# help setting up boundary conditions for combustor

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

 October 31, 2005, 06:04 help setting up boundary conditions for combustor #1 Tomas Guest   Posts: n/a Dear All, I am modelling a simple can combustor and need help setting up initial boundary conditions. The physical conditions are: compressor delivers air mass flow of 0.32 kg/s at comp. ratio 2 (pabs = 202650 Pa), static temp. = 378 K (inlet velocity calculated to be approx. 60 m/s). Pressure loss at outflow is expected to be 2-3%. For fuel delivery, there are 16 fuel holes arranged in a circular pattern, each hole is 1 mm in diameter. Fuel velocity should be approx. 80 m/s. Fuel mass flow (CH4) should be 0.00232 kg/s divided by 16 holes = 1.4e-04 kg/s, which means calculated fuel pressure relative to operating pressure (202650 Pa) should be 350420 Pa at fuel static temp of 293 K. Since the combustor operates at pabs 202650, pabs at the fuel holes should be 350420 + 202650 = 553078 Pa. I set up the boundary condition in CFX-pre as follows: OPERATING PRESSURE: pref + prel = pop => 202650 + 0 = 202650 Pa INLET: -airin- velocity = 60 m/s, static temp = 378 K -fuelin- velocity = 80 m/s, static temp = 293 K OUTFLOW: -outlet- static pressure = 0 Pa. THE PROBLEM AFTER CFX-post: The sum of fuel mass flow at fuel inlet is not 0.00232 kg/s but 0.00180!? (pabs is only approx 203000 Pa at fuel inlets when it should be 553078 Pa . What am I doing wrong? With less mass flow of fuel, I get incorrect temperature fields and as a result, incorrect NOx ang CO predictions. Any help would greatly be appreciated! Tom

 November 3, 2005, 03:31 Re: help setting up boundary conditions for combus #2 Joe Guest   Posts: n/a Hi, check first the simple things. Look at the balances in the outfile and the solver are they converged? Regards Joe

 November 3, 2005, 04:34 Re: help setting up boundary conditions for combus #3 Tomas Guest   Posts: n/a Hello Joe, Thanks for your reply. I just want to know if I've setup the correct boundary conditions at the inflows and outflow. Maybe there is a better way to set them.

 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 lost.identity CFX 41 May 22, 2013 07:21 HMR CFX 3 March 6, 2011 21:10 Ardalan Main CFD Forum 6 April 17, 2010 23:40 ibzyuk FLUENT 0 April 9, 2010 07:47 lyang Main CFD Forum 0 September 19, 1999 18:29

All times are GMT -4. The time now is 13:54.