基于有限体积法的含无压段泵站水锤模拟及调压井优化. (Chinese)

The water hammer simulation for pump station water supply systems with free-surface flow commonly employs the method of characteristics (MOC), often neglecting the influence of unsteady friction and the interaction between pressure and free-surface flow. In complex pipeline network systems, MOC often requires interpolation calculations or adjustments to wave speeds for computation. However, this can lead to issues such as numerical instability and reduced accuracy. This study establishes a second-order finite volume method model that considers unsteady friction for real-time joint calculations of pressure and free-surface flow. The second-order Godunov scheme is utilized to discretize the flow control equations independently for the pressure and free-surface flow. Riemann solvers are employed to compute the discretized fluxes. Simultaneously, the unsteady friction effect is taken into account to accurately simulate energy dissipation during hydraulic transient processes. The model is validated using experimental data. And a variable time-step approach is adopted at the interface between the pressure and free-surface flow. Furthermore, sensitivity analyses are conducted on the dimensions and locations of the throttled surge chamber in practical engineering scenarios. The results indicate that when unsteady friction effects are not considered, the model only matches experimental values at the first peak. However, when unsteady friction effects are taken into account, the model's simulation results are in good agreement with experimental results in terms of pressure peak, decay, and periodicity, and the maximum value of the water hammer pressure error at the valve is only 4.58%. Compared to the characteristics method, the second-order Godunov scheme exhibits higher stability and produces simulation results that are essentially the same when the Courant number is less than 1 as when the Courant number is set to 1.0. The real)time joint calculation method established in this paper can adequately consider the impact of water level fluctuations of the pressure flow outlet pool and the backflow of the free-surface flow. The water hammer pressure and the water levels of the throttled surge chamber obtained from the joint calculation of pressure and free-surface flow exhibit a faster decay compared to the results obtained from pure pressure flow calculations. For power outage conditions of pumps, the engineering scenarios studied in this paper would result in significant water hammer pressures and negative pressures if surge chambers were not installed. Optimization studies on the throttled surge chamber show that as the diameter of the connection tube increases, the maximum pressure head, the highest surge level of the throttled surge chamber, and the maximum reverse rotation speed of the pump increase, and the lowest surge level of the throttled surge chamber decreases. As the diameter of the throttled surge chamber increases, the highest surge level decreases, the lowest surge level increases and the maximum pressure decreases all the time when the connection tube diameter is relatively small, and will decrease first and then increase when the connection tube diameter is relatively large; when the connection tube diameter 3.5 m, throttled surge chamber diameter 15 m can meet the requirements of the system control parameters and also reduce the amount of engineering work. The closer the throttled surge chamber is to the pump station, the larger the maximum pressure, reverse rotation speed, and highest surge level, and the smaller the lowest surge level. When the throttled surge chamber is arranged 1.0 km behind the pump, the maximum surge level will reach 172.35 m, which does not meet the requirements of the control standards. In summary, the established model exhibits high accuracy, stability, and applicability, providing valuable insights for water hammer simulations in pump station water supply systems with free-surface flow. [ABSTRACT FROM AUTHOR]

针对含无压段的泵站输水工程水锤模拟常采用特征线法,且往往忽略动态摩阻和有压-无压相互干扰影响的问 题,该研究建立了考虑动态摩阻的二阶有限体积法模型,进行有压段-无压段实时联合计算。首先,采用二阶( 格式分别对有压流、无压流流动控制方程进行求解,同时考虑了动态摩阻效应以准确模拟水力瞬变过程中的能量耗散, 并进行试验验证。进一步地,对有压段、无压段交接处采用变时步法传递数据,结合实际工程对阻抗式调压井的尺寸、 位置进行了敏感性分析。结果表明:考虑动态摩阻效应后模型模拟结果与试验结果基本一致,阀门处水锤压力误差最大 值仅有4.58%;与特征线法相比,二阶 Godunov格式稳定性更高,库朗数小于1时水锤压力只有轻微的数值衰减。本文 建立的有压段-无压段实时联合计算方法能够充分考虑有压段出水池水位变化以及无压段倒流的影响。针对水泵失电工 况,对阻抗式调压井进行的优化研究表明,随连接管直径增大,系统内最大压力水头、调压井最高涌浪水位和水泵最大 反转转速增大,调压井最低涌浪水位降低;随调压井直径增大,最高涌浪减小,最低涌浪增高,最大压力在连接管直径 较小时一直降低,在连接管直径较大时先减小后增大;当连接管管径3.5m,调压井直径15m时,既能满足系统控制 参数要求,也能减少工程量。调压井位置离泵站越近,最大压力、反转转速、最高涌浪越大,最低涌浪越小,当调压井 布置在泵后 1.0 km时,最高涌浪水位会达到172.35m,不满足控制标准要求。综上,建立的模型具有较高的准确性、 稳定性和适用性,研究结果可为含无压段泵站输水工程的水锤模拟提供参考。 [ABSTRACT FROM AUTHOR]

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