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For as-cataloged diffuser performance, a straight section of duct needs serve a diffuser. An elbow, or kinked flex duct, just before a diffuser often leads to poor air distribution and increased noise. Diffusers can be as a shape of round, rectangular, or can be as linear slot diffusers (LSDs).
The diffuser converts the high velocity of the air approaching the intake into high (static) pressure required for combustion. High combustion pressures minimise entropy rise during heat addition, [20] this minimising wasted thermal energy in the exhaust gases [21] Subsonic and low-supersonic ramjets use a pitot-type opening for the inlet. This ...
The visible cone is a supersonic diffuser with a requirement for low loss in total pressure, and the rear, streamlined part, together with the internal surface profile of the duct, forms the subsonic diffuser, also with a requirement for low loss in total pressure as the air slows to the compressor entry Mach number.
For supersonic aircraft, the inlet has features such as cones and ramps to produce the most efficient series of shockwaves which form when supersonic flow slows down. The air slows down from the flight speed to subsonic velocity through the shockwaves, then to about half the speed of sound at the compressor through the subsonic part of the inlet.
Ejector refers to the pumping action of the very hot, high speed, engine exhaust entraining (ejecting) a surrounding airflow which, together with the internal geometry of the secondary, or diverging, nozzle controls the expansion of the engine exhaust. At subsonic speeds, the airflow constricts the exhaust to a convergent shape.
An axial compressor consists of alternating rows of rotating and stationary diffusers, [69] each pair being a stage. These diffusers are diverging as necessary for subsonic flow. [70] The channel formed by adjacent blades, amount of diffusion, is adjusted by varying their angle relative to tangential, known as stagger angle. [71]
A nozzle for a supersonic flow must increase in area in the flow direction, and a diffuser must decrease in area, opposite to a nozzle and diffuser for a subsonic flow. So, for a supersonic flow to develop from a reservoir where the velocity is zero, the subsonic flow must first accelerate through a converging area to a throat, followed by ...
In the subsonic case the noise is produced by eddies and in the supersonic case by Mach waves. [85] The sound power radiated from a jet varies with the jet velocity raised to the eighth power for velocities up to 600 m/s (2,000 ft/s) and varies with the velocity cubed above 600 m/s (2,000 ft/s). [ 86 ]