# Simulation of an expending gas

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

 February 25, 2004, 19:05 Simulation of an expending gas #1 Mehdi Guest   Posts: n/a Sponsored Links Hi, I am trying to simulate a 2-D the expension of a gas released in the vaccum form a spherical source. To do that, I am using the TVD lax-freidrich method with a second-order MUSCL reconstruction to solve the Euler equations. I am using also an Adaptive Mesh with a very high resolution near the source, and going lower as I go far form the source. My gas is modeled by the rho, u, v, and p primitive variables. Normaly the solution need to be in r^-2 for the density and in log(r) for the velocity norm. The velocity is starting around mach 2 and increase very quickly as the gas is cooling. I have trouble in getting the desired solution. In fact my velocity solution is not radial as it should be. I found that the flux moving on the mesh main directions has lower velocity that the one moving on the grid diagonals, giving me a star pattern (it is like having jets). And it gives me a star pattern for the density and the pressure too. I tried many things : higher order scheme, correct the coarse solution at the refinement jump with the finer solution fluxes, interpolate and restrict the conservative variables and not the primitive variables ...etc. Nothings seems to work. If any body has any idea about the subject, I will be very glad to send you some figures showing the problems and discuss the problem togother. Your help will be appreciated. Regards Mehdi

 February 26, 2004, 04:22 Re: Simulation of an expending gas #2 Bart Prast Guest   Posts: n/a Are you solving time accurate (transient) or do you use a local timestep?

 February 26, 2004, 13:04 Re: Simulation of an expending gas #3 Mehdi Guest   Posts: n/a Hi Brat, I am using a local timestep ! I have more than 20 level of refinement so I can't really use the time accurate scheme. And since I am only looking for a steady state solution, the local time stepping is convienent. I was discussing with a collegue who told me that maybe I should check about the V scheme for multigrid. Until now I just solve the equations in all the cells with a local time stepping (I have block structures with 16 central cells for each block with also 2 extra lines and rows of guradcells coming form the neighbors). After that I interpolate the solution from coarse to fine blocks and I restrite it from fine to coarse blocks to be able to fill the blocks guardcells. And I move to the next time step, and so on. so What I am suppose to do with a V scheme ? Do you think that it is the source of my probleme ? Regards

 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 Suzzn CFX 18 October 2, 2009 04:18 chris_sev OpenFOAM Running, Solving & CFD 0 July 30, 2008 03:16 CFX 4.3 users CFX 3 August 15, 2003 05:38 Andrew Chernousov Main CFD Forum 1 September 4, 1998 23:42