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 April 8, 2010, 10:39 Steady vs Unsteady #1 New Member   Join Date: Jan 2010 Posts: 4 Rep Power: 8 Hello, I have a question, maybe stupid, but I really need answers. I am running a simulation in 3D, with constant boundary conditions and I am particularly interested in the flow (recirculation, eddy, etc.). Since all the variables are constants, does it make any sense to run an unsteady simulation? SteffB

April 8, 2010, 15:13
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Fidel Arzola
Join Date: Mar 2010
Location: Venezuela
Posts: 5
Rep Power: 7
Quote:
 Originally Posted by Steff54 Hello, I have a question, maybe stupid, but I really need answers. I am running a simulation in 3D, with constant boundary conditions and I am particularly interested in the flow (recirculation, eddy, etc.). Since all the variables are constants, does it make any sense to run an unsteady simulation? SteffB

Hello,
In my opinion yes!, for instance, I simulated the hydrodynamic of a cavitating vortex in the draft tube of a Francis turbine, called Vortex Rope in the field of hydroturbines, just imposing a constant and symmetric velocity profile (taked from 2D LDV measurements) in the inlet and then pressure fluctuactions were very well computed and I never used a rotor-stator simulation. But I was sure that that phenomenon is time-dependant and transient simulations were necesary. Transient phenomena are also dependent of geometry, boundary conditions, numrical scheme, time and spatial resolution, etc...

A final suggestion, used a converged steady simulation to start a transient one with a well-defined time step and give enought time to capture expected physical time-dependant phenomena.
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Thanks,
Fidel

 April 9, 2010, 05:59 think "NATURE" #3 New Member   Amin Feizi Join Date: Apr 2010 Posts: 8 Rep Power: 7 Hi, There is no inconvenience in running an unsteady simulation whith steady BCs . But it is better to think "NATURE", sort of speaking. There is no instant changes in boundaries in the reality. So the best results are obtained with unsteady BCs if you know them. Good Luck, Amin

 April 9, 2010, 10:12 #4 New Member   Join Date: Jan 2010 Posts: 4 Rep Power: 8 Hi, Thanks for your answer guys, it was very useful.

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