Calculation of Aerodynamic Characteristics of Hypersonic Vehicles Based on the Surface Element Method

A program for calculating the aerodynamic properties of hypersonic vehicles based on the surface element method was developed using the general-purpose programming language C++. The calculated values of lift coefficients, drag coefficients, and surface pressure coefficients are discussed with the results of wind tunnel experiments using the HL-20 lift body and the NASA hypersonic aircraft STS Columbia OV-102 as research subjects. Finally, the results of the experimental and wind tunnel studies of the aerodynamic characteristics of the HL-20 lift body at an altitude of 65 km and Mach numbers of 6 and 10 Ma are discussed. The maximum error in the aerodynamic characteristics at 6 Ma does not exceed 3%, consistent with the results. The maximum error at 10 Ma occurs in the 11° - 14° angle of attack and does not exceed 10%, which is still within the error tolerance. The STS results for NASA’s hypersonic aircraft were also tested using this procedure. Experimental aerodynamic data for the Colombian OV-102 aircraft. The results show that the program takes only 10 minutes to calculate the results, with no more than 2% error from the wind tunnel experimental results.

Aerodynamic characteristics of moving vehicles of two trains passing each other on bridge under crosswinds

Two trains passing each other is controlling factor for the wind-vehicle-bridge systems.To test the aerodynamic characteristics of moving vehicles under crosswinds when two trains are passing each other,a wind tunnel test device,which has two moving tracks,was developed.The rationality of the test result was discussed,the effects of intersection mode,yaw angle and lane spacing on the aerodynamic coefficients of the leeward train were analyzed,and the difference of aerodynamic coefficients between the head vehicle and the tail vehicle was discussed.The results show that the proposed test device has good repeatability.The intersection modes have a certain effect on the aerodynamic force of the leeward train when two trains are passing each other,and the results should be more reasonable during the two trains dynamic passing each other.With the decrease of yaw angle,the sudden change of train aerodynamic coefficients is more obvious.The decrease of lane spacing will increase the sudden change of leeward vehicles.In the process of two trains passing each other,the aerodynamic coefficients of the head vehicle and tail vehicle are significantly different,so the coupling vibration analysis of wind-vehicle-bridge system should be considered separately.

Effect of Fuselage Cross Section on Aerodynamic Characteristics of Reusable Launch Vehicles

An experimental study on examining aerodynamic characteristics of fuselage cross sections for RLVs (Reusable Launch Vehicles) was conducted at Mach number 0.3, 0.9 and 4.0 in the wind tunnel of ISAS (Institute of Space and Astronautical Science), JAXA (Japan Aerospace Exploration Agency). Three bodies, having the same projected area and length, with and without a set of fins, were tested. Their cross sections are a circle, a square and a triangle with rounded corners. The results showed that the fuselage cross sections had large effects on aerodynamic characteristics in subsonic and transonic flow. The lift coefficient of the model having the triangular cross section with a set of the fins was larger than that of the others in high angles of attack region due to contributions of the separation vortices generated from the fuselage expanding to the wing surface.

Numerical Analysis of Aerodynamic Characteristics of the HALE Diamond Joined-Wing Configuration UAV

The investigation on the aerodynamic characteristics of the high-attitude long-endurance (HALE) Diamond Joined-Wing configuration unmanned aerial vehicle ( UAV) was carried out by the theoretical analysis method and numerical simulation. Research indicates that as the wing of the UAV is composed of the front wing and the after wing, the after wing has the ability to transmit the front wing's boundary layer to the after wing root which can inhibit the front wing's flow separation. Although the front wing was affected by the retardation of the after wing, the aerodynamic performance of the front wing was better than that of alone front wing in most cases. The after wing was also affected by the wake and downwash of the front wing, and its aerodynamic performance was greatly decreased. The characteristic curve of the pitching moment of the UAV had nonlinear characteristics. The flow field structure of the after wing changed by the front wing wake direct sweep and flow separation at the after wing root were the main reasons that non-linear ′rise′phenomenon occurred in two segments ( α = 0° and α = 8° ) of the characteristic curve of pitching moment. Moreover, coupling of the flow separation characteristic of the front wing and the after wing resulted in the pitching moment ′pitchup′ phenomenon. The lateral-directional static stability of the flat layout was weak. The HALE Diamond Joined-Wing configuration UAV ' s aerodynamic performance can be improved and the problems in engineering applications can be effectively alleviated by adjusting the overall layout parameters.

Aerodynamic Characteristics of Projectile with Exotic Wraparound Wings Configuration

A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configuration are simulated numerically by applying the Roe scheme. The shear-stress transport turbulence models and the lower-upper symmetric Gauss-Seidel implicit method are used to solve 3D Reynoldsaveraged Navier—Stokes equations. The differences in aerodynamic coefficients and aerodynamic characteristics of the projectiles when the Mach number varies from 0. 35 to 0. 95 are obtained,and the cause of these differences is analyzed. The calculation results indicate that the lift-to-drag ratio of the projectile significantly increases,the rolling moment decreases,and the position of the pressure center of the projectile shows relatively small changes when the exotic WAW configuration is used. Therefore,this projectile can obviously reduce rolling effect,enlarge range and improve flying stability.

Aerodynamic characteristics research on wide-speed range waverider configuration

Waverider generated from a given flow field has a high lift-to-drag ratio because of attached bow shock on leading edge. However, leading edge blunt and off-design condition can make bow shock off leading edge and have unfavorable influence on aerodynamic characteristics. So these two problems have always been concerned as important engineering science issues by aeronautical engineering scientists. In this paper, through respectively using low speed and high speed waverider design principles, a wide-speed rang vehicle is designed, which can level takeoff and accelerate to hypersonic speed for cruise. In addition, sharp leading edge is blunted to alleviated aeroheating. Theoretical study and wind tunnel test show that this vehicle has good aerodynamic performance in wide-speed range of subsonic, transonic, supersonic and hypersonic speeds.

Prediction of Aerothermal Environment and Heat Transfer for Hypersonic Vehicles with Different Aerodynamic Shapes Based on C++

This research paper discusses constructing a unified framework to develop a full-rate scheme for hypersonic heating calculations. The method uses a flow tracing technique with normal phase vector adjustment in a non-structured delineated grid combined with empirical formulations for convective heat transfer standing and non-standing heat flow engineering. This is done using dev-C++ programming in the C++ language environment. Comparisons of the aerodynamic thermal environment with wind tunnel experimental data for the Space Shuttle and Apollo return capsules and standing point heat transfer measurements for the Fire II return capsule was carried out in the hypersonic Mach number range of 6 - 35 Ma. The tests were carried out on an 11th Gen Intel(R) Core(TM) i5-1135G7 processor with a valuable test time of 45 mins. The agreement is good, but due to the complexity of the space shuttle tail, the measurements are still subject to large errors compared to wind tunnel experiments. A comparison of the measured Fire-II return capsule standing-point heat values with the theory for calculating standing-point heat fluxes simulated using Fay & Riddell and wind tunnel experiments is provided to verify the validity of this procedure for hypersonic vehicle heat transfer prediction. The heat fluxes assessed using this method for different aerodynamic profiles of hypersonic vehicles agree very well with the theoretical solution.

Extended Range Guided Munition Aerodynamic Configuration Design

Based on the analysis of the flying scheme and flying style of an extended range guided munition(ERGM), the aerodynamic characteristics design standards were put forward. According to the standards, the ERGM aerodynamic configuration was designed, and the wind tunnel experiments were processed. The experimental results show that the configuration has lower drag and good static stability at unguided flying stage. Moreover, the stability, maneuverability, rudder deflection angle and balance angle of attack of the configuration are all reasonably matched at guided flying stage, and the munition with the configuration can glide with larger lift-drag ratio at little balance angle of attack. The experimental results also indicate that the canard can't conduct rolling control when 1.0 ＜ Ma ＜ 1.5, so the ERGM must take rolling flight style with certain limited rolling speed.

Control for Underactuated Reentry Aircraft in Small Angle of Attack

The control problem for under-actuated reentry vehicle like HTV-2 is considered with small angle of attack.The control strategy for an aircraft with positive lateral control departure parameter relies on strong lateral stability,which declines with the decrease of the angle of attack.Thus,to control the lateral-directional motion in a stable state is hard and even impossible in some scenarios where the under-actuated reentry vehicle,like HTV-2,flies in a low angle of attack.To address this problem,the lateral-directional open-loop motion characteristics are analyzed.The results show that in an uncontrolled state,the lateral-directional motion can automatically converge to stabilization thanks to the aerodynamic damping effect.Therefore,a method of turning-off the lateral-directional control and inviting aerodynamic damping to control can achieve stability.The six-degree-of-freedom simulation show that the lateral-directional motion can be stabilized by the aerodynamic damping,and the lateral position error caused by the bank angle deviation is limited near the zero-rise angle of attack.The control strategy is effective.

Aerodynamic configuration optimization by the integration of aerodynamics, aerothermodynamics and trajectory for hypersonic vehicles

The problem of aerodynamic configuration design optimization is a multidisciplinary design optimization(MDO) problem, and recently the MDO method is widely adopted in the field of hypersonic vehicle configuration design. From the aerodynamic point of view, the aerodynamics, aerothermodynamics and trajectory are considered in this paper. Generally speaking, the aerodynamic characteristics, aerodynamic heating and trajectory are determined by the aerodynamic configuration and the design of flight trajectory. The design method considering these three disciplines is proposed. The parametric geometrical configurations are proposed, and the aerodynamic characteristics are predicted by the rapid and effective engineering method. The optimization of aerodynamic configuration considering the integration of aerodynamics,aerothermodynamics and trajectory is investigated based on the parametric geometrical configuration. Maximum lift-to-drag ratio, maximum range of the trajectory and minimum total heat load of the stagnation point are chosen as the three optimal goals. The detailed research indicates that the optimal configurations and trajectories with different weighting factors can be obtained by the optimization, and there are obvious differences between them. The optimal configuration and flight trajectory obtained by the optimization can be used as the feasible schemes in the future work.

Trim Drag Prediction for Blended-Wing-Body UAV Configuration

A rapid method of the trim drag prediction for the blended-wing-body unmanned aerial vehicle(UAV)configuration is proposed.The method consists of four steps.The first step is to parameterizedly model the blended-wing-body UAV configuration;the second is to analyze the aerodynamics of the geometric model;the third is to create aerodynamic surrogate model;and the final step is to predict the trim drag using the surrogate model.Hence,a tool for trim drag prediction is developed by integration of the four steps.The impacts of the allocation of control surfaces,position of gravity center and planform parameters on the trim drag are investigated by using the tool.Results show that using the control surface in outer wing for trim has an advantage of lower trim drag,and the position of gravity center has a primary impact on the trim drag.Moreover,the planform has secondary impacts on the trim drag.

典型布局无人机流场和气动特性数值模拟

典型布局无人机(unmanned aerial vehicle, UAV)作为模型飞行试验的研究载体,研究其流场和气动性能至关重要.旨在分析典型布局无人机在马赫数Ma=0.2、雷诺数Re=4.3×106流动条件下的气动特性,重点考察攻角(angle of attack, AoA)变化对无人机升阻比、表面压力分布及流场结构的影响.采用高精度数值模拟方法,系统评估了不同攻角下的飞行性能.研究结果显示,攻角约为3°时,无人机可实现最优升阻特性,且随着攻角的增大,在机翼表面会呈现λ型流线分布.此外,探讨了无人机在非定常大攻角工况下的涡结构演变,揭示了涡结构与无人机气动特性的关系.

纵列双桨无人机的气动仿真分析

为解决纵列双桨无人机的桨叶重叠部分的气动干扰导致的旋翼效率减少问题,基于计算流体力学(CFD)方法对纵列双桨无人机的气动特性进行了仿真分析,包括不同攻角、两桨叶相对位置变化以及整流罩气动外型优化。结果表明:在不同攻角下,无人机的攻角对升力系数的影响大于阻力系数;无人机两桨叶在纵向距离3420 mm、轴向距离540 mm时旋翼的干扰最小,效率最高。之后进行了无人机整流罩优化,得到了更加理想的气动外型。为纵列双桨无人机的气动设计提供了重要的参考和指导,同时也为无人机的发展和应用提供了有益的实践经验。

小型巡飞弹螺旋桨布局气动特性研究

基于CFD方法研究了某型巡飞弹螺旋桨前置/后置两种布局的气动特性,以及对整弹气动特性的影响,结果显示,在20~40 m/s的来流速度下,螺旋桨有效避开了巡飞弹机身的尾流影响,两种布局形式对螺旋桨气动特性的影响并不显著,但与整弹的气动耦合效应明显。由于前置布局螺旋桨加速了流经巡飞弹的气流,因此整弹升力系数最大增加12.65%、阻力系数最大增加28.32%。总体来看,螺旋桨后置布局具有更高的整弹升阻比,在螺旋桨前进比为0.40时增幅最大,相较于前置布局增加了1.01。

蝴蝶飞行机理及仿蝴蝶扑翼飞行器研究进展综述

仿生扑翼飞行器具有高机动性、高隐蔽性以及高效率等突出优势,在军事侦查、探险搜救等领域具有较好的应用前景,而其应用的基础是对生物飞行机理的深入探究.随着先进运动观测和实验技术的引入,对昆虫飞行行为的记录和分析更为便捷和准确.研究表明常见的昆虫拍打频率较高,在25~400 Hz之间,而蝴蝶较为特殊,其扑打频率较低,大约为10 Hz,对于蝴蝶的许多独特的飞行技能尚缺少足够的认识.蝴蝶前翼和后翼的翼面积都较大,身体同侧的前后翼几乎为同步拍打,且扑打幅度较大,甚至接近180°.蝴蝶飞行中身体有较大幅度的上下和俯仰震荡,翼和身体运动高度耦合.即便如此,蝴蝶仍具有敏捷的飞行能力,可以达到点对点的飞行目标,甚至上千公里的长途迁徙,是优秀的仿生学研究对象.因此,蝴蝶启发的仿生扑翼飞行器也得到了全世界研究人员的关注.蝴蝶的飞行机制相对于其他昆虫更加特殊,飞行行为和气动特性更为复杂,这使得仿蝴蝶扑翼飞行器的研制更加困难.目前对于仿蝴蝶飞行器的研制大多数对蝴蝶翼–身耦合的机理进行了简化,很少能实现受控的稳定飞行.最后,本文梳理了真实蝴蝶的飞行行为特点和飞行机理,指出了仿蝴蝶扑翼飞行器研制的关键技术,总结了该类飞行器未来的发展方向和应用前景.

升力翼对列车气动特性及运行安全性的影响研究

为探究升力翼高速列车的可行性,结合列车空气动力学和车辆多体系统动力学理论,建立了有/无升力翼高速列车空气动力学模型和车辆系统动力学模型,对有/无升力翼高速列车在明线无风及横风运行环境下的气动特性及运行安全性进行了仿真研究。研究结果表明:安装升力翼可提升高速列车的气动升力及升阻比,但气动阻力也大幅度增大;有/无翼高速列车周围流场特性差异较大,安装升力翼后列车表面压力分布及流线流向改变,列车滑流速度峰值增大,两侧及尾流区域速度分布改变。横风下列车表面压力分布及背风测涡脱结构改变,头车受到的气动阻力、升力、侧力及点头力矩相比于无翼时有明显的增大,升力与侧滚力矩差异明显,侧滚力矩方向改变且数值增大,摇头力矩变化很小。明线无风下,安装升力翼能够减小6%~13%的轮轨垂向力,其中尾车由于气动升力最大,轮轨垂向力减幅最显著;运行速度在450 km/h及以下时升力翼高速列车能够安全平稳运行,运行速度在500 km/h时升力翼高速列车轮轨垂向力和轮重减载率超限;影响安全性的主要原因是升力翼扩大了各节车之间气动载荷的差异,升力翼的气动布局有待进一步改善,建议减小头车和尾车的升力;横风环境下,升力翼高速列车头车受到升力、侧力及侧滚力矩数值明显增大,运行安全性恶化,横风安全域缩小。

预报风强度对火箭最大气动载荷精度影响及建模分析

针对不同预报风强度的精度以及其对应的最大气动载荷预报值精度的研究文献极少。以某地区实况风为基准,分别对不同预报风强度的精度以及其对应的最大气动载荷预报值精度特征进行了分析,并利用多元线性回归方法建立了订正模型,结果表明在预报日数第1~11天,预报风强度越大,预报风精度及其对应的最大气动载荷预报值精度越高;利用多元线性回归方法可提高最大气动载荷预报值精度,且预报风强度越小,最大气动载荷预报精度提高越明显。这些发现在火箭发射前的飞行保障及安全决策方面具有参考价值。

倾转机翼旋翼无人机倾转过渡状态数值模拟

倾转机翼旋翼无人机相较于传统构型倾转旋翼机能够显著改善悬停状态旋翼尾迹对机翼的气动干扰影响,提高飞行效率。针对该构型无人机具有复杂非定常气动特性的连续倾转过渡过程,采用由经典的分离涡模拟方法(DES)改进得到的延迟分离涡模拟方法(DDES)对其进行流场气动干扰计算,倾转过渡过程中无人机前飞速度、旋翼桨距角、机身与固定翼迎角以及短舱倾转角都随时间动态变化。通过与无倾转机翼传统构型对比,分析了倾转过渡过程气动性能变化以及流场机理。仿真计算结果表明,倾转初始状态无人机受到旋翼下洗流影响较小,在30°短舱倾转角以前的倾转过程,由于倾转机翼段阻力增大,导致旋翼需用拉力增大。倾转机翼段在倾转过程中产生的分离涡与旋翼下洗流尾迹产生碰撞干扰,导致在机翼翼梢位置产生更大的尾迹干扰区域,并且对内侧固定翼翼梢产生下洗效果,降低了整机升力。

临近空间球载飞行器投放控制关键技术综述

临近空间作为地球新的认知领域和重要的国家安全空间逐渐受到世界主要大国的重视.临近空间飞行器球载投放起飞方式能够使飞行器快速达到期望的飞行高度,同时减少因穿越对流层稠密大气所需的能源消耗,因而受到广泛关注并迅速发展成为临近空间飞行器起飞的一种重要方式.独特的球载投放起飞方式对高空气球及被投放飞行器的多项控制关键技术提出了较高的要求,高空低密度的飞行环境使得低速飞行具有明显的低雷诺数特性,随高度剧烈变化的风场增加了球载平台定点区域驻空的难度,载球系统上升过程的旋转运动给投放控制带来巨大的干扰,投放时刻的判断与拉起控制给大翼展柔性飞行器带来了新挑战.本文梳理了临近空间球载飞行器投放控制的关键技术及其研究现状,并对其未来的应用进行了展望.

材料属性对柔性仿生扑翼气动特性的影响

为探究不同材料属性柔性扑翼飞行器气动特性的变化,通过ANSYS中Fluent与Transient Structural的双向流固耦合方法,采用k-ω湍流模型,分别对三维柔性扑翼飞行器在不同材料属性下的气动特性进行数值模拟,得到了其瞬时升力、推力随翼面弹性模量的变化情况,并研究了一周期内扑翼展向流场压力分布与涡结构变化情况。研究结果表明,在一定范围内增加翼面弹性模量,对瞬时升力的提升效果并不明显,瞬时推力会随弹性模量的增加而降低。