Supersonic speed

As supersonic speed, short ( of ) supersonic, the speed of objects is called that move faster than the sound propagates in the same medium.

Description

In air, the speed of sound under normal conditions ( air at 20 ° C) 343 m / s, which corresponds to about 1235 km / h ( 768 mph or 666 knots ). The relative speed of an object to the speed of sound in air is referred to with the dimensionless Mach number, it means Mach 1, the movement speed of sound, that of Mach 2 with twice the speed of sound, etc.

It is in the Mach number is not a speed unit, but the ratio of flow velocity to the speed of sound ( depending on temperature). Although the term supersonic speed all velocities are referred to with a Mach number > 1, in principle, a distinction is additionally the range of Mach numbers > 5, since change through the concept of hypersonic speed here the aerodynamic properties.

Particularities at supersonic speed

Achieving and exceeding the speed of sound requires very high power ratings. When the speed of sound is exceeded, forms around the moving object, a conical shock wave (Mach shear cone, see also supersonic flight ). This shock wave can be perceived by a distant observer as a bang or clap of thunder.

The breaking of the sound barrier means overcoming the greatly increasing when it reaches the speed of sound of air resistance, which provided aircraft designers long time before some problems. Another design challenge is at flight speeds well above Mach 2: By compressing the air the missile on the carrying capacity of common construction materials such as aluminum heated. This speed region is also referred to as heat wall.

Due to the adiabatic cooling of the air in the vacuum zone at the rear of the aircraft, the water vapor condenses in the air and forms a cloud of water mist in a characteristic cone shape (cloud sheet effect ).

Gas dynamics

Neglecting the potential energy can be expressed for a compressible adiabatic flow in the following form for ideal gases the energy equation:

The enthalpy and the kinetic energy represents the total enthalpy, the exhaustion for energy supply or in the case of adiabatic flow without does not change for a current thread.

The enthalpy of an ideal gas can be described by the specific heat capacity cp and the isentropic exponent ( specific gas constant ).

For the speed of sound a is true at isentropic change of state ( index "s" ):

If an idle flow is assumed for the state with " 1", and the enthalpy total enthalpy are identical. When the critical speed of sound is reached in the state " 2 ", the following applies

The Mach number is the ratio of the speed to the critical speed of sound. In the event that exactly the speed of sound in a cross section we reached, then apply with.

With the energy equation, the critical speeds of sound from the data of the total state ( = idle; index "t" ) can be determined:

With the change of the state variables changes and the sound velocity.

The continuity equation ( mass conservation law ) of a flow is given by:

The equation is differentiated benefits to x:

Using the product rule we obtain:

With the differential form of the energy theorem

Can be formed under the condition of isentropic flow:

The Mach number is defined by the ratio of speed to the speed of sound

This gives the equation of Hugoniot:

From the equation can be taken:

• In the case of subsonic flow with mA < 1, a further acceleration ( DC> 0), when the cross section is reduced (dA < 0); This is the case of a nozzle with a convex design.

• The sound velocity (Ma = 1) can then be achieved, if dA = 0. This case is achieved at the narrowest cross-section of a Laval nozzle, which has a convex run- over and goes to the narrowest cross -section in a diffuser having a converging design. A further condition in order to achieve the speed of sound in the narrowest cross section, exceeding the critical pressure ratio.

• From the equation of Hugoniot it can be seen that, when the Schallgeschwingigkeit and dc> 0, a further increase in speed is then possible, if dA > 0 and the cross-section is designed as a diffuser.

Technically a supersonic velocity is caused in a Laval nozzle. In the narrowing inlet cross-section, the flow is accelerated up to the speed of sound, insofar as the critical pressure ratio is reached p0/pa. In the diffuser part of a further acceleration of the flow takes place. At the outlet of the diffuser to the environment, a shock wave occurs, which is not isentropic.

Objects with supersonic speed

The following list enumerates different objects that reach supersonic speed:

• The tip of the whip in the whip (relevant eg for the Goaßlschnalzen )
• Many explosives produce a supersonic shock wave
• Rifle and cannon balls: since the late 19th century, projectiles with high muzzle velocities are aerodynamically optimized for supersonic flight ( ogival form)
• Meteoroids usually occur at a speed from 12 to 72 km / sec in the earth's atmosphere, which is about 35 - to 215 -fold speed of sound. You burn up due to the high heating usually already in the higher layers of the atmosphere.
• Return and debris from spacecraft and launchers. You burn up or wear heat shields or elements. The speed of re-entry is about Mach 25
• Turbine parts of jet engines can reach supersonic speeds, propellers, turbo fans and helicopter rotors but one is anxious to avoid this.

In aircraft ( a rocket plane actually ) was in 1947 with the Bell X-1 first achieved supersonic speed. To fly at supersonic speed, see supersonic flight.

For the first time in 1942 with the V2 rocket hypersonic speed (greater than Mach 5 ) was achieved.

In addition to aircraft and missiles and rockets sledges were (ie rail-guided rocket-powered sled ) built for testing purposes, which reached in the 1950s, for the first time at supersonic speed.

For record attempts, some driven by rockets or jet engines cars were constructed, which were designed to reach supersonic speed:

• Spirit of America ( without success)
• Budweiser Rocket (17 December 1979 - not officially recognized )
• ThrustSSC (October 15, 1997 - first recognized supersonic land vehicle (Super Sonic Car) )

Supersonic cars have the problem that the negative pressure between the underside of the vehicle and the substrate is absent when it approaches the Schallgeschwingkeit and even a positive pressure is created, so that the risk of cars to float thereon.

People with supersonic speed

The following list enumerates different people, who have reached supersonic speed:

• Felix Baumgartner on October 14, 2012 in Roswell, New Mexico to a 1342.8 km / h (Mach 1.1 ) quick jump from the stratosphere ( 39 045 m height ) using a helium balloon and a returning pressure capsule.

( The values ​​obtained were informed at the press conference. Official values ​​, especially about the speed reached, there is only after a long time after evaluation of the recorded data by the Civil Aviation Authority. Drogue Chute records must also be confirmed by Austrian authorities. )

• The French Jacqueline Marie -Thérèse Suzanne Auriol Douet broke through in 1953 as the first woman the sound barrier. With a jet plane, it reached 1195 km / h she could in later records still increase to 2150 km / h with a Mirage III.