Browsing by Author "Polyzos, Nikolaos D."
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Item Open Access Impact of optimized variable rotor speed and active blade twist control on helicopter blade-vortex interaction noise and environmental impact(Elsevier, 2021-05-19) Vouros, Stavros; Polyzos, Nikolaos D.; Goulos, Ioannis; Pachidis, VassiliosCombined variable rotor speed and active blade twist helicopter technologies have the potential to reduce the environmental and acoustic impact of modern rotorcraft. This paper explores the aeroacoustics, environmental and ground noise impact of combined variable rotor speed and active blade twist helicopter rotors, optimized for simultaneous mitigation of source noise and NOx" role="presentation" style="display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border-width: 0px; border-style: initial; position: relative;" >x emissions. An integrated approach is employed including free-wake aeroelastic rotor modeling and time-domain aeroacoustic formulations fundamentally based on Acoustic Analogy. The overall method is incorporated into a multi-disciplinary design space exploration and surrogate-model-assisted optimization algorithm. The developed framework is deployed towards devising optimal variable rotor speed and active blade twist control for a representative twin-engine light helicopter operating in a realistic descent trajectory. The obtained rotor control schedules achieve overall ground noise reductions of up to 7 dB with concurrent NOx" role >x reductions of 11%, relative to the conventional rotor. The proposed approach provides new insight into rotor wake behavior and blade–vortex interactions, as well as environmental impact and ground noise footprint of combined variable rotor speed and active blade twist helicopter concepts.Item Open Access Multi-disciplinary optimization of variable rotor speed and active blade twist rotorcraft: Trade-off between noise and emissions(Elsevier, 2020-11-17) Polyzos, Nikolaos D.; Vouros, Stavros; Goulos, Ioannis; Pachidis, VassiliosThe concepts of variable rotor speed and active blade twist are emerging technologies for the next generation of civil rotorcraft. Previous research has focused on the optimum implementation of these technologies for improved fuel economy and environmental impact. Within this work, an integrated approach is deployed to quantify the concurrent reductions in rotor noise and NOx emissions. A relaxation-based free-wake inflow model, coupled with unsteady blade aerodynamics modeling, resolves the flow-field around the main rotor. Aero-acoustic predictions are performed through an acoustic-analogy-based formulation. Gaseous emissions are then predicted via stirred-reactor modeling, coupled with zero-dimensional engine performance analysis method. This strategy is incorporated into a multi-disciplinary genetic algorithm optimization process based on surrogate modeling. Optimal schedules of combined variable rotor speed and active blade twist controls are derived for a twin-engine light helicopter in descent. The accrued schedules suggest NOx reductions between 6% and 21%, simultaneously with source-noise reductions of the order of 2–8 dB, relative to the non-morphing rotor case. The developed strategy constitutes an enabling methodology for the holistic and multi-disciplinary assessment of morphing helicopter rotor configurations.