Effect of aerodynamic moment on high-speed maglev train under complicated conditions

As the next generation of high-speed rail transportation, the high-speed maglev train has a design speed of 600km/h, whose Mach number is about 0.49. The severe aerodynamic effect caused by this high speed has a substantial impact on the train's stability and safety. In this paper, the aerodynamic moments of two three-carriage maglev trains passing by each other in open air are investigated by numerical simulation. To get transient moments acting on the train, this study adopted the sliding mesh method and the k-e turbulent model, and a user-defined function was compiled to define the motion of maglev. The results show that the pitching moment is the most important factor for the steady of maglev trains running in the open air. The oscillation of the total aerodynamic moment mainly comes from the moment acting on the lower part. The coupling of the pitching moment acting on the upper and lower part of carriages make the peak of the total pitching moment behind the total yawing moment. © 2021 by ASME

Hydrodynamic performance of a penguin wing: Effect of feathering and flapping

The penguin is the fastest underwater swimmer among the wing-propelled diving birds. To figure out the mechanism for its excellent swimming, the hydrodynamic performance of a penguin wing is numerically investigated using an immersed boundary method with the incompressible flow solver. This study examines the effects of feathering, flapping, and Strouhal number (St) under preset motion. Results indicate that feathering is the primary contributor to thrust generation. The change in angle of attack (AoA) can qualitatively reflect the change in lift but not thrust. Therefore, a new variable, angle of thrust (AoT, a(T)), is introduced to effectively reflect the change of thrust across different kinematic parameters. Optimal feathering amplitude balances the decrease in AoA and the increase in feathering angle to achieve the highest AoT and thrust. Excessive feathering amplitude degrades the leading-edge vortex to shear layers, transforms the pressure side to the suction side, and ultimately causes negative thrust (drag). Spatial analysis of the thrust shows that the outer three-fifths of the wing are the primary source of thrust, contributing 85.4% of thrust generation at optimal feathering amplitude. Flapping amplitude has little impact on the optimal feathering amplitude. The optimal feathering amplitude increases linearly with the St number in the scope of examination, leading to larger thrust but lower swimming efficiency. Thus, a dimensionless number, St(m), is introduced to describe the optimal wing motion. This work provides new insights into the propulsion mechanism of aquatic swimmers with flapping-feathering wings and helps design novel bio-inspired aquatic vehicles

Study on Aerodynamic Performance of Maglev Train Passing by Each Other at Constant Speed

As the next generation of high-speed rail transportation, the high-speed maglev train has a design speed of 600 km/h and a Mach number of about 0.49. The complex aerodynamic effects caused by such a high speed have a significant impact on the stability and safety of train operation. This paper uses numerical simulation to study the aerodynamic drag, lift, and side force acting on different carriages of the three-carriage maglev trains when they passing by each other at the same speed. In this study, the sliding mesh method and the k-ε turbulence model are used, and a user-defined function is compiled to determine the moving speed of the maglev train. The results show that the aerodynamic lift has very strong instability during the operation of the train, which is the main factor affecting the stable operation of the train. Its oscillation is mainly derived from the unstable lift at the bottom of the train, and the aerodynamic lift on the tail car is much larger than the head car. When two cars passing by each other, the aerodynamic drag of the train does not change synchronously with the aerodynamic lift and side force, and the influence on the lower part of the aerodynamic lift is greater than the influence on the upper part of the aerodynamic lift

典型气动荷载作用下磁浮列车动力学特性研究

研究强气动荷载作用下磁浮列车的动力学特性对磁浮列车的悬浮稳定设计有重要意义。本文基于简化的TR08型磁浮列车，采用滑移网格方法，研究了明线单车运行和会车场景下作用在列车上的瞬态气动荷载特性、气动荷载振荡的来源及气动荷载作用下列车的动力学特性。结果表明：TR08型磁浮列车受到的气动荷载随速度的增大而增大，总体呈现尾车>头车>中车的规律。俯仰力矩在气动荷载中占主导地位，是影响列车安全运行最重要的因素。列车气动荷载振荡主要由下部结构引起，与上/下部结构相比，单节列车俯仰力矩的峰值出现了迟滞现象，偏航力矩则无此现象。单车以600 km/h的速度运行时，悬浮磁铁间隙波动的幅值将超过安全极限；以600 km/h的速度交会时，将发生失稳。本文的结论可为磁浮列车的稳定设计提供参考

Wing Kinematics and Dynamics during Takeoff in Honeybees

Abstract In this paper, we utilized an array of four high-speed cameras to capture intricate wing kinematics, allowing us to calculate flapping amplitudes, frequencies, wingtip velocities, the ratio of upstroke to downstroke duration, and the angles between the forewings and hindwings. Preliminary analysis revealed that bees typically perform at least 15 wingbeats before taking off, with wing stroke amplitudes exceeding 100 degrees and frequencies within the range of 220 to 260 Hz. Additionally, the maximum angle between the forewings and hindwings generally surpasses 50 degrees. The kinematic parameters of takeoff are distinctive, and the relationships among various kinematic parameters are presented in this paper. Of particular note is the variation in the angle between the forewings and hindwings, which increases and then decreases with changing wingbeat speeds. In addition, we reconstructed the kinematic model of the wing motion for computational fluid dynamics (CFD) simulation, which will further reveal the aerodynamic mechanisms involved.</p

基于PINN神经网络的圆柱绕流部分流场的构建

二维圆柱绕流作为基本的物理模型,很多方法用其验证。目前的研究手段大多是实验和数值计算。本文引入了一种基于物理信息的神经网络模型(PINN)建模的方法,首先介绍了其网络构架的基本原理,对雷诺数100的二维圆柱绕流非定常流场进行CFD数值模拟,得到训练数据。通过网络训练部分流场数据得到的速度压力分布云图与商业软件Fluent得到的速度压力分布云图对比,结果表明PINN模型可以为圆柱绕流问题提供有效的建模方法,为接下来的复杂模型提供一定的基础