Abstract
As a high resolution airload with accurate rotor wake is pivotal for rotor BVI (Blade-vortex interaction) analysis, a hybrid method with combined Navier-Stokes equation, viscous wake model, and FW-H (Ffowcs Williams-Hawkings) equation is developed for BVI airload and noise in this paper. A comparison with the CFD (Computational Fluid Dynamics)/FW-H method for the AH-1/OLS (Operational Load Survey) rotor demonstrates its capability for favorable accuracy and high computation efficiency. This paper further discusses the mechanisms for the impacts of four flight parameters (i.e., tip-path-plane angle, thrust coefficient, tip Mach number, advance ratio) on BVI noise. Under the BVI condition, several BVI events concurrently occur on the rotor disk. Each interaction has a distinct radiation direction which depends on the interaction azimuth, and its noise intensity is highly associated with the characteristic parameters (e.g., miss-distance, interaction angle, vortex strength). The BVI noise is dominated by the interactions at 30–90° in azimuth on the advancing side, of which the wake angle range is from 180° to 540°. Furthermore, the tip-path-plane angle, thrust coefficient, and tip Mach number change the noise intensity mainly via miss-distance, interaction angle, and vortex strength, but for different advance ratios, the noise intensity and propagation direction are more dependent on the interaction angle and interaction azimuth.
Highlights
It is well known that helicopter rotor impulsive noise originates from high-speed impulsive noise, which is due to a high tip Mach number on the rotor’s advancing side, and the blade-vortex interaction noise on the advancing and retreating sides of the rotor disk
Each interaction has a distinct radiation direction which depends on the interaction azimuth, and its noise intensity is highly associated with the characteristic parameters
Blade-vortex interaction (BVI) [1] occurs when the strong tip vortices shed from the main rotor pass in close to the following blades during descending or maneuvering flight; this results in impulsive changes in blade loading, which radiates noise
Summary
It is well known that helicopter rotor impulsive noise originates from high-speed impulsive noise, which is due to a high tip Mach number on the rotor’s advancing side, and the blade-vortex interaction noise on the advancing and retreating sides of the rotor disk. Blade-vortex interaction (BVI) [1] occurs when the strong tip vortices shed from the main rotor pass in close to the following blades during descending or maneuvering flight; this results in impulsive changes in blade loading, which radiates noise. The calculation and analysis of BVI noise remain a challenging task in the field of helicopter aerodynamics and aerodynamic acoustics [2]. The BVI aerodynamic load and noise strength, as well as the radiation direction, relate to many factors, such as the location of BVI events, the blade tip vortex structure, and the miss-distance. The rotor wake structure and the unsteady aerodynamic load distribution on the blade surface have been recognized as the most important parameters in order to better predict BVI noise. In 1990s, the computational fluid dynamics (CFD) method was gradually applied to rotor
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