| 内容提要: |
To improve the measurement accuracy of sonic nozzle, the amplitude-frequency characteristic of pressure oscillation induced by vapor condensation was investigated. Experiment was performed based on a nozzle and adjustable humidification apparatus to obtain transient pressure signal. Then the signal feature extraction was implemented based on Morlet wavelet of which the parameters, bandwidth and central frequency, were optimized by minimizing the Shannon wavelet entropy. The time-frequency spectrums obtained from the continuous wavelet transform (CWT) show more information than that of fast Fourier transform (FFT), such as the change of amplitude and frequency with time. The results indicated that the pressure frequency is positively correlated with temperature and relative humidity, but negatively with pressure. |