A PRELIMINARY ACOUSTIC INVESTIGATION OF A COAXIAL HELICOPTER IN HIGH-SPEED FLIGHT

Open Access
Author:
Walsh, Gregory Daniel
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 18, 2016
Committee Members:
  • Kenneth Steven Brentner, Thesis Advisor
  • Jacob Willem Langelaan, Committee Member
  • George A Lesieutre, Committee Member
Keywords:
  • Acoustics
  • Coaxial Helicopter
  • Rotorcraft
  • Rotorcraft Acoustics
  • Helicopter
Abstract:
The desire for a vertical takeoff and landing (VTOL) aircraft capable of high forward flight speeds is very strong. Compound lift-offset coaxial helicopter designs have been proposed and have demonstrated the ability to fulfill this desire. However, with high forward speeds, noise is an important concern that has yet to be thoroughly addressed with this rotorcraft configuration. This work utilizes a coupling between the Rotorcraft Comprehensive Analysis System (RCAS) and PSU-WOPWOP, to computationally explore the acoustics of a lift-offset coaxial rotor system. Specifically, unique characteristics of lift-offset coaxial rotor system noise are identified, and design features and trim settings specific to a compound lift-offset coaxial helicopter are considered for noise reduction. At some observer locations, there is constructive interference of the coaxial acoustic pressure pulses, such that the two signals add completely. The locations of these constructive interferences can be altered by modifying the upper-lower rotor blade phasing, providing an overall acoustic benefit. Significant noise reduction (and power reduction) is possible by reducing rotor tip speeds $-$ an option available because the coaxial rotor in a compound configuration does not need to provide all the propulsive force. Alternative blade designs and blade configurations also enable noise reduction at an in-plane, forward, target observer. This research is a preliminary investigation into compound lift-offset coaxial helicopter noise with the intention of future research spawning from it.