不同旋转雷诺数和内外半径比对泰勒库特流动特性的影响

为了提高电转子散热性能,提升旋转机械性能和机器的长周期运行稳定性,对转定子之间的气隙流动特性进行了研究,采用数值模拟方法对冷却工质在电机转定子之间气隙内的泰勒库特流动进行模拟,获得了气隙和转速变化下的涡流场信息,对比分析不同条件下的涡形态。结果表明,当雷诺数从8000开始增大时,随着雷诺数的增加,泰勒涡变得越来越清晰越来越大,当雷诺数增大到16000以后,泰勒涡结构发生了严重的扭曲。随着半径比的增大,流体的流动特性更加趋近于剪切作用起主导的平板库特流动。

毛细管中两相流动特性的电导测量方法

建立了单毛细管中两相流动传递参数实验系统,基于该系统开发了测取泰勒流下气泡速度、气含率、气泡频率以及液栓长度等参数的双电导测试系统。结果表明,与常用的摄像法进行比较,双电导探针具有在线、实时和动态响应快等特点,可替代摄像法,并可扩展应用于结构化催化剂内部测定气液两相流动参数分布。同时,采用电导法对毛细通道中多种流型——包括分散气泡流、气泡串流、泰勒流、膜流及多种过渡流型——进行辨识,取得了较好的实验结果。

沟槽壁面对泰勒涡流稳定性影响的数值模拟

利用CFD数值模拟方法对光滑壁面与沟槽数量为18的2种同心圆柱模型内的泰勒-库艾特流动进行计算,在对比光壁模型的PIV试验与CFD数值计算结果后,发现两者吻合良好,验证了文中采用数值计算方法的准确性;针对泰勒涡流流态,定量分析了光壁模型R-Z平面上径向速度以及轴向速度的周期波动性,讨论了环隙中不同径向位置的径向以及轴向速度分布规律,获得了泰勒涡胞尺寸随着Re数增大而减小的变化规律;在相同的Re数下,沟槽数量为18的模型内也出现了泰勒涡流,通过比较2种不同结构模型内流场以及涡量场,发现沟槽的存在显著改变了流场分布,增大了环隙内涡量的大小及泰勒涡胞的尺寸,环隙中部指向外圆柱方向的径向速度也较光壁模型增大了20%,同时,计算获得R-θ平面内沟槽区域的流场分布表明该区域存在着明显的旋涡运动.

Velocity Component Comparison between CFD and EFD in Taylor Vortex Flow

Since the classical investigation of the Taylor vortex by G. I. Taylor in 1923, many researchers have studied the Taylor vortex as one of the most important vortex types in flow. In this study, the inner cylinder is rotating, while the outer cylinder, which is concentric with the inner cylinder, is stationary. In addition, the measurement of the velocity distribution is carried out by the PIV （Particle Image Velocimetry） method. The radius of the inner cylinder is 20 mm, and that of the outer cylinder is 30 mm. In this study, Re = 650-1,200 is assumed. In the upper part of the apparatus, movable ends are fixed to the upper and lower sides of the cylinder to change the aspect ratio. The aspect ratio is defined as the ratio of cylinder height to gap distance. A servo motor to rotate the inner cylinder, a servo-motor control device, a servo amplifier for rotation speed control, and a YAG laser light source are installed in the apparatus. For the visualization of Taylor vortex flow, aluminum powder composed of scale like fine particles is used. As tracer particles used in the PIV method, fluorescent particles with a size of 48 Ixm were used. The governing equations are Navier-Stokes equations with cylindrical coordinates （r, θ, z） and the equations of continuity. Each physical value is nondimensionalized using the angular velocity of the inner cylinder as the representative velocity, and the radius difference between the inner and outer cylinders as the representative length. Discretization of the governing equations is based on the MAC method. The results of EFD and CFD （computational fluid dynamics） are compared. The mode bifurcation is observed, and the flow structure is investigated.

Assembling Stabilization of the R-T Instability by the Effects of Finite Larmor Radius and Sheared Axial Flow

In the present paper, based on the incomepressible finite Larmor radius （FLR） magnetohydrodynamic （ MHD ） equations, we consider the stabilizing effect of the finite Larmor radius on the Rayleigh-Taylor （ RT ） instability in implosions of annular Z-pinch plasma. Here, the FLR is considered as a type of viscositytll, independent of any collisions （i.e., collisionless viscosity, or gyrouiscosity ）. Since we are introducing a sheared velocity,

On the Rayleigh-Taylor Instability for Two Uniform Viscous Incompressible Flows

The authors study the Rayleigh-Taylor instability for two incompressible immiscible fluids with or without surface tension, evolving with a free interface in the presence of a uniform gravitational field in Eulerian coordinates. To deal with the free surface, instead of using the transformation to Lagrangian coordinates, the perturbed equations in Eulerian coordinates are transformed to an integral form and the two-fluid flow is formulated as a single-fluid flow in a fixed domain, thus offering an alternative approach to deal with the jump conditions at the free interface. First, the linearized problem around the steady state which describes a denser immiscible fluid lying above a light one with a free interface separating the two fluids, both fluids being in(unstable) equilibrium is analyzed. By a general method of studying a family of modes, the smooth(when restricted to each fluid domain) solutions to the linearized problem that grow exponentially fast in time in Sobolev spaces are constructed, thus leading to a global instability result for the linearized problem.Then, by using these pathological solutions, the global instability for the corresponding nonlinear problem in an appropriate sense is demonstrated.

Dynamic Transition and Pattern Formation in Taylor Problem

The main objective of this article is to study both dynamic and structural transitions of the Taylor-Couette flow, by using the dynamic transition theory and geometric theory of incompressible flows developed recently by the authors. In particular, it is shown that as the Taylor number crosses the critical number, the system undergoes either a continuous or a jump dynamic transition, dictated by the sign of a computable, nondimensional parameter R. In addition, it is also shown that the new transition states have the Taylor vortex type of flow structure, which is structurally stable.