基于连续小波分析的明渠恒定均匀流紊动尺度研究

Turbulence scale analysis of steady uniform open channel flow based on the continuous wavelet transform

对明渠紊流的紊动尺度和相干结构的深入认识是进一步分析水流能量传递、物质输送的基础。本文在水槽中开展了光滑床面、粗糙定床及粗糙动床3种不同边界条件的水流试验,首先对试验时均流速分布、紊动强度及雷诺应力分布与现有成果进行了对比,然后利用连续小波分析对各组试验不同高程处的纵向、垂向流速及雷诺应力进行了系统分析,对比了采用不同时间长度数据和小波基函数选取对分析结果的影响,并对各组试验的紊流含能尺度沿水深的分布进行了研究。结果表明,Mexican hat小波基函数在利用连续小波对紊流数据分析时具有较好的效果;床面粗糙度及推移质运动对明渠流紊动相干结构影响不大,3种床面最大含能涡旋的时间尺度均为0.3~1s。

Analysis on turbulent scales and coherent structures is one of the bases for further study of tur-bulence energy transfer,material conveying and sediment transport in the open channel flow. Three runs ofexperiments with different boundary conditions,namely smooth bed,fixed rough bed and rough bed withslightly bed load movement,were conducted in a flume. Firstly,the mean velocity profile,turbulence inten-sity and Reynolds stress distribution of each test were compared with the existing results. Then the energet-ic vortex detection of the longitudinal velocity,vertical velocity and the Reynolds stress in different eleva-tion by using the continuous wavelet transform were computed. The effect of selection on length of time da-ta and different wavelet function in wavelet transform for the calculation results were also analyzed. Finally,the maximum energetic turbulent scales along the water depth were studied. The results show that the wave-let base of Mexico hat function is better than other bases on continuous wavelet analysis of the open chan-nel turbulent flow;the roughness and bed load movement have little effect on the turbulent coherent struc-ture in the open channel flow;the energetic vortex time scales are 0.3~1s in all the three runs of experi-ments.