Life cycle cost improvements from FOD elimination on turbofan compressor rotor blades
Guadamuz, Mauricio J.
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Currently, Original Equipment Manufacturers (OEMs) and operators of military aircraft with low-bypass jet engines do not consider the expensive and possibly catastrophic consequences of damage to the High Pressure Compressor (HPC) rotor blades due to impacts from Foreign Object Debris (FOD) during runway operations early in the takeoff phase in a systematic/symbiotic practice – 1st level approximations to the affect/effect of FOD to these critical, rotating structures are needed during early design studies of conceptual military jet aircraft – equally important is the need by operators of current aircraft to be able to gage the effectiveness and affordability of their operational paradigm and of enhanced configurations. The presence, distribution and nature of FOD on the runway are analyzed separately from its structural or economic degradation to turbomachinery of the engine. Missing in the public domain is a symbiosis of the physics and probabilistic models for how debris on the runway is aspirated via ground vortex action, how and where it is then ingested by the engine at the fan face, what trajectory through the turbomachinery does it follow to impact the rotor blades, where and at what velocities do impacts occur and ultimately what is the ensuing damage and its effect on crack growth at the location of the impact sites. Also missing in the public domain is a synergistic assessment of the Life Cycle Cost (LCC) impact of the current methodologies for mitigating the deleterious effects from FOD on the runway – equally needed is a methodology to gage the LCC implications of improved or new processes, technologies and design improvements to mitigate the effects of FOD on current and future engine/engine on aircraft designs. A research and business case for the elimination of the FOD-exacerbated High Cycle Fatigue failure mode caused by Hard Body Foreign Object Debris impact damage on blades on the 1st rotor disk of the HPC (High Pressure Compressor) of a modeled low bypass, turbofan engine of a military jet during runway operations, early during takeoff is made. A research effort is undertaken to determine if FOD elimination, the minimization of the FOD-exacerbated High Cycle Fatigue failure mode that leads to 1st HPC rotor blade replacements and/or catastrophic engine losses while reducing or marginally increasing LCCs, is achievable and if so by what mix of technologies, processes and/or design changes at the Primary (the rotor blade) and Support (runway) systems. A detailed discussion on a proposed methodology and process is presented along with a numerical/analytical experimental plan and questions to systematically test if FOD elimination can be achieved affordably in a Life Cycle Cost context. Case study numerical/analytical experiments for two debris sizes are conducted to reveal statistically important experimental factors and their effect on the affordability of FOD elimination - the mix of technologies, processes and/or design changes at the Primary and Support systems that affordably achieve FOD elimination is determined. Recommendations are presented based on the trends revealed by the studies that may lead to enhanced/improved current and future engine/engine on aircraft designs that operate more robustly and affordably in the midst of FOD.