Broadband and discrete frequency radiation from subsonic rotors

https://acoustique.ec-lyon.fr/publi/posson_jsv11.pdf

Broadband noise prediction of fan outlet guide vane using a cascade response function

A theoretical and experimental investigation of the noise of a model helicoper rotor due to ingestion of turbulence was conducted. Experiments were performed with a 0.76 m dia, articulated model rotor for a range of inflow turbulence and rotor operating conditions. Inflow turbulence levels varied from approximately 2 to 19 percent and tip Mach number was varied from 0.3 to 0.52. Test conditions included ingestion of a atmospheric turbulence in outdoor hover as well as ingestion of grid generated isotropic turbulence in the wind tunnel airstream. In wind tunnel testing, both forward flight and vertical ascent (climb) were simulated. Far field noise spectra and directivity were measured in addition to incident turbulence intensities, length scales, and spectra. Results indicate that ingestion of atmospheric turbulence is the dominant helicopter rotor hover noise mechanism at the moderate to high frequencies which determine perceived noise level.

/pdf/noise-of-a-model-helicopter-rotor-due-to-ingestion-of-2lng9q15jf.pdf

Noise of a model helicopter rotor due to ingestion of turbulence

This chapter presents the details for the design, construction, and evaluation of a low-speed, low-turbulence, anechoic wind tunnel facility This facility allows for the experimental examination of an acoustic field generated by fluid/structure interaction The chapter begins by describing the motivation for the design of one such facility, located at the University of Notre Dame This is followed by a detailed description of the design and construction of its major components Methods for characterization of facility performance are presented and applied to the specific tunnel described Finally, the contributions of this facility, specifically in the area of a marine propeller’s response to inflow distortions, are summarized

An Anechoic Facility for Basic Aeroacoustic Research

Broadband rotor noise predictions using a time domain approach

The broadband sound radiated by a subsonic rotor subjected to turbulence in the approach stream has been analyzed. The power spectral density of the sound intensity has been found to depend on a characteristic time scale-namely, the integral scale of the turbulence divided by the axial flow velocity-as well as several length-scale ratios. These consist of the ratio of the integral scale to the acoustic wavelength, rotor radius, and blade chord. Due to the simplified model chosen, only a limited number of cascade parameters appear. Limited comparisons with experimental data indicate good agreement with predicted values.

M. Sevik

Papers

Sound radiation from a subsonic rotor subjected to turbulence