The unsteady pressure field and the aerodynamic performances of a Savonius rotor based on the discrete vortex method

The aim of this paper is to numerically explore the non-linear two-dimensional unsteady potential flow over a Savonius rotor and to develop a code for predicting its aerodynamics performances. In the model developed, the rotor is represented in a median plane by two semicircles, displaced along their common diameter. The two semicircles can be considered to produce lifting effects. As a result, they are modelled by a collection of discrete vortices on their contours. The flow field is then governed by the Laplace equation. The versatile Neumann boundary condition, applied over the contour of the semicircles and the Kutta Joukowsky condition applied at the four extremities of the semicircles have been used in the modelling. The torque distribution of the stationary rotor and the unsteady pressure field on the blades of the rotating rotor, predicted by the code developed, have been compared and validated by some experimental data.     

Quantum Turbulence in Trapped Atomic Bose-Einstein Condensates

Generally there are two kinds of cooperative phenomena comprised of quantized vortices. One is a vortex lattice under rotation, and the other is a vortex tangle (quantum turbulence) made by some flow. Both have been studied in the field of superfluid helium through the long research history. On the other hand, the research of atomic Bose-Einstein condensates (BECs) has been limited to the former case, namely a vortex lattice. In this work, we address for the first time quantum turbulence in atomic BECs theoretically and numerically. We propose how to make quantum turbulence in a trapped BEC by combining rotation around two axes, and confirm the Kolmogorov spectra by the Gross-Pitaevskii model.      

面向无线通信的轨道角动量关键技术研究进展

电磁涡旋因携带轨道角动量而具有高维可调制自由度,被引入无线通信中以提升频谱效率和抗干扰能力。该文首先介绍了轨道角动量和电磁涡旋的基本原理与特性;然后比较了电磁涡旋的产生方法,给出了超表面产生轨道角动量的工作原理,综述了基于超表面的轨道角动量产生方法和研究现状;总结了轨道角动量的传输性能、接收与检测方法、复用与解复用性能;最后讨论了未来在应用无线通信轨道角动量时需要解决的关键问题。

     

汽车流场及尾部涡系数值模拟

对红旗ＣＡ７７４轿车进行了数值模拟,得到了整车的流场结构和尾流场的涡系结构。成功地模拟出了气流分离和拖拽涡现象。在数值模拟基础上对流场气流的横、纵向流动状况,尾部涡系结构,气流分离及拖拽涡的形成与发展机理作了详细分析与讨论。通过与试验结果对比,证实了数值模拟结果是正确的。     

非定常不稳定气固两相流动的离散涡数值仿真Ⅲ.非定常不稳定气固两相流动中颗粒运动与旋涡的相关结构

基于气固两相流动的离散涡模型与数值仿真方法,分别模拟了与重力方向垂直和与重力方向平行的平面内气固两相圆柱绕流(其中颗粒的St数为1.0),得到了流场中颗粒分布与旋涡分布的时间序列,由此进一步证明了高雷诺数下的二维气固两相流动中固体颗粒运动与流体旋涡存在着明确的相关结构:气体流经圆柱体时产生不稳定的剧烈分离流动,在圆柱绕流的尾迹区内存在着复杂的旋涡发展演化过程,由于流体旋涡对其周围固体颗粒的诱导作用,使得在尾迹区内中等尺度(St～o(1.0))的固体颗粒从均匀气固混合物中分离出来而往旋涡区运动,并最终在旋涡结构的外沿聚集.     

中空纤维膜渗透汽化过程中Dean涡强化传质的CFD模拟

建立了一个三维的弯管式中空纤维膜渗透汽化传质CFD模型,研究Dean涡对渗透汽化过程传质的影响,描述了膜内侧的浓度和速率变化情况,该模型与Leveque传质关联式具有良好的一致性。研究结果显示：弯管膜中Dean涡的存在能降低边界层传质阻力,总传质系数比直管膜提高了4倍;在不同的入口速率和浓度条件下,弯管膜内侧的壁面剪应力均大于直管膜。在膜阻力远小于边界层阻力的情况下,入口速率0.275 m·s^-1,水浓度10%（质量）时,弯管膜的渗透通量为12636 g·m^-2·h^-1,是直管膜的5倍。可见,弯管式中空纤维膜在渗透汽化过程中具有显著的强化传质效果。     

A numerical study on pressure drop and separation efficiency of a new swirl tube cleaner

In this paper, a new design of Swirl Tube Cleaner (STC) was introduced. The performance of an STC in terms of the separation efficiency and pressure drop was numerically investigated for different vane angles, vane lengths, and inlet velocities. The Reynolds stress turbulence model was used to detect the main flow structures of the highly swirling flow inside the STC. The discrete phase model that employs the Lagrangian frame of reference was utilized for particle tracking. The results are in good agreement with experimental data available in the literature. For all cases under investigation, the main flow characteristics of the STC consist of a hub vortex flow downstream of the back cone and tip vortices in the wake flow of the vanes. Around the initiation point of the vortex flow, the centrifugal accelerations are one order of magnitude higher than that of the upstream flow around vanes. The results show that the overall separation efficiency with the specified particle size distribution can reach 88% at a pressure drop lower than 250 [Pa] for the highest flow rate. Compared to traditional STCs, the new STC decreases the pressure drop by about 50% while enhancing overall separation efficiency by approximately 2%, considering the numerical accuracy.     

Photo-Thermal Transport Effects in a Thick Film YBCO Bolometer Under Magnetic Fields

Thick (~50 m) YBCO superconducting film bolometers have been fabricated to operate in the temperature range 89–92 K. Responsivities greater than 1 V/W have been achieved by biasing with a current slightly less than that of the critical current, and observing the photo-voltage in the resistive state. The time response of these films due to photo-conduction is slow (ms). The present work concentrates on the resistive transition and the width of the photo-signal peak under the effect of applied magnetic fields. The width of the photo-signal peak over the transition is found to be strongly magnetic field dependent at low field values while at higher field values it has been used to determine a value for the vortex tilt modulus. Further, it is found that a temperature difference in the position of the photo-signal peak relative to that of the dR/dT peak changes with applied field.     

On a modified Kim-Anderson model of the current-voltage characteristics of high-temperature superconducting ceramics

In comparison with the classical Kim-Anderson model for the current-voltage characteristics of type-II superconductors, another model with a less sharp pinning potential is presented. In addition to the approximate solution, for currents close to the critical one, a complete solution of this model is derived, which better fits the experimentally obtained current-voltage characteristics.     

Pancake Vortices

I describe the magnetic-field and current-density distributions generated by two-dimensional (2D) pancake vortices in infinite, semi-infinite, and finite-thickness stacks of Josephson-decoupled superconducting layers. Arrays of such vortices have been used to model the magnetic structure in highly anisotropic layered cuprate high-temperature superconductors. I show how the electromagnetic forces between pancake vortices can be calculatated, and I briefly discuss the effects of interlayer Josephson coupling.