Shock Wave

4 Key excerpts on "Shock Wave"

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  Flame and Combustion

  • J.F. Griffiths, J.A. Barnard(Authors)
  • 2019(Publication Date)
  • Routledge

    (Publisher)

  69 ].

  Shock Waves are generated by explosions. Since the source is a single event, energy is not provided continuously and the shock front in the surrounding atmosphere is immediately followed by an expansion or rarefaction wave which degrades the front. The pressure profile therefore changes shape as the wave moves further from the source, taking a form which is normally called a blast wave (Fig. 5.4 ).

  5.3  Application of shock tubes in kinetic and combustion studies

  In order to understand the chemical processes in flames in a quantitative way, it is essential to obtain kinetic data on elementary reactions over very wide ranges of temperatures. Sometimes these data can be derived from flame studies, but another source of data at high temperatures is the study of reactions behind a Shock Wave under controlled experimental conditions in a shock tube.

  A high temperature is readily attained in a shock heated gas, governed ideally by the pressure ratio across the shock front and the ratio of heat capacities of the gases (eqn (5.16) ). The discontinuity means that a reactant gas is raised instantaneously to T2 . The time interval available before a rapid cooling occurs, 10–1000 μs say, is short, but this is kinetically significant at high temperatures. The system is virtually adiabatic over the reaction interval. These are ideal circumstances in which quantitative kinetic measurements may be made.

  A plane Shock Wave is produced in a long, closed tube by the sudden bursting of a diaphragm (e.g. aluminium foil) which separates one gas at high pressure, the driver gas, from another at low pressure, the test gas. The reactants in the test gas are usually heavily diluted with inert gas (> 95%). A diagrammatic representation of a shock tube and how some of the events infold in time are shown in Fig. 5.5 . The contact surface represents the interface between the driver gas and the test gas. It moves rapidly along the tube but only at a subsonic velocity as opposed to the supersonic velocity of the shock front. The driver gas at the contact surface is cold, and so when it envelopes the test gas, any high temperature reactions are quenched instantly. The reaction time is represented by the interval between the arrival of the incident shock front and the arrival of the contact surface. Its duration is determined by the point in the tube at which the kinetic measurements are being made. The rarefaction fan

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  Shockwave Medicine

  • C. -J. Wang, W. Schaden, J. -Y. Ko, C.-J., Wang, W., Schaden, J.-Y., Ko, Samuel H. H. Chan, Julie Y. H. Chan, Samuel H.H., Chan, Julie Y.H., Chan(Authors)
  • 2018(Publication Date)
  • S. Karger

    (Publisher)

  Fig. 1 ).

  Shockwaves utilized in medicine bear these characteristics (Fig. 1 ) and are propagated utilizing electrohydraulic (Fig. 2a ), electromagnetic (Fig. 2b ), or piezoelectric (Fig. 2c ) technology [35 , 76 , 78 , 79 ]. SWs created by each of these 3 sources are primarily propagated by a contained high-voltage discharge within a three-dimensional (3D) fluid-filled chamber that causes an ephemeral high pressure disturbance, where each discharge propagates a biphasic sonic impulse (Fig. 1 ) within the chamber. The accelerated and sudden rise from ambient pressure within the chamber creates an extremely short duration broad frequency spectrum (16–20 MHz) SW, that rises to its peak pressure (100 MPa) and implodes (–10 MPa) within nanoseconds (Fig. 1 ) of its lifecycle [26 , 28 , 35 , 76 , 78 , 79 ].

  Fig. 1 .

  Characteristics of a shockwave: phase 1: high pressure wave rise-time from basic ambient value, to a pressure value of approximately 100 MPa within <10 nanoseconds (ns). Phase 2: wave implosion to a negative pressure value of approximately –10 MPa within microseconds. Image adapted from [8 ].

  In order to ensure minimal attenuation of the shockwave’s energy at the refraction point (entry point onto target tissue), ultrasonic gel is utilized for maximal force transmission. Modern SW devices are capable of producing both focused and unfocused SW impulses of varying penetration depths and energy flux densities in order to cater to multiple treatment parameters. Pertinent factors to consider when comparing SWT technology are; pressure distribution, focal zone area, energy flux density, and the total energy concentration at the second wave (focal refraction) zone [28 , 29 , 34 ]. More recently the introduction of radial pulse devices have emerged, and due to the lower economic cost associated with radial type devices, its use has increased in popularity. It is of great importance to note that radial pulse devices often referred to as “radial shockwave therapy” produce a wave that has completely divergent physical characteristics (Fig. 3 ) from those of medical shockwaves as classified by the International Consensus Conference 1997 and as described in Figure 1 [28 , 78 , 79 , 81 , 84 , 85 ]. Radial pulses are propagated by either compressed air or by a magnetic motor, where a metallic projectile within a barrel chute in the applicator is rapidly accelerated linearly within the chute. The ensuing ballistic energy occurring at the tip of the applicator (refraction point) is placed onto the skin of the target region, and this energy is then transferred onto the target tissue region as spherical radial pulse waves [28 , 78 , 79 , 81 , 84 , 85 ]. The following are the key factors of wave divergence between medical shockwave treatment (SWT), and radial pulse therapy (RPT): principle of stimulus propagation, wave length, maximal energy pressure, wave speed, penetration depth, focal zone size, and maximal energy at the secondary focal (refraction) region. Although SWs, ultrasound waves, and radial pulses are considered as being acoustic waves, they each have completely divergent characteristics (Fig. 4

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  Essentials of Supersonic Commercial Aircraft Conceptual Design

  • Egbert Torenbeek, Peter Belobaba, Jonathan Cooper, Allan Seabridge(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  1 . In going through the Shock Wave, the density and pressure of the flow are increased, but the velocity is reduced. This process is associated with energy dissipation and increased entropy, but mathematically a Shock Wave can be treated as a discontinuity. The viscosity of the air inside the Shock Wave converts kinetic flow energy into heat, and the associated entropy increment causes a stagnation pressure loss of the flow downstream of a body, which becomes manifest as wave drag.

  If a Shock Wave interacts with a boundary layer it promotes the local flow to separate, usually resulting in another source of drag. If, however, a pressure rise due to a Shock Wave acts on the lower wing surface, this can be utilized as a contribution to the lift. Altogether, Shock Waves may cause a significant drag penalty, loss of lift and a reduced aerodynamic efficiency. The Shock Waves generated by a supersonic airplane travel through the atmosphere over long distances outward and downward behind the plane and, when arriving on the earth's surface, they produce a sonic boom. Shock Waves cannot be avoided altogether but it is of utmost importance to minimize their strength during critical phases of the flight.

  4.4 Normal Shock Waves

  Figure 4.3 (a) depicts a channel with constant cross sectional area in which a uniform supersonic flow enters the channel with velocity , Mach number , density and pressure . Normal to the oncoming flow, air particles decelerate abruptly to subsonic speed through a stationary Shock Wave forming a planar surface perpendicular to the streamlines of the oncoming flow. The particles continue their original direction and hence the streamlines are not kinked. For given conditions of the oncoming flow (index 1), the flow properties behind the Shock Wave (index 2) can be computed by combining the conservation laws of mass ( ), momentum ( ) and energy ( ). The enthalpy 

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  Introduction to Fluid Dynamics in Physics and Astrophysics

  • Hendrik Jan van Eerten(Author)
  • 2024(Publication Date)
  • CRC Press

    (Publisher)

  7 Shock Waves

  DOI: 10.1201/9781003095088-7

  7.1 THE SHOCK-JUMP CONDITIONS

  In Chapter 5 we discussed sound waves, the mechanism by which small disturbances propagate through a fluid. Mathematically, we assumed these perturbations of the fluid state to be sufficiently small that maintaining only linear perturbation terms was a valid approximation for the purpose of deriving the properties of sound waves. It is however certainly feasible for fluid flow to exceed the sound speed. In astrophysical settings this is even quite common, with gravity pulling surrounding plasma towards massive objects such as black holes with a velocity that reaches the free-fall velocity as the plasma motion becomes increasingly supersonic (i.e. ‘faster than sound’). Other examples of supersonic flow occur in astrophysical explosions, such as novae or supernovae, driven by pressure. A third astrophysical scenario is the supersonic flow of jets launched by electro-magnetic forces, occurring in e.g. X-ray binaries, active galactic nuclei and gamma-ray bursts. When a supersonic flow encounters subsonic flow, shock fronts are formed. In this case, first-order perturbation theory is no longer appropriate and the solution to the conservation laws of fluid dynamics becomes non-linear. Similarly, when the non-linear terms in a propagating sound wave grow without dissipating away, the fluid profile steepens locally and a shock front can be formed.

  From a mathematical perspective it is perfectly feasible to have solutions to Euler's equations (and the viscous Navier-Stokes equations) that are discontinuous across space. In terms of physical interpretation, these amount to the aforementioned shock fronts. While exhibiting rich behaviour on the micro-physical level, they can be considered as infinitesimally thin on the macro-physical level. Here we discuss how to treat shocks in fluid dynamics. Throughout this discussion it is important to keep in mind that a shock is like a sound wave in that it outruns the motions of the fluid parcels. While shocks convey information, this information jumps from parcel to parcel—it is not advecting

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