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

the difference between solving compressible and in

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 21, 2006, 11:59
Default the difference between solving compressible and in
  #1
ztdep
Guest
 
Posts: n/a
Hi: I have noted that many people write the discretized equain in a matrix form when solving the compressible flow, while we do not do in this way when solving the incompressbile flow! so what is the difference between the two methods!

  Reply With Quote

Old   June 22, 2006, 07:10
Default Re: the difference between solving compressible an
  #2
Dominic
Guest
 
Posts: n/a
Hi,

Well, the matrix form originates whether ur solving it implicitly or not. As per my observation, for incompressible flows, owing to the absence of pressure update (apart from pseudo compressibility methods) we solve for pressure : Del^2 P = F(Del dot U).. so this discretization results in a system of equations ..a sparse matrix system.

Also the presence of viscous terms, we cannot afford to use explicit discretization..So again implicit

For compressible flows explicit discretization is very easy and straightforward, the problem being stability. In this case u choose an implicit method, u get the matrix form again.

-Dominic
  Reply With Quote

Old   June 23, 2006, 01:20
Default Re: the difference between solving compressible an
  #3
ztdep
Guest
 
Posts: n/a
I am really confused about how to assemble all of the points to a matrix, do you have any good instruction! regards
  Reply With Quote

Old   June 23, 2006, 04:49
Default Re: the difference between solving compressible an
  #4
Dominic
Guest
 
Posts: n/a
Hi,

Yes, when its 2D or 3D the matrix is huge and its banded.

Here is a ref which may help you, it has what you want :

Computational fluid dynamics for engineers (2 volumes) Hoffmann, Klaus A.

Publisher: Engineering Education System, Pub date: 1993 ISBN: 0962373176

Regards, Dominic

  Reply With Quote

Old   June 23, 2006, 09:43
Default Re: the difference between solving compressible an
  #5
ztdep
Guest
 
Posts: n/a
Thank you again! then how to solve the sparse matrix, i want to use the direct method , do yo know is there some free package for the direct gaussian elimination ! regards
  Reply With Quote

Old   June 26, 2006, 10:31
Default Re: the difference between solving compressible an
  #6
Dominic
Guest
 
Posts: n/a
Hi,

May be can Try : LAPACK http://www.netlib.org/lapack/

or PETSc : http://www-unix.mcs.anl.gov/petsc/petsc-as/.. they are free

regards,

Dominic
  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



All times are GMT -4. The time now is 03:08.