Jet engine performance: Difference between revisions

Revision as of 22:30, 2 January 2024

Revision as of 16:45, 9 January 2024

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=== Reduced pressure loss in ducts ===

Air passing through the engine goes through two components where velocitesvelocities need to be high, of the order of the speed of sound. They are the components in which work is done, the compressor and turbine. In all the remaining components no work is done and the need to reduce pressure losses requires lower Mach numbers. These components are the engine combustor and afterburner, and the connecting ducting between components such as the tailpipe between the turbine and propelling nozzle.

The first duct in the powerplant is the inlet and loss in total pressure in front of the engine is particularly important because it appears twice in the production of thrust. Thrust is proportional to mass flow which is proportional to total pressure. Jet nozzle pressure and therefore thrust is also proportional to the total pressure at engine entry.<ref>"A Review Of Supersonic Air Intake Problems, Wyatt", Agardograph No. 27, p. 22</ref> In subsonic inlets the only total pressure losses are those due to friction along the duct passage walls. For supersonic inlets shockwave losses are also present and shockwave systems are required to minimize pressure loss with increasing supersonic Mn. Additional losses in total pressure come with boundary layer growth as the flow slows down. Boundary layers have to be removed before the ___location of the terminal shock to prevent shock-induced separation and excessive loss.