准确合理地模拟具有自由表面的渠/管道明流和具有压力的管道满流运动过程,是设计、评价和管理灌区输配水系统的基础.为此,该文基于Preissmann窄缝法的概念,采用Saint-Venant方程组描述灌溉输配水系统的明满流过程,在交错空间离散单元格上,建立了基于全隐式标量耗散有限体积法的明满流耦合模拟模型.借助标准的室内物理模型观测数据和石家庄冶河灌区山尹村试验站野外原型观测数据,对模型的模拟效果进行了验证.结果表明,与基于显式向量耗散有限体积法建立的模型相比,该文建立的明满流耦合模拟模型具有类似的模拟精度,但水量平衡误差在室内和野外试验条件下仅为前者的13%和1.2%,且计算效率提高了约5.2倍;与基于四点偏心有限差分法建立的模型相比,模拟精度显著提高,水量平衡误差在室内和野外试验条件下仅为前者的7.6%和0.6%,且效率提高了1.3倍,故该文建立的模型有效克服了已有模型无法统一模拟精度和效率的缺陷,更适于实际工程问题,为灌区输配水系统的设计优化和管理评价提供了数值模拟方法.%In the irrigation water distribution system including pipe and cannel as well as control valve/gate, water flow presents both free surface and pressurized flows. Saint-Venant equations are often applied to discribe the free-surface-pressurized water flow in pipe/channel by means of Preissmann slot approach and then four-point implicit finite difference and vector-dissipation finite-volume approaches with explicit-time scheme are applied to simulation of unsteady flow in pipe/channel. However, it is very different for gravity diffusion wave in free-surface water flow and pipe elastic wave in pressure water flow, which induces different constraint on time step size, low computational efficiency and large water balance error in the modes based on these 2 numerical solutions. To solve these problems, Saint-Venant equations was applied to describe the free surface and pressure water flows in irrigation water distribution system, conjunctive with the Preissmann slot approach. Then a scalar-dissipation finite-volume scheme was developed to spatially discretize all terms of the governing equations. This scheme exhibited more simple expression and was more suitable to written computational code than the four-point implicit finite difference approach and vector-dissipation finite-volume approaches. On the basis of the spatial scheme, a fully implicit time scheme was implemented to temporally discretize all terms of the governing equations to result in a nonlinear algebraic equation system. To efficiently solve this nonlinear algebraic equation system, a dual time approach was introduced, which included real- and pseudo-time steps, to make a linearization. The advantage of the dual time approach was the existence of a ratio between real- and pseudo-time steps. The value of the ratio could be automatically adjusted according to the known pipe water flow conditions and then the coefficient matrix of the algebraic equation system could maintain diagonally dominant all the time. In such case, the absolute convergence could be achieved whether free surface or pressurized flow was in pipe according to numerical analysis theory. As a result, a fully coupled model of free-surface-pressure flow for irrigation water distribution system was proposed. A standard physical test, which strictly controlled the initial and boundary conditions under the indoor condition, was firstly applied to validate the performance of the proposed model. The validated results showed that the proposed model could well simulate the free surface and pressurized water flow processes, which was similar to vector-dissipation finite-volume approach and better than four-point implicit finite difference approach. Meanwhile, the water balance error of the proposed model was only 0.16%. By contrast, the error values of the models based on four-point implicit finite difference and vector-dissipation finite-volume approaches were 2.1% and 1.2%, respectively. The computational efficiency of the proposed model was 1.3 and 5.2 times higher than the existing 2 models. Furthermore, a field experiment was performed in Hebei Yehe irrigation area, April 5, 2013. On the basis of the field observed data, the proposed model still exhibited better performance than the 2 existing models. In details, the water balance error of the proposed model was only 0.016%, by contrast, 2.68% and 1.35% for the 2 existing models. The efficiency of the proposed model was still 1.3 and 5.2 times higher than the existing 2 models. Consequently, the proposed model overcomes the disadvantages of the existing models and is suitable to practical engineering, and provides a useful method for tool design, evaluation and management of water distribution system in irrigation area.
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