A wavelet-based separation method for tonal and broadband components of low Reynolds-number propeller noise

Propeller noise generally exhibits a rich mixture of tonal and broadband components related to different physical mechanisms. Specifically, the tones are characterized by having deterministic and persistent characteristics, while the broadband counterpart has random behaviour. The separation is essential for the experimenters as they provide...

A Numerical Study on Aircraft Noise Mitigation Using Porous Stator Concepts

This manuscript presents the application of a recently developed noise reduction technology, constituted by poro-serrated stator blades on a full-scale aircraft model, in order to reduce rotor-stator interaction noise in the fan stage. This study was carried out using the commercial lattice Boltzmann solver 3DS-SIMULIA PowerFLOW. The simulation...

Small-Scale Rotor Aeroacoustics for Drone Propulsion: A Review of Noise Sources and Control Strategies

In the last decade, the drone market has grown rapidly for both civil and military purposes. Due to their versatility, the demand for drones is constantly increasing, with several industrial players joining the venture to transfer urban mobility to the air. This has exacerbated the problem of noise pollution, mainly due to the relatively lower...

A physics-based description and modelling of the wall-pressure fluctuations on a serrated trailing edge

A physical description of the flow mechanisms that govern the distribution of the wall-pressure fluctuations over the surface of a serrated trailing edge is proposed. Three main mechanisms that define the variation of turbulent pressure fluctuations across the serrated edge are discussed and semi-empirical models are formulated accordingly....

Aeroacoustics of sawtooth trailing-edge serrations under aerodynamic loading

The impact of aerodynamic loading on a serrated trailing edge is studied experimentally. Aerodynamic and acoustic measurements are conducted on a sawtooth-shaped trailing edge, retrofitted to a flat plate featuring a trailing-edge flap, and placed at incidence to the free-stream flow. The turbulent flow across the trailing edge is inspected...

A proper framework for studying noise from jets with non-compact sources

A quantitative assessment of the acoustic source field produced by a laboratory-scale heated jet with a gas dynamic Mach number of 1.55 and an acoustic Mach number of 2.41 is performed using arrays of microphones that are traversed across the axial and radial plane of the jet's acoustic field. The nozzle contour comprises a method of...

Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at...

Noise reduction mechanisms of an open-cell metal-foam trailing edge

Open-cell porous materials have been reported as a promising concept for mitigating turbulent boundary-layer trailing-edge noise. This manuscript examines the aeroacoustics of a porous trailing edge to study its noise reduction mechanisms. Numerical investigations have been carried out for a NACA 0018 aerofoil with three different types of...

Jet-installation noise and near-field characteristics of jet-surface interaction

The link between jet-installation noise and the near-field flow features of the corresponding isolated jet is studied by means of lattice-Boltzmann numerical simulations. The computational set-up consists of a flat plate placed in proximity to a jet, replicating the interaction benchmark study carried out at NASA Glenn. Installation effects...

Transition in a separation bubble under tonal and broadband acoustic excitation

Transition and flow development in a separation bubble formed on an airfoil are studied experimentally. The effects of tonal and broadband acoustic excitation are considered since such acoustic emissions commonly result from airfoil self-noise and can influence flow development via a feedback loop. This interdependence is decoupled, and the...

Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations

Trailing-edge serrations are add ons retrofitted to wind-turbine blades to mitigate turbulent boundary-layer trailing-edge noise. This manuscript studies the physical mechanisms behind the noise reduction by investigating the far-field noise and the hydrodynamic flow field. A conventional sawtooth and a combed-sawtooth trailing-edge serration...

Benefits of curved serrations on broadband trailing-edge noise reduction

Far-field noise and flow field over a novel curved trailing-edge serration (named as iron-shaped serration) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new...

Experimental investigation of aerofoil tonal noise generation

The present study investigates the mechanisms associated with tonal noise emission from a NACA 0012 aerofoil at moderate incidence (0; 1; 2 and 4 angle of attack) and with Reynolds numbers ranging from 100 000 to 270 000. Simultaneous time-resolved particle image velocimetry (PIV) of the aeroacoustic source region near the trailing edge and...

Three-dimensional vortex analysis and aeroacoustic source characterization of jet core breakdown

The three-dimensional behavior of jet core breakdown is investigated with experiments conducted on a free water jet at Re = 5000 by time-resolved tomographic particle image velocimetry (TR-TOMO PIV). The investigated domain encompasses the range between 0 and 10 jet diameters. The characteristic pulsatile motion of vortex ring shedding and...

Experimental investigation of the flow inside a saxophone mouthpiece by particle image velocimetry

An experimental study of the flow inside a saxophone mouthpiece in playing conditions is carried out by means of particle image velocimetry at high acquisition rate. Planar velocity measurements on the midsection of a Plexiglas tenor saxophone mouthpiece are performed, respectively, in the mouthpiece baffle and in the reed channel. Sequences of...

Three-dimensional evolution of flow structures in transitional circular and chevron jets

The three-dimensional behavior of flow transition in circular and 6-chevron jets at Re?=?5000 is investigated with experiments conducted on a free water jet by time-resolved tomographic particle image velocimetry. The emphasis is on the unsteady organization of coherent flow structures, which play a role in the generation of acoustic noise....

A study on the application of two different acoustic analogies to experimental PIV data

The aim of the present study is to compare two different acoustic analogies applied to time-resolved particle image velocimetry (PIV) data for the prediction of the acoustic far-field generated by the flow over a rectangular cavity. We consider the model problem of sound radiating from an open, two-dimensional, shallow cavity with an aspect...

Investigation of higher spanwise Helmholtz resonance modes in slender covered cavities

Cavity aeroacoustic noise is relevant for aerospace and automotive industries and widely investigated since the 1950s. Most investigations so far consider cavities where opening length and width are of similar scale. The present investigation focuses on a less investigated setup, namely cavities that resemble the door gaps of automobiles. These...