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3. Multi-scale Physics of Rotating Detonation Engines: Autosolitons and Modulational Instabilities

Author

Koch, James, Kurosaka, Mitsuru, Knowlen, Carl, and Kutz, J. Nathan

Subjects
Physics - Fluid Dynamics, Nonlinear Sciences - Pattern Formation and Solitons
Abstract

We develop a theoretical framework that predicts and fully characterizes the diverse experimental observations of the nonlinear, combustion wave propagation in a rotating detonation engine (RDE), including the nucleation and formation of combustion pulses, the soliton-like interactions between these combustion fronts, and the fundamental, underlying Hopf bifurcation to time-periodic modulation of the waves. In this framework, the mode-locked structures are classified as autosolitons, or stably-propagating nonlinear waves where the local physics of nonlinearity, dispersion, gain, and dissipation exactly balance. We find that the global dominant balance physics in the RDE combustion chamber are dissipative and multi-scale in nature, with local fast scale (nano- to microseconds) combustion balances generating the fundamental mode-locked autosoliton state, while slow scale (milliseconds) gain-loss balances determine the instabilities and structure of the total number of autosolitons. In this manner, the global multi-scale balance physics give rise to the stable structures - not exclusively the frontal dynamics prescribed by classical detonation theory. Experimental observations and numerical models of the RDE combustion chamber are in strong qualitative agreement with no parameter tuning. Moreover, numerical continuation (computational bifurcation tracking) of the RDE analog system establishes that a Hopf bifurcation of the steadily propagating pulse train leads to the fundamental instability of the RDE, or time-periodic modulation of the waves. Along branches of Hopf orbits in parameter space exist a continuum of wave-pair interactions that exhibit solitonic interactions of varying strength., Comment: 18 pages, 13 figures

Published
2020
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4. Mode-Locked Rotating Detonation Waves: Experiments and a Model Equation

Author

Koch, James, Kurosaka, Mitsuru, Knowlen, Carl, and Kutz, J. Nathan

Subjects
Nonlinear Sciences - Pattern Formation and Solitons, Physics - Fluid Dynamics
Abstract

Direct observation of a Rotating Detonation Engine combustion chamber has enabled the extraction of the kinematics of its detonation waves. These records exhibit a rich set of instabilities and bifurcations arising from the interaction of coherent wave fronts and global gain dynamics. We develop a model of the observed dynamics by recasting the Majda detonation analog as an autowave. The solution fronts become attractors of the engine; i.e., mode-locked rotating detonation waves. We find that detonative energy release competes with dissipation and gain recovery to produce the observed dynamics and a bifurcation structure common to driven-dissipative systems, such as mode-locked lasers., Comment: 10 pages, 11 figures

Published
2019
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44. Direct space launch using ram accelerator technology.

Author

Knowlen, Carl and Bruckner, Adam P.

Subjects
*HYPERVELOCITY guns, *PROJECTILES -- Speed
Abstract

The ram accelerator is a hypervelocity launcher that operates on the principles of a chemically propelled intube ramjet. This concept is unique in its potential to launch large-scale projectiles to Earth orbit velocity while controlling the in-tube acceleration. Experimental investigation of the operating characteristics of the ram accelerator at several different facilities around the world has resulted in the demonstration of many key gas dynamic principles and logistical aspects needed for a space launch facility. These experimental results have been used to determine the parameters for a ram accelerator system capable of launching a 2000 kg projectile having an effective density of 1000 kg/m[sup 3] at velocities of 6-8 km/s, without exceeding 1500 g. The results of this study indicate that a multi-stage ram accelerator system would be an effective means to launch large-scale projectiles into orbit. [ABSTRACT FROM AUTHOR]

Published
2001

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