CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Problems with a compressible shear flow

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 25, 2010, 08:44
Question Problems with a compressible shear flow
  #1
Senior Member
 
Ivan Flaminio Cozza
Join Date: Mar 2009
Location: Torino, Piemonte, Italia
Posts: 210
Rep Power: 18
ivan_cozza is on a distinguished road
Send a message via MSN to ivan_cozza
Hi Foamers,

In my research group we are having some problems running the flow field proposed in "Fourth NASA-CAA Workshop", 2004, Category 4 Problem 2 proposed by S.K. Lele.

It is a 2D compressible mixing layer flow formed by a splitter plate with a blunt trailing edge. On the upper stream there is a freestream at Mach1 = 0.1, while the lower one is at Mach2 = 0.6.

The Re number is 250, based on the the momentum thickness of the boundary layer at the inlet of the domain at the lower surface. So we expect a laminar steady solution.

We are trying to solve the flowfield with rhoSimpleFoam, laminar turbulence model, first order upwind schemes for div.

As bc we use:

Inlet (same condition for up and down, with different values):
p - zeroGradient
T - totalTemperature fixed
U - a Von Karman boundary layer profile that matches the freeStream Mach in the far field and that has the correct momentum thickness, using groovyBc.

Outlet:
p - waveTransmissive in order to prevent reflections, with a fixed value of 103682 Pa, consistent with the far field thermodynamics.
T - zeroGradient
U - zeroGradient

Up and down:
p - zeroGradient
T - zeroGradient
U - slip

wall:
p - zeroGradient
T - fixedValue, 300k (required)
U - fixedValue (0 0 0)

The calculation blows up after a few of iterations, so we tryed to smoothly past from a quiescent state to the final using a time-variable inlet velocity that gives a linear ramp from 0 to Mach1, and then another ramp that rises the lower inlet from Mach1 to Mach2, but the calculations is not capable to reach a converged state. It blows up prior to reach the Mach1 conditions.

Anyone can help? Is there any error in the setup, or are there some better solver or bc to use?

Thanks in advance,
Ivan
Attached Images
File Type: jpg mesh.jpg (96.1 KB, 29 views)
ivan_cozza is offline   Reply With Quote

Old   April 14, 2010, 05:27
Default
  #2
Senior Member
 
Ivan Flaminio Cozza
Join Date: Mar 2009
Location: Torino, Piemonte, Italia
Posts: 210
Rep Power: 18
ivan_cozza is on a distinguished road
Send a message via MSN to ivan_cozza
Update:

Not even capable to obtain a stable solution, with rhoSimpleFoam, rhoPisoFoam and rhoPimpleFoam, even with a full-hex mesh.
I tried to run this case with star-ccm+, but no solutions.
I tried to run with simpleFoam, and I had a stable solution, but clearly wrong, as the inlet Mach in the lower flow is 0.6...

Any suggestions?
Thanks, Ivan
ivan_cozza is offline   Reply With Quote

Old   May 26, 2010, 11:08
Default
  #3
Senior Member
 
Join Date: Dec 2009
Posts: 112
Rep Power: 16
heavy_user is on a distinguished road
HI Ivan,

i am trying to simulate a jet-flame and came up with some problems that might be similar.

I once used a time dependent inlet to raise velocity...but you have to do it REALY slow!
Did you try with a lower constant speed? (try to lower it until it works)

You might want to check your overall massflow over time!

I have the problem that in my simple jetflame-case (which should converge to some kind of steady state), despite of the constant BC, I have a time dependent massflow as soon as i use a compressible solver !
[see picture, really ugly: (m_{out,max}-m_{out,min})/m_{in} ~~80% ]

regards&good luck with your work!
Attached Images
File Type: png fluxOVERtime.png (6.6 KB, 16 views)
heavy_user is offline   Reply With Quote

Reply


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
Incompressible and compressible flow. Confused student. Main CFD Forum 27 March 18, 2017 13:25
compressible flow in CFX! Ihsan CFX 9 January 15, 2008 19:50
Can 'shock waves' occur in viscous fluid flows? diaw Main CFD Forum 104 February 16, 2006 06:44
Compressible Flow Modelling? yeo FLUENT 4 March 7, 2003 08:08
compressible channel flow.. R.D.Prabhu Main CFD Forum 0 July 17, 1998 18:23


All times are GMT -4. The time now is 03:32.