Oblique shock

About: Oblique shock is a research topic. Over the lifetime, 6551 publications have been published within this topic receiving 119823 citations.

Shock waves at a slow-fast gas interface

Abstract: This paper describes the results of our experiments with shock waves refracting at a CO2/CH4 interface. The refraction is slow-fast because the speed of sound in the incident gas (CO2) is less than that in the transmitting gas (CH4). We found three phenomena which apparently have not been reported before and which all have free precursor shocks in their wave systems; schlieren photographs of them are presented. As a result of the present and earlier work, we can assert that there exist at least four different free precursor refractions. Theoretical studies suggest that the slow-fast phenomena can be conveniently classified into three groups characterized by different ranges of values of the inverse strength ζi of the incident shock i. The classification may be an exhaustive list of the phenomena, at least when the gases are nearly perfect, but we cannot be sure. We present experimental data on all the phenomena in each group, including data on the transition conditions from one wave system to another both within and across the groups.

Experimental study of Richtmyer-Meshkov instability induced by cylindrical shock waves

Abstract: The paper describes the results of holographic interferometric flow visualization of the Richtmyer-Meshkov instability induced by cylindrical shock waves propagating across cylindrical interfaces. Experiments were conducted in an annular coaxial vertical diaphragmless shock tube, which can produce converging cylindrical shock waves with minimum disturbances. The shock wave converged and interacted with a cylindrical soap bubble filled with He, Ne, air, Ar, Kr, Xe, or SF6. The soap bubble was placed coaxially in the test section. The effects of density variation on the Richtmyer-Meshkov instability for a wide range of Atwood numbers were determined. Pressure histories at different radii during the shock wave implosion and reflection from the center were measured. Double-exposure holographic interferometry was used and the motion of the converging shock wave and its interaction with the gaseous interface were visualized. The variation of the pressure at the center with interface Atwood number for constant i...

Simulations of Electron Acceleration at Collisionless Shocks: The Effects of Surface Fluctuations

Abstract: Energetic electrons are a common feature of interplanetary shocks and planetary bow shocks, and they are invoked as a key component of models of nonthermal radio emission, such as solar radio bursts. A simulation study is carried out of electron acceleration for high Mach number, quasi-perpendicular shocks, typical of the shocks in the solar wind. Two-dimensional self-consistent hybrid shock simulations provide the electric and magnetic fields in which test particle electrons are followed. A range of different shock types, shock normal angles, and injection energies are studied. When the Mach number is low, or the simulation configuration suppresses fluctuations along the magnetic field direction, the results agree with theory assuming magnetic moment conserving reflection (or fast Fermi acceleration), with electron energy gains of a factor only 2-3. For high Mach numbers, with a realistic simulation configuration, the shock front has a dynamic rippled character. The corresponding electron energization is radically different: energy spectra display (1) considerably higher maximum energies than fast Fermi acceleration; (2) a plateau or shallow sloped region at intermediate energies 2-5 times the injection energy; (3) power-law falloff with increasing energy, for both upstream and downstream particles, with a slope decreasing as the shock normal angle approaches perpendicular; (4) sustained flux levels over a broader region of shock normal angle than for adiabatic reflection. All these features are in good qualitative agreement with observations, and show that dynamic structure in the shock surface at ion scales produces effective scattering and can be responsible for making high Mach number shocks effective sites for electron acceleration.