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高坝工程泄洪形成的泄洪雾化现象对水利枢纽的正常运行、交通安全、周围环境甚至下游岸坡稳定均可能造成危害。通过全面细致的文献调研,对我国泄洪雾化相关的研究进展进行了归纳总结,梳理了对泄洪雾化危害的认识过程,总结了对泄洪雾化形成过程的逐步了解,对比了不同模型试验和数值分析的研究成果。在对当前研究现状的认识基础上,指出今后泄洪雾化相关研究工作的开展应该注重测量技术的改进,以获得更详尽的原型和模型观测资料。此外,对泄洪雾化雾源特性的研究是今后研究的一个重要方向。  相似文献
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Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.  相似文献
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Numerical simulation and 3-D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition. The pressure fluctuation intensity coefficient (PFIC) based on the standard deviation method, the time-averaged velocity unsteadiness intensity coefficient (VUIC) and the time-averaged turbulence intensity coefficient (TIC) are defined by averaging the results at each grid node for an entire impeller revolution period. Therefore, the strength distributions of the periodic flow unsteadiness based on the unsteady Reynolds-averaged Navier-Stokes (URANS) equations can be analyzed directly and in detail. It is shown that under the 0.6Qd~. condition, the pressure fluctuation intensity is larger near the blade pressure side than near the suction side, and a high fluctuation intensity can be observed at the beginning section of the spiral of the volute. The flow velocity unsteadiness intensity is larger near the blade suction side than near the pressure side. A strong turbulence intensity can be found near the blade suction side, the impeller shroud side as well as in the side chamber. The leakage flow has a significant effect on the inflow of the impeller, and can increase both the flow velocity unsteadiness intensity and the turbulence intensity near the wall. The accumulative flow unstea- diness results of an impeller revolution can be an important aspect to be considered in the centrifugal pump optimum design for obtaining a more stable inner flow of the pump and reducing the flow-induced vibration and noise in certain components.  相似文献
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针对传统马尔可夫链及其改进的预测方法只能进行状态预测的局限,根据相依随机变量的特点,在以传统马尔可夫链预测方法求得的各状态的预测概率的基础上,进一步以状态预测概率为权重与状态平均值加权求和,实现了马尔可夫链预测方法从状态预测到数值预测的关键性改进。利用我国西南国际大河怒江干流道街坝水文站1957~2010年径流和1964~2010年悬移质输沙序列为分析期,2011~2015年径流和悬移质输沙为验证期,对所建立的复权马尔可夫链预测方法步骤进行验证表明,复权马尔可夫链预测方法具有较高的数值预测精度,能够满足随机时间序列短期数值预测的需要。  相似文献
5.
导出了固体颗粒在任意流场中运动的Lagrangian方程,对此方程进行线性化,并求出了其颗粒运动方程的解析通解。使用颗粒运动方程数值求解和分析了稀疏颗粒湍流场中固体颗粒的运动。建立了湍流固-液两相流的K-ε双方程湍流模型、体积分数湍流模型、Eunlerian-Lagransian混合湍流模型以及颗粒磨损模型,利用这些模型对一些水涡轮机械过流通道内的流动及固壁磨损进行了数值模拟,其预测结果与实验结果较为一致  相似文献
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水库水温变化是评价环境影响的主要指标之一.为评估三峡水库蓄水后水温变化,本文采用数学模型分析了库首105 km范围内的水温分布规律.结果显示:(1)三峡水库蓄水后水温变化对气象条件的响应变慢,沿程温差有所加强,在升温期上游水温高于下游;(2)在给定的水文气象条件下,库首江段在4~6月份将会出现弱分层,垂向温差在1~2 ℃.采用蓄水前后的实测资料对数值预测结果进行了分析,论证了本文预测结果的合理性.  相似文献
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