Hiroaki Hyodo

Derivation of coupling conditions of amplitude death in delay-coupled thermoacoustic oscillators

Amplitude death, meaning the stabilization of an unstable equilibrium state, appears in delay coupled oscillators even if the oscillators have the same frequency. In this study, we aim to stop thermoacoustic oscillations by the amplitude death induced by delay. Thermoacoustic oscillations in combustors of gas turbine engines cause serious damage to the engine. Development of the method for suppressing thermoacoustic oscillations is urgent necessity. Recently, the amplitude death in the thermoacoustic oscillators was demonstrated by using delay and diffusive couplings. The delay coupling was introduced by gas-filled tubes. The experimental death regions were compared with the delay-coupled van der Pol systems and qualitative agreement was achieved, but the acoustic feature of the connecting tube was not considered. For a full acoustical modeling of the coupled thermoacoustic oscillator, we modelled two thermoacoustic oscillators coupled by connecting tubes by the linear acoustic theory based on hydrodynami...

A looped-tube traveling-wave engine with liquid pistons

This report describes the operation of a liquid piston engine that uses thermoacoustic spontaneous oscillations of liquid and gas columns connected in series to form a loop. Analysis of the analogous mass-spring model and the numerical calculation based on hydrodynamic equations shows that the natural mode oscillations of the system allow the working gas to execute a Stirling thermodynamic cycle. Numerical results of the operating temperature difference were confirmed from experimentally obtained results.

Amplitude death in delay-coupled thermoacoustic oscillators

A phenomenon of thermoacoustic oscillation is seen as an undesirable vibration in combustion engineering as it can cause serious damage to the combustor. Lots of methods such as controlling a secondary fuel supply and addition of Helmholtz resonators are proposed to suppress the oscillations, but they often become complicated. As a simple and reliable method, we try to make use of mutual interaction of the coupled thermoacoustic oscillators to stop oscillations completely. It has been demonstrated in the system of coupled electrical circuits that “amplitude death,” meaning the stabilization of zero amplitude states, is induced by time-delay coupling even when the oscillators have the same frequency. In this study, we introduce the time-delay coupling in thermoacoustic oscillators by using hollow tubes. In the tube coupling, the sound propagation time through the tube corresponds to the delay time, while the tube diameter controls the coupling strength. The condition of amplitude death is experimentally fo...

Effects of heat conduction in wall on thermoacoustic wave propagation in a gas-filled, channel subject to temperature gradient

This paper examines effects of heat conduction on acoustic wave propagation in a gas-filled, channel subject to temperature gradient axially and extending infinitely. Within the narrow-tube approximation in the sense that a typical axial length is much longer than a channel width, the system of linearized equations for the gas supplemented by the equation for heat conduction in the solid wall is reduced to a thermoacoustic-wave equation for excess pressure uniform over the cross-section. This is the one-dimensional equation taking account of the wall friction and the heat flux at the wall surfaces given in the form of hereditary integrals. This equation is derived rigorously under the narrow-tube approximation, and is valid for any form of disturbances. The effects of heat conduction appear in the form proportional to the square root of the product of the ratio of the heat capacity per volume of the gas to that of the solid, and the ratio of the thermal conductivity of the gas to that of the solid. Althou...