Embodied linearity of speed control in Drosophila melanogaster

Fruitflies regulate flight speed by adjusting their body angle. To understand how low-level posture control serves an overall linear visual speed control strategy, we visually induced free-flight acceleration responses in a wind tunnel and measured the body kinematics using high-speed videography. Subsequently, we reverse engineered the transfer function mapping body pitch angle onto flight speed. A linear model is able to reproduce the behavioural data with good accuracy. Our results show that linearity in speed control is realized already at the level of body posture-mediated speed control and is therefore embodied at the level of the complex aerodynamic mechanisms of body and wings. Together with previous results, this study reveals the existence of a linear hierarchical control strategy, which can provide relevant control principles for biomimetic implementations, such as autonomous flying micro air vehicles.     

圆锥跨、超音速绕流的数值仿真

显式、二阶精度、总变差下降（TVD）有限体积格式解无粘、可压缩气体流动方程组。数值仿真了跨、超音速气体沿圆锥绕流的前部流场。获得波后流场的等压力线、等密度线、等马赫线和圆锥表面的压力系数，确定了锥激波的几何位置。仿真结果与精确解和实验结果吻合较好。     

基于格子玻尔兹曼方法的侧窗水相分析与控制

侧窗雨水污染会损害侧窗的清晰度,进而影响汽车的安全驾驶. 针对汽车雨天行驶时侧窗水污染问题,将空气动力学与多相流理论结合,采用格子玻尔兹曼方法求解汽车瞬时外流场,拉格朗日方法求解液滴运动,获得液滴运动轨迹和侧窗区域水相分布情况. 分析得到侧窗区域水污染的影响因素及产生机理,在此基础上对A柱型面进行改型,对比不同改型方案的侧窗区域水相分布情况以及污染面积. 研究结果表明,在4种A柱方案中,方案2侧窗视野最佳,水相覆盖率为38.2%,较basic模型降低了19.2%.     

大型高速滑坡体运动的空气动力学试验研究

对于大型高速滑坡，大多要经历一个凌空高速飞行的阶段，这必然要产生空气动力效应。根据空气动力学理论，通过对4种不同形状滑坡模型的风洞试验结果分析，得出空气动力学效应对凌空飞行滑坡体运动的影响规律，并在此基础上导出了大型高速滑坡近程活动阶段凌空飞行运动的微分方程式。     

Predicting power-optimal kinematics of avian wings

A theoretical model of avian flight is developed which simulates wing motion through a class of methods known as predictive simulation. This approach uses numerical optimization to predict power-optimal kinematics of avian wings in hover, cruise, climb and descent. The wing dynamics capture both aerodynamic and inertial loads. The model is used to simulate the flight of the pigeon, Columba livia, and the results are compared with previous experimental measurements. In cruise, the model unearths a vast range of kinematic modes that are capable of generating the required forces for flight. The most efficient mode uses a near-vertical stroke–plane and a flexed-wing upstroke, similar to kinematics recorded experimentally. In hover, the model predicts that the power-optimal mode uses an extended-wing upstroke, similar to hummingbirds. In flexing their wings, pigeons are predicted to consume 20% more power than if they kept their wings full extended, implying that the typical kinematics used by pigeons in hover are suboptimal. Predictions of climbing flight suggest that the most energy-efficient way to reach a given altitude is to climb as steeply as possible, subjected to the availability of power.     

Unsteady RANS modelling of flow past a rectangular cylinder: Investigation of Reynolds number effects

The unsteady flow field around a two-dimensional rectangular prism with a fineness ratio (chord-to-thickness) of 5.0, is studied using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. A noncommercial unstructured flow solver is used in the simulations at various Reynolds numbers (from 26,000 to 1,850,000 based on the chord length), two different angles of attack (0° and 4°) and low Mach number (0.1). A grid-convergence study is presented in order to investigate the dependence of the flow solution on the spatial and temporal discretization. Results obtained with one- and two-equation turbulence models are compared, including models based on the Explicit Algebraic Reynolds Stress (EARSM) approach. The aim of this work is to assess the capability of the computationally efficient two-dimensional URANS calculations to predict the features of complex massively separated flow around this type of geometry. A further goal is to use numerical simulations to investigate the strong Reynolds number effects observed in wind-tunnel experiments. Satisfactory agreement with the wind-tunnel data is obtained for several test cases, but only the turbulence model based on the EARSM approach captured the significant lift increase at non-zero angles of attack due to variation of Reynolds number. This phenomenon is shown to be related to the progressive upstream migration of the time-averaged shear-layer reattachment location on one side of the rectangular cylinder. The effects of the Reynolds number on the mechanism of vortex shedding are also explored in the simulations.     

大跨度桥梁空气动力学的理论研究与工程应用

指出随着对于风致作用的不断深入的认识，桥梁空气动力学的理论在不断地进步与完善，在工程中的应用也越来越多，主要针对当前的桥梁空气动力学理论以及相关的工程应用进行了总结和分析，并提出了一些看法与建议。     

A comparison of different methods to evaluate the wind induced forces on a high sided lorry

This paper examines the wind induced forces and moments experienced by a high sided lorry. Full-scale measurements are combined with wind tunnel and CFD simulations in order to gain an insight into the flow field around the vehicle. Differences and similarities between the three techniques are noted. It is shown that the rolling moment coefficient obtained from full-scale measurements and CFD simulations agree consistently across a wide range of yaw angles. With respect to the side force coefficient, good agreement between the wind tunnel and full-scale data are achieved. Pressure distributions over selected sections of the lorry reveal that despite good agreement with the overall forces, the localised pressure field can be significantly different.     

Investigating the aerodynamic performance of a model offshore floating wind turbine

Understanding the impact of wave-induced dynamic effects on the aerodynamic performance of Offshore Floating Wind Turbines (OFWTs) is crucial towards developing cost-effective floating wind turbines to harness wind energy in deep water sites. The complexity of the wake of an OFWT has not yet been fully understood. Measurements and numerical simulations are essential. An experiment to investigate the aerodynamics of a model OFWT was undertaken at the University of Malta. Established experimental techniques used to analyse fixed HAWTs were applied and modified for the floating turbine condition. The effects of wave induced motions on the rotor aerodynamic variables were analysed in detail. An open source free-wake vortex code was also used to examine whether certain phenomena observed in the experiments could be reproduced numerically by the lifting line method. Results from hot wire measurements and free-wake vortex simulations have shown that for OFWTs surge-induced torque fluctuations are evident. At high λ a discrepancy in the mean C_P between the fixed and floating conditions was found from measurements and numerical simulations.     

高精度迎风格式的射弹粘性绕流场数值模拟

应用四阶的NUSCL TVD格式,求解雷诺平均的N－S方程,对超音速射流与弹体绕流流场和弧形翼的空气动力特性进行了数值模拟研究,计算结果与实验对比表明,该方法可以获得高分辨率的流场结构。