odd propeller flow

s0me0ne · July 11, 2010, 11:44

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, 19:55

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, 05:24

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, 07:59

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, 08:00

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

July 11, 2010, 11:44	odd propeller flow	#1
s0me0ne New Member anon Join Date: Jun 2010 Posts: 6 Rep Power: 16	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/ Last edited by s0me0ne; July 11, 2010 at 13:20.

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July 11, 2010, 19:55		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	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.

July 12, 2010, 05:24		#3
s0me0ne New Member anon Join Date: Jun 2010 Posts: 6 Rep Power: 16	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?

July 12, 2010, 08:00		#5
s0me0ne New Member anon Join Date: Jun 2010 Posts: 6 Rep Power: 16	ok thank you ! , i will try doing the tutorial now