共查询到18条相似文献,搜索用时 128 毫秒
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<正> 水跃情况下动水压力脉动的模拟问题,巳有一系列作者进行了研究,他们在各种比例的模型上做了实验室试验,从而得以按雷诺准则确定压力脉动的模拟下限,并根据弗劳德和斯特罗哈尔相似准则确定模型和原型之间脉动特性数据的换算条件。但是大家知道,模型试验时不可能充分估计到原型条件下所发生的水流掺气和微紊动。鉴于上述情况,为了定量评价水跃情况下水流掺气和微紊动可能对压力脉动的影响,近 相似文献
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针对渠系建筑物涵闸下游水流特点,采用一种适合于低弗劳德数消能的新型消能结构拱网消力池,通过模型试验和原型观测,研究了影响拱网水力特性的参数和拱网的消能率。工程应用结果表明,消力池中设置拱网可大大降低消力池的规模和工程费用。 相似文献
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水库水温垂向分层模型及黑河水库水温预测 总被引:5,自引:0,他引:5
水库水温垂向分层模型将水库水体离散为具有一定厚度的水平层次,同一层内水体充分混合,水温相同,在此基础上考虑太阳辐射、出入水流、垂向扩散及密度对流等因素,根据质量、热量平衡原理计算各层水温。对黑河水库水温结构的预测表明,水温的垂向分布与径流过程和水库运行方式关系密切。建议水库设置活动分层取水设施,并在泄水方式上适当考虑对温跃层的破坏和对农灌水质的影响。 相似文献
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初生空化的模型数据应用到原型上的问题 总被引:2,自引:0,他引:2
夏维洪 《水利水运科学研究》1993,(4):371-379
初生空化数由韦伯数W和空泡相对膨胀速度M所组成。在分析了中,德联合对比试验数据的基础上,发现W和M的关系呈一条对数直线。由模型试验得到直线方程后,再根据原型的空化数决定韦伯数,从直线上求得M值,有了W和M,就可得原型的初生空化数,从而判断在原型水流中是否发生空化。 相似文献
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应用辐射水流特性计算窄缝挑坎中线水面线,提出一级直线窄缝挑坎水力计算方法,可以比较简单地计算水面线和水舌挑距。水力模型试验验证结果表明,计算结果与试验值基本吻合;同样来流宽深比情况下,水面线与来流弗劳德数基本无关。 相似文献
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低含沙量异重流运动规律及其对水温分布的影响 总被引:1,自引:0,他引:1
当挟沙水流进入清水时,在特定的条件下会潜入底部向前运动,形成浑水异重流。水库水温分层使得水体密度在垂向出现差异,低含沙量浑水形成的异重流与周围水体密度接近,因而在运动过程中会受到垂向温度分层的干扰。浑水异重流是泥沙运动的特殊形式,还可能改变环境水体的温度,是水库调水调沙必须考虑的因素。该文应用水槽试验结合数值模拟,探究了水温分层条件下低含沙量异重流的运动规律及其对水温分布的影响。结果表明,异重流潜入点处形成回流,交界面以下含沙量以均匀梯度增加,前锋运动速度沿程不变;中层异重流不改变水温分布,而底层异重流则会对水温结构造成破坏,使得水温分布由分层型转变为混合型。 相似文献
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本文研究了气液均相流的模型相似律,推导得出竖井式水平旋流洞的模型相似律是:原、模型几何相似;原、模型佛罗德数 相同;原、模型含气率相同。推导得出竖井式水平旋流洞原、模型通气管截面积的换算关系和原、模型含气率分布的换算关系。最后,应用所得理论公式分析公伯峡水电站竖井式水平旋流式泄洪洞模型试验结果,为改进和完善模型设计提供了科学依据。 相似文献
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A physical,movable-bed model for non-uniform sediment transport,fluvial erosion and bank failure in rivers 总被引:1,自引:0,他引:1
《Journal of Hydro》2014,8(2):95-114
Sediment transport processes in rivers continue to pose a challenge when designing movable-bed physical models, particularly for reproducing the grain sorting and bank erosion (fluvial erosion and mass failure). This paper presents and discusses scale effects of a specific scaling approach for multi-grain size mixtures that preserves similarity of initial motion for each grain size class and of the bank stability coefficient between the model and the prototype, but relaxes strict similarity of the Shields and particle Reynolds numbers. This approach is appropriate when bed load transport near incipient motion conditions is being studied, and allows for larger grain size scales than when full Shields parameter similarity is enforced. As part of an environmental project to rehabilitate sediment transport through bank erosion, this method has been applied to scale a Froude number criterion physical model of a reach of the Old Rhine (France). This has resulted in an undistorted scale of 40, and the use of sand as the model bank material. Each grain size has a different geometrical scale. The time scale for sediment motion is grain size and flow discharge dependent. An average time scale of 6 has therefore been used (four model hours = one prototype day). A strategy devised for the field case consists of two higher, larger island groynes that replace the three existing groynes, producing bank erosion for flow rates below the mean annual flow rate. Extrapolation of model behaviour to the prototype is not a major problem, but the volume of eroded bank material may be underestimated, mainly because of the relaxation of the Shields number similarity and the apparent cohesive properties of the model bank material. 相似文献
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掺气分流墩墩头脉动壁压及其模型律试验研究 总被引:2,自引:0,他引:2
本文研究了中、低弗氏数掺气分流墩墩头脉动壁压及其模型律,得到时均和脉动壁压和分布规律、脉动壁压概念分布,自功率谱密度、自相关系数及墩头初生空化数,研究结果表明,墩头脉动壁压幅值模型律为重力律,优势频率模型律则为fλ≈1。 相似文献
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Experimental visualizations and numerical simulations of a horizontal hot water jet entering cold water into a rectangular storage tank are described. Three different temperature differences and their corresponding Reynolds numbers are considered. Both experimental visualization and numerical computations are carried out for the same flow and thermal conditions. The realizable k-e model is used for modeling the turbulent flow while the buoyancy is modeled using the Boussinesq approximation. Polynomial approximations of the water properties are used to compare with the Boussinesq approximation. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank as well as the Froude number are analyzed. The experimental visualizations are performed at intervals of five seconds for all different cases. The simulated results are compared with the visualized results, and both of them show the stratification phenomena and buoyancy force effects due to temperature difference and density variation. After certain times, depending on the case condition, the flow tends to reach a steady state. 相似文献
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《水动力学研究与进展(B辑)》2018,(5)
In view of the fact that the SPH model is easy to handle the flows with the free surface of large deformation, a 2-D flow induced by vertical water entry of a 2-D structure is simulated using the two-phase SPH model. The local pressure of the boundary particles is obtained by pressure of the fluid particles nearby through a modified kernel approximation. To evaluate the accuracy of the method, water entry of a 2-D symmetric wedge with fixed separation point of the free surface on the wedge surface is simulated. The pressure distribution of the wedge at the initial stage agrees well with the analytical results available. Evolution of the free surface and the air flow in the cavity induced by the water entry are obtained. A higher speed air jet is found at the neck of the cavity when the neck of the cavity becomes smaller. For the case of a horizontal cylinder entering the water with an unknown separation point of flow on the model surface, the early stage of the water entry is simulated for the rigid body with different density. Evolution of the free surface deformation of the half-buoyant cylinder and neutrally buoyant cylinder water entry is compared with the experimental data. The effects of the density ratio and Froude number on the pinch-off of the cavity are discussed. It is found that the pinch-off time remains almost constant for different density ratio and Froude number. Meanwhile, for a given Froude number, the dimensionless pinch-off depth and the location of the cylinder at the time of pinch-off increase with the density ratio. Further, for a given density ratio, these two parameters increase with the Froude number and, however, the relative cavity shape appears to be a self-similar shape when Fr ?8.35. 相似文献
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By combining the results of prototype observation of flood discharge atomization at the Wujiangdu Hydropower Station, and by adopting the serial model test method, the model scale effect was examined, the influences of the Reynolds and Weber numbers of water flow on the rain intensity of flood discharge atomization were analyzed and a rain intensity conversion relation was established. It is demonstrated that the level of atomization follows the geometric similarity relations and it is possible to ignore the influence of the surface tension of the flow when the Weber number is greater than 500. Despite limitations such as incomplete data sets, it is undoubtedly helpful to study the scale effect of atomization flow, and it is beneficial to identify the rules of the model test results in order to extrapolate to prototype prediction. 相似文献