CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

Boundary conditions for underexpanded jet

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

LinkBack Thread Tools Display Modes
Old   April 5, 2008, 06:57
Default Boundary conditions for underexpanded jet
Posts: n/a
I am trying to use upwind TVD schemes to simulate an free underexpanded jet. What boundary conditions should I use and how long does it need to be with respect to the nozzle diameter. I am not simulating the flow within the nozzle itself hence the domians is just a rectangle.

Thanks Shuo
  Reply With Quote

Old   April 5, 2008, 08:38
Default Re: Boundary conditions for underexpanded jet
Posts: n/a
Dear Shuo,

You need to use NRBC conditions at the far boundary (such as those of Giles or Thomson&Lele), but an easier workable alternative is to employ a really far outer boundary (say 1000d, where d is nozzle diameter) and coarsen the grid as you approach the far boundary and employ Reimann invariant BC. (Reimann invariants are valid only under 1d isentropic assumption, this is violated here for sure, but the coarse grid close to the boundary adds enough diffusion to avoid any numerical instability; and the large length ensures that the shock diamond pattern typical of this problem is reasonably well resolved in the near field of the nozzle.


  Reply With Quote

Old   April 6, 2008, 00:40
Default Re: Boundary conditions for underexpanded jet
Posts: n/a
For a free underpanded jet I ran a 2D simulation with a domain of D*3D, 100*300 grids. I used a = 0.085 and n = 6 for the sponge layer boundary parallel to the jet centerline. Initially you could see the shock diamonds within the jet but eventually the velocity became uniform. The region adjacent to the free jet was uniformly non-stationary. Can anyone please advise me on this?


  Reply With Quote


Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
natural convection mehrdadeng CFX 10 February 25, 2011 06:25
CFX does not continue Shafiul CFX 10 February 17, 2011 08:57
mesh file for flow over a circular cylinder Ardalan Main CFD Forum 6 April 17, 2010 23:40
Proper Pressure Boundary Conditions for Buoyant Flow mchurchf OpenFOAM 0 March 25, 2010 13:16
Boundary Conditions Jan Ramboer Main CFD Forum 11 August 16, 1999 08:59

All times are GMT -4. The time now is 05:06.