Rotorcraft Simulations with Coupled Flight Dynamics, Free Wake, and Acoustics

Open Access
Author:
Saetti, Umberto
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 18, 2016
Committee Members:
  • Joseph Francis Horn, Thesis Advisor
  • Kenneth Steven Brentner, Committee Member
  • George A Lesieutre, Committee Member
Keywords:
  • rotorcraft
  • noise
  • control
  • control systems
  • dynamic inversion
  • feedback
  • flight dynamics
  • free wake
  • CHARM
  • PSUHeloSim
  • PSUWOPWOP
Abstract:
This study presents the integration of a flight simulation code (PSUHeloSim), a high fidelity rotor aeromechanics model with free wake (CHARM Rotor Module), and an industry standard noise prediction tool (PSU-WOPWOP) into a comprehensive noise prediction system. The flight simulation uses a Dynamic Inversion autonomous controller to follow a prescribed trajectory for both steady and maneuvering flight conditions. The aeromechanical model calculates blade loads and blade motion that couple to the vehicle flight dynamics with suitable resolution to allow high fidelity acoustics analysis (including prediction of blade-vortex interaction (BVI) noise). The blade loads and motion data is sent to PSU-WOPWOP in a post-processing step to predict external noise. Particular attention is paid to the development of PSUHeloSim and to the enhancement of the closed-loop response characteristics of the coupled simulation. Specifically, is studied the use of reduced-order linear models, derived by linearization of the coupled simulation, in the feedback linearization of the Dynamic Inversion controller in different flight conditions. The different reduced-order models obtained are compared by the use of eigenvalue analysis and frequency response in order to link their differences to physical phenomena occuring in the coupled simulation. A validation of these reduced-order models is provided by performing a frequency sweep of the coupled simulation. Finally their effectiveness in the feedback linearization loop is evaluated by analysing the closed loop time response of the coupled simulation to the coupling. The coupled analysis is being used to evaluate the influence of flight path on aircraft noise certification metrics like EPNL and SEL for various rotorcraft in work for the FAA. The software was used to analyze the acoustic properties of a blade planform similar to the Blue Edge rotor blades developed by DLR and Airbus Helicopters - predicting BVI noise reduction as compared to more conventional blade geometries on the same order as that reported for the Blue Edge rotor.