In physics, the shock wave (also spelled shockwave ), or surprise , is a type of propagation disorder. When the waves move faster than the speed of local noise in the liquid, it is a shock wave. Like ordinary waves, shock waves carry energy and can spread through the medium; However, it is characterized by sudden, almost non-continuous changes in temperature, temperature and density.
For a comparison context, in supersonic flow, an increase in additional expansion can be achieved through the expansion fan, also known as the Prandtl-Meyer expansion fan. The accompanying wave of expansion can approach and eventually collide and rejoin the shock wave, creating a destructive interference process. The sonic boom associated with supersonic plane travel is a type of sound wave generated by constructive interference.
Unlike the soliton (other nonlinear wave types), the energy and speed of the shock wave just disappear relatively quickly with distance. When the shock wave passes through matter, energy is maintained but the entropy increases. The change in this material manifests itself as a decrease in energy that can be extracted as work, and as a drag force on supersonic objects; shock wave is a very irreversible process.
Video Shock wave
Terminology
Shock waves can:
- Normal: at 90 ° (perpendicular) towards the shock wave flow.
- Oblique: at an angle toward the flow.
- Arc: Occurs upstream in front (bow) blunt object when upstream flow velocity exceed Mach 1.
Some other terms
- Shock Front: The limit on which physical conditions undergo sudden changes due to shock waves.
- Front Contacts: in shock waves caused by driving gases (eg "high explosive" impacts in the surrounding air), the boundary between the driver (explosive product) and the actuated gas (air). Front Contacts follow Front Shock.
Maps Shock wave
In supersonic stream
Sudden changes in the medium feature, which characterize shock waves, can be seen as transition phases: pressure-time diagrams of propagation of supersonic objects show how the transitions caused by shock waves are analogous to dynamic phase transitions .
When an object (or disturbance) moves faster than information that can spread into the surrounding liquid, the fluid near the disturbance can not react or "get out of the way" before the disturbance comes. In shock waves fluid properties (density, pressure, temperature, flow velocity, Mach number) change almost instantaneously. The measurement of the thickness of the shock waves in the air has resulted in a value of about 200 nm (about 10 -5 in), which is in the same order of magnitude as the average free molecular gas path. In reference to the continuum, this means the shock wave can be treated as a line or plane if the field is two-dimensional or three-dimensional flow, respectively.
Shock waves are formed when the forward pressure moves at supersonic speed and pushes on the surrounding air. In the region where this occurs, the sound waves that move against the current reach the point where they can not travel further upstream and increasing pressure in the region; high pressure shock waves are quickly formed.
Shock waves are not conventional sound waves; the shock wave takes the form of a very sharp change in the properties of the gas. The shock waves in the air are heard as loud "crack" or "snap" sounds. Longer distances, shock waves can change from nonlinear waves to linear waves, degenerating into conventional sound waves when heating air and losing energy. Sound waves sound as a known "boom" or "boom" of the sonic boom, commonly made by supersonic flight of aircraft.
Shock wave is one of several different ways in which gas in supersonic flow can be compressed. Some other methods are isentropic compression, including Prandtl-Meyer compression. The method of compression of gas yields at various temperatures and densities for a certain analytical ratio can be calculated analytically for unreacted gases. Compression of the shock wave results in a loss of total pressure, which means that this is a less efficient gas compression method for some purposes, for example in scramjet retrieval. The emergence of drag-pressure on supersonic aircraft is largely due to the effects of shock compression on the flow.
Normal shock
In basic fluid mechanics utilizing the ideal gas, the shock wave is treated as a discontinuity in which entropy rises over an almost infinite region. Since no fluid flow is broken, the control volume is formed around the shock wave, with the control surface binding this volume parallel to the shock wave (with one surface on the pre-shock side of the fluid medium and one on the shock positions). The two surfaces are separated by very small depths so that the shock itself is entirely contained between the two. On such control surfaces, momentum, mass flux and energy are constant; in combustion, detonation can be modeled as a heat introduction in shock waves. It is assumed an adiabatic system (no heat exits or enters the system) and no work is done. The Rankine-Hugoniot condition arises from this consideration.
Taking into account the prescribed assumptions, in a system in which the downstream properties become subsonic: the upstream and downstream flow properties of the fluid are considered to be isentropic. Since the total amount of energy in the system is constant, the enthalpy of stagnation remains constant in both regions. In fact, entropy is increasing; this should be taken into account by the decrease in the stagnation pressure of the downstream liquid.
Other shocks
Left shock
When analyzing the shock wave in the flow field, which is still attached to the body, the shock waves that deviate at some random angle from the flow direction are called oblique shock. This shock requires flow vector component analysis; doing so allows for the treatment of flow in an orthogonal direction against the oblique shock as a normal shock.
Arch bend
When an oblique shock may form at an angle that can not remain on the surface, a nonlinear phenomenon arises where the shock wave will form a continuous pattern around the body. This is called a shock bow. In this case, the 1d flow model is invalid and further analysis is needed to predict the pressure force applied on the surface.
Shock waves due to nonlinear relics
Shock waves can form due to ordinary upward waves. The most famous example of this phenomenon is the ocean waves that make up the breaker at the beach. In shallow water, surface wave velocity depends on the depth of water. Incoming sea waves have slightly higher wave velocities near the peak of each wave than near the trough between waves, as the wave height is not too small compared to the water depth. These peaks pass through the trough until the leading edge of the waveform forms a vertical face and spills upward to form a turbulent shake (breaker) that removes wave energy as sound and heat.
A similar phenomenon affects the strong sound waves in gas or plasma, due to the dependence of sound velocity on temperature and pressure. Strong waves heat the media near each front pressure, due to the adiabatic compression of the air itself, so that the high pressure front runs faster than the appropriate pressure trough. There is a theory that the level of sound pressure in a brass instrument such as trombone becomes high enough so that it occurs steeply, forming an important part of the bright timbre of the instrument. While shock formation by this process usually does not occur in unexplored sound waves in the Earth's atmosphere, it is considered to be one of the mechanisms by which the sun's chromosphere and corona are heated, through waves spreading from the interior of the sun.
Analogy
Shock waves can be described as the farthest point in the upstream of a moving object that "knows" about an object's approach. In this description, the position of the shock wave is defined as the boundary between zones that have no information about the shock-driving events and zones that are aware of the shock-driving events, analogous to the cone of light described in the special theory of relativity.
To produce shock waves, objects in certain mediums (such as air or water) must travel faster than local sound speed. In the case of aircraft traveling at high subsonic speeds, airspace around the aircraft can travel at the correct speed of sound, so the sound waves that make the planes piled on each other, similar to the traffic jam on the highway. When shock waves are formed, local air pressure increases and then spreads to the side. Because of this amplification effect, shock waves can be very powerful, more like explosions when heard in the distance (not coincidental, because the explosion creates shock waves).
The analog phenomenon is known outside the fluid mechanics. For example, particles accelerate beyond the speed of light in the bias medium (where the speed of light is less than that in a vacuum, like water) creates a visible shock effect, a phenomenon known as Cherenkov radiation.
Type of Phenomenon
Below are a number of examples of shock waves, broadly grouped with similar shock phenomena:
Moving shock
- Usually consists of a shock wave propagating into a stationary medium
- In this case, the gas in front of stationary shock (in the laboratory frame) and the gas behind the shock can be supersonic in the laboratory frame. Shock spreads with a normal wavefront (at right angle) in the direction of flow. The shock speed is a function of the original pressure ratio between the two gas bodies.
- Moving shocks are usually generated by the interaction of two bodies of gas at different pressures, with shock waves propagating to lower pressure gas and extending the propagating waves to higher pressure gas.
- Example: Exploding balloon, Tube shock, shock wave from explosion.
Detonation wave
- Detonation waves are basically surprises that are supported by exothermic trailing reactions. It involves traveling waves through highly flammable or chemically unstable media, such as a mixture of oxygen-methane or high explosion. The chemical reactions of the medium occur following the shock wave, and the chemical energy of the reaction propels the wave forward.
- Detonation waves follow rules that are slightly different from the usual surprises of being driven by chemical reactions that occur behind shock waves. In the simplest theory for detonation, unsupported detonation blast waves continue at the Chapman-Jouguet flow velocity. Blasting will also cause type 1 shock, above to propagate into the surrounding air due to overpressure caused by the explosion.
- When shock waves are made by high explosives such as TNT (which has a detonation rate of 6,900 m/sec), they will always travel at supersonic speeds high from their original point.
Shock arc (detached shock)
- This shock is curved and forms a small distance in front of the body. Right in front of the body, they stand at 90 degrees to an approaching stream and then curve around the body. The detached shock allows the same kind of analytical calculation as for the inherent shock, for the flow near the shock. They are a topic that continues to be interesting, because the rules governing the distance of shock in front of a blunt body are complicated and are a function of body shape. In addition, shock shock distances vary drastically with temperatures for non-ideal gases, causing major differences in heat transfer to vehicle thermal protection systems. See extended discussions on this topic in the Entry Atmosphere. This follows the "strong-shock" solution of the analytic equation, which means that for some oblique shocks very close to the deflection edge limit, the amount of downstream Mach is subsonic. See also bow shock or oblique shock
- This shock occurs when the maximum deflection angle is exceeded. The detached shock is generally seen on a blunt object, but can also be seen on sharp objects with low Mach counts.
- Example: Space return vehicles (Apollo, spacecraft), bullets, boundaries (shock arc) of the magnetosphere. The name "bow shock" is derived from an arc wave example, a separate shock formed at the front (front) of a ship or boat moving through the water, whose slow surface wave velocity is easily exceeded (see sea level waves)./li>
Attach shock
- This shock appears as attached to the sharp end of the body moving at supersonic speed.
- Example: Supersonic slices and cones with small apex angles.
- The attached shock wave is a classical structure in aerodynamics because, for the perfect gas flow and inviscid fields, an analytical solution is available, so the ratio of pressure, temperature ratio, slice angle and downstream Mach number can all be calculated by knowing the upstream Mach number and angle shock. The smaller shock angle is associated with higher upstream Mach number, and a special case where the shock wave is at 90 ° to the approaching stream (normal shock), is associated with the number of Machs one. This follows the "weak-shock" solution of the analytic equation.
In fast granular stream
Shock waves may also occur in the rapid flow of dense granular materials into slopes or slopes. Strong shocks in solid granular flow can be studied theoretically and analyzed for comparison with experimental data. Consider the configuration in which matter moves rapidly down the channel that strikes a barrier wall perpendicular to the end of a long, steep channel. The impact leads to a sudden change in the flow regime of the supercritical thin film that moves rapidly into a thick stagnant pile. This flow configuration is very interesting because it is analogous to some of the hydraulic and aerodynamic situations associated with the flow regime change from supercritical flow to subcritical.
In astrophysics
The astrophysical environment has many types of shock waves. Some common examples are supernova shock waves or explosive waves passing through the interstellar medium, arc shocks caused by the Earth's magnetic field colliding with the solar wind and shock waves caused by galaxies that collide with each other. Another type of exciting shock in astrophysics is the quasi-steady reverse shock or termination that ends the ultra relativistic wind from the young pulsar.
Meteor enters event
The Tunguska event and the Russian meteor event 2013 are the best documented evidence of shock waves generated by large meteoroids.
When the 2013 meteor enters the Earth's atmosphere with an energy release equivalent to 100 or more kilotons of TNT, tens of times stronger than the atomic bomb dropped on Hiroshima, meteor shock waves produce damage as in supersonic jet flying (directly beneath the meteor path) and as waves detonation, with a circular shock wave centered on a meteor explosion, causing several examples of broken glass in the city of Chelyabinsk and the surrounding area (pictured).
Technology apps
In the example below, the shock wave is controlled, produced by (eg airfoil) or inside the technological device, such as a turbine.
Recompression Shock
- This shock occurs when the flow above the transonal body slows down to the subsonic velocity.
- Example: Transonic wings, turbines
- Where the flow above the suction side of the transonic wing is accelerated to supersonic speed, the re-compression results can be performed by Prandtl-Meyer compression or by normal shock formation. This shock is of great interest to the maker of transonic devices as it may lead to the separation of the boundary layer at the point where it touches the transonic profile. This can then lead to full separation and stop at higher profile, drag, or shock-buffer, a condition in which separation and shock interact in resonance conditions, causing a resonating load to the underlying structure.
Flow pipe
- This shock occurs when supersonic flow in the pipeline is slowed.
- Example:
-
- In Supersonic Propulsion - ramjet, scramjet, unstart.
- In Flow Control - needle valve, venturi faltered.
In this case the gas in front of the shock is supersonic (in the laboratory frame), and the gas behind the shock system is supersonic ( oblique shock s) or subsonic (normal shock) ) (Although for some oblique shocks very close to the deflection corner limit, the amount of downstream Mach is subsonic.) The shock is the result of the convergent gas deceleration. channel, or by the growth of boundary layer on parallel channel walls. - NASA Glenn Research Center Information about:
- Oblique shock
- Multiple Stacked Shocks
- Expansion Enthusiasts
- Selkirk University: Aviation intranet: High speed (supersonic)
- Loss of energy in shock waves, normal shock and tilt waves
- Formation of normal shock wave
- Compressible stream basics, 2007
- KB Elementary finance educational software to simulate shocks and detonations.
- NASA 2015 Schlieren shock wave image T-38C
Combustion Engine
The disk wave machine (also called "Radial Internal Combustion Wave Rotor") is a kind of non-piston rotary engine that utilizes shock waves to transfer energy between high-energy fluids to low-energy energies, thereby increasing the temperature and low-pressure fluid energy.
Memristors
In the memristor, under an electric field applied externally, the shock wave can be launched across the transition metal oxide, creating rapid and non volatile resistivity changes.
Shock capture and detect
Advanced techniques are required to capture shockwaves and to detect shock waves in both numerical and experimental observations.
The dynamics of computational fluids are generally used to obtain a flow field with shock waves. Although the shock wave is a sharp discontinuity, in numerical solutions of fluid flow with discontinuity (shock wave, discontinuity contact or slip line), the shock wave can be smoothed by a low level numerical method (due to numerical dissipation) or there is false oscillation near the shock surface by numerical high (due to Gibbs phenomenon).
There are several other discontinuities in the fluid flow compared to shock waves. The slip (3D) or slip line (2D) surface is the plane where the tangent velocity is disconnected, while the normal pressure and velocity are continuous. Across the contact discontinuity, the pressure and velocity are continuous and the density is interrupted. Strong expansion waves or shear layers may also contain high gradient areas that appear to be discontinuities. Some common features of the flow structure and shock wave and insufficient numerical and experimental tools cause two important problems in practice: (1) some shock waves can not be detected or their positions are detected incorrectly; (2) some flow structures are not shock waves which is incorrectly detected as a shock wave.
In fact, capturing and detecting the correct shock waves is important because shock waves have the following effects: (1) causing a loss of total pressure, which may be a concern related to the performance of scramjet engines, (2) providing lift for wave rider configuration, the undercarriage of the vehicle can produce high pressure to generate lift, (3) causing high-speed vehicle tensile waves that are harmful to the performance of the vehicle, (4) inducing heavy pressure loads and heat fluxes, eg Type IV shock-shock failure can produce 17 times increased heating on the surface of the vehicle, (5) interacting with other structures, such as boundary layer, to produce new flow structures such as flow separation, transitions, etc.
See also
References
External links
Further reading
Krehl, Peter OK (2011), "Physics of shock waves and detonation physics - a stimulus for the emergence of many new branches in science and engineering", CITEREFKrehl2011 "class =" citation " European Physical Journal H , 36 : 85, Bibcode: 2011EPJH... 36... 85K, doi: 10.1140/epjh/e2011-10037-x.Source of the article : Wikipedia
0 Comments