导弹出水过程中气/水动力学的研究

阐述了潜射导弹头体外形的气动与水动一体化设计方法，揭示了水下运动头部产生空化的机理．根据理论与试验研究结果，分析了导弹出水过程中空泡溃灭对弹体的影响以及出水后导弹的气动特性．     

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。     

Parametric study on buffeting performance of a long-span triple-tower suspension bridge

The triple-tower suspension bridge is a brand new type of structural form that is equipped with a dominant mid-tower. The dynamic characteristics of this multiple main-span suspension bridge present a significant difference with that of the conventional single main-span suspension bridge. Hence, taking the Taizhou Yangtze River Bridge as an example, the buffeting performance of a long-span triple-tower suspension bridge under strong winds is comprehensively investigated via finite element method. Specifically, the sensitivity of structural buffeting performance to some major structural parameters, aerodynamic parameters as well as parameters of turbulence inputs is analysed in time domain. It was found that the structural buffeting performance heavily depends on the dead load of the main girder, sag-to-span ratio of the main cable, longitudinal stiffness and structural type of the mid-tower. Also, appropriate selection of aerodynamic admittance function, power spectrum model of fluctuating wind and the spatial coherence coefficient is important in the buffeting analysis. Besides, the self-excited forces have small impact on the calculation of buffeting responses of such a bridge. The analytical results can provide references for the buffeting analyses and wind-resistant design of similar long-span triple-tower suspension bridges.     

Optimisation and performance analysis of vertical axis wind turbine with blade pitching at best position angle for different tip speed ratios

ABSTRACT

Best pitch position of each blade in the rotation of turbine at different azimuth angle has been calculated at different Tip Speed Ratios (TSRs) by using the aerodynamic analysis. This paper analyses and optimises the various design parameters and its influence on the starting turbine by itself, power coefficient and overall performance of the Vertical Axis Wind Turbine (VAWT). The results indicate that the best pitch position blade method improves the self-starting capacity and power coefficient. The best position blade pitching curve-1 gives maximum power coefficient at 45° pitch angles for TSRs of 0.5 and the best position blade pitching curve-5 with 15° pitch angle gives maximum coefficient of power about 0.49 for TSRs at 2.5. The results indicate that the variation of pitch angle from 45° to 10° with six best position blade pitching curves give the maximum power coefficient for TSRs from 0.5 to 3.     

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%.     

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.