CFX wall placed error

krishna13j · October 1, 2014, 06:49

hello,

I am modelling a single passage of a centrifugal compressor with splitter blade. i have meshed using turbogrid. I am getting the problem of 'wall is placed at x% of the outlet.' How can this be resolved? I am using periodic interfaces.

AliMadayen · October 3, 2014, 01:00

Hi

Basically this message (not always error) means that at the outlet boundaries, backflow is happening. Depending on the problem you are solving, this might be physical, for instance consider a curved tube, at lower radius backflow is physical and possible.
But what to do, first check if this is physical or not. does the percentage decreases as the residuals reduce, or it converges to a constant value?

if backflow is physical, during solution the area that it covers will converge to a specific value. then, as error instructs, change your BC. if not, check your problem again and refine your mesh.
As a personal experience, try to put the outlet BC in a distance that your are sure fluid flow is fully-developed.

Best

JuPa · October 3, 2014, 09:37

Move your outlet to a region far from the compressor.

A quick fix is to change the outlet to an opening. But you'll face rebustness issues if you do this.

October 1, 2014, 06:49	CFX wall placed error	#1
krishna13j New Member cfd_guy Join Date: Apr 2014 Location: Munich, Germany Posts: 21 Rep Power: 12	hello, I am modelling a single passage of a centrifugal compressor with splitter blade. i have meshed using turbogrid. I am getting the problem of 'wall is placed at x% of the outlet.' How can this be resolved? I am using periodic interfaces.

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October 3, 2014, 01:00		#2
AliMadayen New Member Ali Madayen Join Date: Apr 2014 Posts: 22 Rep Power: 12	Hi Basically this message (not always error) means that at the outlet boundaries, backflow is happening. Depending on the problem you are solving, this might be physical, for instance consider a curved tube, at lower radius backflow is physical and possible. But what to do, first check if this is physical or not. does the percentage decreases as the residuals reduce, or it converges to a constant value? if backflow is physical, during solution the area that it covers will converge to a specific value. then, as error instructs, change your BC. if not, check your problem again and refine your mesh. As a personal experience, try to put the outlet BC in a distance that your are sure fluid flow is fully-developed. Best

October 3, 2014, 09:37		#3
JuPa Senior Member Mr CFD Join Date: Jun 2012 Location: Britain Posts: 361 Rep Power: 14	Move your outlet to a region far from the compressor. A quick fix is to change the outlet to an opening. But you'll face rebustness issues if you do this.