基于局域波分解的循环射流混合槽内压力脉动信号时频特性分析

为了探讨循环射流混合槽射流混合区内瞬态流动特性，在Re=3660~32940范围内利用动态数据采集系统对射流混合区内不同轴向、径向和周向位置的瞬态脉动压力进行了测量，并采用基于局域波分解的方法分析了循环射流混合槽内压力脉动信号的时频分布。研究表明：瞬态压力波动信号的波动能量分布随瞬时频率的提高明显降低；在θ_m=π/6和π/3时，频率集中分布在为0~0.25Hz，而θ_m=π/4和θ_m=5π/12时，瞬时波动频率主要分布在0~6Hz和0~20Hz。低雷诺数下流体运动随机性频繁，Re=3660时存在32Hz，25Hz，7Hz和5Hz等多个频率集中分布段，而Re=18300和Re=25620时频率范围为0~8Hz和0~3Hz。随着测量位置z/H增加，0~1Hz内低频能量比例先减小然后增加再减少；z/H=0.85时受到自由液面的影响，集中能量频率分布范围较其他轴向位置要广，且0~5Hz低频能量比例减少。

Analysis of the time-frequency attributes of pressure fluctuation signals in a circulating jet tank based on local wave decomposition

In order to investigate the instantaneous flow characteristics in the jet mixing zones of a circulating jet tank (CJT), a dynamic data acquisition system was employed to measure the instantaneous pressure fluctuation signals (PFS) in the Reynolds number (Re) range 3660-32940, at different axial, radial and circumferential positions. Frequency spectra were evaluated based on the local wave decomposition. The fluctuation energy distribution of instantaneous PFS was found to decrease markedly with increasing instantaneous frequency. For positions θ_m= π/6 and θ_m = π/3 the energy distributions were in the range 0-0.25Hz, while it was in the range 0-6Hz and 0-20Hz for θ_m= π/4 and θ_m =5π/12, respectively. The degree of fluid irregularity increased at low values of Re. Four concentrated energy bands at 32Hz, 25Hz, 7Hz and below 5Hz existed for Re=3660. However the energy was distributed in the range 0-8Hz and 0-3Hz for Re=18300 and Re=25620, respectively. With increasing values of z/H, the energy ratio in the range 0-1Hz initially decreased, then increased and finally decreased again. The energy was distributed in a relatively wide frequency brand affected by the free liquid for z/H=0.85 and the energy ratio at low frequency (0-5Hz) decreased.