Generation of spherically converging shock wave based on shock wave lens

Hypersonic drag and heat reduction mechanism of a new hybrid method of spike, multi-row discs and opposing jets aerodynamic configuration

The response of geologic matter when subjected to large-scale impact or explosion is dependent on the time history of the encompassing shock wave. The kinetics of localized physical and chemical transitions brought about by the shock wave are responsive to this time history. Solid-state viscosity of the media is responsible for establishing the time history of a shock wave. In 2003, researcher H. Jay Melosh recognized the need for an understanding of solid viscosity spanning the petrologic and lithologic scales, and accordingly, he undertook the assessment and analysis of available nuclear ground shock measurements. This review furthers Melosh's epic efforts. In pursuing both the nuclear ground shock data and supporting laboratory test data, it undertakes methods for determining and calculations of the viscosity of solid materials on the respective scales. Further, applicability of viscoelasticity in modeling the shock response on the scales of concern is demonstrated and applied. The review closes with a discussion of universal features of the shock wave viscous time history in solid materials. Solid viscosity as an adiabatic invariant is presented, and commonalties of the solid shock wave with the nonlinear dynamics of ocean waves are noted. ▪ This article reviews Melosh's analysis of nuclear ground shock measurements with application to shock wave structuring viscosity. ▪ It discusses viscoelastic calculations with application to wave structure of nuclear ground shocks and laboratory shock waves in brittle granular solids, and universal features of the viscous shock wave structure and invariance of the dissipative action are considered. ▪ It also discusses wave action invariance in both the nonlinear dynamics of ocean waves and the steady wave structure of shock waves in solid matter.

Steady shock waves in porous plastic solids

The physical properties of hot dense plasmas at megabar pressures in a broad area of material phase diagrams are of great interest for astro and planetary physics, and for many applications in inertial confinement fusion, energetics, defense and many other areas. The use of intense shock waves in physical and chemical research has made the exotic extreme state of plasmas an object of laboratory or semilaboratory experiments. In this presentation a brief summary of scientific results of experimental investigations of strongly coupled nonideal plasma by intense shock waves is presented. Equations of state, compositions, and thermodynamic transport properties, as well as the electrical conductivity of strongly coupled plasmas generated by intense shock and rarefaction waves, are presented. Experimental methods for the generation of high energy densities in condensed matter, drivers for shock waves, and fast diagnostics are discussed. The pressure ionization and “dielectrization” of hot coupled matter are studied. The electrical conductivity and adiabatic compressibility of strongly coupled hydrogen and deuterium plasma demonstrate the first signature of plasma phase transition.

Theoretical study of a weak shock wave focusing process on a spherical region in confined 3-D axisymmetric chambers is presented. The chambers are elliptic or parabolic in the plane cross-section containing their axis of symmetry. In the elliptic case a spherical shock wave of constant strength generated at one of the focal points will reflect off the chamber wall and converge on a spherical region around the second focus of the chamber. It is shown that the pressure distribution on the converging spherical shock wave is not homogeneous. In the parabolic case two possibilities of shock generation are considered. In the first one a plane shock wave of constant intensity is send in the inner of the chamber. This shock wave with the plane perpendicular to the symmetry axis will after the reflection off the chamber wall transform to a spherical shock with non-homogeneous pressure distribution. Alternatively, a spherical shock of constant intensity generated at the focus of the paraboloidal chamber will after the reflection transform to a plane shock with non-homogeneous pressure distribution propagating in the outer of the chamber. The above mentioned problems are solved within the frame of the geometrical acoustics approximation and the flow fields as well as the non-uniform shock strengths behind the converging wave fronts are calculated.

Actual formation and intensity of shock wave generated during gradual opening and closure between each port and passages of wave rotor are studied by means of experiment and computational fluid dynamics simulation. The results show that the intensity of shock wave increases with the distance from high-pressure inlet, and the reason for the variation tendency is the superposition of compression waves. By changing the rotational speed and the expansion ratio, the shock wave intensity can be adjusted, but the position where the intensity reaches maximum stays constant basically and keeps the distance near 300 mm from high-pressure inlet. Comparing with the one-dimensional simplification result, the actual intensity of shock wave is lower. The difference between the fact and simplification increases with the rotational speed and expansion ratio. The internal mechanism has been analyzed from the aspect of intake mass. Then, the maximum shock wave intensity is found approximately linear to the intake mass of each rotor passage in each cycle.

Chapter 3.3 - Theory of Shock Waves: 3.3 Shock Waves in Solids

To solve the problem of excessive shock wave intensity in the channel of the launch box during the shock wave opening process, a baffle is installed at the rear end of the launch box to reduce the shock wave intensity. The effects of the baffle on the evolution of shock wave and gas flow field are investigated using computational fluid dynamics methods. Results show that the baffle effectively limits the propagation path of the shock wave and high-pressure gas, significantly reducing both the intensity and speed of the shock wave. Additionally, the baffle, as a reflective surface, increases the intensity of reflected shock wave at the rear end of the launch box. Further, a smaller baffle hole diameter leads to a weaker shock wave intensity within the launch box. By adjusting the baffle hole diameter, the shock wave intensity can be effectively controlled, ensuring that the launch box pressure meets launch requirements.

Parameter study on drag and heat reduction of a novel combinational spiked blunt body and rear opposing jet concept in hypersonic flows

Radial flow Variable Nozzle Turbine (VNT) enables better matching between a turbocharger and engine, and can improve the engine performance as well as decrease the engine emissions, especially when the engine works at low-end operation points. With increased nozzle loading, stronger shock wave and clearance leakage flow may be generated. The shock wave consequently introduces strong rotor-stator interaction between turbine nozzle and impeller, which is also a key concern of impeller high cycle fatigue failure. With the purpose of developing a shock wave free or low shock wave intensity turbine nozzle, the influence of grooved vane on the shock wave characteristics is investigated in present paper. A Schlieren visualization experiment was first carried out on a linear turbine nozzle with smooth surface and the behavior of the shock wave was studied. Numerical simulations were also performed on the turbine nozzle. The predicted shock wave shape, position and intensity were compared against the Schlieren images. Guided by the visualization and numerical simulation, grooves were designed on the nozzle surface where the shock wave was originated and numerical simulations were performed to investigate the influence of grooves on the shock wave characteristics. Results indicate that for a smooth nozzle configuration, the intensity of the shock wave increases as the expansion ratios increase, while the onset position is shifted downstream to the nozzle trailing edge. For a nozzle configuration with grooved vane, the position of the shock wave onset is shifted upstream compared to the one with a smooth surface configuration, and the intensity of the shock wave as well as the static pressure distortion at the nozzle vane exit plane are significantly depressed.

For many materials the shock wave speed in uniaxial strain compression increases linearly with increasing particle velocity with a slope generally characterized by s. From the Rankine-Hugoniot jump relations, the longitudinal compressive stress behind the shock wave becomes infinite at a critical compressive strain εc = 1/s. This paper raises the possibility that such behavior could be indicative of a jamming transition that occurs near a percolation threshold pc. Motivation for this line of inquiry comes from the results of pressure-shear plate impact (PSPI) experiments on polyurea, a block co-polymer comprised of hard and soft polymeric regions. At the high shear strain rates (105 - 106 s-1) of these PSPI experiments the shearing resistance increases proportionately, and strongly, with increasing pressure – suggesting the possibility that the response of polyurea may have similarities with that of a lubricated granular medium. The strong resistance would be due to interaction of the hard regions, whereas the apparent viscosity would be due to the lubrication provided by the soft regions.

Safety Relief Valves plays an important role in any pressurised system. The proper design of safety relief valves should consider the eective opening and closing characteristics to achieve the desired valve performance. One of the challenges in any valve design is the elimination of Shock waves. Shock waves are characterised by sudden pressure increase and Mach number drop. Detecting shock waves in safety relief valves using computational uid dy- namics could asses valve design to eliminate the shock waves. I t have been proven that the Reynolds Averaged Navier Stocks (RANS) equations with the k- turbulence model could model the internal gas ow in safety relief valves. The RANS and k- turbulence have been solved by a commercial CFD code. In safety valves discharge ow rate and closing and opening behaviours dependon the upstream pressure and certain critical areas. In this study, the eect of the upstream pressure has been discussed. Upstream pressure range was from 7 to 140 bars. The eect of the valve geometry has been discussed as well. Dierent critical outlet areas and divergent angles have been changed to investigate its eect on the shock wave parameters.The upstream pressure eect on shock wave occurrence and intensity have been studied. The results showed that, computational uid dynamics can be used to predict the location of the shock wave. In addition to determining the pressure peak and the Mach number drop and other properties which help eliminating shock wave occurrence in valve design. An e cient design should consider the geometrical and ow parameters that aect the shock wave occurrence and intensity.

ABSTRACTThe effects of non-uniformity of flows and initial disturbance intensity of the incident shock wave on Richtmyer–Meshkov instability (RMI) when a sinusoidal shock wave with Ma = 1.25 impinging an unperturbed interface are numerically investigated. The interface morphology, turbulent mixing zone width (TMZW), Y-integrated vorticity, circulation, and turbulent kinetic energy (TKE) are qualitatively and quantitatively compared before and after reshock. The numerical results indicate that the non-uniformity of flows and initial disturbance intensity of sinusoidal shock wave are significant factors of RMI evolution. On the one hand, the TMZW and its growth rate increase with the decrease of the parameter of non-uniformity before reshock; while, those discrepancies are reduced after reshock. On the other hand, the increase of the initial disturbance intensity of sinusoidal shock wave leads to the increase of the vorticity, circulation and TKE, the TMZW and it growth rate increase accordingly, all the time. Further analysis points out that the TMZW evolves with time as a power law before reshock, and the value of θ is sensitive to the initial conditions. After reshock and the first reflected rarefaction wave, the TMZW grows in time as a negative exponential law , but t* is different for the two stages.

The notion of plane shock waves is a macroscopic, very fruitful idealization of near discontinuous disturbance propagating at supersonic speed. Such a picture is comparable to the picture of shorelines seen from a very high altitude. When viewed at the grain scale where the structure of solids is inherently heterogeneous and stochastic, features of shock waves are non-laminar and field variables, such as particle velocity and pressure, fluctuate. This paper reviews select aspects of such fluctuating nonequilibrium features of plane shock waves in solids with focus on grain scale phenomena and raises the need for a paradigm change to achieve a deeper understanding of plane shock waves in solids.

With increasing concern of environmental and energy issues, ejector is more and more widely applied in various fields owing to the advantages of using low grade heat. In the ejector, the Mach waves may be generated at the nozzle outlet and diffuser chamber. Under different expansion ratios, the Mach waves at the nozzle outlet will appear to be expansion waves, oblique shock waves and normal shock waves successively. This paper theoretically studies the characteristics of the Mach waves at the nozzle exit of the ejector with steam, ammonia, R22, R290, R134a and R600a as working fluids. The results indicate that the higher the adiabatic indexes, the lower the Mach wave intensity if there are oblique shock waves or expansion waves in the nozzle exit and; the cross section ratio and shock wave intensity vary gently with the rise of expansion ratio. At the same time, expansion wave intensity and shock wave intensity also decrease with the increase of nozzle cone angle. Therefore, there should be an optimal parametric range for nozzle structure design to obtain higher efficiency.