明渠自掺气水流中气泡尺寸和个数的分布

Distribution of the bubble chord length and numbers in self-aerated open channel flows

针对目前有关明渠自掺气水流中气泡尺寸和个数分布的实测资料极少的现状,本文采用针式掺气流速仪在坡度为45°的陡槽上对三种流量下自掺气水流沿程四个不同断面中部的气泡尺寸、个数进行了测量和统计分析。三种流量下,气泡的最小弦长、最大弦长、平均弦长自槽底向上都呈增大趋势,其中最小弦长存在一上限值,靠近槽底大概10%水深范围内实测的气泡平均弦长小于1.5mm。距槽底1mm处,个数比例≥5%的气泡弦长≤1mm,而个数份额≥10%的气泡弦长≤0.5mm。气泡的弦长不同,其个数份额沿水深的变化趋势不同,弦长在0.4mm^2mm范围内的气泡的个数比例在0.09~0.15倍水深处(由槽底向上算起)达到最大值,而弦长在2mm^10mm范围内的气泡的个数比例在0.7~0.85倍水深处(由槽底向上算起)达到最大值。

There are little data reported about the distribution of the bubble size and the bubble number in selfaerated open channel flows. Experiments are performed with different discharges at four sections along a steep flume with a 45° slope. The bubble sizes and numbers are recorded by using a tip aerated probe on the centerline. The minimum, maximum, and mean bubble chord lengths increase from the bottom to the free surface. The minimum chord length is limited at 0.06 millimeters and the mean chord length is under 1.5 millimeters in the range of 10 % water depth near the bottom. The bubbles chord lengths are less than or equal to 1 millimeters when their proportions are greater than or equal to 5 %, the other corresponding relationships is ≤ 0.5 millimeters and ≥ 10%. The variety trends of bubble number proportions are different as bubble chord length varies. When their chord lengths range between 0.4 millimeters and 2 millimeters （or 2 millimeters and 10 millimeters）, bubbles number proportions reach maximum near 0.12 （or 0.78） times water depth（from bottom to surface）.