What is over expansion and under expansion in nozzle?
When an overexpanded flow passes through a nozzle, the higher atmospheric pressure causes it to squeeze back inward and separate from the walls of the nozzle. The opposite situation, in which the atmospheric pressure is lower than the exit pressure, is called underexpanded.
How does a nozzle increase thrust?
Jet propulsion is about increasing the momentum of the ejected gas. The propulsive force is mass flow rate times exit velocity. So if you can increase the exit velocity, you develop more thrust for the same amount of fuel burnt.
What is under expanding nozzle flow?
This type of flow is called perfectly-expanded flow or flow at design conditions. Dropping the back pressure ratio further results in a condition known as under-expanded flow. For this condition, the pressure at the exit is larger than the back pressure so the flow must continue to expand upon leaving the device.
What type of expansion takes place in a nozzle?
The work done is equal to the adiabatic heat drop which in turn is equal to the Rankine area. The flow of steam through nozzles may be regarded as adiabatic expansion. The steam has a very high velocity at the end of the expansion, and the enthalpy decreases as expansion takes place.
What is over expanded?
Definition of overexpand transitive + intransitive. : to expand too much or too quickly …
What is the meaning of over expansion?
overexpansion
Definition of overexpansion : excessive expansion : the act or an instance of expanding too much or too quickly …
How does nozzle size affect thrust?
The length/diameter ratio of a nozzle affected the performance of an engine slightly and the averaged thrust declined slightly with the increase of length/diameter ratio.
How does a nozzle increases velocity?
Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them. In a nozzle, the velocity of fluid increases at the expense of its pressure energy.
What is a convergent nozzle?
A convergent nozzle is a nozzle that starts big and gets smaller-a decrease in cross-sectional area. As a fluid enters the smaller cross-section, it has to speed up due to the conservation of mass. To maintain a constant amount of fluid moving through the restricted portion of the nozzle, the fluid must move faster.
How does an Aerospike engine work?
The idea behind the aerospike design is that at low altitude the ambient pressure compresses the exhaust against the spike. As the vehicle climbs to higher altitudes, the air pressure holding the exhaust against the spike decreases, as does the drag in front of the vehicle.
How does overexpanded flow reduce thrust?
When an overexpanded flow passes through a nozzle, the higher atmospheric pressure causes it to squeeze back inward and separate from the walls of the nozzle. This “pinching” of the flow reduces efficiency because that extra nozzle wall is wasted and does nothing to generate any additional thrust.
What determines the amount of thrust produced by the nozzle?
The exit velocity, pressure, and mass flow through the nozzle determines the amount of thrust produced by the nozzle. On this slide we derive the equations which explain and describe why a supersonic flow accelerates in the divergent section of the nozzle while a subsonic flow decelerates in a divergent duct.
What is the exit pressure of an ideal nozzle?
In an ideal nozzle that optimizes performance, the exit pressure (P exit) will be equal to the ambient pressure of the external atmosphere (P ¥ ). The flow in this case is perfectly expanded inside the nozzle and maximizes thrust. Unfortunately, this situation can only occur at one specific atmospheric pressure on a fixed-geometry nozzle.
What is underexpanded nozzle?
The opposite situation, in which the atmospheric pressure is lower than the exit pressure, is called underexpanded. In this case, the flow continues to expand outward after it has exited the nozzle. This behavior also reduces efficiency because that external expansion does not exert any force on the nozzle wall.