CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

simpleFoam convergence problems and boundary conditions

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 23, 2019, 03:58
Question simpleFoam convergence problems and boundary conditions
  #1
New Member
 
Nikhil Joshi
Join Date: May 2013
Location: Germany
Posts: 7
Rep Power: 13
nikz123 is on a distinguished road
Hello ereryone,

I have a simple incompressible case of fan with three regions meshed separately (inlet, rotor, outlet) and coupled with intersecting patches. The aim of the problem is to calculate the volume flow rate that a fan can pull in.

The problem I am facing is with the turbulence model when I include turbulence model into the simulation the solver blows up. Things I did to come to this conclusion are the following

1) After coupling the meshes and checkMesh OK

2) Since I do not know the inlet velocity. I specified pressureInletOutletVelocity for inlet and outlet in 'U' and totalPressure for inlet and outlet in 'p'. Rest of it is standard noSlip and zeroGradient and cyclicAMI for corresponding wall patches and intersecting sections

3) With standard solver settings for fvSchemes and fvSolution adapted from pitzdaily tutorial I run the simulation with turbulence mode 'off' and I have the converged solution.

4) If I leave the simulation sufficiently to be in steadystate with laminar condition and switch on the turbulence mode later the solver suddenly blows up

5) The problem is since I do not know the inlet velocity or I want to calculate it from the simulation I have no idea how to provide boundary conditions in 'k' and 'omega' if I use komegaSST model for example. I have tried my luck with different values of 'k' and 'omega' (providing 'k' sufficiently small and 'omega' sufficiently large) nothing seems to work. The standard procedure to apply the rough estimate of 'k' at inlet from turbulence intensity does not apply in this case (or am I missing something here I don't know)

If anybody can give me some idea as to how one can specify the boundary conditions for turbulence models for such a case or any other approach to solve such simulation by providing meaningful boundary conditions would be very helpful. Thank you.

Regards
nikz123 is offline   Reply With Quote

Old   August 28, 2019, 02:13
Default
  #2
New Member
 
Aashay Tinaikar
Join Date: May 2019
Location: Boston
Posts: 19
Rep Power: 7
ARTisticCFD is on a distinguished road
Hii Nikhil,



Looks like a complicated problem to deal with. I was trying to simulate a centrifugal pump couple of years back and I remember that I had to face the same problems. Due to some reasons, the solver blows off when turbulence model is included. I don't remember how I solved it exactly, but you can try the following things,



1) Try increasing the value of viscosity and lowering the value of density so as to affect the properties. Ideally, solution should become more and more stable.

2) Try increasing the nNonOrthogonalCorrectors from fvSolution file

3) Try changing the velocity BC at inlet to fixedValue or flow rate. If you increase the velocity value, the solver should become more stable.

Above steps had helped me to correctly identify the source of this problem. Hope this helps a little.



Good luck!!
ARTisticCFD is offline   Reply With Quote

Reply

Tags
bounadry condition, fan, openfaom, simplefoam convergence


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
3D Windturbine simulation in SU2 k.vimalakanthan SU2 15 October 12, 2023 06:53
CFD analaysis of Pelton turbine amodpanthee CFX 31 April 19, 2018 19:02
Problem with SIMPLEC-like finite volume channel flow boundary conditions ghobold Main CFD Forum 3 June 15, 2015 12:14
ribbed channel / simpleFoam / boundary conditions beeo OpenFOAM Pre-Processing 20 July 17, 2013 09:39
Water subcooled boiling Attesz CFX 7 January 5, 2013 04:32


All times are GMT -4. The time now is 16:44.