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

Does incompressible assumption increase complexity

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 3, 2003, 08:47
Default Does incompressible assumption increase complexity
  #1
Joel
Guest
 
Posts: n/a
I have been told recently that assuming incompressible flow does not simplify CFD simulation and does in fact increase numerical dificulties and complexity greatly. Is this true and if so why? What does the incompressible assumtion do numerically to cause problems (this is all at v low mach numbers by the way, i.e. no where near supersonic). Anybody got any references that might be of use.
  Reply With Quote

Old   October 3, 2003, 11:18
Default Re: Does incompressible assumption increase comple
  #2
xueying
Guest
 
Posts: n/a
Iterative method doesn't converge well might be one aspect. Some zero diagonal entries in Jacobian matrix induced from incompressible equation.
  Reply With Quote

Old   October 3, 2003, 11:54
Default Re: Does incompressible assumption increase comple
  #3
ryoga
Guest
 
Posts: n/a
I have worked on numerical methods for both incompressible (viscous) and compressible (inviscid) flow and I am not sure that one is necessarily simpler than the other. Both regimes definitely have their own share of challenges.

In incompressible flow, the pressure propagates at an infinite speed and hence a disturbance is instantly "felt" everywhere in the flow. Furthermore, in the incompressible Navier-Stokes equation, there is no explicit equation to use to solve the pressure. The pressure is obtained by coupling the momentum equations with continuity, usually through iterative methods like the SIMPLE family of methods. In contrast, when solving compressible inviscid flow, pressure is obtained through an equation of state.

Actually by combining the momentum and continuity equations, an explicit equation can be obtained for the pressure -- the Poisson pressure equation. Although this provides an explicit equation for the pressure, some numerical method that use this formulation may experience difficulty keeping the flow everywhere divergence free.

Two good references are Tannehill, Andersen, and Pletcher's Computational Fluid Mechanics and Heat Transfer and Patankar's Numerical Heat Transfrer and Fluid Flow.

Ryoga
  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
Incompressible turbulence models: strange implementations? AleDR OpenFOAM 3 November 18, 2014 12:23
Incompressible Ideal gas law Leverkin FLUENT 5 March 5, 2009 17:41
How can I increase Heat Transfer at Domain Interf? B.Simon CFX 3 October 28, 2008 19:53
Abt: the speed of sound in incompressible flows jinwon park Main CFD Forum 3 August 21, 2008 20:44
Compressible vs. Incompressible formulations Fernando Velasco Hurtado Main CFD Forum 3 January 7, 2000 17:51


All times are GMT -4. The time now is 06:12.