无压输水隧洞中受到闸门启闭而引起的明满交替流水力瞬变现象,通常会造成洞内的压力剧增,对工程安全运行造成威胁。为了探究城门洞型隧洞的明满交替流和明流过渡过程,实测了模型隧洞沿线断面水深或压力变化曲线,基于窄缝法原理,使用扩散法对实测工况进行数值模拟计算,将实测数据与计算结果进行了对比分析。研究表明:在下游初始水深逼近城门洞直墙高时,下游闸门突然关闭后,在大来流量下管路中出现压力瞬间陡增的完全明满流现象,水流向上游传播并伴随剧烈的掺气,在小来流量下表现为不掺气压力突升的临界明满交替流,回波造成二次压力剧增,断面压力达到峰值。窄缝扩散法对于从明流完全转化成满流的明满流过渡过程模拟效果较好,而对于临界明满流的模拟有较大的误差。无压流水力过渡过程数值模拟计算结果与实测值基本一致,反映了明渠水力过渡过程数学模型的合理性。研究成果可为深入研究这一复杂水力现象提供借鉴和参考。
Abstract
The operation of gates in non-pressure water conveyance tunnels often induces hydraulic transients in the form of free-surface-pressurized flow (mixed flow), which can lead to pressure surges that pose a threat to the project’s safe operation. An experimental investigation was conducted to study the hydraulic transition process of mixed flow and pressureless flow in a rectangular tunnel with an arched crown. Water depth or pressure measurements were taken along the length of the model tunnel under different flow conditions, and the results were compared with calculated values obtained using the diffusion method based on the narrow slot assumption. The experiments revealed a complete free-surface-pressurized flow regime, where the closure of the downstream gate caused a sharp increase in pipeline pressure when the initial downstream water depth approached the height of the vertical wall in the arched tunnel under high flow conditions. This process is accompanied by intense air entrainment and upstream flow propagation. Under low flow conditions, a critical mixed flow regime was observed, characterized by a sudden pressure rise without aeration. The water echo resulted in a secondary pressure spike, reaching its peak value. The research findings demonstrate that the narrow slot diffusion method could accurately simulate the complete free-surface-pressurized flow regime, but generates a larger error when simulating the critical regime. The calculated results and experimental data are in good agreement for the hydraulic transition process of pressureless flow, validating the rationality of the mathematical model.
关键词
城门洞型输水隧洞 /
明满流 /
窄缝法 /
数值模拟计算 /
试验验证
Key words
rectangular water conveyance tunnel with arch crown /
free-surface-pressurized flow /
narrow slot method /
numerical simulation /
model experiment
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