Particle Image Velocimetry in a 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. The objective of this paper is to present an attempt at quantitative flow visualization by Particle Image Velocimetry. PIV measurements are conducted in a supersonic air ejector. Several ejector operating conditions (with or without secondary flow entrainment) are studied. Different flow seeding methods (natural seeding by condensation microdroplets, artificial tracers added into the secondary flow) are tested. The velocity fields obtained are compared with CFD simulations of the flow and allow the rigorous validation of numerical models.