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Article
Publication date: 31 August 2021

Zbigniew Rarata

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability…

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Abstract

Purpose

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.

Design/methodology/approach

Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.

Findings

The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.

Practical implications

The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.

Originality/value

The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

Details

Aircraft Engineering and Aerospace Technology, vol. 94 no. 2
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 8 May 2018

Antonio Memmolo, Matteo Bernardini and Sergio Pirozzoli

This paper aims to show results of numerical simulations of transonic flow around a supercritical airfoil at chord Reynolds number Rec = 3 × 106, with the aim of elucidating the…

Abstract

Purpose

This paper aims to show results of numerical simulations of transonic flow around a supercritical airfoil at chord Reynolds number Rec = 3 × 106, with the aim of elucidating the mechanisms responsible for large-scale shock oscillations, namely, transonic buffet.

Design/methodology/approach

Unsteady Reynolds-averaged Navier–Stokes simulations and detached-eddy simulations provide a preliminary buffet map, while a high fidelity implicit large-eddy simulation with an upstream laminar boundary layer is used to ascertain the physical feasibility of the various buffet mechanisms. Numerical experiments with unsteady RANS highlight the role of waves travelling on pressure side in the buffet mechanism. Estimates of the propagation velocities of coherent disturbances and of acoustic waves are obtained, to check the validity of popular mechanisms based on acoustic feedback from the trailing edge.

Findings

Unsteady RANS numerical experiments demonstrate that the pressure side of the airfoil plays a marginal role in the buffet mechanism. Implicit LES data show that the only plausible self-sustaining mechanism involves waves scattered from the trailing edge and penetrating the sonic region from above the suction side shock. An interesting side result of this study is that buffet appears to be more intense in the case that the boundary layer state upstream of the shock is turbulent, rather than laminar.

Originality/value

The results of the study will be of interest to any researcher involved with transonic buffet.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 July 2021

Zi Kan, Daochun Li, Shiwei Zhao, Jinwu Xiang and Enlai Sha

This paper aims to assess the aeroacoustic and aerodynamic performance of a morphing airfoil with a flexible trailing edge (FTE). The objective is to make a comparison of the…

Abstract

Purpose

This paper aims to assess the aeroacoustic and aerodynamic performance of a morphing airfoil with a flexible trailing edge (FTE). The objective is to make a comparison of the aerodynamic noise characteristics between the conventional airfoil with a flap and morphing airfoil and analyse the noise reduction mechanisms of the morphing airfoil.

Design/methodology/approach

The computational fluid dynamic method was used to calculate the aerodynamic coefficients of morphing airfoil and the Ffowcs-Williams and Hawking’s acoustic analogy methods were performed to predict the far-field noise of different airfoils.

Findings

Results show that compared with the conventional airfoil, the morphing airfoil can generate higher lift and lower noise, but a greater drag. Additionally, the noise caused by the one-unit lift of the morphing airfoil is significantly lower than that of the conventional airfoil. For the morphing airfoil, the shedding vortex in the trailing edge was the main noise resource. As the angle of attack (AoA) increases, the overall sound pressure level of the morphing airfoil increases significantly. With the increase of the trailing edge deflection angle, the amplitude and the period of sound pressure of the morning airfoil fluctuation increase.

Practical implications

Presented results could be very useful during designing the morphing airfoil with FTE, which has significant advantages in aerodynamic efficiency and aeroacoustic performance.

Originality/value

This paper presents the aerodynamic and aeroacoustic characteristics of the morphing airfoil. The effect of trailing edge deflection angle and AoA on morphing airfoil was investigated. In the future, using a morphing airfoil instead of a traditional flap can reduce the aircraft`s fuel consumption and noise pollution.

Details

Aircraft Engineering and Aerospace Technology, vol. 93 no. 5
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 2 February 2023

Xiang Shen, Eldad Avital, Zaheer Ikram, Liming Yang, Theodosios Korakianitis and Laurent Dala

This paper aims to investigate the influence of smooth curvature distributions on the self-noise of a low Reynolds number aerofoil and to unveil the flow mechanisms in the…

Abstract

Purpose

This paper aims to investigate the influence of smooth curvature distributions on the self-noise of a low Reynolds number aerofoil and to unveil the flow mechanisms in the phenomenon.

Design/methodology/approach

In this paper, large Eddy simulation (LES) approach was performed to investigate the unsteady aerodynamic performance of both the original aerofoil E387 and the redesigned aerofoil A7 in a time-dependent study of boundary layer characteristics at Reynolds number 100,000 and angle of attack (AoA) 4-degree. The aerofoil A7 is redesigned from E387 by removing the irregularities in the surface curvature distributions and keeping a nearly identical geometry. Flow vorticity magnitude of both aerofoils, along with the spectra of the vertical fluctuating velocity component and noise level, are analysed to demonstrate the bubble flapping process near the trailing edge (TE) and the vortex shedding phenomenon.

Findings

This paper provides quantitative insights about how the flapping process of the laminar separation bubble (LSB) within the boundary layer near the TE affects the aerofoil self-noise. It is found that the aerofoil A7 with smooth curvature distributions presents a 10% smaller LSB compared to the aerofoil E387 at Reynolds number 100,000 and AoA 4-degree. The LES results also suggest that curvature distribution smoothing leads to a 6.5% reduction in overall broadband noise level.

Originality/value

This paper fulfils an identified need to reveal the unknown flow structure and the boundary layer characteristics that resulted in the self-noise reduction phenomenon yielded by curvature distribution smoothing.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 33 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 7 November 2016

Abdelkader Frendi and Michael R. Brown

The purpose of this paper is to carry out an extensive numerical study in order to understand the flow structures and the resulting noise generated by a supersonic impinging jet…

Abstract

Purpose

The purpose of this paper is to carry out an extensive numerical study in order to understand the flow structures and the resulting noise generated by a supersonic impinging jet on a flat plate. One of the parameters varied in this study is the distance between the jet exit plane and the flat plate.

Design/methodology/approach

Because of the unsteady nature of the problem a time-dependent computation is carried out using the detached eddy simulation turbulence model. The OVERFLOW 2 CFD code was used with a highly resolved grid and small time steps.

Findings

The authors found that as the separation distance increases, the dominant frequencies in the noise spectrum decrease. In addition, the relative strength of the various frequencies to each other changes with changing distance, indicating the changing modes of the jet. The CFD results indicate a strong interaction between the acoustic waves emanating from the impingement plate and the jet plume. This feedback mechanism is responsible for destabilizing the jet shear layer leading to the jet changing modes. The computed near field spectra, convection velocities of the jet vortical structures and mean jet centerline velocity profile are in good agreement with experimental measurements. The results also show very high sound pressure levels all over the impingement plate but especially near the impingement point. These levels, if sustained, are detrimental to both human operators as well as the surrounding structures.

Research limitations/implications

Given the large-scale nature of the computations carried out, it is very costly to run the computations long enough to collect a good, statistically steady time sample to achieve a low frequency bandwidth resolution. Such a long time sample could actually improve the results in terms of frequency resolution and obtained an even better agreement with experiments. Off course there is always the issue of grid resolution as well, but given the good agreement with experiments that the authors obtained, the authors are confident in their results.

Practical implications

The practical implications of the results the authors obtained are significant in that, the authors now know that hybrid RANS-large eddy simulation methods can be used for this complex, unsteady engineering problems. In addition, the results also show the high noise level both on the impingement surface and in the surroundings of the jet. This could have a negative impact on the structural integrity of the flat surface.

Social implications

Noisy environments are never desirable anywhere especially in places where human operations take place. Therefore, given the high noise levels obtained in the simulations and confirmed by experiments, any human presence around the jet will be harmful to hearing and precautions need to be taken.

Originality/value

This is a physics-based study; i.e. understanding the physical phenomena involved in supersonic jet impingement. Of particular interest is the interaction of the jet shear layer with the acoustic waves emanating from the impingement area. This feedback loop is found to be responsible for intensifying the instability of the jet shear layer.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 28 October 2014

Kok-Leong Ong, Simone Leao and Adam Krezel

This paper aims to present a project in Australia, where participants use smartphones to measure the level of traffic noise in their homes. Through the data collected…

Abstract

Purpose

This paper aims to present a project in Australia, where participants use smartphones to measure the level of traffic noise in their homes. Through the data collected, participants learn if they are subjected to sleep disturbances and, if so, understand how they can manage the issue to protect their health. The project also has a secondary purpose: the local council would like to engage its community through the exercise and be seen as acting on the community’s problems.

Design/methodology/approach

The approach taken was the development of a mobile app call 2Loud? that turns the smartphones of participants into noise sensors with accuracies comparable to professional sound-meters. The data collected are analyzed by environment and acoustic experts, and personalized feedback, in the form of mitigation strategies, is then provided. The strategies are delivered through the app to allow participants to share within the community and hence, propagate the solution to non-participants.

Findings

Participants who are technologically literate find a sense of empowerment as a result. They confirmed the importance of “closing the loop” with the feedback they received after their voluntary data collection effort. They also reported some sense of satisfaction with the technology as an interim solution and noted the council’s creative approach.

Originality/value

This project first showcases how a participatory setup could be extended to create a “closed-loopfeedback system that further empowers its users. It is also a case example of how an organization could engage and manage its stakeholders’ expectations through innovative use of participatory sensing systems.

Details

International Journal of Pervasive Computing and Communications, vol. 10 no. 4
Type: Research Article
ISSN: 1742-7371

Keywords

Article
Publication date: 6 October 2023

Omotayo Farai, Nicole Metje, Carl Anthony, Ali Sadeghioon and David Chapman

Wireless sensor networks (WSN), as a solution for buried water pipe monitoring, face a new set of challenges compared to traditional application for above-ground infrastructure…

Abstract

Purpose

Wireless sensor networks (WSN), as a solution for buried water pipe monitoring, face a new set of challenges compared to traditional application for above-ground infrastructure monitoring. One of the main challenges for underground WSN deployment is the limited range (less than 3 m) at which reliable wireless underground communication can be achieved using radio signal propagation through the soil. To overcome this challenge, the purpose of this paper is to investigate a new approach for wireless underground communication using acoustic signal propagation along a buried water pipe.

Design/methodology/approach

An acoustic communication system was developed based on the requirements of low cost (tens of pounds at most), low power supply capacity (in the order of 1 W-h) and miniature (centimetre scale) size for a wireless communication node. The developed system was further tested along a buried steel pipe in poorly graded SAND and a buried medium density polyethylene (MDPE) pipe in well graded SAND.

Findings

With predicted acoustic attenuation of 1.3 dB/m and 2.1 dB/m along the buried steel and MDPE pipes, respectively, reliable acoustic communication is possible up to 17 m for the buried steel pipe and 11 m for the buried MDPE pipe.

Research limitations/implications

Although an important first step, more research is needed to validate the acoustic communication system along a wider water distribution pipe network.

Originality/value

This paper shows the possibility of achieving reliable wireless underground communication along a buried water pipe (especially non-metallic material ones) using low-frequency acoustic propagation along the pipe wall.

Details

International Journal of Pervasive Computing and Communications, vol. 20 no. 2
Type: Research Article
ISSN: 1742-7371

Keywords

Article
Publication date: 1 December 2003

M. Kaiserseder, J. Schmid, W. Amrhein and V. Scheef

A torque ripple minimization technique for switched reluctance motors is shown in this paper. Precalculated current shapes are applied to reduce torque ripple and to raise the…

Abstract

A torque ripple minimization technique for switched reluctance motors is shown in this paper. Precalculated current shapes are applied to reduce torque ripple and to raise the degrees of freedom of the application in the commutation region. The optimization criteria for this region can be chosen freely. Therefore, it is possible to take positive effect to some motor characteristics like power losses, mechanical vibrations or acoustic noise.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 22 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 March 1987

V.J. Hughes, J.G. Boulton, J.M. Coles, T.R. Empson and N.J. Kerry

A new type of hydrophone using optical technologies has distinct advantages over traditional types.

Abstract

A new type of hydrophone using optical technologies has distinct advantages over traditional types.

Details

Sensor Review, vol. 7 no. 3
Type: Research Article
ISSN: 0260-2288

Article
Publication date: 9 August 2011

Jonas Braasch

The purpose of this paper is to better understand communication between musicians in a free jazz improvisation in comparison to traditional jazz.

Abstract

Purpose

The purpose of this paper is to better understand communication between musicians in a free jazz improvisation in comparison to traditional jazz.

Design/methodology/approach

A cybernetic informative feedback model was used to study communication between musicians for free jazz. The conceptual model consists of the ears as sensors, an auditory analysis stage to convert the acoustic signals into symbolic information (e.g. notated music), a cognitive processing stage (to make decisions and adapt the performance to what is being heard), and an effector (e.g. muscle movement to control an instrument). It was determined which musical features of the co‐players have to be extracted to be able to respond adequately in a music improvisation, and how this knowledge can be used to build an automated music improvisation system for free jazz.

Findings

The three major findings of this analysis were: in traditional jazz a soloist only needs to analyze a very limited set of music ensemble features, but in free jazz the performer has to observe each musician individually; unlike traditional jazz, free jazz is not a strict rule‐based system. Consequently, the musicians need to develop their personal symbolic representation; which could be a machine‐adequate music representation for an automated music improvisation system. The latter could be based on acoustic features that can be extracted robustly by a computer algorithm.

Practical implications

Gained knowledge can be applied to build automated music improvisation systems for free jazz.

Originality/value

The paper expands our knowledge to create intelligent music improvisation algorithms to algorithms that can improvise with a free jazz ensemble.

1 – 10 of 246