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-   -   odd propeller flow (http://www.cfd-online.com/Forums/cfx/78043-odd-propeller-flow.html)

 s0me0ne July 11, 2010 10:44

odd propeller flow

hi all once again... i want to quickly ask what causes the flow to act like this on this fan? (assume fan is rotating with a direction inwards towards the flat plane in order to accelerate flow downstream)

Surely flow must be 'sucked in' from upstream (left) and pushed at higher velocity downstream (right) ?

CFX1.png is velocity contour
CFX2.png is flow streamlines with velocity variable
CFX3.png is velocity vectors

What am i doing wrong?

Ideally if someone could briefly explain the CFX-Pre steps one should take when dealing with domain interfaces and the different types of periodicity for this problem and where once should apply them on the domains

http://img191.imageshack.us/i/cfx1.png/
http://img27.imageshack.us/i/cfx2.png/
http://img138.imageshack.us/i/cfx3.png/

 ghorrocks July 11, 2010 18:55

Are you sure it is not just a startup thing? That is, after running for a while longer the flow settles down as you expect.

 s0me0ne July 12, 2010 04:24

well i did let it run for about 30 iterations or so. (dont know if this is enough)

But it seemed that the RMS values for U,V,W-MOM all decreased and then stayed at some constant value at about 1e-4. Is this maybe too few iterations?

Also, regarding the domain interfaces, i use translational periodicity a lot throughout, with a rotating domain for the fan (which the domain is like a cylinder that encloses it). Is this the correct approach?

 ghorrocks July 12, 2010 06:59

Quote:
 well i did let it run for about 30 iterations or so. (dont know if this is enough)
Maybe not. Run it longer and find out.

Quote:
 Also, regarding the domain interfaces, i use translational periodicity a lot throughout, with a rotating domain for the fan (which the domain is like a cylinder that encloses it). Is this the correct approach?
Unlikely. Do the tutorial example on an axial rotor/stator for how to link rotating domains to stationary domains.

 s0me0ne July 12, 2010 07:00

ok thank you ! , i will try doing the tutorial now

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