Prediction of combustion noise for an aeroengine combustor

Combustion noise may become an important noise source for lean-burn gas turbine engines, and this noise is usually associated with highly unsteady flames. This work aims to compute the broadband combustion noise spectrum for a realistic aeroengine combustor, and to compare with available measured noise data on a demonstrator aeroengine. A low-order linear network model is applied to a demonstrator engine combustor to obtain the transfer function that relates to unsteadiness in the rate of heat release, acoustic, entropic and vortical fluctuations. A spectral model is used for the heat release rate fluctuation, which is the source of the noise. The mean flow of the aeroengine combustor required as input data to this spectral model is obtained from RANS simulations. The computed acoustic field for a low-medium power setting indicates that the models used in this study capture the main characteristics of the broadband spectral shape of combustion noise. Reasonable agreement with the measured spectral level is achieved.The current research has been conducted under UK Technology Strategy Board contract TP11/HVM/6/I/AB201K.This is the accepted manuscript. The final published version is available from ARC at http://arc.aiaa.org/doi/abs/10.2514/1.B34857. Copyright © 2013 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission

Accounting for convective effects in zero-Mach-number thermoacoustic models

This paper presents a methodology to account for some mean-flow effects on thermo-acoustic instabilities when using the zero-Mach-number assumption. It is shown that when a computational domain is represented under the M=0 assumption, a nonzero-Mach-number element can simply be taken into account by imposing a proper acoustic impedance at the boundaries so as to mimic the mean flow effects in the outer, not computed flow domain. A model that accounts for the coupling between acoustic and entropy waves is presented. It relies on a “delayed entropy coupled boundary condition” (DECBC) for the Helmholtz equation satisfied by the acoustic pressure. The model proves able to capture low-frequency entropic modes even without mean-flow terms in the fluctuating pressure equation

The Measurement and Prediction of Gaseous Hydrocarbon Fuel AutoIgnition Delay Time at Realistic Gas Turbine Operating Conditions,” ASME Paper

ABSTRACT Auto-ignition delay time measurements have been attempted for a variety of gaseous fuels on a flow rig at gas turbine relevant operating conditions. The residence time of the flow rig test section was approximately 175 ms. A chemical kinetic model has been used in Senkin, one of the applications within the Chemkin package, to predict the auto-ignition delay time measured in the experiment. The model assumes that chemistry is the limiting factor in the prediction and makes no account of the fluid dynamic properties of the experiment. Auto-ignition delay time events were successfully recorded for ethylene at approximately 16 bar, 850K and at equivalence ratios between 2.6 and 3.3. Methane, natural gas and ethylene (0.5 < φ < 2.5) failed to auto-ignite within the test section. Model predictions were found to agree with the ethylene measurements, although improved qualification of the experimental boundary conditions is required in order to better understand the dependence of auto-ignition delay on the physical characteristics of the flow rig. The chemical kinetic model used in this study was compared with existing 'low temperature' measurements and correlations for methane and natural gas and was found to be in good agreement

Reaping the benefits of digitisation:Pilot study exploring revenue generation from digitised collections through technological Innovation

In the last decade significant resources have been invested for the digitisation of the collections of a large number of museums and galleries worldwide. In Europe alone, 10 million EUR is annually invested in Europeana (Europeana 2014). However, as we gradually move on from “the start-up phase” of digitisation (Hughes 2004), revenue generation and sustainability must be considered (Hughes 2004). Even beyond digitisation, generating revenue through innovation and in particular “finding new business models to sustain funding” (Simon 2011) ranks amongst museums’ top challenges (Simon 2011). More importantly, despite the significant wealth of digitised assets museums now own, little has been done to investigate ways these institutions could financially benefit from their digitised collections. For art institutions in particular, this has been largely limited to the sale of image licenses, with the fear of losing this revenue posing as one of the key reasons art museums are reluctant to join the Open Content movement (Kapsalis 2016). This paper examines how recent technological advancements, such as image recognition and Print-on-Demand automation, can be utilised to take advantage of the wealth of digitised artworks museums and galleries have in their possession. A pilot study of the proposed solution at the State Museum of Contemporary Art (SMCA) in Thessaloniki, Greece, is covered and the findings are examined. Early feedback indicates that there is a significant potential in the utilisation of the aforementioned technologies for the monetisation of digitised collections. However, challenges such as blending the real-world experience with the digital experience, as well as flattening the learning curve of the technological solution for museum visitors, need to be addressed. Based on the pilot study at SMCA, this paper investigates how emerging technologies can be utilised to facilitate revenue generation for all museums and galleries with digitised collections

The Pulsed Electric Discharge As An Acoustic Probe For Combustion Chamber Diagnostics

A brief review is given of combustion as an acoustic source with special reference to the acoustic stability of working combustion chambers. A theoretical model is developed of the pulsed arc discharge as an acoustic source under free field conditions following a review of previous work. A specific feature of the model is that account is taken of the fractional heat loss to the electrodes due to thermal conduction. The experimentally determined acoustic emission from the discharge is shown to follow the trends predicted by the model. A theoretical model is also developed of the acoustic impedance 'seen' by the pulsed arc at the fundamental resonant frequency in a working combustion chamber. The model is based on electrical transmission line theory and takes into account the radiation resistance of the chamber ends, the mean temperature inside the chamber, and the acoustic impedance of the burner and fuel supply system. The model is further developed to include the effects of ceramic fibre material used as an end termination. Lt shows the way that the acoustic impedance 'seen' by the source is altered by the additional acoustic resistance introduced to the system and shows how the resistance and reactance of the material may be determined from relatively simple acoustic pressure measurements. An experimental system is described whereby the relevant electrical power to the arc is derived from the Fourier series of the periodic power pulse. This enables the relevant source strength to be determined easily and from which the impedance at system resonance may be calculated. The performance and limitation of the pulsed arc as an acoustic transducer for stability diagnosis are discussed

Prediction of Combustion Noise for an Aeroengine Combustor

Combustion noise may become an important noise source for lean-burn gas turbine engines, and this noise is usually associated with highly unsteady flames. This work aims to compute the broadband combustion noise spectrum for a realistic aeroengine combustor, and to compare with available measured noise data on a demonstrator aeroengine. A low-order linear network model is applied to a demonstrator engine combustor to obtain the transfer function that relates to unsteadiness in the rate of heat release, acoustic, entropic and vortical fluctuations. A spectral model is used for the heat release rate fluctuation, which is the source of the noise. The mean flow of the aeroengine combustor required as input data to this spectral model is obtained from RANS simulations. The computed acoustic field for a low-medium power setting indicates that the models used in this study capture the main characteristics of the broadband spectral shape of combustion noise. Reasonable agreement with the measured spectral level is achieved