Multiple Reference Frame around an impeller

Spark · October 18, 2016, 07:38

Hi,
If I am considering a single impeller a cylinder around the impeller is considered for applying moving reference frame. Suppose now if I have 2 impellers on a single shaft, should I consider 2 separate cylinders enclosing the impellers or a single cylinder enclosing both the impellers?
Kindly help me out with this.

Thanks and regards.

CeesH · October 24, 2016, 04:04

You could do both, and probably it won't make much of a difference.
There was some study published in conference proceedings, I believe in the proceedings of the 10th european mixing forum in 2000, held in Delft. (can't find the book anymore since I moved office unfortunately), by Oshinowo if I'm correct. He claimed keeping the MRF-rotorzone relatively small yielded slightly more reliable results (smaller being approx 1.5x the impeller radius, with a zone height of approx. the impeller diamater).

Personally, I typically follow this guideline, even with a slightly more shallow zone sometimes. (+/- 1.5 blade height). Of course, it also depends on the inter-impeller spacing. If that is less than 1 impeller diameter, I typically put them in 1 rotating frame.

Hope this helps!

Cees

October 18, 2016, 07:38	Multiple Reference Frame around an impeller	#1
Spark New Member Ravi Join Date: Aug 2016 Posts: 2 Rep Power: 0	Hi, If I am considering a single impeller a cylinder around the impeller is considered for applying moving reference frame. Suppose now if I have 2 impellers on a single shaft, should I consider 2 separate cylinders enclosing the impellers or a single cylinder enclosing both the impellers? Kindly help me out with this. Thanks and regards.

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October 24, 2016, 04:04		#2
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	You could do both, and probably it won't make much of a difference. There was some study published in conference proceedings, I believe in the proceedings of the 10th european mixing forum in 2000, held in Delft. (can't find the book anymore since I moved office unfortunately), by Oshinowo if I'm correct. He claimed keeping the MRF-rotorzone relatively small yielded slightly more reliable results (smaller being approx 1.5x the impeller radius, with a zone height of approx. the impeller diamater). Personally, I typically follow this guideline, even with a slightly more shallow zone sometimes. (+/- 1.5 blade height). Of course, it also depends on the inter-impeller spacing. If that is less than 1 impeller diameter, I typically put them in 1 rotating frame. Hope this helps! Cees