Boundary layer separation

federico.bruni · May 29, 2012, 02:46

Hi everyone,
I have to simulate the fluid flow into a pipeline valve to calculate head losses during valve operating and when it's fully open in function of mass flow. This can lead to boundary layer separation so what is the best fluent configuration to handle this?

Secondly I tried to run a first simulation with incompressible flow (liquid water, Re > 10^6, valve fully open, k-omega SST, initialization with velocity inlet data) but solution shows big vortices both upstream and downstream of tha valve. And also a large amount of reverse flow at pressure outlet. I think it's physically unrealistic, don't you?

Thank you very much

delaneyluke · May 30, 2012, 05:13

Hi Federico,
Your set up seems correct.
What kind of mesh are you using (Tet of Hex)? What is your first cell height near the wall? What is your Y+ values at the wall? Did you extend your outlet far from the valve to prevent any recirc of flow at the outlet?

Regards
Luke

federico.bruni · May 30, 2012, 07:16

Mesh is Tet with inflation layer.
y+ is about 40/100... Obviously it has to be reduced to a value less than 1 to use Low-Re correction but I guess it's enough to have some sort of preliminary results. Maybe it's better to start with standard k epsilon model...

I'm also planning to switch to ICEM to have hex mesh but it takes a relevant amount of time.

Inlet is about twice the diameter of the pipeline far from the valve, 6/7 times for the outlet...

May 29, 2012, 02:46	Boundary layer separation	#1
federico.bruni New Member Federico Bruni Join Date: May 2012 Posts: 3 Rep Power: 13	Hi everyone, I have to simulate the fluid flow into a pipeline valve to calculate head losses during valve operating and when it's fully open in function of mass flow. This can lead to boundary layer separation so what is the best fluent configuration to handle this? Secondly I tried to run a first simulation with incompressible flow (liquid water, Re > 10^6, valve fully open, k-omega SST, initialization with velocity inlet data) but solution shows big vortices both upstream and downstream of tha valve. And also a large amount of reverse flow at pressure outlet. I think it's physically unrealistic, don't you? Thank you very much

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May 30, 2012, 05:13		#2
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Hi Federico, Your set up seems correct. What kind of mesh are you using (Tet of Hex)? What is your first cell height near the wall? What is your Y+ values at the wall? Did you extend your outlet far from the valve to prevent any recirc of flow at the outlet? Regards Luke

May 30, 2012, 07:16		#3
federico.bruni New Member Federico Bruni Join Date: May 2012 Posts: 3 Rep Power: 13	Mesh is Tet with inflation layer. y+ is about 40/100... Obviously it has to be reduced to a value less than 1 to use Low-Re correction but I guess it's enough to have some sort of preliminary results. Maybe it's better to start with standard k epsilon model... I'm also planning to switch to ICEM to have hex mesh but it takes a relevant amount of time. Inlet is about twice the diameter of the pipeline far from the valve, 6/7 times for the outlet...