壁面粗糙度突变对明渠流速分布的影响

Effects of Sudden Change of Bed Roughness on Velocity Distribution in Open-Channel Flow

应用激光测速仪在矩形水槽中实测了光滑和粗糙底板以及粗糙度突变情况下的时均流速分布,根据实测资料分析了粗糙度突变以后流速在内区和外区沿程变化情况,得到粗糙度改变后发展过程中的紊流,其流速在黏性底层区比粗糙度改变前和充分发展的紊流小,而在对数律区其流速增长最快。对y/H>0．2的外区,发展中的紊流与充分发展的紊流在外区流速分布有明显的不同,其不同表现可从尾流强度系数∏看出,∏值变化从负值到正值,当形成新的均匀流后∏值趋于常数。

A Laser Doppler Velocimeter was used to measure the hour-faveraged velocity of water in a rectangular flume with the wall of smooth, rough and sudden change （from smooth to rough） in bed. According to the data, the change of the velocity was analyzed in inner and outer regions after sudden changed roughness. The turbulence after roughness change was gotten. Its velocity was smaller in viscous boundary layer than before roughness change and full-developed while it increased fastest in logarithmic distribution. In outer region with y/H greater than 0.2, velocity distributions were different for developing turbulence and full-developed turbulence, which could be seen from dimensionless parameter П with its value changed from negative to positive and ran to a constant when formed new even flow.