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Turbulence Disturbance in CFD

The velocity of the fluid divides into average and oscillating components. The average velocity influences the mean particle velocity, while the oscillating velocity is effective on the propagation of particle turbulence.

In turbulent flows, there are different structures of large sizes. Eddies in a turbulent flow has a wide range of size, life and energy levels. Particles that move in a turbulent flow are caught up in this range, and as a result, the eddies affect the path of particle and particle energy.

Considerations should be made to study the effects of turbulent flow on particles. In general, each vortex has velocity and length characteristics. When a particle enters the vortex, to calculate the instantaneous velocity, the velocity of the vortex should be added rapidly to the mean flow. The turbulent fluctuation velocity is important in the following cases:

1- When the characteristic of the interaction of particle and eddy is less than eddy’s life.

2- The displacement of the particle relative to the eddy is less than the eddy’s length.

  1. The particle has reached a GGI boundary.

When the particle is exited from an Eddy, it is assumed that the particle enters another Eddy with different characteristics. In the figure below, the particle path is shown in the same flow. In the first picture, the effect of turbulent flow is considered, and the particles affected by the turbulent flow are streamlined in an arbitrary manner, but in the second image, they follow the regular direction because the turbulent flow effects are not considered.



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