明渠收缩过渡段流速分布及紊动特性试验

受地形、地质等条件影响，明渠收缩过渡段在输水工程中十分常见，过渡段长度过短，会导致水面波动，水体紊动加剧。为研究明渠不同长度过渡段内纵向时均流速及紊动强度的分布规律，通过室内模型试验，利用二维电磁流速仪ACM2-RS测量了渠道内沿程中垂线不同深度处瞬时流速。试验结果表明:收缩段内，纵向时均流速沿程增加，紊动强度沿程降低，遵循涡旋的拉伸机制和线性扭曲理论；受二次流影响，最大流速位于水面以下，且最大流速的位置随二次流作用的增强而降低；不同长度过渡段对下游纵向流速分布和紊动强度影响不同，过渡段越短，下游水流紊动越强，但非渠底附近紊动强度沿垂向先减后增的规律不变。

Experimental study on velocity profile and turbulence characteristics in open channel contractions

Channel contractions are widely used in water diversion projects due to topographical and geological limitations. Short transitions would lead to water surface fluctuations and higher turbulence. To investigate the velocity and turbulence characteristics along transitions of different length, laboratory experiments were carried out using a two-dimensional electromagnetic current meter ACM2-RS. Results show that the longitudinal mean velocity increases along the centerline of the contraction while the longitudinal turbulence intensity decreases, which can be explained by vortex stretching mechanism and linear distortion theory. Influenced by secondary currents, the maximum velocity occurs below the surface. The stronger secondary circulation is, the lower the maximum velocity is located. Contractions of different length affect the velocity profiles and turbulence intensities downstream differently. Shorter contractions lead to higher magnitude of turbulence intensity downstream, while its vertical distribution remains the same in the region away from the bed, which decreases first and then increases with the vertical position going up.