The Laval Nozzle.
The Laval nozzle, a gas channel of a special profile that increases passing through it the gas stream to supersonic velocities. The nozzle is a channel tapering in the middle.
The Laval nozzle — gas channel of a special profile that increases passing through it the gas stream to supersonic velocities. The nozzle is a channel tapering in the middle. In the simplest case, the nozzle may consist of a pair of truncated cones, paired narrow ends.
The phenomenon of accelerating a gas to supersonic velocity in a Laval nozzle was discovered at the end of the XIX century experimentally. The nozzle was first proposed in 1890 by Swedish inventor Gustaf de Laval steam turbines, and therefore named for its inventor. Then, in 1913 R. Goddard filed a patent application on the use of Laval nozzle in a two-stage solid fuel rocket. Currently, the Laval nozzle is widely used in some types of steam turbines, in rocket engines and supersonic jet aircraft engines.
Later this phenomenon – acceleration of gas to supersonic velocities found theoretical explanation in the framework of gas dynamics and the corresponding gas-dynamic calculations.
In the illustration below shows the operation of the Laval nozzle.
As the movement of the gas nozzle, the absolute temperature T and pressure P is reduced, and the speed V increases. Internal energy of gas is converted into kinetic energy of directed motion. The efficiency of this conversion in some cases (for example, in the nozzles of modern rocket engines) can exceed 70 %. M – Mach number (speed of sound).
On tapering, sub-critical section of the nozzle the movement of gas occurs at subsonic speeds (M < 1). In the narrowest critical section of the nozzle, the local velocity of the gas reaches sonic (M = 1). On expanding, a supercritical phase, a gas stream moving at supersonic speeds (M > 1).
Convergent part of the nozzle is called the confuser and expanding cone. The diffuser length is always more of a confuser. Sometimes the length of the diffuser is greater than the length of the nozzles 250 times. The lengthening of the diffuser increases the velocity of the gas from the nozzle, and therefore the thrust.
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