INTERACTION OF VORTICES WITH A PROGRESSIVE SURFACE WAVE

ＩＮＴＥＲＡＣＴＩＯＮＯＦＶＯＲＴＩＣＥＳＷＩＴＨＡＰＲＯＧＲＥＳＳＩＶＥＳＵＲＦＡＣＥＷＡＶＥＷａｎｇＬｉｎ－ｌｉｎ；ＭａＨｕｔ－ｙａｎｇ（ＧｒａｄｕａｔｅＳｃｕｄｏｆＡｃａｄｅｍｉｃａＳｉｎｉｃａＢｅｉｊｉｎｇ１０００３９Ｐ．Ｒ．Ｃｈｉｎａ）Ａｂ...     

吉音水利枢纽竖井旋流泄洪洞水力特性试验研究

通过1∶30的水工模型对吉音水利枢纽竖井旋流泄洪洞的水流流态、压力分布、流量系数等水力特性进行了研究,分析了在进水口溢流堰末端增设掺气坎对进水口及竖井内流态及通气孔风速的影响。研究结果表明:在溢流堰末端增设掺气跌坎有利于减小溢流堰面的负压、防止空蚀破坏、简化进口体型设计,且有利于泄洪洞的安全运行。     

The inception cavitating flows over an axisymmetric body with a blunt head-form

The inception cavitating flows around a blunt body are studied based on flow visualizations and velocity field measurements. The main purpose of the present work is to study the incipient cavity evolution and the interplay between the inception cavitation and the local turbulent flows. A high-speed video camera is used to visualize the cavitating flow structures, and the particle image velocimetry(PIV) technique is used to measure the velocity field, the vorticity, and the Reynolds stresses under non-cavitating and inception cavitating flow conditions. It is found that the appearance of visible cavities is preceded by the formation of a cluster of micro-bubbles not attached to the body surface and in a hairpin-shaped vortex structure. During its evolution, the cavity moves downstream with a lower speed. The effect of the incipient cavity is significant on the local vortical structures but slight on the timeaveraged velocity distribution. The mean Reynolds stress distributions in the turbulent shear flow can be substantially altered by the incipient cavities. The presence of the incipient cavities can lead to the production of turbulent fluctuations.     

NUMERICAL SIMULATION OF FLOW OVER TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT

In this article,the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes.The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid.The great source term technique is employed to identify the cylinders placed in the flow field.To apply the boundary conditions,the ghost-cell technique is used.The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder.Finally,the flow around two circular cylinders in a tandem arrangement is simulated and analyzed.The flow visualization parameters,the Strouhal numbers,and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow.The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.     

考虑水平隐蔽度影响的卵石周围水流结构分析

基于二维数值水槽,在高雷诺数Re=5×104~20×104条件下,从卵石在床面不同排列方式下单颗粒到多颗粒圆状卵石的位置及受力情况的角度出发,综合考虑水平与竖直两个方向定义的隐蔽度,颗粒起动采用滚动模式,结合水流结构,进一步探讨其起动规律,亦对沙卵石河床冲刷和粗化的研究提供基础。通过比较9种情况下阻力与升力的数值结果分析表明,水平隐蔽度对水动力因素亦有较大影响,阻力系数随着相对水平隐蔽度的增大先减小后增大,经综合考虑其更符合真实情况,最后对附近作用区域涡量分布的影响进行了讨论。     

侧向进水口立轴旋涡数值模拟

为了研究侧向进水口立轴旋涡的运动特性,以RNG模型为基础,引入VOF方法捕捉自由液面的变化,对立轴旋涡的形态及其运动轨迹进行了三维数值模拟,并对旋涡水面线和三维速度分布进行了分析。结果表明,侧向进水口前的旋涡是非对称的,其涡轴是一条空间曲线,旋涡下部在进水口的抽吸拉伸作用下发生扭曲。旋涡运动可分为三部分,第一部分水面线呈漏斗状,与对称旋涡类似,第二部分旋涡运动逐渐从竖向转为横向,第三部分为横向运动。在旋涡的上半部,轴向速度随着水深的增加而增大,当旋涡逐渐由竖向转为横向运动时,轴向速度逐渐减小直至为零。最大切向速度发生在淹没深度的52%处。     

EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

平面旋涡(中心型奇点)水力特性的探讨

本文讨论了平面旋涡(中心型奇点)的水力特性.说明了这种旋涡的中心被封闭的流线所包围，中心点的流速为零，封闭流线为椭圆曲线；给出了旋涡内流速与压强，旋涡的环量、涡量以及角动量的表达式；建立了旋涡水力参数和主流水力参数的连接条件，包括两个运动连接条件和两个动力连接条件；将得到的理论结果应用于侧墙突扩或跌坎流，得到的旋涡中心压强表明，在一般明渠条件下，主流流速大于20m/s时旋涡区有可能出现空蚀；应用于水跃时发现，跃长与跃高之比和突扩流旋涡的长宽比基本相同，估计了水跃旋滚区的紊流运动粘滞系数；应用于交岔渠道的旋涡时，指出了旋涡宽度与渠宽之比必须小于0.160，给出了一个数例     

三峡地下电站进水口漩涡特性研究

为了探明三峡地下电站进水口前漩涡特性而进行了1:100三峡水利枢纽水工整体模型和1:70地下电站水工整体模型试验.成果表明,各机组进口前均未出现危害机组安全稳定运行的吸气漩涡,仅在1号机和6号机进口处偶尔出现浅层不吸气漩涡,这是由于拦污栅起到了消涡作用.     

排水系统入海口新型消能工

通过实体模型试验研究了某排水系统入海口水工建筑物的水力性能,设计提出一种新型的墩栅涡流室消能工。该新型消能工的水力特点是:流出排水隧洞的高速水流大部分通过进口墩栅空隙流入涡流室,小部分在进口墩栅前发生水跃后扎入涡流室中产生强烈的顺时针漩涡,通过水跃、墩栅的阻力和涡流室漩涡的共同作用消能,并将来流的动能转换为势能,之后,涡流室中的大部分水流在重力作用下通过出口墩栅空隙流向下游,其余水流从墩栅顶部溢流。这种新型的墩栅涡流室不仅消能效果良好而且出流均匀,并容许各种杂物如石块、泥沙等自由通过,避免涡流室中发生严重的淤积。