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March 12, 2014, 13:59 
fluent convergence problem

#1 
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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 
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Simas
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March 13, 2014, 08:31 

#3 
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Philipp
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itzme,
1) What turbulence model do you use? 2) Can you show the residuals? 3) Numerics ("Solution Methods") are?
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March 13, 2014, 08:46 

#4  
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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 
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Philipp
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Di you try to run the whole case with much lower massflow? Try e5 inlet massflow instead of e4, and tell us what happens.
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March 13, 2014, 10:51 

#6  
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Quote:
Will improving mesh or increasing no. of elements yield correct results?? Thanks in advance 

March 13, 2014, 10:52 

#7 
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Philipp
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You mean convergence for the e5 case?
Can you post a picture of the y+ value on your surfaces?
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March 13, 2014, 11:15 

#8  
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Quote:
(sorry, I am only a beginner in cfd analysis) Thanks 

March 13, 2014, 11:18 

#9 
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Philipp
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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?
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March 13, 2014, 11:32 

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I refined mesh a bit and changed the relaxation parameters. I am not familiar with icem meshing. 

March 14, 2014, 07:11 

#11 
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Philipp
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You should have a look at the y+ anyway. Maybe post the pictures!
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March 16, 2014, 00:23 

#12 
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Is it possible to do a 2D analysis for this case ???


March 16, 2014, 06:49 

#13 
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Daniele
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March 17, 2014, 10:11 
weird CP distribution near trailing edge for NACA0012

#14 
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shubham jain
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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 

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