Time stepping difference in CFD code and particle paths scheme

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 October 17, 2014, 10:25 Time stepping difference in CFD code and particle paths scheme #1 New Member   Join Date: Jul 2014 Posts: 2 Rep Power: 0 Hi, I simulated an unsteady flow by injecting two oscillating flows in anti-phase in a rectangular 2D domain. I extracted the velocity field for each time step. In Matlab i created a massless particle tracking script using a Taylor-Galerkin integration scheme. In my loop i calculate each particle position but i noticed the positions are very dependent on the time step in the particle tracking script. If i make this time step smaller the particles still move with the flow field but they travel less far. Does this time step needs to be the same as the time step i used in the unsteady CFD solver? Thanks in advance!

October 17, 2014, 12:11
#2
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Filippo Maria Denaro
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 Originally Posted by Jokert Hi, I simulated an unsteady flow by injecting two oscillating flows in anti-phase in a rectangular 2D domain. I extracted the velocity field for each time step. In Matlab i created a massless particle tracking script using a Taylor-Galerkin integration scheme. In my loop i calculate each particle position but i noticed the positions are very dependent on the time step in the particle tracking script. If i make this time step smaller the particles still move with the flow field but they travel less far. Does this time step needs to be the same as the time step i used in the unsteady CFD solver? Thanks in advance!

are you solving the particle tracking using a velocity database ? What about the time interval of the sampling of the velocity field?

October 19, 2014, 11:35
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 Originally Posted by FMDenaro are you solving the particle tracking using a velocity database ? What about the time interval of the sampling of the velocity field?
Yes i do, i use the velocity database(velocity field) calculated from the unsteady solver for every timestep. The sampling interval is the same as the time step for solver.

October 19, 2014, 12:06
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Filippo Maria Denaro
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 Originally Posted by Jokert Yes i do, i use the velocity database(velocity field) calculated from the unsteady solver for every timestep. The sampling interval is the same as the time step for solver.

ok, I suppose you have a second order time integration but what about your interpolation on the spatial grid?
However, if the flow contains relevant oscillations within the frequency pi/dt you must integrate the Lagrangian problem using the velocity field computed at each time step dt ...

 Tags integrate variables, particle flow, time step, unsteady flow

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