Slip-Wall Behaviour

InfernoxCJC · November 21, 2017, 15:32

Hey everyone,
As always, please forgive me if I am doing something stupid.

I am currently trying to replicate a wind tunnel experiment in STAR-CCM+ as a way of verifying that I can achieve some form of experimental correlation in my work.

With this in mind, I have established a model of the Wind Tunnel using the dimensions of the Working Section of the Tunnel in addition to extended slip-wall regions before the inlet and outlet in order to prevent inaccurate boundary layer. The method was recommended by my supervisor and is utilised in this paper.

The problem I am having is that I am experiencing what I believe to be strange behaviour along these slip-walls that is preventing any meaningful convergence. An example of this behaviour can be seen here, with 'odd' TKE behaviour prior to, and beyond, the working section, along these slip-walls. In addition to this, I am also seeing significant increase in free-stream velocity, above that of the inlet, throughout these regions.

I understand that this might not be sufficient information to fully explain the problem, and am happy to provide further details on request, but if anyone has any advice, I would be grateful.

Conor

me3840 · November 22, 2017, 01:48

I don't think your slip wall is working. How did you specify it? Does it create a boundary layer like a normal wall?

InfernoxCJC · November 22, 2017, 13:34

It turns out it was to do with still having Prism Layers despite being a slip-wall. Rookie error on my part and a waste of compute time even if they hadn't caused an issue, but it seems the small size of the near wall cell was causing some form of disturbance at the inlet that was replicating the effects of a boundary layer.

November 21, 2017, 15:32	Slip-Wall Behaviour	#1
InfernoxCJC New Member Conor Crickmore Join Date: Oct 2017 Location: Loughborough University, UK Posts: 12 Rep Power: 8	Hey everyone, As always, please forgive me if I am doing something stupid. I am currently trying to replicate a wind tunnel experiment in STAR-CCM+ as a way of verifying that I can achieve some form of experimental correlation in my work. With this in mind, I have established a model of the Wind Tunnel using the dimensions of the Working Section of the Tunnel in addition to extended slip-wall regions before the inlet and outlet in order to prevent inaccurate boundary layer. The method was recommended by my supervisor and is utilised in this paper. The problem I am having is that I am experiencing what I believe to be strange behaviour along these slip-walls that is preventing any meaningful convergence. An example of this behaviour can be seen here, with 'odd' TKE behaviour prior to, and beyond, the working section, along these slip-walls. In addition to this, I am also seeing significant increase in free-stream velocity, above that of the inlet, throughout these regions. I understand that this might not be sufficient information to fully explain the problem, and am happy to provide further details on request, but if anyone has any advice, I would be grateful. Conor

November 22, 2017, 01:48		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	I don't think your slip wall is working. How did you specify it? Does it create a boundary layer like a normal wall? InfernoxCJC likes this.

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November 22, 2017, 13:34		#3
InfernoxCJC New Member Conor Crickmore Join Date: Oct 2017 Location: Loughborough University, UK Posts: 12 Rep Power: 8	It turns out it was to do with still having Prism Layers despite being a slip-wall. Rookie error on my part and a waste of compute time even if they hadn't caused an issue, but it seems the small size of the near wall cell was causing some form of disturbance at the inlet that was replicating the effects of a boundary layer.