Investigation of the impact characteristics and pulse mechanism of a self-excited aspiration pulsed jet device

Abstract

In this paper, based on the traditional low-frequency self-excited oscillation pulsed jet device, a self-excited aspiration pulsed jet device is designed. For the structural parameters, including the aspiration capacity, impact characteristics, and pulse generation mechanism, the jet impingement is analyzed experimentally under the aspiration and non-aspiration conditions. It was found that, compared to the non-aspiration condition, the maximum aspiration capacity, the increase of instantaneous impact force, and the obvious pulse period, which is between 1 and 2 s, can be obtained under appropriate structural device parameters. The db10 orthogonal wavelet and the empirical mode decomposition methods can decompose instantaneous impact force into time-varying and fluctuating impact forces. However, under different confining pressures, each method has its own advantages in extracting the time-varying impact force. In addition, after aspiration, the confining pressure and target distance have little effect on the pulse frequency of the time-varying impact force, while higher confining pressure and larger target distance result in smaller pulse amplitude. Under different confining pressures and target distances, after aspiration, the time-average impact force at and near the target center increases, while far away from the target center it decreases. Moreover, after aspiration, the fluctuation amplitude and intensity of the fluctuating impact force increase, and the confining pressure has little effect on the pulse frequency. However, higher confining pressure results in smaller fluctuation amplitude, intensity, and energy spectral density. After aspiration, subsonic and supersonic water flows are formed inside the device. In addition, it was found that there is a relationship between the aspiration capacity, the time-variation pressure of the collision body measuring point, and the impact force. Based on this relation, the pulse generation mechanism of the device is revealed.