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Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/jspui/handle/10054/12574

Title: Reduced-order modeling and dynamics of nonlinear acoustic waves in a combustion chamber
Authors: ANANTHKRISHNAN, N
DEO, S
CULICK, FEC
Keywords: solid rocket motors
amplitude limit-cycles
propellant rocket
pressure oscillations
instability
stability
systems
gas
Issue Date: 2005
Publisher: TAYLOR & FRANCIS LTD
Citation: COMBUSTION SCIENCE AND TECHNOLOGY, 177(2), 221-247
Abstract: For understanding the fundamental properties of unsteady motions in combustion chambers, and for applications of active feedback control, reduced-order models occupy a uniquely important position. A framework exists for transforming the representation of general behavior by a set of infinite-dimensional partial differential equations to a finite set of nonlinear second-order ordinary differential equations in time. The procedure rests on an expansion of the pressure and velocity fields in modal or basis functions, followed by spatial averaging to give the set of second-order equations in time. Nonlinear gasdynamics is accounted for explicitly, but all other contributing processes require modeling. Reduced-order models of the global behavior of the chamber dynamics, most importantly of the pressure, are obtained simply by truncating the modal expansion to the desired number of terms. Central to the procedures is a criterion for deciding how many modes must be retained to give accurate results. Addressing that problem is the principal purpose of this paper. Our analysis shows that, in the case of longitudinal modes, a first-mode instability problem requires a minimum of four modes in the modal truncation, whereas, for a second-mode instability, one needs to retain at least the first eight modes. A second important problem concerns the conditions under which a linearly stable system becomes unstable to sufficiently large disturbances. Previous work has given a partial answer, suggesting that nonlinear gasdynamics alone cannot produce pulsed or "triggered" true nonlinear instabilities, that suggestion is now theoretically established. Also, a certain form of the nonlinear energy addition by combustion processes is known to lead to stable limit cycles in a linearly stable system. A second form of nonlinear combustion dynamics with a new velocity coupling function that naturally displays a threshold character is shown here also to produce triggered limit-cycle behavior.
URI: http://dx.doi.org/10.1080/00102200590900219
http://dspace.library.iitb.ac.in/xmlui/handle/10054/12574
http://hdl.handle.net/10054/12574
ISSN: 0010-2202
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