掺气减蚀研究的新方向

利用针式掺气流速仪测量掺气浓度场、流速场，气泡尺寸及其概率分布的研究成果表明，原型水流韦伯数高，形成微小气泡的能力比模型强，气泡上浮慢，接近底部的小尺寸气泡概率及掺气浓度比模型大，0．2mm或0．5mm以下的微小气泡可能在掺气减蚀中起着主要作用，完善掺气检测仪器，加强掺气水流中气泡尺寸及其概率分布的观测，比较不同气泡尺寸的掺气减蚀作用，建立多级气泡尺寸的掺气水流数学模型，是今后掺气减蚀研究的新方向。     

掺气减蚀保护作用的新概念

利用针式掺气流速仪测量原型和模型掺气浓度场、流速场，气泡尺寸及其概率分布的研究成果表明，原型水流韦伯数高，形成微小气泡的能力比模型强，气泡上浮慢，接近底部的小尺寸气泡概率及掺气浓度比模型大。初步研究认为：0.2mm或0.5mm以下的微小气泡在掺气减蚀中起着主要作用，可能只要很小掺气浓度即可达到掺气减蚀的效果。因此以小尺寸气泡的掺气浓度，作为判断掺气减蚀保护作用的指标将更为准确。     

掺气减蚀技术及掺气设施研究进展

为优化掺气设施体型并对其水力特性进行研究,在已有理论研究成果与工程实践经验基础上,从水流掺气减蚀机理、掺气水流运动特性及掺气设施体型及布置三方面评述了水流掺气减蚀技术研究进展。针对目前掺气减蚀技术研究中存在的不足,认为今后应进一步加强多泡情况下空化泡-空气泡-边壁微观作用机制,近壁(底板、侧壁)水体掺气浓度、气泡特征的沿程演变规律,复杂条件下掺气设施体型优化等方面的研究。     

论掺气减蚀

根据国内外大量的工程实例，对掺气减蚀作用、掺气减蚀风险、“龙抬头”式泄洪洞反弧的掺气减蚀问题，掺气槽的数量及掺气槽的布置方法进行了广阔的讨论，得到了几个实用性结论，供有关设计、科研人员参考。     

掺气水流的气泡尺寸检测

近年研究表明,高速水流泄水建筑物的掺气减蚀效果,不仅与掺气浓度有关,还应考虑气泡密度;认为0.2 mm或0.5 mm以下的微小气泡在掺气减蚀中起主要作用,可能只要很小掺气浓度即可达到掺气减蚀效果。因此在掺气减蚀研究中,必须加强对气泡尺寸的检测。分析总结了针式掺气流速仪应用经验,建议气泡当量尺寸直接采用探针检测得出的中值尺寸d50。虽然预计d50、气泡间距比实际偏大,气泡密度偏小,但是测量成果对于研究掺气减蚀机理,制定掺气减蚀的新标准,有重大意义。     

气泡尺寸与气核数目对初生空化的影响综述

衡量掺气效果的传统方法主要以掺气浓度为指标,认为掺气浓度大于2%时很少发生空蚀破坏。但新的研究表明,掺气浓度即使在很低的范围也可能不发生空蚀破坏。从气泡尺寸和气核数目对初生空化的影响入手,通过分析已有数据,探索衡量掺气效果的因素,得出初步结论。掺气减蚀效果不仅与掺气浓度有关,而且还与气泡尺寸有关,低于10-3m级尺寸的气泡对空泡溃灭冲击波的削弱作用不可忽略;其他条件一定时,气核数目增大,会促进空化现象的发生。     

岸边溢洪道掺气减蚀设施设计研究与实践综述

综述岸边式溢洪道设计研究技术，阐述了掺气减蚀原因，探讨了掺气减蚀设施的体型和水力设计原则，研究了水力特性及通气孔的布置，介绍了国内外工程典型实例及水工模型试验研究进展情况，并总结了掺气减蚀技术、原型运行及应用于岸边溢洪道的经济和社会效益。     

百色水利枢纽溢流坝掺气减蚀研究

百色水利枢纽工程RCC主坝高130m，最大水头差102m，溢流坝最大单宽流量约166m^3／S，流速超过40m／s，采用宽尾墩加消力池联合消能，由于水头高，流速大，堰面气蚀问题突出，水流掺气是减灭气蚀的有效方法，通过分析其它工程掺气减蚀的经验，就百色水利枢纽大比例尺模型试验来研究百色掺气水流的特性，掺气减蚀效果的评估以及掺气坎的最佳布置。     

盘石头水库泄洪洞的掺气减蚀研究

盘石头水库是正在进行规划设计的一座大型综合性水利枢纽工程，其泄洪（导流）洞流量大、流速高，且结构体型复杂。在综合防蚀减措施设计中，掺气减蚀是一种经济又可靠的措施。     

弧门突扩跌坎掺气减蚀应注意的问题

偏心铰弧形闸门门座结构特殊，水流条件复杂，对其进行总结，提出注意事项，找出发生空蚀的原因及改善优化措施是十分必要的。本文综述了多项有关试验成果及观点，认为偏心铰弧闸门突扩跌坎减蚀的最佳体型，不仅要满足这种闸门止水结构的要求，而且要有较优的掺气性能，确保掺气减蚀的各项参数的要求。此外，还介绍了研究三峡工程深孔弧门突扩跌坎掺气减蚀的工况和继续深入研究的必要性。     

IMPROVEMENT OF BUBBLE MODEL FOR CAVITATING FLOW SIMULATIONS

In the present research,a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications.The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction.The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius(or void fraction)reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem.This procedure is expected to stabilize the numerical calculation.The results of simple two-dimensional flow field are presented compared with the existing bubble model.     

Experimental study of the interaction between the spark-induced cavitation bubble and the air bubble

Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in detail： the impact of the air bubble upon the development of the cavitation bubble, the evolution of the air bubble under the influence of the cavitation bubble, and the change of the fluid pressure during the development of a micro jet of the cavitation bubble. Based on the experimental results, under the condition of no air bubble present, the lifetime of the cavitation bubble from expansion to contraction increases with the increase of the maximum radius. On the other hand, when there is an air bubble present, different sized cavitation bubbles have similarity with one another generally in terms of the lifetime from expansion to contraction, which does not depend on the maximum radius. Also, with the presence of an air bubble, the lifetime of the smaller cavitation bubble is extended while that of the bigger ones reduced. Furthermore, it is shown in the experiment that the low pressure formed in the opposite direction to the cavitation bubble micro jet makes the air bubble in the low pressure area being stretched into a steplike shape.     

Orifice plate cavitation mechanism and its influencing factors

The orifice plate energy dissipater is an economic and highly efficient dissipater.However,there is a risk of cavitaion around the orifice plate flow.In order to provide references for engineering practice,we examined the cavitation mechanism around the orifice plate and its influencing factors by utilizing mathematical analysis methods to analyze the flow conditions around the orifice plate in view of gas bubble dynamics.Through the research presented in this paper,the following can be observed:The critical radius and the critical pressure of the gas nucleus in orifice plate flow increase with its initial state parameter τ0;the development speed of bubbles stabilizes at a certain value after experiencing a peak value and a small valley value;and the orifice plate cavitation is closely related to the distribution of the gas nucleus in flow.For computing the orifice plate cavitation number,we ought to take into account the effects of pressure fluctuation.The development time of the gas nucleus from the initial radius to the critical radius is about10-7-10-5 s;therefore,the gas nucleus has sufficient time to develop into bubbles in the negative half-cycle of flow fluctuation.The orifice critical cavitation number is closely related to the orifice plate size,and especially closely related with the ratio of the orifice plate radius to the tunnel radius.The approximate formula for the critical cavitation number of the square orifice plate that only considers the main influencing factor was obtained by model experiments.     

水激波管空穴现象数值模拟

水激波管是一种用于标定爆炸压力传感器的装置，本文构造出管内流动的数学模型，并进行数值计算，从而揭开了其中的非线性波动过程及其引起的水中瞬态空穴现象。     

Direct numerical simuiation of bubble-cluster''s dynamic characteristics

A Direct Numerical Simulation （DNS） for understanding the dynamic response of bubble cluster to pulses of pressure perturbations has been studied by using a front-tracking method. The results show that owing to high nonlinearity, the bubble shape and volume oscillations caused by passing by pressure wave will be transformed into an in-phase volumetric oscillation of whole bubble cluster at a particular low-frequency. The value of the frequency is independent of the pulse excitations but the characteristics of the bubble cluster such as its bubble size, bulk void fraction and its spacial distribution etc. It is believed that this study provides important information for us to understand the coupling mechanism of cavitation cloud involved in cavitation resonance, a phenomenon noticed by one of the authors more than two decades ago.     

DIRECT NUMERICAL SIMUIATION OF BUBBLE-CLUSTER’S DYNAMIC CHARACTERISTICS

A Direct Numerical Simulation (DNS) for understanding the dynamic response of bubble cluster to pulses of pressure perturbations has been studied by using a front-tracking method. The results show that owing to high nonlinearity, the bubble shape and volume oscillations caused by passing by pressure wave will be transformed into an in-phase volumetric oscillation of whole bubble cluster at a particular low-frequency. The value of the frequency is independent of the pulse excitations but the characteristics of the bubble cluster such as its bubble size, bulk void fraction and its spacial distribution etc. It is believed that this study provides important information for us to understand the coupling mechanism of cavitation cloud involved in cavitation resonance, a phenomenon noticed by one of the authors more than two decades ago.     

单气泡在压力脉动场中运动的数值计算

本文对地均匀规则脉动场中的单气泡运动进行了数值计算，采用不做线化假定而直接对文献[1]中提出的气泡在自由流场中运动的控制方程进行计算，得出了一些很有意义的结论。     

脉动压力及压力梯度对不平整突体空化初生的影响

本文对六种不平整突体在正负压力梯度状况下的初生空化数进行了试验研究和理论分析，并根据气泡动力学方程建立了脉动压力与气泡振荡半径之间的关系，讨论了脉动压力及压力梯度对不平整突体空化初生的影响，试验结果表明，同一突体在负压力梯度状况下的初生空化数高于正压力梯度状况下的初生空化数；对于非流线型突体，在负压力梯度状况下空化初生时的壁面脉动压力强度低于正压力梯度状况下的脉动压力强度，脉动压力峰值约为七至十二倍的脉动压力均方根值。     

NUMERICAL SIMULATION OF SPHERICAL, CYLINDRICAL AND AXIAL BUBBLE CLOUDS COLLAPSE

The nonlinear dynamics of a spherical,cylindrical and axial cloud of cavitation bubbles were numerically simulated in order to learn more about the physical phenomena occurring in the cloud cavitation....     

幂律型流体劈裂注浆机理研究

劈裂注浆技术已广泛应用于各种地下工程之中,但其理论研究远落后于工程实践。为了明确幂律型流体劈裂注浆机理,基于平板裂缝模型及幂律型流变方程,推导出幂律型流体劈裂注浆最大扩散半径计算公式,并分析其适用范围及参数确定方法,最后通过现场注浆试验对其进行验证。结果表明:① 劈裂注浆最大扩散半径与起裂注浆压力、浆液锋前压力、裂缝劈裂宽度、黏度系数、浆液平均流动速率及流变指数等有关;②通过分析浆液最大扩散半径与注浆压力差之间的关系,发现注浆压力差越大,浆液最大扩散半径越大;同时,根据裂缝宽度与浆液压力差的关系,可知裂缝宽度越大,所需要的注浆压力差越小;③根据工程试验结果,得到幂律型流体劈裂注浆最大扩散半径理论计算值与实际测量值之间的误差,验证了幂律型流体劈裂注浆最大扩散半径计算公式的正确性与可行性。研究成果可为同类型注浆工程提供一定的理论支撑与技术支持。