Table of Contents
UNSW Sydney
ABSTRACT
The flow-induced noise produced by a surface-mounted three-dimensional (or finite length) airfoil is important for many aerodynamic and hydrodynamic applications. Examples include wing-fuselage junctions, turbomachinery blade, rotor tip and end-wall flows, and ship appendage and hull-junction flows. This paper provides an overview of the three-dimensional airfoil noise program at UNSW Sydney. In general, there are four flow regimes for a three-dimensional airfoil. These are the airfoil-wall junction flow featuring a horseshoe vortex that wraps around the airfoil base; turbulent flow interaction with the leading edge; trailing edge flow whose structure depends upon the Reynolds number; and the tip flow that consists of vortices that form as the flow wraps around the free-end of the airfoil. The acoustic signature and turbulent noise sources associated with each of these flow regimes will be examined using anechoic wind tunnel measurements obtained with acoustic array, unsteady surface pressure and turbulence measurement methods.
University of Technology Sydney
ABSTRACT
The impact of the invention of the laser cannot be over-stated. In vibration and acoustics engineering, the laser Doppler vibrometer has revolutionised the means by which scientists and engineers can interpret and control the natural and man-made environment, both on and off the planet. Combining high sensitivity, dynamic and frequency ranges, non-invasiveness and high spatial resolution, laser Doppler vibrometers (LDVs) have received significant and increasing attention in both research and industry. This paper will briefly investigate the origins, working principles and evolution of LDVs, focusing on industrially relevant, practical applications. Particular focus will be on overcoming specific challenges associated with making successful measurement campaigns in challenging scenarios, including directly from rotating equipment and from vibrating platforms, a UTS topic of interest.
Defence Science and Technology Group
ABSTRACT
Acoustic metamaterials are rationally designed composites for which the effective medium properties go beyond those of their bulk ingredients. The basic structure of an acoustic metamaterial is composed of a lattice of resonant scatterers embedded in an elastic matrix. This composite design facilitates multiple scattering effects and strong acoustic coupling between scatterers. Due to their extraordinary wave manipulation capabilities and the tremendous progress in fabrication technology, acoustic metamaterials are becoming immensely popular for noise control. However, the analytical and numerical treatment of acoustic metamaterials is still a challenging undertaking. In this talk, we present simple designs of acoustic metamaterials and their analytical treatment using both an effective medium approximation and an effective boundary approach. To this end, we translate some well-known analytical results from electrostatics, fluid dynamics, diffusion kinetics and solid state physics to the acoustic domain. Results demonstrate how the proposed framework can be applied for the tailored design of acoustic metamaterials
Flinders University
ABSTRACT
Despite widespread community acceptance of renewable power generation to reduce CO2 emissions and natu-ral resource impacts, large-scale expansion of wind farms has prompted significant community debate regard-ing adverse health impacts of wind farm noise (WFN). Our research has aimed to investigate this issue by identifying, quantifying, and characterising the components of WFN that are responsible for annoyance and sleep disturbance. In this study, we carried out 1-year-long acoustic and meteorological measurements at three residences located near different wind farms, allowing detailed characterisation of WFN and its relation-ship with meteorological conditions. At two of these residences, participants recorded their subjective annoy-ance, providing insight into the relationship between specific noise features and human response. To detect amplitude modulation (AM), which is a particularly annoying component of WFN, we used a novel detection algorithm which significantly outperformed previous methods. Application of this algorithm revealed that AM prevalence was 2 to 5 times higher during the nighttime compared to the daytime. Annoyance due to WFN was reported most often during the nighttime and early morning, consistent with the measured AM prevalence. Participants most often described the noise as a "swish" or "swoosh" and the presence of these signal com-ponents was confirmed via spectral analysis.
(1) Acoustic Studio
ABSTRACT
The Australian rail industry has made remarkable progress over the last fifteen years to better understand rail noise and devise mitigation strategies. There have been significant developments in curve noise, locomotive noise, and general rolling noise, both in understanding their root causes in Australia and in how to reduce these types of noise. But the industry has been slow to implement these developments and risks losing its reputation as an environmentally friendly mode of transport. This paper explores the successes, failures, and untapped opportunities in regards to implementing noise mitigation. We emphasise understanding the broader rail system and the drivers of rolling stock and network operators, and how acousticians can leverage this broader context. We then examine rail noise mitigation through the lens of opportunity cost. With reference to recent examples, and the current rail infrastructure boom, we pose a challenge to regulators, planners, operators and proponents to be open to different ways of implementing mitigation.
(1) UNSW Sydney (2) Bundeswehr University Munich
ABSTRACT
Measurements of the far-field sound radiated by two and three-dimensional supercritical airfoils operating in a low Mach number flow were performed in an anechoic open-jet facility. For the three-dimensional case, two aspect ratios (AR = span/chord) of 1.0 and 1.5 were considered. The far-field sound was measured using a 64 microphone phased array placed outside the flow region and the array output was beamformed to reveal the acoustic sources. The results show that the trailing-edge noise from the 2D airfoil is larger than the 3D cases up to a frequency of 5 kHz, while above 7 kHz, the 3D airfoils generate more noise. Further, for the 3D airfoils, trailing-edge is the dominant noise source at 4 kHz, whereas at 8 kHz the source is concentrated near the free-end of the trailing-edge. Qualitatively, the source behaviour is the same for both ARs, but the airfoil with lower AR generates less broadband noise.
(1) Defence Science and Technology Group (2) YTEK Pty Ltd
ABSTRACT
Vehicles moving through a fluid all suffer from unwanted noise and vibration from turbulent boundary layer ex-citation. Industries involved with designing planes, trains and automobiles have consequently invested heavily in its control. Large levels of noise and vibration can negatively impact on passenger and crew comfort as well as contributing to environmental noise. This paper details a novel approach for estimating the unsteady pres-sure at the trailing edge (TE) resulting from the turbulent boundary layer of a rotating propeller blade. This methodology is based on the semi-empirical method of Brooks, Pope and Marcolini known as the BPM meth-od. Using a spanwise-strip implementation, the far-field TE noise is calculated for multiple points along the TE of the propeller surface of interest and at different positions of the propeller rotation. To provide quantitative validation of the numerical model, we present a comparison of estimated noise and trailing edge pressure characteristics with results obtained via experiment in the open literature. The noise estimates shown provide varying agreement using predictions of the flow field from the original empirical relationships and with those calculated using Reynolds Averaged Navier Stokes (RANS) CFD and the potential flow panel code XFOIL. The derived surface pressure characteristics are useful when evaluating the unsteady loading from the blade boundary layer flow.
(1) UNSW Sydney
ABSTRACT
Airfoil-turbulence-interaction noise, which is created whenever turbulent flow encounters an airfoil, is a major contributor of unwanted noise emitted by aircraft, turbomachinery and alike. The experimental study presented here is the precursor to a larger investigation of the impact of complex turbulence on noise generation at the airfoil's leading-edge and airfoil-wall junction. In the current study, we examine links between the experimentally acquired properties of isotropic turbulence and the sound radiation of the immersed airfoil. This is achieved by varying the in-flow turbulence intensity using two different turbulence grids. A NACA0012 airfoil was analysed at a range of geometric angles of attack up to 16 degrees and Reynolds numbers of 1.10^5 up to 3.10^5. Stereoscopic Particle Image Velocimetry (SPIV) was conducted beforehand to capture the turbulence characteristics of the free flow. Additionally, acoustic beamforming with a phased microphone array provides insight into the sound generation at the leading-edge. Pressure taps along the centre chord-line were used to measure the mean static pressure, thereby allowing for an open-jet deflection correction of the angle of attack.
(1) RMIT University (2) Defence Science and Technology Group (3) UNSW Sydney
ABSTRACT
Large eddy simulation (LES) has the potential to be a high-fidelity approach for predicting broadband noise from turbulent boundary layer flow, with the predicted surface pressure fluctuations providing an input to acoustics analogies. However, the practical application of conventional wall-resolved LES is limited by high computational cost. Therefore, wall-modelled LES (WMLES) has been investigated as a means to reduce this cost. Simulations were carried out using OpenFOAM, with channel flow as a test case. Predictions from both wall-resolved and wall-modelled approaches were compared against data from direct numerical simulation (DNS). The accuracy of WMLES was found to be comparable to that of wall-resolved LES over most of the channel, while incurring less than a tenth of the cost. However, near-wall accuracy of the boundary layer statistics from WMLES was reduced, resulting in a reduction in accuracy for the estimated wall pressure fluctuations. As an alternative approach, a semi-analytical method has been tested, which does not rely on the pressure fluctuations. Instead, a model derived from a Fourier transform solution of the pressure Poisson equation was implemented, with the boundary layer parameters supplied by LES. The accuracy of the resulting spectra for each LES method is discussed.
(1) UNSW Sydney
ABSTRACT
An experimental study on aeroacoustics of low Mach number flow over a forward-backward facing step (FBS) with aspect ratio of 8 is presented. The height of the step being considered was 50% of the incoming boundary layer thickness (h/d = 0.5) and the Reynolds number based on the step height Reh ranged from 1.4 x 10^5 to 2.8 x 10^5. The acoustic measurement was conducted using a 64-microphone-phased array in the UNSW Anechoic Wind Tunnel (UAT). The beamforming results show that the noise source locates at the leading edge of the step. The sound spectra obtained from the centre microphone of the array show that noise produced by the step is generally broadband without any distinct tonal noise. The data at different flow speeds collapse well using the scaling law proposed by Doolan and Moreau (2014).
(1) Monash University
ABSTRACT
An analysis of the symmetry-locking mechanism in screeching twin-jet systems dominated by axisymmetric modes is performed in this work. The different waves supported by the flow in a range of jet conditions are obtained by means of a twin-jet vortex sheet model, which considers the shear layer as an infinitesimal region. Analysis of the bands of existence of upstream waves in the flow suggest that the jet separation greatly affects the ability of the flow to support anti-symmetric screech modes, while symmetric modes remain relatively unaffected by this parameter. Comparison with acoustic data shows that most tones lie in the frequency bands of existence of guided jet modes, supporting the hypothesis that resonance is closed by these waves. The dominant symmetry for each condition is obtained by means of a symmetry-imposed spectral proper orthogonal decomposition of schlieren data, which provides both mode shapes and energies of the most amplified coherent structures in the flow. Overall, it is shown that symmetric modes are more energetic for very low spacings, and no clear dominance is found for large spacings.
(1) Defence Science and Technology Group (2) UNSW Sydney (3) Swedish Defence Research Agency
ABSTRACT
Noise generated by turbulent flow over high-aspect ratio bluff bodies is of interest in many engineering applications including the design wind turbines, aircraft and marine vessels. This study investigates the noise produced by a large span circular cylinder in cross-flow at a Reynolds number based on diameter (ReD) of 22,000. Large eddy simulations and the Ffowcs Williams and Hawkings acoustic analogy were used to simulate the aerodynamic and aeroacoustic fields around both full- and reduced-span cylinders, with aspect ratios of 18.75 and 4.0 respectively. At ReD=22,000, there is well-documented evidence of a low-frequency modulation of the fluctuating lift force, which is evident in the present results. The modulation means that very long runtimes are required to reach statistical convergence for the full-span cylinder. The modulation is not observed in the reduced-span simulation results, which significantly reduces the time taken to reach statistical convergence. The sound pressure levels (SPL) predicted from the full-span simulation are consistently 3-6 dB below experimental values. The SPLs predicted by scaling the reduced span simulation were in better agreement with the measured values, particularly around the vortex shedding frequency. These results show that more accurate far-field acoustic predictions can be obtained by scaling the results from the reduced-span simulation, when compared to the full-span predictions.
(1) UNSW Sydney
ABSTRACT
This paper presents an experimental investigation of the tip vortex formation noise produced by a wall-mounted finite airfoil. To characterise the noise at the wingtip, acoustic measurements taken in the UNSW open jet anechoic wind tunnel with a planar microphone array are presented for a NACA 0012 airfoil with varying aspect ratios at different geometric angles of attack and chord-based Reynolds numbers. Measurements of the mean streamwise total pressure field at the wingtip using a single pitot probe for selected test cases are included to link the flow dynamics with noise production. Furthermore, the flow interaction between the wingtip and the wing-wall junction region and its effect on tip noise generation for a low aspect ratio (AR = 0.2) NACA 0012 airfoil will also be examined.
(1) UNSW Sydney (2) Defence Science and Technology Group (3) Technical University of Munich
ABSTRACT
A technique to investigate the contributions of aeroacoustic sources to the sound power is presented. The method combines the Lighthill source distribution with an acoustic impedance matrix constructed from radiation kernels of the free-field Green's function. By calculating the contributions of aeroacoustic sources to sound power, the location and nature of the dominant flow noise sources are identified. To demonstrate the technique, the flow noise produced by a pair of co-rotating vortices is examined. The aeroacoustic contribution of each component of the Lighthill tensor is determined for a range of wavenumbers, with key findings discussed.
(1) Consultant Engineer (2) Pulse White Noise Acoustics (3) UNSW Sydney
ABSTRACT
Buildings are an enormous consumer of energy, due to air leaks alone buildings waste up to 5% of all energy worldwide. Building envelope airtightness is therefore of paramount importance to minimise energy consumption and to meet cut carbon emissions by 2050, as set out by the Australian Government. Air permeability rate testing is also becoming a requirement for various building rating systems such as WELL and Green Star and must be performed to obtain the relevant credit points. The commonly used current standard measuring technique for air permeability is the blower door test, while thermography and smoke pens are widely used for air leak detection. All these metho