|
[Sponsors] |
May 11, 2010, 07:28 |
Too high mach number...
|
#1 |
Senior Member
Roland Rakos
Join Date: Mar 2009
Posts: 131
Rep Power: 17 |
Hello,
I have a complicated geometry which contains some narrow cross sections. In my tutorial simulation (see below) there is a simple choke. It is a 2D axisymmetrical geometry, the pressure ratio is 3. The main settings: - steady state - total pressure inflow/static pressure outflow - air ideal gas - SST turb.modell - high resolution The results: http://img405.imageshack.us/i/chokedens.png/ http://img686.imageshack.us/i/chokemach.png/ http://img697.imageshack.us/i/chokemesh.png/ http://img683.imageshack.us/i/chokepress.png/ http://img413.imageshack.us/i/chokeyplus.png/ Based on the convergence history the simulation is converged. I don't understand the cause of the too high Mach number. The geometry doesn't contain Laval tube, this is a simple choke. I have tried to set the expert parameter/high speed models but the result is unchanged. Can the material model cause the problem? ...perhabs other ideas? Thanks in advance; Roland Last edited by wyldckat; September 3, 2015 at 17:38. Reason: disabled embedded images |
|
May 11, 2010, 07:58 |
|
#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
Looks like a standard expansion shock to me. What don't you like about it?
If you want to see an expansion shock in real life have a look at a fighter jet engine exhaust, especially with afterburners on. You can see it clearly then. |
|
May 11, 2010, 10:14 |
|
#3 |
Senior Member
Roland Rakos
Join Date: Mar 2009
Posts: 131
Rep Power: 17 |
Hello Glenn,
As far as I know, the Mach number can not be larger than 1. Although a laval nozzle develops from the flow separations after the choke, but Ma=2.5??? In my opinion this is unrealistic... I have some measurements to the original investigated geometry. The total temperature was measured before and after the choke. The total temp. is in the case of my simulation ~24C (after the choke). This value was ~15C in case of the measurement... Roland |
|
May 11, 2010, 18:27 |
|
#4 | ||
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
Quote:
Quote:
|
|||
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
mesh file for flow over a circular cylinder | Ardalan | Main CFD Forum | 7 | December 15, 2020 13:06 |
mach number and CFX 11.0 solver | turbinesv | CFX | 5 | January 5, 2009 05:43 |
compressible at low Mach number with uniteration | ricklee | Main CFD Forum | 2 | October 20, 2005 23:15 |
How to find Mach Number | Tobias | FLUENT | 2 | October 18, 2005 09:59 |
Difficulties in solving a high Reynolds number Flow? | wowakai | Main CFD Forum | 10 | December 29, 1998 13:46 |