Hubei Key Laboratory of Waterjet Theory and New Technology, Wuhan University, Wuhan 430072, China
Self-resonating waterjet is a new type of waterjet technology that has been widely used for many practical applications. In order to further improve the performance of self-resonating waterjet, the Helmholtz nozzle was improved by replacing the upper part of a traditional contract structure with a venture tube one. This composite nozzle of a venturi tube structure and a Helmholtz resonator was proposed based on the working mechanism of self-resonating waterjet nozzles and the instability of cavitation flow in venturi tubes. Furthermore, the results were also compared with those generated by a conventional Helmholtz nozzle under the same conditions. The frequency of the pressure pulsation in the oscillating cavity and at the outlet was obtained and analyzed by the classical Fast Fourier transform (FFT) method. The results showed that the main frequency of the pressure oscillation rises to 2362.78Hz, and the peak and average values of the pressure are increased by 45% and 12.5% respectively at the outlet of the composite nozzle. In the oscillating cavity of composite nozzle, the pressure oscillations in the central region have higher frequencies and amplitudes, while near the wall are reversed.