|
[Sponsors] |
![]() |
![]() |
#1 |
New Member
mike
Join Date: Aug 2013
Posts: 11
Rep Power: 13 ![]() |
Hi everyone,
i have a question about my unsteady cfd results. I am simulating a time-dependent (unsteady at inlet velocity 20 m/s) flow over a sphere with Star CCM+ which is in the middle of the wind tunnel. Also some pictures are saved in every time-step. After some time-steps I mean the time= about 0.5 s, the velocity and also vorticity distributions change really minimally, as opposed to the time between 0-0.5s. So that i cant see the turbulent structures on these distributions. The solution is like an end result of a steady state! (Time-Step is chosen= 0.002s) I have expected that the periodic fluctating behaviour could be clearly seen. Is it normal that the flow can be stable in this case? Or is it unrealistic how I define the problem? ![]() Thanks in advance. |
|
![]() |
![]() |
![]() |
![]() |
#2 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,896
Rep Power: 73 ![]() ![]() ![]() |
Quote:
What about the diameter and the fluid? What about the details of your numerical formulation? |
||
![]() |
![]() |
![]() |
![]() |
#3 |
New Member
mike
Join Date: Aug 2013
Posts: 11
Rep Power: 13 ![]() |
Sorry for the missing informations about my model. It is an air flow over a sphere with 220 mm diameter like a soccer ball. The mesh size in the wake is 6 mm.
I think it is a general question for me, because the same thing occured when i tried to simulate a vehicle aerodynamic problem in transient case. I observed, it doesnt come to almost no changes when i looked at velocity distributions after certain time-steps. So, could it be a problem at the my problem definition or is the time step i have chosen a wrong value? Or Do I have to make the mesh size finer in the wake? Thanks |
|
![]() |
![]() |
![]() |
![]() |
#4 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,896
Rep Power: 73 ![]() ![]() ![]() |
Quote:
No, the first and more relevant think is about the mathematical set of equations you are solving. What kind of formulation are you using? Be aware that your Re is O(10^5). This is a very critical regime, see https://www.grc.nasa.gov/www/k-12/ai...ragsphere.html This flow is very challenging, requires a proper formulation and a very refined grid |
||
![]() |
![]() |
![]() |
Tags |
sphere, transient, unsteady |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
About Some Concepts:Laminar flow, turbulent flow, steady flow and time-dependent flow | Jing | Main CFD Forum | 8 | October 5, 2018 18:02 |
Gate valve flow simulations... | nikesh | FloEFD, FloWorks & FloTHERM | 5 | January 28, 2014 02:31 |
steady for unsteady flow? | Shenren_CN | Main CFD Forum | 7 | July 19, 2013 06:32 |
Unsteady interna flow | yhoarau | OpenFOAM Running, Solving & CFD | 2 | June 5, 2012 11:42 |
Problem with results of simulation of flow past sphere at Re=250 | quarkz | Main CFD Forum | 2 | December 30, 2011 07:31 |