梯形明渠–马蹄形隧洞过渡段流动形态与局部水头损失研究

Flow characteristics and minor losses in transition section from trapezoidal open channel to horseshoe-shaped tunnel

本文以新疆克拉玛依引水工程西千渠为背景，通过物理模型试验研究了从梯形明渠到马蹄形隧洞进口过渡段的水面衔接特点和局部水头损失规律。模型采用重力相似设计，比尺为1：25，由有机玻璃制成。在试验过程中，测量了流量在3．88～17．05L／s范围内水面线的纵向变化，发现当流量大于13．37L／s时，洞口水面壅高，洞内存在水面波动，分析认为是由侧壁收缩引起的水面紊动所致。根据水深变化和平均流速计算得到过渡段局部水头损失，发现其随水面收缩角增加呈先减小后增大的趋势，进口过渡段局部水头损失系数为0．19～1．24。针对原模型试验发现的问题，模型试验中延长了过渡段，对扭曲面段、矩形段长度进行了优化。模型改进后，水流平稳，波动减弱，局部水头损失系数减小至0．05～0．82。试验结果为实际工程梯形明渠到无压隧洞的过渡段设计提供了依据。

Flow characteristics and local losses in transition section from trapezoidal open channel to horseshoe-shaped tunnel has been studied and tested on a hydraulic scale model of the western main canal of water diversion project in Karamay. The model made ofplexiglass, had a geometric scale of 1/25 in accord with Froude similitude. Longitudinal water surface profiles were measured in steady flow conditions of flow rate range of 3.88 to 17.05 L/s. At a flow rate greater than 13.37 L/s, water level was rising rapidly near the tunnel entrance and fluctuating in the tunnel. This should be a phenomenon caused by the flow turbulences generated by wall contraction. Minor loss coefficients of the transition section in a range of 0.19 to 1.24 were calculated using the measured water surface profiles and cross-sectional average velocities. As the contraction angle of the transition increases, the minor losses were decreasing first and then increasing. To solve the problems with the original design of the tunnel found in our experiment, the transition section was lengthened and the lengths of warped surface channel and rectangular channel were optimized. Measurements show smooth streamlines and a reduction in water surface fluctuations in the modified transition, along with a reduction in its minor loss to a range of 0.05 to 0.82. The results are helpful to the design of transition section from trapezoidal open channel to horseshoe-shaped tunnel in real water diversion projects.