The interaction of a planar shock wave with a square cavity is studied experimentally and numerically. It is shown that such a complex, time-dependent, process can be modelled in a relatively simple manner. The proposed physical model is the Euler equations which are solved numerically, using the second-order-accurate high-resolution GRP scheme, resulting in very good agreement with experimentally obtained findings. Specifically, the wave pattern is numerically simulated throughout the entire interaction process. Excellent agreement is found between the experimentally obtained shadowgraphs and numerical simulations of the various flow discontinuities inside and around the cavity at all times. As could be expected, it is confirmed that the highest pressure acts on the cavity wall which experiences a head-on collision with the incident shock wave while the lowest pressures are encountered on the wall along which the incident shock wave diffracts. The proposed physical model and the numerical simulation used in the present work can be employed in solving shock wave interactions with other complex boundaries.

A model is proposed to simulate turbulent combustion in confined TNT explosions. It is based on: (i) the multi-component gasdynamic conservation laws, (ii) a fast-chemistry model for TNT-air combustion, (iii) a thermodynamic model for frozen reactants and equilibrium products, (iv) a high-order Godunov scheme providing a non-diffusive solution of the governing equations, and (v) an ILES approach whereby adaptive mesh refinement is used to capture the energy bearing scales of the turbulence on the grid. Three-dimensional numerical simulations of explosion fields from 1.5-g PETN/TNT charges were performed. Explosions in six different chambers were studied: three calorimeters (volumes of 6.6-l, 21.2-l and 40.5-l with L/D = 1), and three tunnels (L/D = 3.8, 4.65 and 12.5 with volumes of 6.3-l)-to investigate the influence of chamber volume and geometry on the combustion process. Predicted pressures histories were quite similar to measured pressure histories for all cases studied. Experimentally, mass fraction of products, ! Y P exp , reached a peak value of 88% at an excess air ratio of twice stoichiometric, and then decayed with increasing air dilution; mass fractions ! Y P calc computed from the numerical simulations followed similar trends. Based on this agreement, we conclude that the dominant effect that controls the rate of TNT combustion with air is the turbulent mixing rate; the ILES approach along with the fast-chemistry model used here adequately captures this effect.

Often I am asked why the Ernst-Mach-Institut bears the name of a famous philosopher of the 19th century. The question is certainly justi fied, because my institute deals with research in experimental gas dy namics, ballistics, high-speed photography, and cinemaphotography. We are not in any way doing philosophical studies. In this article, I describe the contributions of Ernst Mach to experimental physics, especially to gas dynamics and ballistics, and thus not only explain our institute's name but also serve a great physicist's reputation for noteworthy dis coveries in natural science.

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Results of shock-dispersed-fuel (SDF) explosion experiments will be presented. The SDF charge consisted of a spherical 0.5-g PETN booster surrounded by 1-g of fuel: either flake Aluminum (Al) powder or TNT. The charge was placed at the center of a sealed chamber. Three cylindrical chambers (volumes of 6.6, 20 and 40 liters with L/D = 1) and three tunnels (L/D = 3.8, 4.65 and 12.5) were used to explore the influence of chamber volume and geometry on completeness of combustion. Detonation of the SDF charge created an expanding cloud of explosion product gases and hot fuel (Al or TNT). When this fuel mixed with air, it formed a turbulent combustion cloud that consumed the fuel, and liberated additional energy (31 kJ/g for Al or 15 kJ/g for TNT) over and above detonation of the booster (6 kJ/g) that created the explosion. Static pressure gauges were the main diagnostic. Pressure and impulse histories for explosions in air were much greater than those recorded for explosions in nitrogen-thereby demonstrating that combustion has a dramatic effect on the chamber pressure. This effect increases as the confinement volume decreases and the excess air ratio approaches 2 to 3.5. ___________________________________________________________________________________