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Lagrangian coherent structures of accumulating inertial particles in vortex flow on a disk

Zeekant, Erwin (2011) Lagrangian coherent structures of accumulating inertial particles in vortex flow on a disk.

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Abstract:In this study a numerical investigation into the accumulation of inertial particles in vortex flow on a disk and its Lagrangian Coherent Structures is presented. A numerical simulation of inertial and gas particles, as in a gas-particle separator with a region of high vorticity, is performed. The structures can be shown by calculating the Finite-time Lyapunov Exponent (FTLE) for each grid point. This is a measure for the amount of stretching of particles at a certain location. By integrating forward in time, the forward FTLE can be calculated and by integrating backward in the the backward FTLE. Where the forward FTLE field show repelling Lagrangian Coherent Structures and the back FTLE field the attracting Lagrangian Coherent Structures. A MATLAB code is written to solve the equations of motion of the inertial and gas particles and which immediately calculates the corresponding FTLE fields at that time step. The code is tested for a simple case and is used to analyse the vortex flow. For low Stokes numbers the accumulation is very slow, but when this is increased the accumulation becomes much quicker. Above a critical value of the Stokes number, where the inertial particles will not accumulate anymore and all will move to the wall. There is no attractor or repeller found which should lead to the accumulation of the particles in the FTLE fields. The particles follow the structures that can be seen, but these are not leading to the accumulation. The results are compared to the results which are obtained by the drift flux model. With this model it is possible to give an analytical flow field for the inertial particles. For low Stokes numbers the results show good similarity. When the Stokes number is increased, the paths of the particles do not match anymore, but still give a good approximation for the accumulation point. When the Stokes number is too high the accumulation point and the paths do not show good similarity.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/61677
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