Time–Frequency Analysis of Pressure Pulsation Signal in the Chamber of Self-Resonating Jet Nozzle

Abstract

In this paper, time–frequency (TF) characteristics of pressure pulsation in the self-resonating jet nozzle were thoroughly checked and analyzed by two TF analysis methods. The frequency spectrum including frequency-domain structure and approximate frequency-scope was obtained via the classical fast Fourier transform (FFT) method. Due to the typical nonstationary and time-varying nature, the FFT method is inefficient in analyzing such signals. TF analysis method was introduced to obtain the accurate instantaneous frequency (IF) of the self-resonating jet signal, which makes the quantitative analysis of the resonance frequency possible. In addition, a comparative study on the IF results were carried out by coupling the Morlet wavelet transforms, synchrosqueezed wavelet transforms (SWTs) and the modulus maximum methods together, and the coherence of frequency-domain structure was demonstrated. The result showed that SWT is good at acquiring the frequency distribution of the self-resonating jet with high readability and accuracy, and the TF analysis method is suitable for researching jet nozzle’s TF characteristics with high efficiency.