Experimental tests of an axisymmetric jet of air impinging on both water and wet cement were performed and analyzed. Since the cavities formed on the water were unsteady and irregular, cavities were formed on wet fast-setting cement and allowed to set with the jet impinging. In this way, detailed measurements of the solidified cavity shape were made and shown to agree well with theory. This correlation of the data with the theory indicates that little gas was entrained in the liquid and that the influence of liquid viscosity and surface tension was small for the experimental conditions tested. A simplified analysis is also presented for an incompressible axisymmetric gas jet impinging normally on a liquid surface. The analysis was effected by combining the following physical conditions and assumptions: (i) the stagnation pressure corresponding to the centreline conditions of the jet at the bottom of the cavity is equal to the hydrostatic pressure, wherein an empirical turbulent jet decay law is used to predict the variation of stagnation pressure with distance from the nozzle; (ii) the force on the liquid is equal to the total change in normal momentum, which is equal to the weight of the displaced liquid; (iii) the shape of the cavity is a paraboloid.

Dust explosions pose a serious hazard in many industries. The detonability and flam inability of dust/oxidizer mixtures depend on the ignition delay of the dust particles when suddenly exposed to a high temperature environment. Consequently, the ignition delay time of dust particles behind a shock wave in the Mach number range of 4.0-5.0 has been measured using a photomultiplier tube to determine the onset of ignition. The dusts investigated included Pittsburgh Seam Coal, graphite, diamond, oats, and RDX. The experimental arrangement, consisting of a shock tube and two different dust injection devices, is described in detail, and experimental results for dusts ranging in particle size from 2 to 74 /*m are presented. In the Mach number range considered, ignition delay times varied from 2 to 100 /*s. A detailed analytical model based on a solution of the heat conduction equations for the particle interior coupled with a solution of the particle equation of motion has been developed. Heterogeneous reactions occurring on the particle surface and in the pores within the particle are used to model the chemistry. The results were in reasonable agreement with most of the data. Approximate analyses based on a comparison of characteristic thermal and chemical times were also developed. A key conclusion is that the ignition delay is determined mainly by the heat-up time of the particle surface.

Time-dependent, two-dimensional, numerical simulations of a transmitted detonation show reignition occuring by one of two mechanisms. The first mechanism involves the collision of triple points as they expand along a decaying shock front. In the second mechanism ignition results from the coalescence of a number of small, relatively high pressure regions left over from the decay of weakened transverse waves. The simulations were performed using an improved chemical kinetic model for stoichiometric H2-O2 mixtures. The initial conditions were a propagating, two-dimensional detonation resolved enough to show transverse wave structure. The calculations provide clarification of the reignition mechanism seen in previous H2-O2-Ar simulations, and again demonstrate that the transverse wave structure of the detonation front is critical to the reignition process.

A two-step chemical model for use in the numerical simulation of detonation phenomena in undiluted H 2 -O 2 mixtures is developed in this paper. The use of an induction-time parameter is examined, and its underlying assumptions are discussed. Various previously developed approximations for the induction time are compared with the results of numerical calculations using a detailed reaction mechanism, and on this basis, a new, more-accurate approximation is proposed. The heat-releasing reactions at the end of the induction period are replaced by a suitably calibrated chemical-transformation process. The results obtained using this approach in onedimensional unsteady detonation calculations agree well with theoretical predictions for Chapman-Jouguet detonations once the steady state has been attained. When the new model was applied to the diffraction of a detonation at the exit of a detonation tube, excellent agreement between simulation and experiment was obtained. Keywords: detonations; two-step H 2 -O 2 kinetics; H 2 -O 2 detonation diffraction; numerical simulation of detonations; H 2 -O 2 induction-time models; explosions

An inviscid transonic theory appears to be inadequate to describe the flow near the throat of a converging–diverging nozzle during the transition from the symmetrical Taylor (1930) type of flow to the subsonic–supersonic Meyer (1908) flow. A viscous transonic equation taking account of heat conduction and longitudinal viscosity has been developed previously (Cole 1949; Sichel 1963; Szaniawski 1963). An exact, nozzle-type of similarity solution of the viscous transonic equation, similar to the inviscid solution of Tomotika & Tamada (1950), has been found. This solution does provide a description of the gradual transition from the Taylor to the Meyer flow and shows the initial stages in the development of a shock wave downstream of the nozzle throat. The solution provides a viscous, shock-like transition from an inviscid, supersonic, accelerating flow to an inviscid, subsonic, decelerating flow.

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Abstract. When a plane detonation propagating through an explosive comes into contact with a bounding explosive, different types of diffraction patterns, which may result in the transmission of a detonation into the bounding mixture, are observed. The nature of these diffraction patterns and the mode of detonation transmission depend on the properties of the primary and bounding explosives. An experimental and analytical study of such diffractions, which are fundamental to many explosive applications, has been conducted in a two channel shock tube, using H2-O2 mixtures of diffi~rent equivalence ratios as the primary and bounding or secondary explosive. The combination of mixtures was varied from rich primary / lean secondary to lean primary / rich secondary since the nature of the diffraction was found to depend on whether the Chapman-Jouguet velocity of the primary mixture, Dp, was greater than or less than that of the secondary mixture, Ds. Schlieren framing photographs of the different diffraction patterns were obtained and used to measure shock and oblique detonation wave angles and velocities for the different diffraction patterns, and these were compared with the results of a steady-state shock-polar solution of the diffraction problem. Two basic types of diffraction and modes of detonation reinitiation were observed. When Dp > Ds, an oblique shock connecting the primary detonation to an oblique detonation in the secondary mixture was observed. With ])p < Ds, two modes of reinitiation were observed. In some cases, ignition occurs behind the Mach reflection of the :shock wave, which is transmitted into the secondary mixture when the primary detonation first comes into contact with it, from the walls of the shock tube. In ether cases, a del:onation is initiated in the secondary mixture when the reflected shock crosses the contact surface behind the incident detonation. These observed modes of Mach stem and contact surface ignition have also been observed in numerical simulations of layered detonation interactions, as has the combined oblique-shock oblique-detonation configuration when Dp > Ds. When Dp > Ds, the primary wave acts like a wedge moving into the secondary mixture with velocity Dp after steady state has been reached, a configuration which also arises in oblique-detonation ramjets and hypervelocity drivers.Correspondence to: Ix[. Tonello

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