# Mass flow imbalance in transient state

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 1, 2009, 01:54 Mass flow imbalance in transient state #1 New Member   Join Date: Apr 2009 Posts: 7 Rep Power: 6 Hi, I tested a 2D pipe for transient analysis. BC. is as follows: Inlet, velocity,24*sin(w*t+pi/2),static temperature,900C; Outlet, static pressure,1atm. Solve control is as follows: frenquence,63HZ; total time,5 period;timestep,period/400. The turbulence model is SST. The problem is as follows: When i set the wall as adiabatic,the massFlow() @inlet =massFlow()@outlet,but when i set the wall as HTC=200[wm^-2 K^-1],outside temp.=50C, the massflow()@inlet is not equal to massFlow()@outlet and the massFlow()@outlet becomes higher with periods. I can't find the reason. Don

 June 1, 2009, 18:28 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 8,537 Rep Power: 68 Hi, Is your simulation adequately converged? Are the fluids compressible? Glenn Horrocks

 June 1, 2009, 20:54 #3 New Member   Join Date: Apr 2009 Posts: 7 Rep Power: 6 Hi Glenn The material is helium . Every timestep loops 5. i think the timestep is adequate (one period has 400 timesteps). Don

 June 2, 2009, 01:05 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 8,537 Rep Power: 68 Hi, Well in that case the outlet and inlet mass flow rates can be different due to transient effects, compounded by temperature changing the density. I but you have some sort of acoustic waves in the thing. And unless you have done a sensitivity analysis to show your timestep is adequately small then don't assume so. If acoustic waves are occuring then you have to worry about the compressibility and they requrie much smaller timesteps again. Glenn Horrocks

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Adam CFX 1 April 12, 2007 11:34 ahourri FLUENT 8 October 26, 2004 23:14 Aly FLUENT 7 October 6, 2004 21:07 Andy Main CFD Forum 0 March 11, 2004 14:05 Lisa Main CFD Forum 11 July 5, 2000 14:37

All times are GMT -4. The time now is 10:07.

 Contact Us - CFD Online - Top