Philippe Desevaux

A method for visualizing the mixing zone between two co-axial flows in an ejector

This paper describes an optical method which allows the accurate visualization of the mixing zone between two high-speed flows inside an ejector. This method associates Rayleigh scattering, laser induced fluorescence and image processing.

Visualization of Secondary Flow Choking Phenomena in a Supersonic Air Ejector

The present study deals with the visualization of the air flow inside a supersonic ejector. Our attention is more precisely focused on the choked flow phenomenon which occurs along the mixing chamber of the secondary nozzle and which can be visualized by CFD. Laser tomography visualizations are used to validate the CFD model. The evolution of flow configuration in the ejector with the primary stagnation pressure is examined both in the case of zero secondary flow and in the case of free entrainment of induced air.

An optical analysis of an induced flow ejector using light polarization properties

This paper presents an optical analysis of an induced flow ejector by means of plane laser sheets. The visualization method, which is developed here, takes advantage of the polarization properties of the light scattered by the fine droplets produced by condensation within the flow. This optical analysis shows that the droplets scatter near the Rayleigh scattering regime, thereby proving that their mean radius does not exceed 0.05 μm. Furthermore, the injection of depolarizing tracers into the induced stream makes it is possible to distinguish visually between the supersonic primary jet and the subsonic induced stream, and to obtain information about the mixing of the two streams.

Interface measurement technique for liquid film flowing inside small grooves by laser induced fluorescence

Abstract During the recent past, an optical investigation method of liquid films flowing within grooves of small dimensions, was developed by our research team. This non-intrusive method, based on the visualization of a transverse flow section, uses the laser induced fluorescence and image processing techniques in order to characterize the geometry of the liquid–gas interface. This article proposes to describe the principle and the practical application of this method and to present its possibilities through a certain number of applications carried out within our laboratory on isothermal flows and two-phase flows running in small grooves.

Experimental and Numerical Visualizations of Condensation Process in a Supersonic Ejector

The present study deals with the visualization of the droplet condensation phenomenon that can occur in ejectors powered by moist air. The condensation process is visualized through a numerical model of non-equilibrium condensation in high speed flows implemented by the present authors in a CFD code. The evolution of the region of condensation in the ejector with the primary stagnation pressure is examined both in the case without secondary flows and in the case with free entrainment of induced air. Laser tomography visualization is used to validate the computational results. The effects of some parameters such as the primary stagnation pressure and the humidity ratio in the primary and secondary air flows are also examined. Limitations of the present numerical model are discussed.

CFD Prediction of Supersonic Ejectors Performance

This work deals with the performance analysis of supersonic ejectors. A CFD model to predict the ejector performance in terms of suction and entrainment capacities is presented and applied to different operation modes of an air ejector. Computational results are compared to pressure and mass flow rate measurements. The 2D axisymmetric CFD model proves its ability to correctly predict the optimum operating conditions for supersonic ejectors.

Visualization of flow instabilities in supersonic ejectors using Large Eddy Simulation

Graphical Abstract

Flow Velocity Investigation by Particle Image Velocimetry in Supersonic Air Ejector

Ejectors are devices usually made of two convergent/divergent coaxial nozzles which are used to convert pressure energy into kinetic energy. These devices involve very complex phenomena which strongly affect their performance. Flow visualization methods are often used to provide precious information as for the nature of the flow within the ejectors and the comprehension of the physical phenomena encountered. Unfortunately, the visualization methods used successfully until now in these systems are primarily qualitative techniques. Some attempts at quantitative flow visualization by Particle Image Velocimetry have been carried out in quite specific applications but with mitigated results due to the complicated conditions of investigation. The objective of this paper is to present an attempt at PIV measurements in a supersonic air ejector. Several ejector operating conditions and flow seeding methods are taken into consideration. The velocity fields obtained are compared with CFD simulations of the flow and allow the rigorous validation of numerical models.

Laser photochromic dye activation technique for the measurement of liquid free surface velocity on curved surfaces

An optical method is presented which permits the determination of the free surface velocity of liquid films flowing on curved surfaces. The feasibility of this technique, which involves the laser tomography and photochromic dye activation techniques, is demonstrated on an oil film flowing around a finned tube. Results for different tube geometries and flow conditions are presented. Advantages and limits of the laser photochromic velocimetry technique are discussed.

CFD Design Study of a Pressure Probe for Centerline Static Pressure Measurement in Supersonic Ejectors

Abstract The measurement of the static pressure of the flow inside a supersonic ejector can be achieved by using a thin tube with a radially drilled hole to capture the flow pressure, and which is inserted along the ejector axis. This paper presents a numerical study by CFD permitting to predict the disturbances generated by the presence of the probe in the ejector. Also this study allows guiding the design of the probe, in particular of the capillary tube diameter for the least disturbed measurement. A probe prototype has been built and tested on an ejector test bench.