表面糙率与明渠紊流猝发现象

采用流场综合分析法将流动显示与计算机图像处理相结合，在不同表面糙率的条件下重点研究紊流的猝发形态和特性.研究表明，表面粗糙度对明渠紊流拟序结构的特征有重要影响.猝发喷射角约为35～75度，随表面粗糙雷诺数增加趋于增大；喷射高度可达1/8水深；喷射尺度和清扫尺度均有随雷诺数增大的趋势.增大粗糙雷诺数明显增加了多头群体喷射现象，以致形成“喷射垫层”，清扫须在床面附近逐步深入推进；由于大雷诺数增加了群喷延续时间及清扫与喷射相持时间，无量纲猝发周期明显加大.分析还表明，在喷射迸发区域水体动能和紊流耗散率较床面附近提高了数倍.

Bed surface roughness and bursting phenomena in open channel

The technology of flow field visualization is combined with the image analysis to study the effect of bed surface roughness Reynolds number on flow pattern and characteristics of turbulent bursting phenomenon. Series of experiment are carried out in an open channel flume. The result shows that bed surface roughness may significantly affects the characteristics of turbulent coherent structures. The ejection angle is ranging from 35°to 75°and tends to increase if roughness increases. The ejection height may as high as 1/8 of flow depth. The scale of ejection and sweeping tends to increase as the Reynolds number increases. The increase of roughness Reynolds number results in the increase of multi-ejection phenomenon forming the ejection cushion to prevent from sweeping and reduce the non-dimensional bursting period. Since the duration of multi-ejection and sweeping increases during high Reynolds number, the non-dimensional bursting cycle will be remarkably lengthened. The analysis also shows that the kinetic energy and turbulent dissipation rate in ejection breaking-out region is much higher than that in the vicinity of bed surface.