Register Blogs Members List Search Today's Posts Mark Forums Read

 November 28, 2005, 05:19 steady vs unsteady? #1 Fer Guest   Posts: n/a Hi all, I'm studying the airflow around a vehicle (in 2D and 3D) for different inlet-velocity cases. Now, I'm working with the 2D case. The problem is that I'm not able to reach convergence. I'm using simple turbulence models (k-e standard, RNG and Realizable) and I only reach convergence if I use a 1st order scheme + low vel-inlet. I'm sure that the grid is ok (high quality, I believe). The fact is that I've only used steady simulations. Can anybody tell me if it could be an unsteady case? Fer

 November 28, 2005, 06:33 Re: steady vs unsteady? #2 bharat Guest   Posts: n/a Hi Fer, What range of reynolds number u r using. If its high change to compressible solver. hope this helps bharat

 November 28, 2005, 07:23 Re: steady vs unsteady? #3 Fer Guest   Posts: n/a I think Reynolds isn't too high; well I'm trying with velocities in the range between 10 and 50 m/s. Well, the fact is that in some areas of the car the flux velocity is about 1.7-2*vel_inlet (easy to calculate aproximately using, for example, Bernoulli's equation). Could those zones motive that problems with convergence? Fer

 November 28, 2005, 17:42 Re: steady vs unsteady? #4 Anindya Guest   Posts: n/a what are your other boundary conditions? For your 2D case you should get convergence with higher order schemes instead of just 1st order. Something is not right in your simulation.

 November 28, 2005, 17:59 Re: steady vs unsteady? #5 Freeman Guest   Posts: n/a Hi Fer. I'm having similar problems so I made a Mass-Weighted Average plot of the outlet velocity and it showed me a fluctuation instead of getting stable as one could expect if it would converge, so I am starting to think that I'm in an unsteady case. But when I run an unsteady simulation, after 1500 iterations start to fluctuate periodically, and also the Mass-Weighted average of the outlet velocity: could this be a convergence criterion? All unsteady problems shows these periodic fluctuations? And those fluctuations means that I have arrived to the convergence? ThAnxs to all!

 November 29, 2005, 03:18 Re: steady vs unsteady? #6 Fer Guest   Posts: n/a Well, my boundary conditions are: - Static Wall for the car surface and for the ceiling. - Velocity-intlet at the inlet edge. - Outflow at the outlet edge. - Translational wall at the floor (moving at the same vel as the vel-inlet). Perhaps there are problems using the outflow, but I don't know. In that case, tell me what's the most convenient to use in that edge, please. Thanks Fer

 November 29, 2005, 15:51 Re: steady vs unsteady? #7 Anindya Guest   Posts: n/a Use a pressure boundary condition instead of outlet. See if you get some better results

 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 elobb FLUENT 3 May 31, 2015 04:11 wlt_1985 FLUENT 6 December 4, 2010 17:17 nico Main CFD Forum 0 September 21, 2007 04:50 prem FLUENT 0 March 30, 2006 10:40 winnie FLUENT 1 April 28, 2003 11:30

All times are GMT -4. The time now is 17:42.