Effects of Reversed Shock Waves on Operation Mode in H2/O2 Rotating Detonation Chambers

Operation modes are an important topic in the research of Rotating Detonation Chamber (RDC) as it can affect the stability of RDC. However, they have not been discussed in detail due to the limitation of measurement means in experiments. The aim of this research is to investigate the mechanism of different operation modes by numerical simulation. In this paper, a numerical simulation for RDCs with separate injectors is carried out. Different operation modes and mode switching are analyzed. There is a series of reversed shock waves in the flow field. It was found that they have great effects on operation mode and mode switching in RDCs. A reversed shock wave can transit into a detonation wave after passing through isolated fresh gas region where fresh gas and burnt gas distribute alternatively. This shock-to-detonation transition (SDT) phenomenon will influence the ignition process, contra-rotating waves mode and mode switching in RDCs. SDT makes the number of detonation wave increases, resulting in multi-wave mode with one ignition. Moreover, quenching of detonation waves after collision and SDT after passing through isolated fresh gas region are the mechanism of contra-rotating waves mode in RDCs with separate injectors. In addition, when the inlet total temperature increases, a shock wave is easier to transit into a detonation wave. The distance that a shock wave travels before SDT decreases when temperature increases. This will result in mode switching. Therefore, SDT determines that there is a lower bound of detonation wave number.

Dynamic mode decomposition analysis of rotating detonation waves

A rotating detonation combustor (RDC) is a novel approach to achieving pressure gain combustion. Due to the steady propagation of the detonation wave around the perimeter of the annular combustion chamber, the RDC dynamic behavior is well suited to analysis with reduced-order techniques. For flow fields with such coherent aspects, the dynamic mode decomposition (DMD) has been shown to capture well the dominant oscillatory features corresponding to stable limit-cycle or quasi-periodic behavior within its dynamic modes. Details regarding the application of the technique to RDC—such as the number of frames, the effect of subtracting the temporal mean from the processed dataset, the resulting dynamic mode shapes, and the reconstruction of the dynamics from a reduced set of dynamic modes—are analyzed and interpreted in this study. The DMD analysis is applied to two commonly observed operating conditions of rotating detonation combustion, viz., (1) a single spinning wave with weak counter-rotating waves and (2) a clapping operating mode with two counter-propagating waves at equal speed and strength. We show that care must be taken when applying DMD to RDC datasets due to the presence of standing waves (expressed as either counter-propagating azimuthal waves or longitudinal pulsations). Without accounting for these effects, the reduced-order reconstruction fails using the standard DMD approach. However, successful application of the DMD allows for the reconstruction and separation of specific wave modes, from which models of the stabilization and propagation of the primary and counter-rotating waves can be derived.

Resonant excitation of rotating waves in annular zones

A method and a device are developed for exciting powerful resonant acoustic rotating waves in a gaseous or liquid flowing working medium located in the annular zone between the rotor and stator, for its vibration treatment. Keywords: vibration treatment, vibrations, natural frequency, vibration form, waves, acoustic vibrations, resonance. [email protected]

Investigation of rotating detonation fueled by pre-combustion cracked kerosene under different channel widths

In this study, the effects of channel widths on the characteristics of the rotating detonation wave (RDW) were investigated. Pre-combustion cracked kerosene and 50% oxygen-enriched air were taken as the propellant. Keeping the outer diameter ( D = 150mm) constant, the channel widths ( W) of the combustor range from 15 mm to 50 mm in the experiments. The results indicate that the time for the formation of a stable RDW is longer under the wider channel, while the velocity of the RDW increases significantly with a wider channel. Increasing the ER has a positive effect on the wave velocity and the flow rate has little effect on wave velocity. The wave pressure increases under the higher ER and flow rate. Under the same flow rate and ER, the RDW pressure tends to reach the maximum value when the channel width is 25 mm, and the pressure range is 2 bar to 6 bar. Five kinds of the RDW modes were observed in the experiments, namely the failure “pop-out”, single-wave mode, two-counter rotating waves mode, and two-co rotating waves mode. The two-counter rotating waves mode seems to be an intermediate mode of single-wave mode and two-co rotating waves mode in the conducted experiments, and the multi-wave mode is more likely to occur under the narrower channel and the higher oxygen content.

Solitary states in adaptive nonlocal oscillator networks

In this article, we analyze a nonlocal ring network of adaptively coupled phase oscillators. We observe a variety of frequency-synchronized states such as phase-locked, multicluster and solitary states. For an important subclass of the phase-locked solutions, the rotating waves, we provide a rigorous stability analysis. This analysis shows a strong dependence of their stability on the coupling structure and the wavenumber which is a remarkable difference to an all-to-all coupled network. Despite the fact that solitary states have been observed in a plethora of dynamical systems, the mechanisms behind their emergence were largely unaddressed in the literature. Here, we show how solitary states emerge due to the adaptive feature of the network and classify several bifurcation scenarios in which these states are created and stabilized.