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.

Computational study of heat transfer and gas dynamics in the pulsed laser evaporation of metals

Abstract: Pulsed laser irradiation of nanosecond duration is used in a variety of applications, including laser deposition of thin films and micromachining. Of fundamental interest is the prediction of the evaporative material removal rates, as well as the velocity, density, and temperature distributions of the ejected particles as functions of the laser‐beam pulse energy, temporal distribution, and irradiance density on the target material surface. In order to address these issues, the present work establishes a new computational approach for the thorough treatment of the heat transfer and fluid flow phenomena in pulsed laser processing of metals. The heat conduction in the solid substrate and the liquid melt is solved by a one‐dimensional transient heat transfer model. The ejected high‐pressure vapor generates shock waves against the ambient background pressure. The compressible gas dynamics is computed numerically by solving the system of Euler equations for mass, momentum, and energy, supplemented by an isentropic gas equation of state. The aluminum, copper, and gold targets considered were subjected to pulsed ultraviolet excimer laser irradiation of nanosecond duration. Results are given for the temperature distribution, evaporation rate, and melting depth in the target, as well as the pressure, velocity, and temperature distributions in the vapor phase.

Upstream Waves and Particles

Abstract: The region upstream from terrestrial, planetary, and interplanetary shocks in which the magnetic field lines are connected to the shock is filled with a variety of plasma waves, MHD waves, energetic electrons, and ions associated with the near presence of the shock. These upstream waves and particles present us with a natural plasma laboratory which is providing basic information on plasma instabilities and collisionless shock physics, as well as insight into how cosmic ray acceleration may occur in the interstellar medium. Much remains to be done, however, before our present empirical knowledge is woven into the stronger fabric of theoretical understanding.

Shock compression of quartz to 1.6 TPa: redefining a pressure standard.

Abstract: Evaluation of models and theory of high-pressure material response is largely made through comparison with shock wave data, which rely on impedance match standards. The recent use of quartz as a shock wave standard has prompted a need for improved data. We report here on measurements of the quartz Hugoniot curve from 0.1-1.6 TPa. The new data, in agreement with our ab initio calculations, reveal substantial errors in the standard and have immediate ramifications for the equations of state of deuterium, helium, and carbon at pressures relevant to giant planets and other high-energy density conditions.

Strong Electron Acceleration at High Mach Number Shock Waves: Simulation Study of Electron Dynamics

Abstract: Electron-ion dynamics in a perpendicular magnetosonic shock wave in a high Mach number regime is studied by using the particle-in-cell simulation. It is shown that in the shock transition layer nonlinear evolution of two-stream instabilities plays an important role on the electron rapid heating and acceleration. As the shock Mach number greatly exceeds the critical Mach number, a series of large-amplitude, coherent electrostatic waves with the electron holes in phase space are excited by the two-stream instability between the reflected ions and the incident electrons in the shock transition layer. As the incident electrons are decelerated by the instability, other electrostatic waves grow in time by another two-stream instability between the incident ions and the decelerated incident electrons. The dynamic timescale of these instabilities is of the order of ω, where ωpe is the plasma frequency. The nonlinear interaction of these waves leads to the strong electron heating as well as the nonthermal high-energy electron acceleration in the shock transition layer.

Low-order stochastic modelling of low-frequency motions in reflected shock-wave/boundary-layer interactions

Abstract: A combined numerical and analytical approach is used to study the low-frequency shock motions observed in shock/turbulent-boundary-layer interactions in the particular case of a shock-reflection configuration. Starting from an exact form of the momentum integral equation and guided by data from large-eddy simulations, a stochastic ordinary differential equation for the reflected-shock-foot low-frequency motions is derived. During the derivation a similarity hypothesis is verified for the streamwise evolution of boundary-layer thickness measures in the interaction zone. In its simplest form, the derived governing equation is mathematically equivalent to that postulated without proof by Plotkin (AIAA J., vol. 13, 1975, p. 1036). In the present contribution, all the terms in the equation are modelled, leading to a closed form of the system, which is then applied to a wide range of input parameters. The resulting map of the most energetic low-frequency motions is presented. It is found that while the mean boundary-layer properties are important in controlling the interaction size, they do not contribute significantly to the dynamics. Moreover, the frequency of the most energetic fluctuations is shown to be a robust feature, in agreement with earlier experimental observations. The model is proved capable of reproducing available low-frequency experimental and numerical wall-pressure spectra. The coupling between the shock and the boundary layer is found to be mathematically equivalent to a first-order low-pass filter. It is argued that the observed low-frequency unsteadiness in such interactions is not necessarily a property of the forcing, either from upstream or downstream of the shock, but an intrinsic property of the coupled system, whose response to white-noise forcing is in excellent agreement with actual spectra.