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

Looking for an explanation for two weak oblique shock waves inside de Laval nozzle

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

Like Tree1Likes
  • 1 Post By newid

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 30, 2013, 18:16
Default Looking for an explanation for two weak oblique shock waves inside de Laval nozzle
  #1
Member
 
hekseli
Join Date: Mar 2013
Posts: 49
Rep Power: 13
heksel8i is on a distinguished road
Hey!

I am learning the characteristics of supersonic flows in de Laval nozzles and here I have a tricky question:

I have a strongly underexpanded flow in a relatively long nozzle. My simulations are done by Fluent implicit density based solver with 2nd order upwind scheme for all variables and with AUSM scheme. For laminar and turbulent case I get otherwise really nice looking flow field but there are two oblique shock waves starting near the nozzle throat. I have references about similar cases and there only one shock wave has been detected (similar shape as I have). I have been trying to get rid of the second shock by refining the mesh, changing Courant number and discretization scheme (MUSCL) but without success.

Temperature gradient magnitude plot :

Mach contours:


Mesh quality should be at least adequate:
-200000 cells inside the nozzle, 78000 in a farfield
-max equiangle skewness 0.1 (250k cells below 0.05 and 100k cells below 0.02)
-max aspect ratio 200
-max length ratio 1.12
-y+<1

Thougths:

i) Implicit solver fails to catch a single shock wave? Has worked in some other references generally for shocks though.
ii) second shock wave indeed would exist in reality. After the first shock wave the flow feels again a Prandtl - Meyer expansion due to the geometry of a nozzle creating a second shock wave. No references about this though...
iii) Mesh / nozzle wall geometry problem.

Ideas? Questions? Free chat...
heksel8i is offline   Reply With Quote

Old   December 3, 2013, 11:18
Default
  #2
Member
 
hekseli
Join Date: Mar 2013
Posts: 49
Rep Power: 13
heksel8i is on a distinguished road
To answer for myself:

The reason was a distorted geometry of the nozzle wall. Less than a millimeter "bump" created a local expansion-compression effect which propagated as a weak shock wave through the whole nozzle. I was stunned how sensitive the flow is for nozzle geometry.
heksel8i is offline   Reply With Quote

Old   December 5, 2013, 03:23
Default
  #3
New Member
 
Join Date: Dec 2012
Posts: 1
Rep Power: 0
newid is on a distinguished road
Great job! Heksel8i
I have stuck with a question which about atomizer with gas-liquid two phases flow ,
Which model in FLUENT can simulate the spray angle?even the hollow-cone created by pressure-swirl atomizer?
Please help me,Thanks!
mohammadsoufi likes this.
newid is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to visualise the shock wave in a laval nozzle? xck1986 OpenFOAM 1 January 20, 2011 05:31
Transition of shock waves in CD nozzle (with diffusser) bunty_abhi Main CFD Forum 0 June 15, 2009 04:06
Will compression waves overtake a moving shock? GRA Main CFD Forum 2 October 19, 2006 01:24
meshing F1 front wing Steve FLUENT 0 April 17, 2003 13:37


All times are GMT -4. The time now is 16:04.