The application of sub-micron particle visualisation for PIV (Particle Image Velocimetry) at transonic and supersonic speeds

Abstract

The technique of PIV (Particle Image Velocimetry) provides an instantaneous whole field visualisation in a plane of a flow field. This is achieved by projecting a plane of light into the flow. Two exposures are made to capture the images of particles within the plane using conventional photography. By measuring the distance between any pair of particle double exposures, the velocity of the particle and hence the fluid can be determined. This paper presents a brief review and an evaluation of the PIV method for use in a transonic flow and supersonic flow using a particle seeding in the 0.2 to 0.5 micron range. It also presents a comparison between a PIV measurement and numerical calculation of the flow through a normal shock. The flow field used for comparison was that of a 10mm diameter under expanded nozzle. The ability to track individual particles is dependent upon several factors; the particle size, the speed and turbulence of the flow, the intensity and wavelength of the light source used and the method of recording the information. The application of PIV at transonic flow speeds has been investigated with three critical questions in mind: 1. (i) That there is sufficient light being scattered from individual particles to form high resolution photographic images. 2. (ii) That the particles are small enough to follow the flow at transonic speeds. 3. (iii) That the simplest and most direct presentation and reduction of the particle image data is used to determine the velocity of the flow field.