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

Grid singularity in blunt body simulations

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 16, 2001, 11:21
Default Grid singularity in blunt body simulations
  #1
Stefan
Guest
 
Posts: n/a
We want to simulate the supersonic flow field over 3d blunt body using the shock-fitting technique and a finite-difference scheme. My question is: How can the grid singularity in front of the body nose be removed. Any ideas?
  Reply With Quote

Old   July 16, 2001, 16:59
Default Re: Grid singularity in blunt body simulations
  #2
John C. Chien
Guest
 
Posts: n/a
(1). What do you mean by "grid singularity" in front of the body nose ? (2). Why not take a look at the Joe Thompson's book on "numerical grid generation".
  Reply With Quote

Old   July 16, 2001, 23:13
Default Re: Grid singularity in blunt body simulations
  #3
Dan Williams
Guest
 
Posts: n/a
Many people have done shock fitting in 2D. Most of what I've seen in the last 5-6 years has been releated to shockwave induced detonations around various blunt objects. (See experiments by Lehr et al. in the early 70s, you get very interesting combustion instabilities depending on the size and mach number of the projectile).

Is there some fundamental difference in 3D that creates a grid singularity? I don't see it. Maybe you just need a different grid?

Dan.

  Reply With Quote

Old   July 17, 2001, 03:22
Default Re: Grid singularity in blunt body simulations
  #4
Stefan
Guest
 
Posts: n/a
Hello, if you generate a grid for a 3d axisymmetric body, i.e, the (eta) body-normal grid lines fall into each other at the nose. This is a GRID SINGULARITY. Therefore you cannot obtain the metric coefficients in a common way. Maybe you can to some interpolations around this line. I only wanted to hear other ideas.
  Reply With Quote

Old   July 17, 2001, 04:29
Default Re: Grid singularity in blunt body simulations
  #5
Rajani Kumar
Guest
 
Posts: n/a
Hi, Grid singularity can me eliminated by considering grid method for Doubly connected regions mentioned in the Thompsons book. I hope this info is usefull for u. by A.Rajani kumar
  Reply With Quote

Old   July 17, 2001, 04:47
Default Re: Grid singularity in blunt body simulations
  #6
Joern Beilke
Guest
 
Posts: n/a
Use a grid with multiblock topologie.
  Reply With Quote

Old   July 18, 2001, 11:29
Default Re: Grid singularity in blunt body simulations
  #7
Khurram
Guest
 
Posts: n/a
Try an "O-GRID" topology. Make the interface in the wake. O-Grids are normally suited for subsonic simulations but you can try it in supersonic flow as well. Another option is to assume a small cyliderical spike-similar to the PITOT in front of the nose. make 3D averaging on the small cylinder which runs from the nose to the FAR FIELD. If you have some validation to make, we can collaborate.

Best of luck
  Reply With Quote

Old   July 30, 2001, 22:22
Default Re: Grid singularity in blunt body simulations
  #8
clifford bradford
Guest
 
Posts: n/a
"Use the O grid Luke!" - Obi Wan
  Reply With Quote

Old   August 4, 2001, 22:33
Default Re: Grid singularity in blunt body simulations
  #9
Axel Rohde
Guest
 
Posts: n/a
If you look at the problem in a finite volume context, there is no singularity, because the flux can only travel AROUND that line. Thus for a finite volume Euler code, there is no problem, and shock capturing works just as well. It get's a little more tricky when you try to define the stress tensor or heat flux vector in the vicinity of that line.

I addressed this singularity problem in great detail --from a finite volume and finite difference point of view -- in my dissertation (viscous compressible flow over rotating disc), which can be downloaded from my website,

www.cfd4pc.com/papers.htm

Viel Spass!

Axel
  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
drag reduction using retractable spikes at hypersonic regime on a blunt body prshet CFX 0 March 15, 2011 11:08
blunt body test nico FLUENT 1 June 26, 2003 08:22
Nose singularity of blunt body grids Stefan Maehlmann Main CFD Forum 2 March 19, 2001 11:18
finite volume method for CFD analysis of 2D blunt body Aditya Vaze Main CFD Forum 1 January 19, 2000 14:55
Body fitted grid generation in FLOW3D Nur Ikhwan Main CFD Forum 1 January 25, 1999 06:40


All times are GMT -4. The time now is 18:20.