CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

Simulation of a 2D diffuser

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 10, 2021, 04:03
Default Simulation of a 2D diffuser
  #1
New Member
 
Join Date: Aug 2021
Posts: 4
Rep Power: 4
Sam6789 is on a distinguished road
Hi CFD users, for my CFD cource at the university I have to simulate flow into a 2D diffuser. Section of the diffuser is reptangular. Fluid can be treated as incompressibile. As a data, I know only Reynolds number based on hydraulic diameter, at the outlet, and the exit of the diffuser is at the atmosferic pressure. I calculate the mean velocity at the outlet using the Reynolds number given me as a data, and then the mass flow rate.
As boundary conditions, since I know nothing about the inlet, I calculate the velocity at the inlet based on the mass flow rate,because the fluid can be treated as incompressibile.
Then I imposed velocity inlet as a boundary condition at the inlet, and pressure outlet(gauge pressure equal to zero) at as boundary condition at the outlet.
I simulate the flow for two different Reynolds numbers: 50 and 8200.
However, a strange thing appears: in both cases I have flow separation, but the reattach point in case Re=8200(turbulent flow) is much more far away from the diffuser outlet than in case Re=50 (laminar flow).
Is something wrong with my boundary condition?
Someone can help me? Is very important

Last edited by Sam6789; August 10, 2021 at 07:03.
Sam6789 is offline   Reply With Quote

Old   August 10, 2021, 12:35
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by Sam6789 View Post
Hi CFD users, for my CFD cource at the university I have to simulate flow into a 2D diffuser. Section of the diffuser is reptangular. Fluid can be treated as incompressibile. As a data, I know only Reynolds number based on hydraulic diameter, at the outlet, and the exit of the diffuser is at the atmosferic pressure. I calculate the mean velocity at the outlet using the Reynolds number given me as a data, and then the mass flow rate.
As boundary conditions, since I know nothing about the inlet, I calculate the velocity at the inlet based on the mass flow rate,because the fluid can be treated as incompressibile.
Then I imposed velocity inlet as a boundary condition at the inlet, and pressure outlet(gauge pressure equal to zero) at as boundary condition at the outlet.
I simulate the flow for two different Reynolds numbers: 50 and 8200.
However, a strange thing appears: in both cases I have flow separation, but the reattach point in case Re=8200(turbulent flow) is much more far away from the diffuser outlet than in case Re=50 (laminar flow).
Is something wrong with my boundary condition?
Someone can help me? Is very important

If you say "strange thing" I immagine you already know the solution of your flow problem. What references are you using?



Owing to the 2D model, you are using for sure a RANS formulation, your solution is therefore strongly dependendent on the model parameters.
FMDenaro is offline   Reply With Quote

Old   August 10, 2021, 14:32
Default
  #3
New Member
 
Join Date: Aug 2021
Posts: 4
Rep Power: 4
Sam6789 is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
If you say "strange thing" I immagine you already know the solution of your flow problem. What references are you using?



Owing to the 2D model, you are using for sure a RANS formulation, your solution is therefore strongly dependendent on the model parameters.
I don't have any references about this case, I'm assuming that the reattach point in case Re=50 should be much more far away than in case Re=8200, because turbulent flow gives more resistance to separation than laminar flow.
I'm using a k-omega SST model
Sam6789 is offline   Reply With Quote

Old   August 10, 2021, 14:38
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by Sam6789 View Post
I don't have any references about this case, I'm assuming that the reattach point in case Re=50 should be much more far away than in case Re=8200, because turbulent flow gives more resistance to separation than laminar flow.
I'm using a k-omega SST model
Have you ever studied the test case of the backward facing step in laminar and turbulent regimes?
FMDenaro is offline   Reply With Quote

Old   August 10, 2021, 14:50
Default
  #5
New Member
 
Join Date: Aug 2021
Posts: 4
Rep Power: 4
Sam6789 is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
Have you ever studied the test case of the backward facing step in laminar and turbulent regimes?
No, unfortunatly.
Sam6789 is offline   Reply With Quote

Old   August 10, 2021, 18:01
Default
  #6
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Several papers can be found by searching on internet, for example



https://www.google.com/url?sa=t&rct=...PFMiBHZkJQCi07
FMDenaro is offline   Reply With Quote

Reply

Tags
boundary condition, diffuser pipe flow, separate region

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Some questions about flow boiling simulation in Fluent beastieboys6 FLUENT 8 November 21, 2017 00:47
Confirmation of a simulation in a diffuser. RANS flow, sticks to the wall. wannab_phd OpenFOAM Verification & Validation 0 October 24, 2016 12:49
Control simulation to apply different fields with chtMultiRegionFoam jmdf OpenFOAM Running, Solving & CFD 0 February 29, 2016 08:05
centrifugal compressor-diffuser simulation : Overflow insisivus CFX 7 April 22, 2014 07:41
Convergence of jet flow simulation MiraLisa FLUENT 0 August 15, 2013 05:44


All times are GMT -4. The time now is 08:46.