直升机旋翼桨叶气动力学参数飞行测试系统

根据某型号直升机定型试飞的需要,研制出了动态测量旋翼桨叶气动力学参数的光电测试系统。其中运动参数(挥舞角、摆振角和变距角)由二维位置敏感传感器响应桨叶表贴发光点的位置变化测得,挥舞应变由光纤光栅传感器测得。利用自主搭建的桨叶运动姿态仿真平台开展了相关测试实验。结果表明:各角度值与对应输出电压间有很好的线性关系,测量范围内的角度测量误差小于1%;光纤光栅与电阻应变片对比测试的一致性较好,线性相关系数达到了0.999;光纤光栅应变测量的复现性很好,两次应变测量的相对偏差仅为1.22%。系统具有较高的测试精度。     

Monte Carlo methods in applied mathematics and computational aerodynamics

A survey of the Monte Carlo methods developed in the computational aerodynamics of rarefied gases is given, and application of these methods in unconventional fields is described. A short history of these methods is presented, and their advantages and drawbacks are discussed. A relationship of the direct statistical simulation of aerodynamical processes with the solution of kinetic equations is established; it is shown that the modern stage of the development of computational methods is impossible without the use of the complex approach to the development of algorithms with regard for all the specific features of the problem to be solved (its physical nature, mathematical model, the theory of computational mathematics, and stochastic processes). Possible directions of the development of the statistical simulation methods are discussed.     

Sail aerodynamics: Understanding pressure distributions on upwind sails

The pressure distributions on upwind sails is discussed and related to the flow field around the headsail and the mast/mainsail. Pressures measured on several horizontal sections of model-scale and full-scale sails are used to provide examples. On the leeward side of the sails, leading edge separation and turbulent reattachment occurs, sometimes followed by trailing edge separation. On the windward side, leading edge separation occurs on the mast/mainsail and, at low angles of attack, it can also occur on the headsail. Differences were found between the leading edge bubbles on the two sails. Pressure trends for different angles of attack are presented, and these can be explained in terms of standard aerodynamic theory, particularly in terms of short and long leading edge separation bubble types. It was found that the pressure distributions measured on mainsails at full- and model-scale showed good agreement on both the windward and leeward sides.     

Unsteady airfoil with a harmonically deflected trailing-edge flap

The effects of a harmonically deflected trailing-edge flap, actuated at different start times and amplitudes but with frequency different from the airfoil motion, on the aerodynamic loads of an oscillating NACA 0015 airfoil were investigated experimentally at Re=2.51×10⁵. Both in-phase and 180° out-of-phase flap deflections, relative to the airfoil motion, were tested. The results show that there was a large change in the hysteretic behavior of the dynamic load loops, and that the formation and detachment of the leading-edge vortex (LEV) were not affected by the flap motion, while the low pressure signature of the vortex was affected by the flap actuation start time. The later the flap actuation the larger the change in the strength of the LEV. The present flap control scheme was also found to be as effective as that achieved by a pulsed ramp flap motion, but with a reduced number of control parameters.     

面向控制研究的高超声速飞行器气动力与动力一体的建模新方法

高超声速飞行器采用乘波构形后,将对其模型研究带来新挑战,主要体现在建模过程中应充分考虑气动、推进与控制作用相互耦合,因此为了保证建模的准确性,有必要引入新方法来研究高超声速飞行器的模型.本文基于高超声速空气动力学理论,提出了一种高超声速飞行器纵向模型研究的新方法,该方法采用斜激波理论、普朗特-迈耶关系式及瑞利流原理来估...     

Vocal fold bulging effects on phonation using a biophysical computer model

Glottal adduction is a primary laryngeal variable that helps to determine glottal configuration and phonatory output. Greater adduction of the vocal folds can be produced by narrowing the gap between the vocal processes or by bulging the medial surface of the vocal folds. This study examined phonatory effects due to changing the degree of bulging using a computational model. Bulging was modeled as a quadratic surface and was related to active muscle stress. Results indicated that bulging had a significant effect on glottal flow resistance, maximum glottal width and area, and mean glottal volume velocity. The results are discussed relative to clinical issues of hyperfunction.     

Computational aeroelastic simulations of self-sustained pitch oscillations of a NACA0012 at transitional Reynolds numbers

The phenomenon of low amplitude self-sustained pitch oscillations in the transitional Reynolds number regime is studied numerically through unsteady, two-dimensional aeroelastic simulations. Based on the experimental data, simulations have been limited in the Reynolds number range 5.0×10⁴<Re_c<1.5×10⁵. Both laminar and URANS calculations (using the SST k–ω model with a low-Reynolds-number correction) have been performed and found to produce reasonably accurate limit cycle pitching oscillations (LCO). This investigation confirms that the laminar separation of the boundary layer near the trailing edge plays a critical role in initiating and sustaining the pitching oscillations. For this reason, the phenomenon is being labelled as laminar separation flutter. As a corollary, it is also shown that turbulence tends to inhibit their existence. Furthermore, two regimes of LCO are observed, one where the flow is laminar and separated without re-attachment, and the second for which transition has occurred followed by turbulent re-attachment. Finally, it is established that the high-frequency, shear instabilities present in the flow which lead to von Kármán vortex shedding are not crucial, nor necessary, to the maintaining mechanism of the self-sustained oscillations.     

A novel optimization technique for explicit finite‐difference schemes with application to AeroAcoustics

The present paper addresses the optimization of finite‐difference schemes when these are to be used for numerically approximating spatial derivatives in aeroacoustics evolution problems. With that view in mind, finite‐difference operators are firstly detailed from a theoretical point of view. Secondly, time, the way such operators can be optimized in a spectral‐like sense is recalled, before the main limitations of such an optimization are highlighted. This leads us to propose an alternative optimization approach of innovative character. Such a novel optimization technique consists of enhancing the scheme's formal accuracy through a minimization of its leading‐order truncation error. This so‐called intrinsic optimization procedure is first detailed, before it is thoroughly analyzed, from both a theoretical and a practical point of view. The second part of the paper focuses on two particular intrinsically optimized schemes, which are carefully assessed via a direct comparison against their standard and/or spectral‐like optimized counterparts, such a comparative exercise being conducted utilizing several academic test cases of increasing complexity. There, it is shown how intrinsically optimized schemes indeed constitute an advantageous alternative to either the standard or the spectral‐like optimized ones, being allotted with both (i) the better scalability of the former scheme with respect to grid convergence effects when the grid density increases and (ii) the higher accuracy of the latter scheme when the discretization level becomes marginal. Thanks to that, such intrinsically optimized schemes offer very good trade‐offs in terms of (i) accuracy; (ii) robustness; and (iii) numerical efficiency (CPU cost). Copyright © 2015 John Wiley & Sons, Ltd.     

基于多块对接网格的隐式气体运动论统一算法应用研究

基于玻尔兹曼模型方程的气体运动论统一算法(gas kinetic unified algorithm,GKUA) 给出了一种能模拟从连续流到自由分子流跨流域空气动力学问题的途径. 该算法采用传统计算流体力学技术将分子运动和碰撞解耦处理,若采用显式格式将受格式稳定条件限制,在模拟超声速流动尤其是近连续流和连续流区的流动时计算效率较低. 为了提高计算效率,扩展其工程实用性,采用上下对称高斯-赛德尔(LU-SGS) 方法和有限体积法构造了求解玻尔兹曼模型方程的隐式方法,同时在物理空间采用能处理任意连接关系的多块对接网格技术. 通过模拟近连续过渡区并排圆柱绕流问题,计算结果与直接模拟蒙特卡洛方法模拟值吻合较好,验证了该方法用于跨流域空气动力计算的可靠性与可行性.