CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > Siemens > STAR-CCM+

Supersonic flow in a duct

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 18, 2017, 17:55
Cool Supersonic flow in a duct
  #1
New Member
 
Join Date: Nov 2010
Posts: 23
Rep Power: 14
ecto is on a distinguished road
Hi everybody!
I'm trying to simulate a supersonic flow in a duct (see attached image).
It's something like 15 mm in diameter and 20 cm long. It does a 180 bend at the end. To be specific, I'm interested at the resulting mass flow rate at the outlet (see image) with 25 bar at the inlet.
In my calculations the flow should be supersonic with a Mach number near 2.
I did poly mesh with about 1'200'000 cells (surface target 0.5 mm), 15 prism layers with 1st layer 5E-5 mm.
I initialized with velocity values of 800 m/s in the duct, 1bar pressure in the domain, expert initialization Grid sequencing.

What I managed to do is: going almost to convergence in 40'000 iterations (no errors) with the mass flow with settings:
-Constant density
- Coupled flow (No energy) with Co=0.1 and Explicit Relaxation =0.2 (as per Starccm+ guide)
- k-w turbulence all y+

What I cannot do is switching to Ideal Gas and Coupled Energy, because I immediately get the error you can see in the attached image (Overflow on the turbulence). And temperature limited errors. I wanted to switch to these because with that Mach Number it's better to enable compressibility.
I tried also to start with Segregated flow and Temperature, and also with Segregated Isothermal.

I tried also to do a Directed Meshing but I get error of "Loop... missing cad edge" when I want to Automesh the Source Surface.

Does anyone have an idea?
Thanks a lot
Attached Images
File Type: jpg image.jpg (44.2 KB, 43 views)
File Type: jpg error.JPG (24.5 KB, 28 views)
ecto is offline   Reply With Quote

Old   July 6, 2017, 12:00
Default
  #2
Senior Member
 
Matt
Join Date: Aug 2014
Posts: 947
Rep Power: 17
fluid23 is on a distinguished road
Without seeing your mesh I would have to guess that maybe you haven't refined the shocks sufficiently. Remember, you have extreme gradients at each shock and you must provide sufficient discretization to avoid numerical errors.
fluid23 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 is the accuracy using VOF (pressure based solver) on supersonic flow air_fun Fluent Multiphase 1 August 25, 2021 00:59
[How to obtain supersonic flow inside a supersonic wind tunnel ?] yx213 Siemens 1 September 17, 2014 13:52
Supersonic flow abishek FLUENT 3 July 28, 2008 06:07
Supersonic flow past a wedge with counter flow Mahesh Bailakanavar FLUENT 0 February 14, 2008 00:21
Thin film flow in triangular duct Swapnil CFX 4 December 4, 2002 16:08


All times are GMT -4. The time now is 05:44.