采用Bently Hammer软件分析了事故工况运行条件下奇台高压自流输水工程5种不同支管布置方案下的水力过渡过程。结果表明,在符合支管额定供水量的前提下,小管径支管并联布置代替单根大管径支管输水,能有效减少水锤波在管内反射、叠加次数,降低输水系统水锤压力,缩短压力波动时长。并联支管数从2根增至5根的过程中,最危险事故工况下主管、支管内最大水锤压力相较于单根大管径输水方案最大减幅为10.32%和48.75%;各事故工况下主、支管管内压力波动时长最大减小了63.16%和46.15%,同时消除管线负压力水头防护负压力水锤。研究发现当支管与支管连接位置处主管管径比值(β)满足0.12<β<0.28区间时,能稳定输水系统水力过渡过程又兼具经济实用性。

[Objective] Appropriately reducing the diameter of branch pipes is an effective way to lower the superimposed water hammer pressure in water conveyance systems. However, there is limited research on how replacing a single large-diameter branch pipe with multiple smaller parallel branch pipes affects the hydraulic transient process in such systems. Moreover, there is a lack of research on how to design the diameters of these parallel branches to minimize hydraulic transients while maintaining flow requirements and ensuring economic efficiency. Based on the Qitai high-head gravity-flow water conveyance project, we investigated the impact of branch pipe arrangement on hydraulic transients and proposes principles for determining branch pipe diameters. [Methods] Using numerical simulation, we compared the hydraulic transient behavior in complex pipelines with a single branch pipe versus multiple small-diameter parallel branches, and examined the impact of parallel arrangements on water hammer pressure and pressure fluctuation duration, summarized the design method for branch pipe diameters in parallel schemes, and verified the engineering applicability of the conclusions using a real-world case. [Results] When the number of parallel branch pipes increased from 2 to 5, the maximum positive pressure head in both main and branch pipes significantly decreased under various scenarios. Under the most critical condition, the maximum water hammer pressure was reduced by 10.32% in the main pipe and 48.75% in the branch pipes, respectively, compared to the single large-diameter branch layout. Simultaneous valve closures in the branches did not result in additional pressure increases in the main pipe, and water hammer waves between branches did not interfere with one another. Moreover, replacing a single large branch with multiple smaller branches effectively eliminated negative pressure heads in the branches, thus preventing negative-pressure-induced water hammer, and shortened the duration of pressure fluctuations. The maximum reductions in pressure fluctuation duration at key points in the main and branch pipes were 63.16% and 46.15%, respectively. For stable hydraulic transitions and economic feasibility, the ratio of branch to main pipe diameter at the connection point should be between 0.12<β<0.28. In the Qitai project, using two parallel branch pipes (β=0.226) increased construction costs by 33.33% compared to the single large branch solution, but reduced investment in water hammer protection by 39.10%. [Conclusions] Under the premise of safe water delivery, a water supply scheme that replaces a single large-diameter branch pipe with multiple smaller parallel branches can effectively reduce valve-closing water hammer pressure and shorten the duration of pipeline pressure fluctuations.