小长径比弹丸加装大展弦比尾翼的气动特性研究

为了提高小长径比弹丸射击质量,设计了一种大展弦比张开式尾翼,采用AUSM+格式、SST(shearstress transport)湍流模型和隐式算法(lower-upper symmetric Gauss-Seidel implicit method, LU-SGS),求解三维RANS 方程,对前体形状完全相同,不同展弦比的3 种尾翼弹进行了数值模拟,得到了三者在马赫数1.5~3.5 下的气动力特性的差异,分析其原因,并给出了不同展弦比张开式尾翼的适用范围. 计算结果表明:C型弹的升阻比较B 型弹在1.5 马赫数区域附近增加了7% 以上,当马赫数达到2.5 以上时,A 型弹的升阻比大于B 型弹和C 型弹,在3.5 马赫数区域附近A 型弹的升阻比较B 型弹增加了5.4% 以上. 3 种弹丸的俯仰力矩系数随着马赫数的增大而负向减少,且减少的趋势随着展弦比的增加而增大. A 型弹、B 型弹、C 型弹的静稳定裕度的变化范围分别为4%~20.3%,8.5%~23.2%,11.4%~25.6%.     

旋转固体火箭上面级章动不稳定动力学机理分析

针对上面级旋转固体火箭发动机出现的章动不稳定现象,即锥形运动发散,通过对变质量陀螺运动方程干扰力矩项的研究,得出了发动机内部流动质量产生的附加侧向扰动力矩是诱发上面级固体火箭锥形运动发散的动力学根源,并得到了其章动不稳定的发生判据。基于此判据,给出了通过提高火箭自旋转速和横向转动惯量来解决上面级旋转固体火箭发动机章动不稳定现象的方法;并得出较高的气动静稳定设计和低密度的高空环境,是尾翼稳定旋转火箭弹发生“掉弹”现象的根源。     

直升机旋翼/机体动稳定性研究进展

首先对直升机旋翼/机体动不稳定性问题的种类进行了简要概述,包括旋翼挥舞/变距、变距/摆振、挥舞/摆振和挥舞/摆振/变距耦合等孤立旋翼动不稳定性问题,以及直升机地面共振和空中共振等旋翼/机体耦合动不稳定性问题,然后分别从气动力与结构的高精度数值模型、动稳定性的计算分析方法和实验模型测试3 个方面详细介绍了直升机旋翼/机体动不稳定性问题的研究现状,并着重讨论了直升机旋翼/机体动稳定性分析技术最近的主要研究方向:耦合CFD(computational fluid dynamics)/CSD(computational structuraldynamics) 的直升机旋翼气弹动稳定性分析、复合材料旋翼动稳定性分析及其材料不确定性影响、带减摆器的旋翼/机体动稳定性分析和先进直升机构型的旋翼/机体动稳定性分析,最后对直升机旋翼/机体动稳定性研究的发展趋势进行了展望.     

变转速共轴旋翼载荷建模及实验验证

对共轴双旋翼无人飞行器操纵结构的简化,会引起旋翼载荷变化更加复杂。共轴双旋翼转速控制方法有助于飞行控制系统的实现,但是在飞行控制律设计时,需要透彻了解变转速旋翼的气动载荷变化,建立精准的旋翼载荷模型。本文深入分析了旋翼变转速情况下单旋翼系统和共轴双旋翼系统的旋翼入流分布,建立了单旋翼变转速旋翼载荷计算方法,提出了共轴双旋翼变转速旋翼载荷计算方法。明确了低雷诺数对微型旋翼飞行器的旋翼载荷计算影响,引入雷诺数修正系数完成对旋翼翼型升阻系数气动参数的修正和验证,提高了变转速共轴双旋翼载荷模型的计算精度。设计了一套变转速单旋翼系统和共轴双旋翼系统的旋翼载荷测量实验装置,通过实验测试完成了对共轴双旋翼载荷计算方法的验证,表明了所提出的变转速共轴双旋翼载荷模型和实验测试装置是可信的。     

复合环境下直升机旋翼动力特性分析

考虑直升机旋翼旋转时声场、应力刚化、几何大变形等复合运行环境,对多种影响因素下的旋翼动力特性进行研究。通过实验测试数据建立了直升机旋翼结构的动力有限元模型,对旋翼在静止、应力刚化影响下的动力特性进行了分析;建立旋翼声振耦合动力学模型,考虑外声场和旋翼几何非线性影响因素,深入研究旋翼动力特性的变化规律,分析了其内在机理。研究分析发现:考虑声场影响后结构前三阶的固有频率误差分别减小了0.46%、0.82%、0.45%,更接近实验值,旋翼桨叶的振幅峰值明显降低;应力刚化对旋翼模态影响较大,随着其转速的增加固有频率呈二次曲线上升趋势;几何非线性使旋翼的共振频率值略微增大、振幅极值减小。     

伽辽金有限元素法对旋翼气弹稳定性的应用

采用伽辽金加权余数有限元素法发展了一种悬停状态下无铰旋翼桨叶气弹稳定性的分析方法。分析模型包括预锥角、下垂角、预掠角、总距角、桨根预安装角、桨叶预扭角、变距轴偏置、根部外伸量和操纵线系刚度等结构参数，对无铰旋翼桨叶气弹稳定性研究有普遍适用意义。试验证明该理论可行并能用于研究无铰旋翼结构参数对桨叶气弹稳定性的影响，也能用于直升机旋翼的型号设计。     

平流层飞艇空气动力估算

本文采用有限基本解方法与工程估算方法相结合的气动力工程计算方法,用以计算平流层飞艇的气动力。将飞艇所受的气动力分成飞艇艇身和尾翼所受气动力两部分,每一部分的气动力按照无粘性流产生的线性气动力和粘性引起的非线性气动力分别进行计算。根据势流理论对飞艇艇身线性气动力进行分析计算,由于飞艇艇体是旋成体,故根据Allen的横流阻力理论对其所受的非线性气动力进行计算;尾翼的线性气动力采用有限基本解方法进行计算,非线性气动力用Polhamus-Lamar吸力比拟方法估算。该方法中考虑了由于尾翼安装在体上后,处于艇体产生的上洗流场中,尾翼气动力的变化和尾翼对艇身气动力的干扰作用。通过算例的计算与实验结果比较得出该方法可以快速、准确的计算飞艇所受的气动力。     

三点起爆形成尾翼EFP的数值模拟和实验研究

利用LS-DYNA软件对三点起爆形成尾翼EFP的过程进行了数值模拟,深入研究了爆轰波传播过程中的波形结构和强度的变化规律以及药型罩材料在复合爆轰波作用下驱动变形的特性和规律,加深了对三点起爆条件下药型罩形成带尾翼EFP机理的认识。在此基础上,设计了三点同步起爆装置和EFP装药进行实验。研究结果表明:设计的三点起爆装置作用可靠,满足三点起爆EFP装药的设计要求;形成的EFP弹形稳定,与计算结果吻合较好;尾翼EFP飞行过程中的速度降减小,稳定性提高。     

固定鸭舵双旋弹全弹道动态稳定性及其影响因素

为研究固定鸭舵双旋弹全弹道飞行时的动态稳定性问题,在小攻角条件下建立复攻角运动的状态空间模型,并应用霍尔维茨方法导出其特征根实部皆负的一般性条件.针对起控前/后前体滚转角的运动特点,利用常规旋转弹的稳定性分析方法,建立固定鸭舵双旋弹在不同飞行状态下的动态稳定性判据,其与常规旋转弹的形式相似,无控飞行时在升力和静力矩项中对应增加了舵面控制力和力矩项;有控飞行时进一步增加了有关项相对增量的影响.据此在后体参数确定的条件下推导舵面参数约束条件,并分析操纵舵控制力系数导数、安装位置和舵偏角对动态稳定性的影响,揭示了该类炮弹动不稳定形成的原因.对复攻角运动在不同条件下的仿真分析结果表明,当舵面引起的有关项相对增量同时位于无控和有控飞行的边界曲线内时,固定鸭舵双旋弹全弹道飞行动态稳定,验证了本文推导的动态稳定性判据和舵面参数约束条件合理,为该类炮弹的研制提供了理论依据与设计参考.     

半穿甲弹设计及穿甲实验研究

为提高半穿甲弹的穿甲能力,设计了一种贫铀半穿甲实验弹。对实验弹的飞行稳定性进行了理论分析及数值模拟,两种方法计算得到的实验弹稳定储备量基本吻合,且能够满足实验弹的飞行稳定性要求。采用100mm滑膛炮,开展了贫铀半穿甲弹侵彻装甲靶板实验。实验结果表明,实验弹飞行稳定,与理论分析及数值模拟结果一致;实验弹在25°倾角下贯穿三层20mm厚GY4装甲钢,且回收到的弹体基本完好。通过对实验后的实验弹和靶板进行分析,认为贫铀半穿甲弹的穿甲能力较强。     

仿生扑翼飞行机器人翅型的研制与实验研究

模仿昆虫和小鸟飞行的扑翼飞行机器人将举升、悬停和推进功能集于一个扑翼系统,与固定翼和旋翼完全不同,因此研究只能从生物仿生开始。生物飞行的极端复杂性使得进行完整和精确的扑翼飞行分析非常复杂,因此本文在仿生学进展基础上,通过一些合适的假设和简化,建立了仿生翅运动学和空气动力学模型,并以此为基础研制了多种翅型。研制了气动力测量实验平台,对各种翅型进行了实验研究。实验结果表明,研制的翅型都能产生一定的升力,其中柔性翅具有较好的运动性能和气动性能,并且拍动频率和拍动幅度对升力有较大影响。     

排翼布局飞行器气动性能的实验研究

通过低速低湍流度风洞实验,研究了利用排翼布局改善充气飞机采用大厚度翼型机翼带来的气动效率偏低问题。首先比较了采用不同厚度翼型的单翼与排式双翼布局的气动特性。在此基础上,为了优化排翼布局的气动特性,研究了给后翼安装偏转角对排翼布局气动特性的影响。同时,基于NACA0030翼型,设计了波纹型外形的充气机翼,比较了此外形下单翼和排翼布局气动性能的差异。实验结果表明,采用排翼布局能够改善采用厚翼型单翼布局的气动性能,而给后翼安装一定偏转角可以进一步提高排翼布局的升力和升阻比。采用波纹外形和光滑外形机翼模型的对比结果表明,波纹外形能够在大迎角时改善充气机翼的失速性能。分析认为,造成这一现象的流动机理是由于波纹型机翼在实验条件下提前由层流转捩为湍流,使失速推迟,流动分离现象有所减弱。     

The effects of corrugation and wing planform on the aerodynamic force production of sweeping model insect wings

The effects of corrugation and wing planform (shape and aspect ratio) on the aerodynamic force production of model insect wings in sweeping (rotating after an initial start) motion at Reynolds number 200 and 3500 at angle of attack 40° are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio (AR) of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing (forewing), hawkmoth and dragonfly (forewing), respectively (AR of these wings varies greatly, from 2.84 to 5.45). The following facts are shown. (1) The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex (LEV). (2) The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r ₂ (the radius of the second moment of wing area) is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. (3) The effects of AR are remarkably small: when AR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients. The project supported by the National Natural Science Foundation of China (10232010 and 10472008) and Ph. D. Student Foundation of Chinese Ministry of Education (20030006022) The English text was polished by Keren Wang.     

主动控制翼板抑制悬索桥颤振的研究

主动控制翼板是一种新型桥梁气动措施。本文基于非定常气动力理论，推演了安装主动控制翼板后作用在整个桥梁主梁单位长度上气动力表达式，从增加系统扭转阻尼的角度，研究了翼板主动扭转振动参数的选取。在此基础上，对某大跨悬索桥方案进行了二自由度颤振分析，结果表明：合理选取翼板的主动扭转振动参数，主动控制翼板能够有效地提高该桥的颤振稳定性。     

鸭式旋翼/机翼飞机悬停及小速度前飞气动干扰实验研究

鸭式旋翼/机翼飞机是一种新概念可垂直起降高速飞行器,为了解该飞机在悬停及小速度前飞时的全机气动干扰特性,在南京航空航天大学开口风洞中进行了飞机全机气动力实验,实验采用多台测力天平分别测量主机翼和机身的气动力.结果表明,悬停时受主机翼高速旋转产生的下洗尾流影响,机身产生了较大的法向力和低头力矩;前飞时下洗尾流对机身的法向力和俯仰力矩有比较严重的干扰,对滚转力矩和偏航力矩干扰较小,对侧向力有一定影响.实验结果为飞机的飞行动力学特性研究以及控制律设计提供了参考.＃     

Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight

The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to reduction in the thrust value and increases the lift component. The aerodynamic and performance parameters were nondimensionalized. Appropriate models were introduced which show its aerodynamic performance and may be used in the design process and also optimization of the flapping wing.     

飞机机翼气动外形优化设计研究

本文首先对某飞机原机翼外形进行了详尽的气动分析计算,然后确定了设计思路和方案,探讨了后掠角变化对机翼气动性能的影响,研究选定了减小外翼后掠角的机翼新平面形状,采用先进的CFD软件优化机翼的气动设计,根据不同设计思想进行了多个机翼的外形优化,包括新的翼剖面和弯扭配置,最后将优化设计结果与原机翼进行了对比,对比结果表明,以Q5-M2T和Q5-N2T为代表的优化结果取得了十分理想的改进效果,优化机翼提高了气动性能,机翼升阻比提高了20%-30%,满足了飞机载弹量增大后性能仍可以全面提高的设计要求。     

Aerodynamic Coefficients and Deformation Measurements on Flexible Micro Air Vehicle Wings

This paper documents the elastic deformations and corresponding aerodynamic coefficients of flexible wings used for micro air vehicles (MAVs). These low-aspect ratio wings, developed and fabricated at the University of Florida, incorporate an elastic latex membrane skin covering a thin carbon fiber skeleton. The wings were tested in a unique low-speed wind tunnel facility integrating a visual image correlation (VIC) system with a six-component strain gauge sting balance. Model characteristics are presented, along with the appropriate specimen preparation techniques and wind tunnel instrumentation. The static response characteristics, including full-field displacements and plane strain measurements, for three distinct MAV wing designs are presented. The full-field deformation results show how passive wing flexibility preferably affects aerodynamic performance when compared to a rigid model of similar geometry.     

模型昆虫翼作非定常i运动时的气动力特性

基于Navier-Stokes方程的数值解,研究了一模型昆虫翼在小雷诺数(Re=100)下作非定常运动时的气动力特性.这些运动包括翼启动后的常速转动,快速加、减速转动,常速转动中快速上仰(模拟昆虫翼的上挥或下拍、翻转等运动).有如下结果在小雷诺数下,模型昆虫翼以大攻角(α=35°)作常速转动运动时,由于失速涡不脱落,可产生较大的升力系数.其机理是翼转动时,翼尖附近(该处线速度大)上翼面压强比翼根附近(该处线速度小)的小得多,因而存在展向压强梯度,同时存在着沿展向的离心力,此展向压强梯度和离心力导致的展向流动在失速涡的轴向方向,其可避免失速涡脱落.模型昆虫翼在快速加、减速转动和快速上仰运动中,虽然雷诺数小,但由于在短时间内产生了大涡量,也可产生十分大的气动力,例如在快速上仰运动中,升力系数可大于10.     

The effects of corrugation and wing planform on the aerodynamic force production of sweeping model insect wings

The effects of corrugation and wing planform (shape and aspect ratio) on the aerodynamic force production of model insect wings in sweeping (rotating after an initial start) motion at Reynolds number 200 and 3500 at angle of attack 40° are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio (AR) of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing (forewing), hawkmoth and dragonfly (forewing), respectively (AR of these wings varies greatly, from 2.84 to 5.45). The following facts are shown. (1) The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex (LEV). (2) The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r ₂ (the radius of the second moment of wing area) is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. (3) The effects of AR are remarkably small: when AR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.