divergence due to high pressure drop in two-stroke scavenging

renna.ale · May 16, 2013, 06:29

Hi,
I'm working about a model in fluent of two-stroke engine uniflow scavenging, with dynamic meshes of piston and exhaust valves. The start of my simulation is the exhaust valves opening (lift from 80 CAD to 250 CAD); near BDC, the piston opens 14 ports of intake (opened from 115 CAD to 245 CAD). I initialize my cell zones with exp. data, so I have high pressure and temperature in cylinder (18 bar, 1600 K) and lower conditions in intake volume and exhaust pipes (about 2.5 bar). This high pressure drop between the volumes makes the simulation crash/diverge at first 2 iterations. If I simulate the same model with lower pressure drop (e.g. 0.03 bar and not 15.5 bar!!!) there's no problem.
Can anybody help me?
Thanks.

fluent87 · May 16, 2013, 09:58

Hi,
do you try simple model calculation?

Good Luck!

venkateshaero · May 16, 2013, 10:52

u can slowly rise the pressure after convergence
0.03 to 0.1 similar like

renna.ale · May 17, 2013, 11:47

how can I do this?
Thx

venkateshaero · May 17, 2013, 16:13

Please send some figure to understand your problem....

slowly increases input values from low values

May 16, 2013, 06:29	divergence due to high pressure drop in two-stroke scavenging	#1
renna.ale New Member Alessandro Renna Join Date: May 2013 Posts: 2 Rep Power: 0	Hi, I'm working about a model in fluent of two-stroke engine uniflow scavenging, with dynamic meshes of piston and exhaust valves. The start of my simulation is the exhaust valves opening (lift from 80 CAD to 250 CAD); near BDC, the piston opens 14 ports of intake (opened from 115 CAD to 245 CAD). I initialize my cell zones with exp. data, so I have high pressure and temperature in cylinder (18 bar, 1600 K) and lower conditions in intake volume and exhaust pipes (about 2.5 bar). This high pressure drop between the volumes makes the simulation crash/diverge at first 2 iterations. If I simulate the same model with lower pressure drop (e.g. 0.03 bar and not 15.5 bar!!!) there's no problem. Can anybody help me? Thanks.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Pressure Drop Calculation	mk_mard	STAR-CCM+	3	August 29, 2011 03:06
Pressure drop?	Munni	FLUENT	4	March 25, 2010 15:21
Pressure drop of valve with valve opening of 30%	elogesh	Main CFD Forum	2	January 5, 2007 13:30
Neumann pressure BC and velocity field	Antech	Main CFD Forum	0	April 25, 2006 03:15
Hydrostatic pressure in 2-phase flow modeling (CFX4.2)	HB &DS	CFX	0	January 9, 2000 14:19

May 16, 2013, 09:58		#2
fluent87 New Member Cristiano Join Date: Feb 2013 Posts: 11 Rep Power: 13	Hi, do you try simple model calculation? Good Luck!

May 16, 2013, 10:52		#3
venkateshaero Member venki Join Date: May 2011 Posts: 84 Rep Power: 15	u can slowly rise the pressure after convergence 0.03 to 0.1 similar like

May 17, 2013, 11:47		#4
renna.ale New Member Alessandro Renna Join Date: May 2013 Posts: 2 Rep Power: 0	how can I do this? Thx

May 17, 2013, 16:13		#5
venkateshaero Member venki Join Date: May 2011 Posts: 84 Rep Power: 15	Please send some figure to understand your problem.... slowly increases input values from low values