and created the mesh for each separately in TurboGrid. When I read the file for Stationary section and Rotating section in CFX, the mesh volume are overlapping each other. As if they are referencing the postion as they were created in BladeGen. How do I align these? Is this the right procedure? Or do I have to calculate the position and model it accordingly right from BladeGEN ?

Related second question. If the number of blades on impeller and diffuser are not same and therefore the assembly (as CFX conventionally does) would have the impeller blade and passage little offset to the diffuser one (as per 360/no. of blades etc.)

Is CFX doing this matching or alignment automatically or do I have to manually calculate and offset the two.

Thanking you Dip

Thanking Johnny, deLuther for previous answers and getting me started.


deLuther July 13, 2007 06:46

Re: BladeGen and CFX - basic question
 
I usualy use ICEM for meshing and make my geometry (also not in BladeGen) so that each part is in correct position. For second question: You must choose number of blade and stator passages so that area ratio between theese regions as close to 1 as possible. Maybe I don`t understood your question right... Can you post some picture on this (second) problem?

Dip July 13, 2007 16:59

Re: BladeGen and CFX - basic question
 
Okay atleast found some website to host the pictures related to my question.

I created the rotor and stator in BladeGen quite arbitrarily just to test how all these work. Mesh was generated in TurboGrid, rotor and stator separately and then brought into CFX.

1. It looks like this, one riding on top of other Picture 1. (just choose "free" on the first page and enter the whatever security code it gives on the second page and should download the JPEG) http://rapidshare.com/files/42749154/1.JPG

2. I clicked on a icon regarding aligning. It aligns itself in this way Picture 2. http://rapidshare.com/files/42749732/2.JPG

3. I have to go to "passage alignment" and "theta offset" to align these two. Picture 3. http://rapidshare.com/files/42749764/3.JPG

Now, is this the way this is done ? Do we have to always align the rotor-stator volume in this way?

Second question, from CFX forum-Wiki-Turbomachinery-Multistage Analysis-Frozen Rotor and Sliding Mesh Theory, it says

"Real engine: 36 stator vanes, 41 rotor blades Approximated engine: 41 stator vanes, 41 rotor blades, making it possible to simulate only 1 stator vane and 1 rotor blade Scaling of stator: All stator vanes are scaled by 36/41 = 0.8780 circumferentially."

Does it mean that I have to create 41 blade stator and rotor , say in BladeGen, so that the rotor passage and stator passage always have to match in CFX?

Please briefly explain in terms of BladeGEN-to-CFXPre, what is the logic behind this and how is it done.

Millions of thanks

Dip


Robin July 16, 2007 10:07

Re: BladeGen and CFX - basic question
 
Hi Dip,

The BladeGen models are independant, so it is up to the you to make sure the impeller and diffuser hub and shroud line up and end at the right position. That said, if you are using TurboGrid 11, it is possible to load the diffuser curve files when working on the impeller and have TG automatically locate the interface half way between the trailing and leading edges.

On your second question, there is no need to match the pitch betwen the impeller and diffuser. CFX will automatically account for this at the interface if you use Frozen Rotor, Stage or Transient Rotor Stator interfaces. What it does and which to use when can be found by reading the documentation. The turbo best practices guide is a good place to start.

Regards, Robin

Prachi July 17, 2007 04:04

Re: BladeGen and CFX - basic question
 
Hi Dip,

As Robin said you can move the rotor and stator to the correct positions related to each othr. Also for a steady state periodic simulation it is enough to simulate a single bale of both the rotor and stator and connect them via "stage". However you might need a 360 model for a transient model, but even for that you cna use the current mesh and copy it n -1 times to complete a circle in CFX- Pre( where n is the no of blades). I hope this information helps you.

Regards Prachi


Saima August 5, 2010 17:21

I am new in ICEM CFD and want to to meshing for a blade. Is it possible you can give me some basic steps for that. I will be very thankfull to u.


Quote:

Originally Posted by deLuther
;82617
I usualy use ICEM for meshing and make my geometry (also not in BladeGen) so that each part is in correct position. For second question: You must choose number of blade and stator passages so that area ratio between theese regions as close to 1 as possible. Maybe I don`t understood your question right... Can you post some picture on this (second) problem?



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