Temperature measurements using fluorescent nanoparticles: application to the determination of the thermal effects in turbulent cavitating flows

When a liquid is submitted to severe accelerations, the fluid’s pressure can locally reach values lower than the vapor pressure causing the formation of gas bubbles.

This cavitation phenomenon is a major concern in industrial systems such as fluid machines, pumps and turbines, in which the presence of bubbles can substantially lower the efficiency. Furthermore, through interacting with the turbulence of the fluid, cavitation also alters the properties of the flow causing important dysfunctions. These interactions are suspected to become even more significant in thermosensible fluids such as those used in rocket engine turbopumps for instance, due to their high susceptibility to the thermal effects of cavitation occurring upon the liquid-to-gas transition.

This project aims at investigating the thermophysical properties of cavitating flows, with an emphasis on the thermal effects associated to viscous heating, liquid – vapor latent heat, and temperature inside a collapsing bubble.

Our experimental approach is based on the use of thermosensitive fluorescent nanoparticles to perform local non-intrusive measurements of the temperature and the velocity fields in the liquid phase. We simultaneously measure velocity, density and temperature to describe the coupling of turbulence and thermodynamic effects occurring during phase change.

This will be done using confocal microscopy in micro-channels configurations displaying turbulent cavitating two phase flows. These micro-machine devices will be adapted to X rays-absorption techniques for void ratio measurements and to micro-PIV-LIF(1) in order to obtain instantaneous velocity and temperature fields.

These experimental results should bring an increased understanding of the average and turbulent velocity distributions, and their correlation with the thermal and density distributions. This would represent a major advance in fluid mechanics and should help validating the modelling strategies used in numerical simulations.
 

(1) Particle Image Velocimetry – Laser Induced Fluorescence