Jet engine performance: Difference between revisions

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There are unwanted leaks from the primary gas path and necessary bleeds from the compressor which enter the secondary or internal flow system. They are all controlled by seals with design clearances. When seals rub and wear, opening up clearances, there is performance deterioration (increased fuel consumption).

Sealing of the stators was initially accomplished using knife-edge fins on the rotating part and a smooth surface for the stator shroud. Examples are the Avon and Tumansky R-11. With the invention of the honeycomb seal the labyrinth seal has an abraziveabrasive honeycomb shroud which is easily cut by the rotating seal teeth without overheating and damaging them.<ref>Selecting a Material For Brazing Honeycomb in Turbine Engines, Sporer and Fortuna, Brazing and Soldering Today February 20014, p. 44</ref> Labyrinth seals are also used in the secondary air system between rotating and stationary parts. Example locations for these are shown by Bobo.<ref>https://patents.google.com/patent/US2963307, "Honeycomb seal" Fig.1</ref>

Tip clearance between compressor and turbine blades<ref>https://www.yumpu.com/en/document/view/33920940/8th-israeli-symposium-on-jet-engine-and-gas-turbine, slide 'Effect of tip clearance on turbine efficiency'</ref> and their cases is a significant source of performance loss.

Much of the loss in compressors is associated with tip clearance flow.<ref>Current Aerodynamic Issues For Aircraft Engines, Cumpsty, 11th Australian Fluid Mechanics Conference, University of Tasmania, 14–18 December 1992, p. 804</ref> For a CFM56 engine an increase in high pressure turbine tip clearance of 0.25 mm causes the engine to run 10&nbsp;°C hotter (reduced efficiency) to attain take off thrust.<ref>CFM Flight Ops Support, Performance Deterioration p. 48</ref>