Predicting the high-frequency airloads and acoustics associated with blade-vortex interaction

Kelly, Mary E. (2010) Predicting the high-frequency airloads and acoustics associated with blade-vortex interaction. PhD thesis, University of Glasgow.

Abstract

As a rotorcraft descends or manoeuvres, the interactions which occur between the rotor
blades and vortical structures within the rotor wake produce highly impulsive loads on
the blades and with these a highly intrusive external noise. Brown’s Vorticity Transport
Model has been used to investigate the influence of the fidelity of the local blade aerodynamic
model on the quality of the prediction of the high-frequency airloads associated with
blade-vortex interactions and thus on the accuracy with which the acoustic signature of
the aircraft can be predicted. Aerodynamic, wake structure and acoustic predictions using
the Vorticity Transport Model are compared against the HART II wind tunnel data for an
experimental rotor based on the characteristics of the Bo105 rotor. The model can resolve
very accurately the structure of the wake, and allows significant flexibility in the way that
the blade loading can be represented. The predictions of two models for the local blade
aerodynamics are compared for all three of the HART II flight cases. The first model is
a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord
model based on unsteady thin aerofoil theory. The predicted positions of the vortex cores
agree with measured data to within a fraction of the blade chord, and the strength of
the vortices is preserved to well downstream of the rotor, essentially independently of the
resolution of the calculation or the blade model used. A marked improvement in accuracy
of the predicted high-frequency airloads and acoustic signature of the HART II rotor
is obtained when the lifting-chord model for the blade aerodynamics is used instead of
the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Predictions of the acoustic signature of the rotor are similarly affected, with the lifting-chord model at the highest resolution producing the best representation of the distribution of sound pressure on the ground plane below the
rotor.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: helicopter, rotorcraft, aerodynamic modelling, blade vortex interation, acoustics
• Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
• Colleges/Schools: College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
• Supervisor's Name: Brown, Prof. Richard E.
• Date of Award: 2010
• Depositing User: Miss Mary E. Kelly
• Unique ID: glathesis:2010-1513
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 Mar 2010
• Last Modified: 10 Dec 2012 13:41
• URI: https://theses.gla.ac.uk/id/eprint/1513