Effects of Time Delay and System Noise Upon Active Control of Unstable Combustors PDF Download
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Author: Clifford E. Johnson
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Clifford E. Johnson
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
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ISBN:
Category :
Languages : en
Pages : 0
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To improve the performance of practical active control system (ACS) for unstable combustors, the effects of system noise and ACS time delay upon combustion instabilities and the ACS performance were studied. Experimental and theoretical studies of an uncontrolled liquid fueled combustor showed that the presence of noise apparently causes the 'beating' phenomenon and 'phase jumps' exhibited by the unstable pressure oscillations. Next, experiments in which the ACS was operated in open loop showed that the delay between the command signal to the ACS actuator and the response of the combustor pressure is of the order of two cycles of the oscillations. Subsequent simulations showed that this large time delay adversely affects the ACS performance. Furthermore, simulations and experimental studies of the ACS performance when operated in closed loop showed that the 'beating' phenomenon depends upon the complex relationship between the noise and the process that drives the instability, they poorly attenuate the random component of these oscillations, which is related to the magnitude of the RMS of the pressure oscillations. The combined effects of the long time delay in the control loop cause this.
Author: C. Seywert
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Longitudinal pressure oscillations in a combustion chamber are studied theoretically by means of a low order model obtained by systematic reduction from a complete representation. The formulation is based on the derivation of a generalized wave equation that accommodates the effects of mean flow, combustion, noise and control action. By using spatial averaging, the equations describing the dynamics of the chamber are reduced to a set of coupled ordinary differential equations. The form of the resulting equations is particularly convenient for model reduction and for introducing feedback control terms, while retaining all physical processes. Active feedback control of longitudiual instabilities is then introduced by using the same formulation, rewritten in statespace form. The broad objective of control simulations covered here is to investigate in a unified fashion various aspects of the problem. These include the influences of noise, parameter uncertainties, unmodeled modes and time-delay. A criterion is derived that guarantees the stability of the controlled closed-loop system in the presence of those quantities. The particular controller used here is based on a standard LQR design, but any design technique can be used as long as the stability criterion is fulfilled.
Author:
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Category : Aeronautics
Languages : en
Pages : 656
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Author: Silviu-Iulian Niculescu
Publisher: Springer Science & Business Media
ISBN: 3642184820
Category : Science
Languages : en
Pages : 445
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In the mathematical description of a physical or biological process, it is a common practice \0 assume that the future behavior of Ihe process considered depends only on the present slate, and therefore can be described by a finite sct of ordinary diffe rential equations. This is satisfactory for a large class of practical systems. However. the existence of lime-delay elements, such as material or infonnation transport, of tcn renders such description unsatisfactory in accounting for important behaviors of many practical systems. Indeed. due largely to the current lack of effective metho dology for analysis and control design for such systems, the lime-delay elements arc often either neglected or poorly approximated, which frequently results in analysis and simulation of insufficient accuracy, which in turns leads to poor performance of the systems designed. Indeed, it has been demonstrated in the area of automatic control that a relatively small delay may lead to instability or significantly deteriora ted perfonnances for the corresponding closed-loop systems.
Author: Jackie H. Crawford (III.)
Publisher:
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Category : Aircraft gas-turbines
Languages : en
Pages :
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A full Strouhal number thermo-acoustic model is purposed for the feedback control of self excited noise driven combustors. The inclusion of time delays in the volumetric heat release perturbation models create unique behavioral characteristics which are not properly reproduced within current low Strouhal number thermo acoustic models. New analysis tools using probability density functions are introduced which enable exact expressions for the statistics of a time delayed system. Additionally, preexisting tools from applied mathematics and control theory for spectral analysis of time delay systems are introduced to the combustion community. These new analysis tools can be used to extend sensitivity function analysis used in control theory to explain limits to control effectiveness in self-excited combustors. The control effectiveness of self-excited combustors with actuator constraints are found to be most sensitive to the location of non-minimum phase zeros. Modeling the non-minimum phase zeros correctly require accurate volumetric heat release perturbation models. Designs that removes non-minimum phase zeros are more likely to have poles in the right hand complex plane. As a result, unstable combustors are inherently more responsive to feedback control.
Author:
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Category : Mechanical engineering
Languages : en
Pages : 438
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Author: Tim C. Lieuwen
Publisher: Cambridge University Press
ISBN: 1108841317
Category : Science
Languages : en
Pages : 533
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Explore a unified treatment of the dynamics of combustor systems, including acoustics, fluid mechanics, and combustion in a single rigorous text. This updated new edition features an expansion of data and experimental material, updates the coverage of flow stability, and enhanced treatment of flame dynamics. Addresses system dynamics of clean energy and propulsion systems used in low emissions systems. Synthesizing the fields of fluid mechanics and combustion into a coherent understanding of the intrinsically unsteady processes in combustors. This is a perfect reference for engineers and researchers in fluid mechanics, combustion, and clean energy.
Author: Anna Schwarz
Publisher: Springer Science & Business Media
ISBN: 3642020380
Category : Technology & Engineering
Languages : en
Pages : 304
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November, 2008 Anna Schwarz, Johannes Janicka In the last thirty years noise emission has developed into a topic of increasing importance to society and economy. In ?elds such as air, road and rail traf?c, the control of noise emissions and development of associated noise-reduction techno- gies is a central requirement for social acceptance and economical competitiveness. The noise emission of combustion systems is a major part of the task of noise - duction. The following aspects motivate research: • Modern combustion chambers in technical combustion systems with low pol- tion exhausts are 5 - 8 dB louder compared to their predecessors. In the ope- tional state the noise pressure levels achieved can even be 10-15 dB louder. • High capacity torches in the chemical industry are usually placed at ground level because of the reasons of noise emissions instead of being placed at a height suitable for safety and security. • For airplanes the combustion emissions become a more and more important topic. The combustion instability and noise issues are one major obstacle for the introduction of green technologies as lean fuel combustion and premixed burners in aero-engines. The direct and indirect contribution of combustion noise to the overall core noise is still under discussion. However, it is clear that the core noise besides the fan tone will become an important noise source in future aero-engine designs. To further reduce the jet noise, geared ultra high bypass ratio fans are driven by only a few highly loaded turbine stages.
Author: Shozo Koshigoe
Publisher:
ISBN:
Category :
Languages : en
Pages :
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