Shock wave

About: Shock wave is a research topic. Over the lifetime, 36184 publications have been published within this topic receiving 635848 citations. The topic is also known as: Shock waves & shockwave.

Underwater Electrical Wire Explosion and Its Applications

Abstract: Results of an investigation of underwater electrical wire explosions using high-power microsecond and nanosecond generators are reported. Different diagnostics, including electrical, optical, and spectroscopic, together with hydrodynamic and magnetohydrodynamic simulations, were used to characterize parameters of the discharge channel and generated strong shock waves. It was shown that the increase in the rate of the energy input into exploding wire allows one to increase wire temperature and amplitude of shock waves. Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. The spectroscopic analysis of the emitted radiation has unveiled no evidence for the formation of a shunting plasma channel. Analysis of the generated shock waves shows that ~15% of the deposited energy is transferred into the mechanical energy of the water flow. Also, it was shown that converging shock waves formed by underwater explosion of cylindrical wire arrays can be used to achieve extremely high pressure at the axis of implosion. A pressure up to 0.25 Mbar at 0.1 mm distance from the axis of the implosion at a stored energy of ~4 kj was demonstrated. A model explaining the nature of similarity parameters, which have been phenomenologically introduced in earlier research, was suggested.

The Spiral Modes of the Standing Accretion Shock Instability

Abstract: A stalled spherical accretion shock, such as that arising in core-collapse supernovae, is unstable to non-spherical perturbations. In three dimensions, this Standing Accretion Shock Instability can develop spiral modes that spin-up the protoneutron star. Here, we study these non-axisymmetric modes by combining linear stability analysis and three-dimensional, time-dependent hydrodynamic simulations with Zeus-MP, focusing on characterizing their spatial structure and angular momentum content. We do not impose any rotation on the background accretion flow and use simplified microphysics with no neutrino heating or nuclear dissociation. Spiral modes are examined in isolation by choosing flow parameters such that only the fundamental mode is unstable for a given polar index l, leading to good agreement with linear theory. We find that any superposition of sloshing modes with non-zero relative phases survives in the nonlinear regime and leads to angular momentum redistribution. It follows that the range of perturbations required to obtain spin-up is broader than that needed to obtain the limiting case of a phase shift of {pi}/2. The bulk of the angular momentum redistribution occurs during a phase of exponential growth and arises from internal torques that are second order in the perturbation amplitude. This redistribution gives rise to at least twomore » counter-rotating regions, with the maximum angular momentum of a given sign approaching a significant fraction of the mass accretion rate times the shock radius squared ( M-dot r{sub shock}{sup 2{approx}}10{sup 47} g cm{sup 2} s{sup -1}, spin period {approx}60 ms). Nonlinear mode coupling at saturation causes the angular momentum to fluctuate in all directions with much smaller amplitudes.« less

Dynamics of Shock Dispersion and Interactions in Supersonic Freestreams with Counterflowing Jets

Abstract: This study describes an active flow control concept that uses counterflowing jets to significantly modify external flowfields and strongly disperse the shock waves of supersonic and hypersonic vehicles to reduce aerothermal loads and wave drag. The potential aerothermal and aerodynamic benefits of the concepts were investigated by conducting experiments on a 2.6%-scale Apollo capsule model in Mach 3.48 and 4.0 freestreams in a trisonic blowdown wind tunnel, as well as pretest computational fluid dynamics analyses of the flowfields, with and without counterflowing jets. The model employed three sonic and two supersonic (with design Mach numbers of 2.44 and 2.94) jet nozzles with exit diameters ranging from 0.25 to 0.5 in. The schlieren images were consistent with the pretest computational fluid dynamics predictions, showing a long penetration mode jet interaction at low jet flow rates of 0.05 and 0.1 Ib m /s, whereas a short penetration mode jet was revealed at higher flow rates. The long penetration mode jet appeared to be almost fully expanded and was unsteady, with the bow shock becoming so dispersed that it was no longer discernible. High-speed camera schlieren data revealed the bow shock to be dispersed into striations of compression waves, which suddenly coalesced to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. Heat transfer results showed a significant reduction in heat flux, even giving negative heat flux for some short penetration mode interactions, indicating that the flow wetting the model had a cooling effect, instead of heating, which could significantly impact thermal protection system requirements and design. The findings suggest that high-speed vehicle design and performance can benefit from the application ofcounterflowing jets as an active flow control.

Shock compression of two iron‐silicon alloys to 2.7 megabars

Abstract: The compressibility of iron-silicon alloys of 4.0 and 19.8 wt % silicon has been measured to 2.7 Mb, using a plane-wave explosive-metal driver system. A high-resolution electrical pin contactor method was developed for the measurement of shock wave velocity in the alloy samples. The Gruneisen equation of state was used in calculating temperature and sound speed along the measured Hugoniot of the 19.8 wt % alloy and in constructing a family of isentropes from the measured quantities. The loci of pressure-density and sound speed-density values for the 19.8 wt % alloy along the Hugoniot and isentropes were compared with estimates of these properties for the earth's core. The results are consistent with an outer core containing 14–20 wt % silicon in iron, as has been proposed by Kingwood and by MacDonald and Knopoff.