CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Boundary conditions for a Laval nozzle

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 27, 2000, 08:51
Default Boundary conditions for a Laval nozzle
  #1
Kargl Karl
Guest
 
Posts: n/a
Hi, i'm a student working on my thesis about transonic fluid flow through a Laval nozzle of a spiral jet mill. The fluid is air. My CFD-Software is FIRE(AVL List) and COMET(ICCM). Can anyone help me do find the appropiate boundary conditions for the inlet and outlet for such a problem ? Are there any test cases for such a problem ?
  Reply With Quote

Old   January 31, 2000, 13:45
Default Re: Boundary conditions for a Laval nozzle
  #2
clifford bradford
Guest
 
Posts: n/a
the inlet to a laval nozzle is usual subsonic and so it is necessary to specify 3 boundary values. usually the total pressure and temperature (or enthalpy) are specified along with either the flow angle (usually 0) or the mass flow rate. if the exit is supersonic then no boundary values need be specified if it is subsonic then one boundary value usually the pressure is specified. also you may try using nonreflecting exit conditions if they are available in the codes you are using. hope this helps
  Reply With Quote

Old   February 1, 2000, 05:38
Default Re: Boundary conditions for a Laval nozzle
  #3
Kargl Karl
Guest
 
Posts: n/a
Thank you very much, clifford. Did you know any code which has nonreflecting exit conditions included.
  Reply With Quote

Old   February 1, 2000, 11:48
Default Re: Boundary conditions for a Laval nozzle
  #4
Amadou Sowe
Guest
 
Posts: n/a
When you specify pressures at both boundaries, is it not the case that the pressure drop between your inlet and outlet deterimes your mass flow rate? Consequently, your problem may be ill-posed if you impose mass flow boundary condition at the inlet as well. What do you think?
  Reply With Quote

Old   February 1, 2000, 12:26
Default Re: Boundary conditions for a Laval nozzle
  #5
John C. Chien
Guest
 
Posts: n/a
(1). Yes, you are right. (2). Because I am using the Pressure conditions everyday. (3). I specify inlet total pressure, inlet total temperature, inlet velocity direction components (sine, cosine of the flow angle), and the k-epsilon turbulence levels. (4). At the exit, I specify the static pressure. (5). This set of boundary conditions has been used for the subsonic flows, and the transonic flows at the exit. The problem I am solving is 3-D turbine nozzle flows (stator)
  Reply With Quote

Old   February 1, 2000, 13:49
Default Re: Boundary conditions for a Laval nozzle
  #6
clifford bradford
Guest
 
Posts: n/a
yes sorry i made a goof. the specification of inlet bc depends on the idea you have for the upstream conditions. the typically used To, Po and flow angle constraints are applied when you assume the flow is coming from a large upstream reservoir and the mass flow is free. however if the flow upstream is throttled (choked) then the upstream mass flow is specified and you replace the Po with it. the specification of flow angle is convenient although it may be arbitrary. it is also possible to specify upstream vorticity in place of it
  Reply With Quote

Old   February 1, 2000, 13:54
Default Re: Boundary conditions for a Laval nozzle
  #7
clifford bradford
Guest
 
Posts: n/a
i can't really say because my experience with commercial codes is limited. you can consult with the vendors of your codes if they have this capability (it might be under another name) also your codes may be pressure based in which case i'm not sure about the avialbility of such bc. for more information you can read Kevin Thompson's papers on this subject in Journal of Computational Physics (i referenced them in some of my earlier posts which you can find with the search feature on this list.
  Reply With Quote

Reply

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
Proper Pressure Boundary Conditions for Buoyant Flow mchurchf OpenFOAM 0 March 25, 2010 13:16
Fluent accuracy and boundary conditions Paolo Lampitella FLUENT 0 June 12, 2008 06:25
A problem about setting boundary conditions lyang Main CFD Forum 0 September 19, 1999 18:29


All times are GMT -4. The time now is 09:43.