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。     

调距桨梢涡精细流场的数值模拟

为验证湍流粘度取为mk/的修正剪切应力输运(SST)湍流模型在螺旋桨梢涡精细流场粘性模拟中的适用性,对驱逐舰母型桨DTMB5168调距桨的梢涡流动进行了模拟与校验。结果显示:0.9R以上径向区域周向平均的轴向、周向和径向速度分量均与试验值吻合很好,但0.9R以下区域的径向速度分量存在一定偏差;0.7R和0.92R处沿周向变化的三个速度分量变化形态均与试验值一致,故可由此来确定梢涡涡核区,但周向和径向速度分量峰值比试验值略小;轴向0.3R距离内梢涡涡核运动轨迹的模拟结果与试验值吻合较好。由此证明了修正的SST湍流模型在螺旋桨梢涡流动模拟中的适用性,还表明由叶梢区的径向、周向和轴向方向以及桨叶近壁面法向、叶截面弦长方向和尾流轴向方向的网格节点密度来局部控制叶梢区流动的模拟效果的可行性。     

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.     

基于涡流管能量分离效应的数值模拟

获得涡流管内的温度场分布是揭示涡流管内气体能量分离机制的首要问题和关键问题。考虑到管内气体运动的强旋流特性，采用计算流体力学(CFD)中的Realizable 湍流模型对涡流管内三维可压缩强旋流气体所产生的能量分离效应进行了数值模拟，获得了相应的总温、静温与动温沿轴向、径向的分布。由于涡流管中的零轴速包络面是内外旋气流的分界面，依据数值模拟结果，分别得到了涡流管中内外旋气流的混合平均动能和混合平均滞止焓沿其出口方向的变化曲线。为了验证数值模拟结果的准确性，将冷端气流温降随冷气流率的变化关系与实验值相比较，二者吻合较好。同时采用无量纲的分析方法将数值结果与前人的实测结果加以比较，进一步验证了模拟结果的准确性。     

螺旋桨性能计算的B样条网格面元法研究

螺旋桨水动力性能的准确预报对避免不良设计所带来振动和噪声,改善螺旋桨性能有着重要的意义.应用低阶速度势面元法建立了预报船舶螺旋桨水动力性能的数值方法,重点对桨叶随边和尾涡面进行研究.鉴于传统网格划分方法的不足,根据螺旋桨表面流场特性,采用B样条网格划分方法对桨叶表面单元进行剖分.文中对原有的等压库塔条件形式进行了改进,在考虑横流影响的前提下,满足随边荷载为零的条件.对计算结果与试验结果进行比较分析,表明将基于B样条的网格划分方法应用于已有的面元法程序中,能够很好地改善计算结果的精度.     

NMR Lineshape in Anisotropic Superconductors with Nonregular Vortex Lattice

The nuclear magnetic resonance line shapes within a primitive cell of the vortex lattice of the type II anisotropic superconductors in a case when a vortex is displaced on small distance a from a regular position in a primitive cell are constructed. The results of the numerical calculations show that displacement of the flux line lattice essentially changes the NMR lineshape. The derivative of the power of the absorption energy with respect to the magnetic field is calculated. It allows to obtain more detailed information about the real vortex lattice of a superconductor.     

Effect of near-critical swirl on the Burke-Schumann reaction sheet

The influence of swirl on the shape of the Burke-Schumann reaction sheet in a straight cylindrical pipe is investigated by asymptotic and numerical means. Attention is confined to swirl levels that are near the critical value at which vortex breakdown occurs. A high-Reynolds-number, laminar, isothermal, low-Mach-number reacting flow is considered. An asymptotic analysis is developed to study the nonlinear interaction between near-critical swirl and mixture fraction distribution within the flow. It is first shown that leading-order perturbation of the velocity field from the columnar state, generated by the interaction of near-critical swirl and low viscosity, can be described by a nonlinear reduced-order model. This flow perturbation is computed, and then employed to determine the correction to the classical Burke-Schumann solution. Under lean conditions of reaction the reaction sheet becomes shorter and more compact as swirl is increased. For rich conditions of reaction, increasing swirl first causes the reaction-sheet length to decrease, and then increase after vortex breakdown has appeared. Numerical simulations of the flow and reaction-zone shape are substantiated by, and supplement, the asymptotic results.     

一种小流量旋涡泵的汽蚀性能试验研究

对一种小流量旋涡泵的汽蚀性能进行了理论分析及试验研究.在试验中利用了LabVIEW软件进行数据的实时采集、存储,并用Access及Excel进行数据的记录处理,使用了精度较高的传感器并进行软件及硬件滤波,以克服流体脉动及随机因素造成的误差,使试验精度提高.提供了一份小流量旋涡泵汽蚀试验数据,可为小流量旋涡泵汽蚀性能的研究提供参考.     

充液管路系统中阀门流噪声的研究

用二方程模型封闭的雷诺平均N-S方程组,对水管路系统中三种常见阀门的三维分离流动进行数值模拟.模拟结果表明,随着蝶阀、闸阀和球阀开度的减小,流体在蝶阀背面、球阀阀门内外分别形成两个方向相反的漩涡,闸阀的漩涡出现在挡板与管道的壁角处,并且漩涡在阀门下游逐渐消失.同时实验表明,阀门下游的流噪声大于阀门上游的流噪声,涡声是阀门噪声的主要来源.