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Particle Image Velocity (PIV) is now a well established, non-intrusive technique for the two dimensional measurement of fluid velocity from a single plane of interest within a fluid flow. This thesis presents new work into the application of the double pulsed PIV technique to highspeed flows. The areas of work can be split into three major areas. The first area of work involved a comprehensive study into data reduction using autocorrelation. Results from the study allowed the development of an optimisation method which provides a consistent basis for experimental design. Further work validated this method by comparing equivalent results from sets of PIV transparencies processed using a system developed from commercially available image processing equipment. The second area of work involved supersonic flow studies of a de Laval expansion nozzle. PIV results were recorded from both inside and outside the nozzle. Inside the nozzle the PIV results resolved a normal shock and allowed comparisons with a 1D theoretical model, a CFD prediction and Schlieren photographs. Outside the nozzle the PIV data permitted overexpanded jet shock cell structures to be resolved and compared to a shock cell model. The final area of work involved development of an image labelling system for high speed flows by changing the transfer characteristics of the recording optics between exposures. A general theory of this technique was developed and a system designed and tested which can be applied to flows of arbitrarily high speed.

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It is hoped that the research here outlined will give an additional understanding of the performance of "valves" under dynamic conditions and supplement existing steady state or continuous flow analysis as outlined by Wambsganss, MacLaren etc. The study describes tests carried out on disc valves in which the valve seat was withdrawn from the valve while a pressure difference existed across the valve. Simultaneous measurements were made of the force on the valve, the pressure in the plenum chamber and the displacement of the seat from the valve. Dynamic force measurements are compared with values of force measured during steady continuous flow conditions (static flow) at selected values of pressure difference and displacement of the valve from its seat. The comparison may, therefore, be considered as relating the force on the valve during dynamic withdrawal of the seat from the valve to the steady state force on the valve at corresponding pressures and displacements during steady continuous flow through the valve. It is shown that during the early part of the withdrawal, there are significant differences between the force on the valve and the steady state force. These differences are accentuated by the pressure difference across the valve and the rate at which the valve is opened. This study also deals at some length with the instrumentation used and problems encountered. From the work by Chan on the behaviour of inviscid incompressible fluids, a computer program has been developed for the steady continuous flow condition of the disc valves under study. This program is based on two-dimensional or axisymmetric potential fluid flow and uses the Finite Element method. The method employs the velocity potential Ø as the primary unknown and 8-node quadrilateral elements of arbitrary shape to represent the region of flow under study. This method is equally applicable to both confined and free surface flow problems. The method first computes a solution for the velocity potential throughout the entire flow domain and then calculates secondary unknowns, e.g. velocity, pressure and force distributions. For free surface flow problems, it also predicts the free surface location, and the contraction or discharge coefficient. Quantitative comparisons between this approach and experimental work previously outlined are also made and the quality of comparison is found to be good.

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Various problems, which examine the propagation of gas dynamic disturbances, through an explosive atmosphere, are considered. The first set studies a model relaxing gas, and asymptotic methods are employed. A high frequency expansion is used to investigate piston oscillations in an infinite half space. The first two terms in the velocity perturbation are found in the acoustic case. The amplitude and frequency change on a wavelet are given; the wave number alters from wavelet to wavelet. For an enclosed volume the multi-time method is employed. When a standing wave exists in the vessel the frequency changes: when the vessel oscillates the wave number changes. The situation when forced oscillations at a natural frequency of the container is discussed. Also finite amplitude oscillations in a vessel are considered by using the multi-time method. An integral equation for the amplitude growth is found. A numerical solution of outward wave propagation, in spherical and cylindrical coordinates until shock formation, is given. The second group of problems considers a multi-component gas which can be analysed numerically. The effect of the homogeneous explosion in amplifying or damping a weak ii discontinuity is simulated. Thus proposals for reaction schemes can be analysed. It is found there is a relation- ship between amplification/damping and strong/weak ignition, in a mixture of hydrogen and oxygen in a shock tube. The reactions liberating a significant amount of energy in the chemical reaction, are the reactions causing greatest amplification.