# Reversed Flow...

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

 January 30, 2014, 05:28 #21 New Member   Anvesh Join Date: Jan 2014 Posts: 25 Rep Power: 5 Solution is converging at the end. For a channel with smooth surfaces either side, pressure drop is matching with theoretical drop. But if I use channel with lower surface has steps (such as 25 x 25 microns), we have to stop the simulation after fluid fills the channel (except the pockets), and get the pressure drop. But immediately after the start of flow, reversed flow occurring at outlet. Will it effect the result (in my case, its pressure drop)? If affects, how to avoid reverse flow? P.S. I am new to FLUENT

 January 30, 2014, 05:51 #22 New Member   Ganapathy Iyer Join Date: Mar 2009 Location: Pune, Maharashtra, India Posts: 25 Rep Power: 10 HI, Suppose I have a duct. In the duct, the inlet occupies only 25% of the cross section a the top. The outlet occupies the complete cross section of the duct. In this case, if the duct length is small, the outlet will have reverse flow. This will also happen in the real world. If you want to avoid this, you must know the outlet pressure profile and apply it using a UDF or by dividing the outlet in appropriate number of parts. All this is tedious, so simply pull the outlet much further away from its current location, i.e. if the outlet is at say 100 micron from the inlet, (this may be your actual case), pull it till say 500 micron( this is not real, but this will avoid reverse flow) You can always measure dP across a plain representing the real outlet location

 February 18, 2014, 00:30 #23 New Member   Anvesh Join Date: Jan 2014 Posts: 25 Rep Power: 5 Thank you very much sir. And one more problem I want to pose. Since I am imposing const. velocity condition at the pipe inlet I am getting a greater pressure drop, so I extended the upstream length. It is causing more computational time. So how to impose parabolic velocity inlet at the pipe inlet in FLUENT. Pl help me.

 July 17, 2014, 03:58 backflow #24 Member   Join Date: Jan 2014 Location: Turkey Posts: 36 Rep Power: 5 hi all, ı have an rectangular geometry (lenght:76, width:27 mm). heat flux is applied from one of the vertical walls. ı have velocity inlet BC at lower part and also pressure outlet BC at upper part. velocity magnitute is zero (0) (no forced convection), initial gauge pressure is also zero and temperature is 298 K at velocity inlet BC. also, for pressure outlet BC gauge pressure is 0 and backflow temperature is set 298 K. initial temperature is also 298K. the problem is that reversed flow occured. "reversed flow in 34 faces on pressure-outlet 17" the solution is converged but ı am not sure it is right or not. any suggestion. thanks for you time.

 July 25, 2014, 16:17 reversed flow #25 Member   Join Date: Jan 2014 Location: Turkey Posts: 36 Rep Power: 5 hi all, ı have an rectangular geometry (lenght:76, width:27 mm). heat flux is applied from one of the vertical walls. ı have velocity inlet BC at lower part and also pressure outlet BC at upper part. velocity magnitute is zero (0) (no forced convection), initial gauge pressure is also zero and temperature is 298 K at velocity inlet BC. also, for pressure outlet BC gauge pressure is 0 and backflow temperature is set 298 K. initial temperature is also 298K. the problem is that reversed flow occured. "reversed flow in 34 faces on pressure-outlet 17" the solution is converged but ı am not sure it is right or not. any suggestion. thanks for you time.

 July 28, 2014, 08:47 #26 New Member   S Join Date: Jul 2014 Posts: 3 Rep Power: 5 i don't know if it helps, but if possible: try to use smaller time steps and with multiphase flows you should also enable specified operating density. it solved my problem with the reversed flow. Last edited by svefu14; August 22, 2014 at 14:58.

 July 6, 2016, 04:23 Long pipe (laminar flow) gets reversed flow - not converging #27 Member   Omid Shekari Join Date: Jun 2016 Posts: 36 Rep Power: 3 My model is a u-shape pipe which is pretty long (220 cm total). There is heat flux from walls. The error is repeated continuously while solving. Also the answers are not converging. Can anyone help me please?

 September 7, 2016, 17:06 #28 New Member   hussein Join Date: Aug 2016 Posts: 5 Rep Power: 3 hello I have same problem but the result converge is the result will be right

 February 26, 2017, 02:23 #29 New Member   Rajendra Singh Join Date: Aug 2015 Posts: 16 Rep Power: 4 It happens due to a poor quality of mesh, abnormal boundary condition at inlet/outlet, short downstream length etc. Remedies are: > if vortex formation/recirculation of flow near an outlet boundary, increase the downstream length. > check the mesh quality, improve it. > use higher order scheme > At last reduce the relaxation factor if necessary.

September 15, 2017, 03:28
#30
New Member

shiva krishna
Join Date: Sep 2017
Posts: 2
Rep Power: 0
Hello guys, (Doubt atmospheric conditions)

I am working on rectangular geometry with air as fluid. Actually i have one inlet at the one side face of the rectangle and one outlet is quite opposite to the other side face of the rectangle and reaming all are walls. I want atmospheric conditions at both inlet and outlet, for that i have taken pressure inlet and pressure outlet with default values (i.e. Gauge pressure is Zero).

But unfortunately when I am simulating I am getting reverse flow. Moreover my solution is converging. Could you please any one explain me. What kind of mistake I have done. I am attaching my Residual and geometry images.
Attached Images
 mesh.jpg (88.0 KB, 4 views) Residual.jpg (73.8 KB, 5 views)

 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 free FLUENT 4 February 27, 2014 02:56 Suman Kandula FLUENT 4 April 2, 2012 07:12 sushii FLUENT 14 October 29, 2007 05:27 ib FLUENT 1 March 26, 2007 13:11 Sastry FLUENT 5 March 22, 2007 09:05

All times are GMT -4. The time now is 22:40.

 Contact Us - CFD Online - Privacy Statement - Top