循环射流混合槽压力波动时间序列差异性分析

Difference analysis of pressure fluctuation time series in the circulating jet tank

为了研究循环射流混合槽内压力波动信号的前向和后向符号时间序列的动力学特征的差异性,利用等概率原则对PFS(pressure fluctuation signals)时间序列进行符号化转换,通过修正的Shannon熵选取最佳符号集大小和子序列长度。利用子序列编码图、时间不可逆转性、秩次图和秩次距离等参数对PFS时间序列进行STSA(symbolic time series analysis)研究。研究结果表明:修正的Shannon熵最小时确定优化符号化参数为n=2和L=10。前向与后向时间序列的子序列编码分布相似但其频数不等,表明CJT(circulating jet tank)内湍流流动呈现多尺度混沌确定性特征。PFS的时间不可逆性值随着周向角的增加不断增加,随z/H的增大呈现先降低再上升最后降低的趋势,随雷诺数的增加呈现"W"型分布。时间不可逆性值与秩次距离对PFS前后向序列动力学特征的差异性判断相互吻合。

In this study, we investigated the differences in the flow dynamic characteristics in forward and backward time series of pressure fluctuation signals （ PFS） in the circulating jet tank （ CJT） . We used the principle of equiv-alent possibility to symbolically transform the PFS time series. We also used modified Shannon entropy to choose the optimal parameters, including symbolic set size n and subsequence length L . We performed a symbolic time series analysis （ STSA） for the PFS time series using a sequence coding histogram, time irreversibility, a rank order fig-ure, and rank order distance. The results show that the symbolic set size n = 2 and subsequence length L = 10 a-chieved the minimum of modified Shannon entropy. The non-uniform frequency distributions of forward and back-ward sequence codes are similar, which indicates the existence of multi-scale chaotic deterministic characteristics in the dynamical system of the CJT. The time irreversibility value increases with increasing circumference angles. First it decreases, then increases, and finally decreases again with increasing z/H . It also shows a W-type distribution with increasing the Reynolds number. Our difference evaluation results by time irreversibility have good agreement with the rank order distance of the forward and backward time series of the PFS.