periodic compressible flow

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

 April 24, 2006, 22:35 periodic compressible flow #1 vivian Guest   Posts: n/a Hi，everbody， I used the compressible boundary condition for unsteady 2D laminar flow, prescribing the total pressure, the total pressure and the inlet flow direction.It uses for numerical simulations of resonant oscillations in a tube which has one inflow and three walls(no outflow). But I met two difficulties. First, in certain time-step, the residuals fluctuate dramatically. The code seemed not converge. In most time-step, it was OK. Second, when the inlet velocity specified Uin=u0*sin(wt), I think the velocity wave in the middle of the tube would be the sine wave. Now, in my code, the velocity wave was sine wave when the inlet velocity was positive. When the inlet velocity was negative (3.14+2*k*3.14< t <2*3.14+2*k*3.14,k=1,2,3…….), the velocity was nearly zero.Why？And did I use the right boundary condition? Thanks a lot!

 April 25, 2006, 03:59 Re: periodic compressible flow #2 faber Guest   Posts: n/a not sure if I understood it well, but there seem to be conflict: you've prescribed inlet flow direction together with sine wave velocity. I.e. inlet velocity alternates between positive (inflow) and negative (outflow) values. If the inlet flow direction is prescribed inward, negative velocity violates it. And, imho, sine wave will only proceed into the tube for short portion only and short time - as there's no outlet, the wave will first be deformed (damped) due to rising pressure inside the tube and later due to wave reflections from closed end (-s).

 April 25, 2006, 05:04 Re: periodic compressible flow #3 vivian Guest   Posts: n/a Thanks for your reading! I think you are right.I cann't prescirbe the inlet flow direction. The periodic boundary condition is inlet velocity alternates between positive and negative values. My goal is to simulate the resonant oscillations in a tube. When the inlet velocity is positive,the the pressure rises inside. When the velocity is negative, can the inside pressure descend? I.e.the pressure value near outlet could be less than the inlet pressure value? If it could ,why and how to do? In my simulation results, the pressure value near outlet is always more than the inlet pressure value. It dosen't accord with the literature. I think this is the reason why the velocity wave inside is not accord with the literature. I found when the reflection wave meets with the proceeding wave,the residuals fluctuate dramatically. Is my boundary conditon not appropriate or something wrong with my code? Waiting for your advice. Thanks!

 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 Tyler FLUENT 4 February 5, 2009 20:58 BBG Main CFD Forum 1 November 19, 2008 15:05 librasu FLUENT 1 August 18, 2008 12:24 maria teresa FLUENT 1 September 7, 2007 16:58 atit Main CFD Forum 8 July 31, 2000 13:19

All times are GMT -4. The time now is 04:19.