Vincent Tanguay

Particle momentum effects from the detonation of heterogeneous explosives

Detonation of a spherical high explosive charge containing solid particles generates a high-speed two-phase flow comprised of a decaying spherical air blast wave together with a rapidly expanding cloud of particles. The particle momentum effects associated with this two-phase flow have been investigated experimentally and numerically for a heterogeneous explosive consisting of a packed bed of inert particles saturated with a liquid explosive. Experimentally, the dispersion of the particles was tracked using flash radiography and high-speed photography. A particle streak gauge was developed to measure the rate of arrival of the particles at various locations. Using a cantilever gauge and a free-piston impulse gauge, it was found that the particle momentum flux provided the primary contribution of the multiphase flow to the near-field impulse applied to a nearby small structure. The qualitative features of the interaction between a particle and the flow field are illustrated using simple models for the part...

Aluminum Particle Combustion in High-Speed Detonation Products

Aluminum particles ranging from 2 to 100 μm were subjected to the flow of detonation products of a stoichiometric mixture of hydrogen and oxygen at atmospheric pressure. Luminosity emitted from the reacting particles was used to determine the reaction delay and duration. The reaction duration was found to increase as d n with n ≈ 0.5, which is more consistent with kinetically controlled reaction rather than the classical diffusion-controlled regime. Emission spectroscopy was used to estimate the combustion temperature, which was found to be well below the flow temperature. This fact also suggests combustion in the kinetic regime. Finally, the flow field was modeled with a CFD code, and the results were used to model analytically the behavior of the aluminum particles.

Dynamics of explosively imploded pressurized tubes

The detonation of an explosive layer surrounding a pressurized thin-walled tube causes the formation of a virtual piston that drives a precursor shock wave ahead of the detonation, generating very high temperatures and pressures in the gas contained within the tube. Such a device can be used as the driver for a high energy density shock tube or hypervelocity gas gun. The dynamics of the precursor shock wave were investigated for different tube sizes and initial fill pressures. Shock velocity and standoff distance were found to decrease with increasing fill pressure, mainly due to radial expansion of the tube. Adding a tamper can reduce this effect, but may increase jetting. A simple analytical model based on acoustic wave interactions was developed to calculate pump tube expansion and the resulting effect on the shock velocity and standoff distance. Results from this model agree quite well with experimental data.

The high-explosive channel effect: Influence of boundary layers on the precursor shock wave in air

The high-explosive channel effect is investigated to study the dynamics of the precursor shock wave in air when there is no coupling of the precursor with the detonation. This is achieved experimentally by using Detasheet in square channels. It is found that the precursor shock wave initially propagates at the velocity dictated by one-dimensional gasdynamics, but then slows down from its theoretical velocity. In fact, the precursor eventually (after hundreds of channel diameters) reaches a terminal velocity equal to the detonation velocity. It is found that boundary layers are responsible for this effect: shocked gas leaks past the detonation products through the boundary layer and, as a result, the precursor shock slows down. This phenomenon is modeled analytically and the results are found to agree well with experiments.

The channel effect: Coupling of the detonation and the precursor shock wave by precompression of the explosive

The high-explosive channel effect is investigated to study the coupling dynamics of the precursor shock wave with the detonation. This is achieved experimentally by using porous pentaerythritol tetranitrate (PETN) powder in square channels. It is found that the precursor shock wave causes the detonation to accelerate to approximately 1.5 times the detonation velocity of the porous PETN. This phenomenon is found to be almost independent of the fill gas and the initial pressure in the channel. It is found that the precursor shock wave is insufficiently strong to initiate the PETN layer before the arrival of the main detonation front, and that the mechanism responsible for the observed acceleration is precompression of the explosive layer by the precursor shock wave. This mechanism is modeled analytically by generalizing an existing model for the precursor shock wave dynamics with boundary layers. The results agree well qualitatively and relatively well quantitatively considering the assumptions that are made.

Metal Combustion in High-Speed Flow

*† ‡ § The combustion of reactive metals (aluminum, magnesium, titanium, and zirconium) in a supersonic flow of shock-heated oxygen is investigated. The material samples are cylinders of sufficiently large size (1-3 mm diameter) that the interior of the samples remain cool for the duration of the experiment. The flow of oxygen is heated and accelerated by a strong normal shock wave driven by the detonation of an explosive charge at one end of a 1.2-mlong tube filled with gaseous oxygen; the samples were located at the other end of the tube. The shock Mach number ranged from Mach 5 to 9, generating supersonic (M > 2) flows with static temperatures of 1300 K to 3600 K. Intense surface luminosity was observed on the zirconium and titanium samples for even the weakest shock waves generated. Aluminum and magnesium were seen to be less reactive, requiring a stronger shock before the onset of reaction. The mass of material removed from the samples by reaction with the flow of oxidizer was measured as a function of shock strength. The luminosity and mass removal were shown to be combustion (as opposed to ablation followed by decoupled chemical reaction) by performing a control experiment with pure nitrogen, in which no mass removal or luminosity was observed on the sample surfaces. Nomenclature Eo

Phase velocity enhancement of linear explosive shock tubes

Strong, high-density shocks in a gas can be generated by end-initiating a hollow cylinder of explosive surrounding a pressurized thin-walled tube. Implosion of the tube results in a pinch that travels at the detonation velocity of the explosive, thereby driving a strong shock into the gas ahead of it. In the present study, the pinch velocity was increased beyond the detonation velocity of known explosives by dragging an oblique detonation wave along the surface of the tube. The gas shock and detonation trajectories were measured for a variety of phase velocities and tube fill pressures. Strong shocks with an average velocity of 13 km/s were observed for fill pressures as high as 6.9 MPa in helium while transient velocities as high as 19 km/s were observed. Shock trajectory performance degraded strongly with increasing phase velocity and for a velocity of 16 km/s the gas shock barely advanced ahead of the detonation.

DEVELOPMENT OF A SINGLE‐STAGE IMPLOSION‐DRIVEN HYPERVELOCITY LAUNCHER

Work carried out on the development of a single‐stage implosion‐driven hypervelocity launcher is presented. Explosives surrounding a thin‐walled tube filled with helium works similar to the pump tube of a conventional light gas gun. Implosion of the tube drives a strong shock that reflects back and forth between the projectile and the implosion pinch, generating very high temperatures and pressures. Experiments to evaluate the implosion dynamics and performance of the pump tube were carried out, with attention given to the helium fill pressure, diameter of the pump tube, thickness of the explosive layer, and the presence of a tamper. Simple analytic models were used to approximate the performance of the launcher; their advantages and limitations are discussed. Experiments with an implosion‐driven launcher demonstrated muzzle velocities of 4 km/s with 5‐mm‐diameter aluminum projectiles, agreement with analytical models of performance is discussed. Projectile integrity was verified by high‐speed photography...

Comparison of Critical Conditions for Initiation of Porous PETN by Shock Waves Transmitted from Solids and Gases

The critical conditions for shock initiation are studied experimentally. Experiments were conducted where the shock wave was transmitted to the porous explosive via a solid (PMMA) and a gas (air). The configurations are designed such that the transmitted pressure pulse is nearly a square wave in both cases. This permits a valid comparison of the critical shock strength in both cases. It is found that the critical shock strength is the same within the accuracy of the experimental technique.

Implosion-driven technique to create fast shockwaves in high-density gas

Pressurized tubes surrounded by either one or two layers (separated by a secondary tube) of sensitized nitromethane and encased in a thick-walled tube (the tamper) were imploded. The distance between the detonation wave in the explosive and shock wave in the innermost tube were measured (the standoff). A simple model based on hoop stress and acoustic interactions between the tubing was developed and used to predict the standoff distance. At low initial pressures (on the order of 7MPa), results indicate that the secondary tube and two layers of explosive did not prove to significantly increase the standoff. However, at higher pressures (on the order of 10 MPa), standoff was noticeably greater when the secondary tube was inserted between the pressurized tube and the tamper. The measured values are in reasonable agreement with the predictions of the model.