Performance degradation modelling of rotorcraft engines operating in brownout conditions

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Ellis, M.
Bojdo, N.
Filippone, A.
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Rotorcraft engines are subject to significant damage whilst operating in brownout conditions due to the ingestion of mineral particulates. The high pressure turbine is particularly at risk due to the deposition of molten particles on nozzle guide vanes and first stage rotor blades, causing a roughening of the surface and a reduction in efficiency. The rate of damage is non-linear; predicting the evolution of this damage has proven to be difficult given the wide range of contributory factors related to both engine and particulate. A first-order methodology is presented whereby component level losses in high pressure turbine nozzle guide vane efficiency can be translated via surface roughness changes into a performance loss of the whole engine. Component level computational fluid dynamics simulations are combined with an aero-thermodynamic gas turbine model to evaluate reductions in engine performance during brownout operations for two rotorcraft using the same General Electric T700 engine. It is shown that the rate of engine degradation is proportional to the brownout concentration of the particular rotorcraft. Surface roughness changes alone are shown to be capable of producing up to a 1% reduction in the core mass flow rate and overall engine efficiency. This is demonstrated to occur after only 38 minutes of flight in brownout conditions for the Sikorsky HH-60 �Pave-Hawk� and 120 minutes for the Bell UH-1Y �Venom�.