Publications
165 results found
Goh CS, Morgans AS, 2013, The influence of entropy waves on the thermoacoustic stability of a model combustor, Combustion Science and Technology, Vol: 185, Pages: 249-268
Luzzato CM, Morgans AS, 2013, Investigation of the causes of limit cycle saturation using a G-equationmodel in the case of a laminar anchored flame in a simple combustor, AIA-DAGA Acoustics Conf.
Morgans AS, Goh CS, 2013, Analytical modelling of the dissipation and dispersion of entropywaves in combustor thermoacoustics, AIA-DAGA Acoustics Conf
Rigas G, Morgans AS, Morrison JF, 2013, Stability and coherent structures in the wake of axisymmetric bluff bodies, Int. Conf. on Massively Separated Flows, Publisher: Springer
Thomas PH, Hall C, Morgans AS, 2012, Analytical solutions for acoustic integral solvers
The increasingly stringent noise regulations being set in the aerospace industry mean that the design for low noise of many technologies is becoming increasingly important. A set of tools available to designers for this purpose are known as acoustic integral solvers. These solvers place an integration surface in a near-field numerical calculation of the flow in such a way as to enclose the noise sources. A wave equation is then used to propagate this noise to an observer. Assessing these solvers using realistic numerical flow solutions is made difficult by the assumptions that need to be made in the derivation. Analytical solutions have the ability to isolate the solver from these problems and give it a case that it can theoretically solve exactly. Depending on the solver used, a wide range of flow properties can be required on the surface, including time and space derivatives of pressure and velocity. These are usually taken numerically, however this paper presents a method for taking them analytically in general. Specifically, a moving monopole solution is derived. If such a case is used, the only errors should be due to discretization, and they can be investigated independently from other errors that occur in a realistic calculation. These errors are discussed in more depth than they have been previously, including the identification of three key types of error. The potential of this work is demonstrated using an application to open rotor noise prediction. A simple test case is parameterized and a non-dimensional error study is used to provide resolution guidance for a more complex benchmark case. This approach is shown to give excellent insight into how discretization errors affect the accuracy of an acoustic integral solver. © 2012 by P. H. Thomas.
Dahan JA, Morgans AS, Lardeau S, 2012, Feedback control for form-drag reduction on a bluff body with a blunt trailing edge, Journal of Fluid Mechanics, Vol: 704, Pages: 360-387
Thomas PH, Hall C, Morgans AS, 2012, Analytical solutions for acoustic integral solvers, AIAA/CEAS Aeroacoustics Conf., Publisher: AIAA
Illingworth SJ, Morgans AS, Rowley CW, 2012, Feedback control of cavity flow oscillations using simple linear models, Journal of Fluid Mechanics, Vol: 709, Pages: 223-248
Goh CS, Morgans AS, 2011, The effect of entropy wave dissipation and dispersion on thermoacoustic instability in a model combustor
Thermoacoustic instability can be a major problem for aero-engine combustors, particularly lean-premixed burners designed for low NOx emissions. The instability is caused by the interaction between unsteady heat release and acoustic waves within the combustion chamber, and may be modelled using a one-dimensional linearised analytical approach. Unsteady combustion generates acoustic waves directly, as well as entropy fluctuations that are quiescent by themselves, and convect with the mean flow. The acceleration of these entropy waves at the exit of the combustor creates further acoustic waves, known as entropy noise or indirect combustion noise. This model captures reflected acoustics due to both the 'direct' and 'indirect' mechanisms. In this paper, the thermoacoustic model is extended to study the effects of dissipation and dispersion of the entropy waves on the stability of the combustor. Three combustor configurations are discussed; a stable combustor which may be destabilised due to the presence of entropy noise, an unstable combustor which experiences a 'mode switch' to oscillations at a higher frequency, and a third case where the combustor is driven to instability due to entropy waves but is not necessarily accompanied by an instability in the heat release. © 2011 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc.
Dowling AP, Morgans AS, 2011, Control Strategies for Combustion Instabilities, Turbulent Premixed Flames, Editors: Swaminathan, Bray, Publisher: Cambridge Univ Pr, Pages: 173-202, ISBN: 9780521769617
Dahan JA, Morgans AS, Lardeau S, 2011, Feedback control for drag reduction on a bluff body with a blunt trailing edge
The objective of the present numerical study is to increase the base pressure on a backward-facing step via a simple feedback control method; to be ultimately translated to a drag reduction on a blunt-based bluff body representative of a road vehicle. Two cases are considered: a simplified 2D flow at low Reynolds number and a fully turbulent 3D flow at a Reynolds of Reθ = 1500, deemed sufficient to be representative of automobile applications. Using Large Eddy Simulation (LES), system identification is performed to characterize the flow response to actuation. The control is effected by a full-span slot jet, with zero-net-mass-flux, located near separation and injecting at an angle of 45°. In the two cases, a broad range of frequencies is tested with harmonic inputs. The 2D and 3D flows are found to respond differently to actuation, yielding open-loop responses with different dynamics. The open-loop characterization is used to synthesize a feedback controller. The control target is set to the instantaneous pressure fluctuations on the base of the step, which in turn is expected to give a reduction in time-mean pressure. For both the 2D and 3D cases, a substantial pressure increase, and hence drag reduction, is obtained with a simple controller based on disturbance attenuation. © 2011 by J. A. Dahan and A. S. Morgans.
Goh CS, Morgans AS, 2011, Phase prediction of the response of choked nozzle to entropy and acoustic disturbances, Journal of Sound and Vibration, Vol: 330, Pages: 5184-5198
Zhao D, Morgans AS, Dowling AP, 2011, Tuned passive control of acoustic damping of perforated liners, AIAA Journal, Vol: 49, Pages: 725-734
Goh CS, Morgans AS, 2011, The effect of entropy wave dissipation and dispersion in a model combustor, AIAA/CEAS Aeroacoustics Conference
Dahan JA, Morgans AS, Lardeau S, 2011, Feedback control for drag reduction on a bluff body with a blunt trailing edge, AIAA Fluid Dynamics Conference
Illingworth SJ, Morgans AS, Rowley CW, 2011, Feedback control of flow resonances using balanced reduced order models, Journal of Sound and Vibration, Vol: 330, Pages: 1567-1581
Morgans AS, Huang LX, 2010, Passive control of combustion instability through an acoustic valve, Journal of Propulsion Technology, Vol: 31, Pages: 701-709
Illingworth SJ, Morgans AS, 2010, Advances in feedback control of the Rijke tube thermoacoustic instability, International Journal of Flow Control, Vol: 2, Pages: 197-218
Morgans AS, Zhao D, 2010, Tuned passive control of combustion instabilities, International Congress on Sound and Vibration
Illingworth SJ, Morgans AS, 2010, Adaptive feedback control of combustion instability in annular combustors, Combustion Science and Technology, Vol: 182, Pages: 143-164
Zhao D, A' Barrow C, Morgans AS, et al., 2009, Acoustic damping of a Helmholtz resonator with an oscillating volume, 14th AIAA/CEAS Aeroacoustics Conference, Publisher: AIAA, Pages: 1672-1679
Zhao D, Morgans AS, 2009, Tuned passive control of combustion instabilities using multiple Helmholtz resonators, Journal of Sound and Vibration, Vol: 320, Pages: 744-757
Morgans AS, 2009, Control of combustion instabilities, Flow Control Lecture Series, Publisher: Von Karman Institute for Fluid Dynamics
Zhao D, Morgans AS, 2009, Tuned passive control of perforated liners, AIAA/CEAS Aeroacoustics Conference
Zhao D, A'Barrow C, Morgans AS, et al., 2008, Acoustic damping of a Helmholtz resonator with an oscillating volume
Combustion instabilities are caused by a coupling between acoustic waves and unsteady heat release. Helmholtz resonators are widely used as acoustic dampers to stabilise unsta- ble combustion systems. Such dampers are normally only effective over a narrow frequency range, close to the resonant frequency. In order to increase the effective frequency range, a Helmholtz resonator with an oscillating volume, implemented via an electro-magnetic shaker and vibrating back-plate, was designed and experimentally tested at the University of Loughborough. It was found that volume oscillation can either increase or decrease the acoustic power being absorbed by the resonator, depending on the phase with which it is driven. A nonlinear numerical model of a Helmholtz resonator with an oscillating volume was then developed to simulate the experiments. Excellent agreement between the numer- ical and experimental results is found. Furthermore, insight into how to obtain maximum power absorption was provided by the numerical model and validated by the experiments. Finally, to optimise the phase in real-time (by minimising the amplitude of the pressure oscillations), active control of the back-plate vibration was experimentally investigated, and was found to give increased damping and to increase the effective frequency range. Copyright © 2008 by The authors.
Morgans AS, Annaswamy AM, 2008, Adaptive control of combustion instabilities for combustion systems with right-half plane zeros, Combustion Science and Technology, Vol: 180, Pages: 1549-1571
Illingworth SJ, Morgans AS, 2008, Adaptive control of combustion instabilities in annular combustors, ASME Turbo Expo
Illingworth SJ, Morgans AS, 2008, Adaptive control of combustion instabilities for unknown sign of the high frequency gain, AIAA Fluid Dynamics Conference
Dowling AP, Morgans AS, 2007, Passive and active control of combustion oscillations, Basics of Aero-Acoustics and Thermo-Acoustics Lecture Series, Publisher: Von Karman Institute for Fluid Dynamics
Morgans AS, Annaswamy AM, 2007, Adaptive control of combustion instabilities for non-minimum phase systems, ASME Turbo Expo, Publisher: ASME
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