Assessment of Computational Models for the Effect of Aeroelasticity on BVI Noise Prediction

Abstract

This paper deals with the computational analysis of acoustic fields generated by helicopter rotors when Blade-Vortex Interactions (BVI) occur. The prediction procedure starts from the determination of the steady periodic blade deformations. Then, the BVI-affected, unsteady aerodynamics solution is obtained by a potential-flow boundary integral formulation suited for aeronautical configurations experiencing blade-wake impingements. It is applicable to blades with arbitrary shape and motion and evaluates both wake distortion and blade pressure field. Finally, the noise field radiated by the rotor is computed through an aeroacoustic tool based on the Ffowcs Williams and Hawkings equation. The numerical investigation examines the sensitivity of BVI noise prediction on the aeroelastic model applied for the calculation of blade deformations, and assesses the accuracy of the results through correlation with experimental data concerning a helicopter main rotor in descent flight. Noise predicted is examined in terms of both acoustic pressure signatures and noise radiation characteristics.

Investigation on a High-Frequency Controller for Rotor BVI Noise Alleviation

“…The following sections provide a brief outline of the methodologies applied in this work to obtain BVI noise predictions used for synthesis and verification of the proposed controller (an extensive validation of them is available, for instance, in Gennaretti et al 16 or Bernardini et al 17 ).…”

Frequency-domain method for discrete frequency noise prediction of rotors in arbitrary steady motion

“…For this analysis, the airloads used in the aeroacoustic frequency-domain formulation have been determined by a boundary integral formulation solver for potential flows developed in the past by some of the authors, and successfully applied to the aerodynamic and aeroacoustic analysis of helicopters rotors operating in BVI conditions [5,14]. The helicopter rotor considered in the numerical investigation is the four-bladed EC/ONERA 7A main examined at the DNW wind tunnel within the European Project HELISHAPE [15], in a 61-descent forward flight condition, with rotational speed O ¼ 101 rad=s and advance ratio m ¼ 0:166 (HELISHAPE Datapoint 70).…”

Numerical characterization of helicopter noise hemispheres

“…The numerical investigation described above requires the application of multidisciplinary tools, ranging from flight dynamics to aeroacoustics, with inclusion of rotor aeroelasticity. For each one of the steady flights considered, the main rotor aeroelastic response is evaluated through a freewake, harmonic-balance, modal formulation, followed by the application of a boundary integral approach to predict the aeroacoustic emissions used to determine the corresponding noise hemisphere [25,26,27,28]. Indeed, in this kind of analysis, the introduction of an aeroelastic solver relying on a free-wake aerodynamic model is essential, in that the accurate prediction of aeroacoustic phenomena related to BVIs requires the accurate evaluation of the relative position between blades and wake vortices (miss distance) [27].…”