Open Master Thesis
Jun-Prof. Benoit Fond FVST, Jun-Prof. Jan Heiland FMA
Thermographic Particle Image Velocimetry is an optical technique to measure the temperature and velocity of fluid flows (gas or liquid), by introducing small (micron-size) luminescent particles into the flow1. It has been applied in various types of flows including internal combustion engines, film cooling flows, and in natural convection. When using micron-size particles, the particles follow the flow, and their temperature is at equilibrium with the gas. If we illuminate the particles with a UV laser, the particles absorb the UV light, and then, they re-emit visible light called luminescence. The colour of the emitted light depends on the temperature of the particles, so by recording the light on a camera, we can determine the temperature of the particle, and therefore that of the gas.
Typically, we collect light from the particles with a lens as shown in Fig. 1 a). Only particles that are within the thin laser sheet (shown in purple) are excited, and emit frequency shifted light (here shown by the red rays). A filter is placed in front of the camera to only collect the frequency-shifted luminescence. However, when there are many particles, light emitted by particle can bounce off other particles, and the spatial information may be lost. Pathways for wanted and unwanted luminescence being collected on the detectors are shown on Figures 1. The wanted scenario mentioned above is a). In unwanted scenarios b-d), either excitation light or luminescence emission is scattered by particles outside the probe volume. The objective of this project is to theoretically quantify the contribution of unwanted light by implementing Mie scattering theory2 with random particle positions. More detail on Mie scattering theory can be found the following link:
a) Improve the current model by developing numerical schemes to increase the spatial resolution to computational cost ratio.
b) Quantify the contribution of multiple scattering relative (b and c) for a reference experimental configuration.
c) Validate the model against the result of measurements performed in the reference experimental configuration in Fond´s group.
d) Determine the scaling factor (size of coflow, seeding density ratio, imaginary over real part of index of refraction), and compare with experimental observations.
e) Estimate the relative probability of three particle events compared to the two particle event of scenarios b and c).
The scattering of light may be thought of as the redirection of light that takes place when an electromagnetic (EM) wave (i.e. an incident light ray) encounters an obstacle or nonhomogeneity, in our case the scattering particle… pdf ↩︎