1,720,973 research outputs found
Investigations of broadband fan interaction noise using synthetic turbulence
No full textThe aim of this investigation is to develop computational aeroacoustics methodology to study broadband fan interaction noise. Broadband fan noise has become a major noise source on modern aircraft and it is crucial, for instance, in more fuel-efficient alternatives to turbofan engines. Solving the fluid mechanics of this process either via Direct Numerical Simulation or Large Eddy Simulation remains prohibitive within an industrial context. In the present approach, the sound source is calculated from stochastically generated synthetic turbulence instead of solving the Navier Stokes equations and combined with an aeroacoustic propagation model. This approach is computationally cheaper that DNS or LES and can provide accurate results for engineering purposes.Synthetic two-dimensional isotropic turbulent flows are generated by filtering white noise. The filter is expressed in terms of either the correlation function or the energy spectrum. In contrast with most filter-based models, non-Gaussian filters such as those derived from Liepmann and von Karman spectra are used. While Gaussian filters perform very well from a computational point of view, Liepmann and von Karman filters are more representative of the physics of the problem. The aeroacoustic sound propagation is modelled by the linearised Euler equations implemented in a parallel, multiblock, finite-difference code in the time domain. Particles representing vortices are launched upstream of the airfoil and convected with the mean flow following a purely Lagrangian approach. The turbulent velocity field is computed at each point along the aerofoil and implemented as source in the linearized Euler equations. Simulation results have been compared with the analytical solution proposed by Amiet. This numerical method is being used to assess the influence of various parameters on interaction noise for the cases of frozen and evolving turbulence. The case of inhomogeneous turbulence will also be considered in the final paper.<br/
Stochastic computational methods for broadband fan noise
No full textPredicting broadband fan interaction noise using a random-vortex-particle metho
Random-vortex-particle methods applied to broadband fan interaction noise
No full textThe general aim of this thesis is to investigate the suitability of a stochastic method for computational aeroacoustics, the specific objective being to devise a stochastic method to generate synthetic turbulence and combine it with the linearised Euler equations to predict broadband fan interaction noise. In modern turbofan designs broadband fan noise is a dominant source of aircraft noise, the most efficient source being the interaction between upstream turbulence and the stator vanes. The stochastic method developed to generate synthetic turbulence reproduces twodimensional isotropic turbulent flows by filtering a random field. The fillter is expressed in terms of the energy spectrum and controls the spatial properties of the synthetic turbulence. In contrast with previous work, non-Gaussian filters are developed to model more realistic energy spectra such as Liepmann and von Karman spectra. The temporal decorrelation present in turbulent flows is modelled using Langevin Equations. A standard Langevin equation and a second-order Langevin model are derived in details and validated for fan interaction noise. In contrast with classical methods to generate synthetic turbulence, random-vortex-particle methods can be extended to cope with inhomogeneous non-stationary turbulence with little modification from the formulation for homogeneous turbulence. The stochastic method is applied for first time to broadband fan interaction noise. The method is firstly validated for frozen turbulence interacting with an airfoil. The temporal decorrelation is then included in the method to assess the influence of the integral time scale on the radiated acoustic sound field. The method is also combined with an existing wake model to represent the inhomogeneous non-stationary turbulent flow found downstream of a fan. Finally, comparison with existing experimental data for an isolated airfoil in a turbulent jet demonstrates the benefits of using more realistic energy spectr
On the relationship between Lean practices and environmental performance
Full text linkLean production has emerged in the past decades as one of the most popular topics in business and manufacturing literature and it is the most extended production paradigm currently applied in industry. Lean production is characterized by five principles (value, map the value stream, flow, pull and continuous improvement) and by the importance of reducing waste (muda). Alongside the Lean philosophy, the so-called green strategy has also gained importance in competition between firms. Many companies are trying to develop products that reduce environmental impacts throughout their life cycle. The aim is to reduce resource consumption, to replace hazardous substances, to increase recyclability, to enhance energy efficiency and to bring down CO2 emissions. Lean and Green production paradigms are both focused on waste reduction and several authors have studied the relationship between Lean and Green practices and the synergic effects of joining these two management approaches. This research carries out a literature review in order to investigate if firms which have applied Lean principles and methods have improved their environmental measures. In particular, the work seeks to highlight which green indicators are more positively affected by Lean practices adoption. The results are synthesized in a final chart which illustrates the main green indicators cited in the literature and shows how these indicators have changed after a Lean transformation program. The research is to be understood as a work in progress and is part of a larger study that the authors are conducting on this topic
Random particle methods applied to broadband fan interaction noise
Full text linkPredicting broadband fan noise is key to reduce noise emissions from aircraft and wind turbines. Complete CFD simulations of broadband fan noise generation remain too expensive to be used routinely for engineering design. A more efficient approach consists in synthesizing a turbulent velocity field that captures the main features of the exact solution. This synthetic turbulence is then used in a noise source model. This paper concentrates on predicting broadband fan noise interaction (also called leading edge noise) and demonstrates that a random particle mesh method (RPM) is well suited for simulating this source mechanism. The linearized Euler equations are used to describe sound generation and propagation. In this work, the definition of the filter kernel is generalized to include non-Gaussian filters that can directly follow more realistic energy spectra such as the ones developed by Liepmann and von Kármán. The velocity correlation and energy spectrum of the turbulence are found to be well captured by the RPM. The acoustic predictions are successfully validated against Amiet’s analytical solution for a flat plate in a turbulent stream. A standard Langevin equation is used to model temporal decorrelation, but the presence of numerical issues leads to the introduction and validation of a second-order Langevin model.<br/
The “dark side” of Industry 4.0: How can technology be made more sustainable?
Full text linkPurpose: A positive outlook on the impact of Industry 4.0 (I4.0) on sustainability prevails in the literature. However, some studies have highlighted potential areas of concern that have not yet been systematically addressed. The goal of this study is to challenge the assumption of a sustainable Fourth Industrial Revolution by (1) identifying the possible unintended negative impacts of I4.0 technologies on sustainability; (2) highlighting the underlying motivations and potential actions to mitigate such impacts; and (3) developing and evaluating alternative assumptions on the impacts of I4.0 technologies on sustainability. Design/methodology/approach: Building on a problematization approach, a systematic literature review was conducted to develop potential alternative assumptions about the negative impacts of I4.0 on sustainability. Then, a Delphi study was carried out with 43 experts from academia and practice to evaluate the alternative assumptions. Two rounds of data collection were performed until reaching the convergence or stability of the responses. Findings: The results highlight various unintended negative effects on environmental and social aspects that challenge the literature. The reasons behind the high/low probability of occurrence, the severity of each impact in the next five years and corrective actions are also identified. Unintended negative environmental effects are less controversial than social effects and are therefore more likely to generate widely accepted theoretical propositions. Finally, the alternative hypothesis ground is partially accepted by the panel, indicating that the problematization process has effectively opened up new perspectives for analysis. Originality/value: This study is one of the few to systematically problematize the assumptions of the I4.0 and sustainability literature, generating research propositions that reveal several avenues for future research
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