Time/frequency domain analysis of detonation wave propagation mechanism in a linear rotating detonation combustor

Abstract

Controlling the rotating detonation combustor (RDC) is crucial for enhancing propulsion system safety, efficiency, and overall performance. Swift and precise identification of the operational mode of RDC is of great significance for refining the propulsion dynamics of detonation-based technologies. In this study, two-dimensional numerical simulations are performed to investigate time-domain characteristics and frequency-domain characteristics of various operational modes of the RDC, hydrogen–air mixtures are used as fuel, and fast Fourier transformation (FFT) is applied to the analysis of frequency-domain. The alteration of the RDC operational mode is achieved through adjustments to the chemical equivalent ratio (ER) of the fuel, spanning from 0.52 to 3.50. Our findings reveal four distinct operational modes within this equivalent ratio range: ignition failure (ER ≤ 0.52 and ER ≥ 3.50), collision failure (ER = 0.85, 1.60 and 1.65), single wave (0.53 ≤ ER ≤ 0.80 and 1.70 ≤ ER ≤ 3.40) and multiple wave mode (0.90 ≤ ER ≤ 1.50). For the ignition failure mode, the detonation waves in RDC decouple from the flame and fail after ignition. In the collision failure mode, the inability of detonation waves to propagate sustainably within the RDC is evident. Frequency-domain analysis underscores the significance of a characteristic low-frequency (0.3 kHz) in distinguishing this mode from others. For single wave mode, it represents the steady and continuous propagation of a detonation wave in the RDC. Frequency-domain analysis reveals characteristic frequencies approximately equal to integer multiples of the propagation frequency (fD), where fD ∼ 10fD serves as the primary characteristic frequencies. The multiple wave mode can be categorized into two subtypes: the forward and reverse single detonation waves appear alternately or the forward and reverse single detonation waves finally co-direction double detonation waves. In the former subtype, characteristic frequencies are integer multiples of the fD, but the amplitude distribution is different with single wave mode. In contrast, primary characteristic frequencies of the latter subtype are fD ∼ 4fD, accompanied by two adjacent characteristic frequencies near each integer multiples of fD. These findings promise advancements in the controllability of RDC and lay the foundations for the development of RDC control systems.