
[Sponsors] 
March 12, 2014, 13:59 
fluent convergence problem

#1 
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
hi guys,
I am having difficulty with convergence,especially continuity residuals. My model and boundary conditions are shown below.Air flows in a swirling pattern and creates negative pressure in the central region. the nozzle is 1.5 mm and the gap between skirt and workpiece is 0.3 mm. I want to find the pressure distribution on the workpiece.. The peak velocity is around 100 m/s only and so pressure based solver is sufficient...right? The mesh created has a max skewness of .7 with average skewness of .2 Is the mesh too coarse.do i have to increase the no. of elements where thickness is very less.( I am modelling the fluid domain only and considered an outer envelope to apply pressure boundary condition) How to attain faster convergence for this case. should I use simplec or coupled ?? do i need to modify the underrelaxation factors ? also,how to reduce backflow ? Any help is appreciated... thanks in advance... 

March 13, 2014, 03:24 

#2 
Member
Simas
Join Date: Mar 2012
Posts: 37
Rep Power: 7 

March 13, 2014, 08:31 

#3 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20 
itzme,
1) What turbulence model do you use? 2) Can you show the residuals? 3) Numerics ("Solution Methods") are?
__________________
The skeleton ran out of shampoo in the shower. 

March 13, 2014, 08:46 

#4  
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
Quote:
Ke RNG model I dont currently have the residuals picture...everything except continuity converges... Simplec... Initially with first order and then to second order... 

March 13, 2014, 10:34 

#5 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20 
Di you try to run the whole case with much lower massflow? Try e5 inlet massflow instead of e4, and tell us what happens.
__________________
The skeleton ran out of shampoo in the shower. 

March 13, 2014, 10:51 

#6  
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
Quote:
Will improving mesh or increasing no. of elements yield correct results?? Thanks in advance 

March 13, 2014, 10:52 

#7 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20 
You mean convergence for the e5 case?
Can you post a picture of the y+ value on your surfaces?
__________________
The skeleton ran out of shampoo in the shower. 

March 13, 2014, 11:15 

#8  
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
Quote:
(sorry, I am only a beginner in cfd analysis) Thanks 

March 13, 2014, 11:18 

#9 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20 
y+ is the normalized size of your cells, perpendicular to the surface, so its always plotted on the surface of your domain. If it is too large, the boundary conditions of the turbulence model become garbage.
What did you change to achieve convergence? To your question: Of course results can get better if you make the grid even smaller. But you already have 1.3 mio cells for such a simple geometry. Do you have ICEM for meshing or just the ansys meshing?
__________________
The skeleton ran out of shampoo in the shower. 

March 13, 2014, 11:32 

#10  
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
Quote:
I refined mesh a bit and changed the relaxation parameters. I am not familiar with icem meshing. 

March 14, 2014, 07:11 

#11 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20 
You should have a look at the y+ anyway. Maybe post the pictures!
__________________
The skeleton ran out of shampoo in the shower. 

March 16, 2014, 00:23 

#12 
New Member
Join Date: Feb 2014
Posts: 8
Rep Power: 5 
Is it possible to do a 2D analysis for this case ???


March 16, 2014, 06:49 

#13 
Senior Member
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 998
Rep Power: 17 

March 17, 2014, 10:11 
weird CP distribution near trailing edge for NACA0012

#14 
New Member
shubham jain
Join Date: Dec 2013
Posts: 25
Rep Power: 5 
i am simulating naca0012 with Gurney flap
mesh using ICEM CFD simulation using FLUENT, ke RNG, Re=3e06 I have a problem in CLEAN Airfoil (without any gurney flap) in its Static pressure distribution (CP). 1. CP values of pressure and suction surface intersect each other near the trailing edge for every angle of attack. 2. Also there are many riggles (wavy nature of CP) in the CP distribution Though the pathlines seem to be fine can anybody explain this weird CP distribution and how can i rectify it??? thanks in advance 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Convergence  Centurion2011  FLUENT  44  June 20, 2017 09:57 
serial/parallel problem in force saving convergence history  behest  FLUENT  11  July 22, 2014 03:49 
Problem in using parallel process in fluent 14  Tleja  FLUENT  3  September 13, 2013 10:54 
Fluent  license problem.  Marcin  FLUENT  1  March 4, 2005 12:41 
convergence problem  limseokmin  FLUENT  3  November 14, 2004 13:43 