INFLUENCE OF NOSE PERTURBATIONS ON BEHAVIORS OF ASYMMETRIC VORTICES OVER SLENDER BODY

The influence of nose perturbations on the behaviors of asymmetric vortices over a slender body with a three-caliber ogive nose is studied in this paper. The tests of a nose-disturbed slender body with surface pressure measurement were conducted at a low speed wind tunnel with subcritical Reynolds number of 1×105 at angle of attack α=50°. The experiment results show that the behaviors and structure of asymmetric vortices over the slender body are mainly controlled by manual perturbation on the nose of body as compared with geometrical minute irregularities on the test model from the machining tolerances. The effect of the perturbation axial location on asymmetric vortices is the strongest if its location is near the model apex. There are four sensitive circumferential locations of manual perturbation at which bistable vortices over the slender body are switched by the perturbation. The flowfield near the reattachment line of lee side is more sensitive to the perturbation, because the saddle point to saddle point topological structure in this reattachment flowfield is unstable. Various types of perturbation do not change the perturbation effect on the behaviors of bistable asymmetric vortices.

ASYMMETRIC VORTICES FLOW OVER SLENDER BODY AND ITS ACTIVE CONTROL AT HIGH ANGLE OF ATTACK

The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area.This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices.This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices.The critical issues are discussed, which include the formation and evolution mechanism of asymmetric multi-vortices;main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure;the evolution and development of asymmetric vortices under the perturbation on the model nose;forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail.However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks.

Recent progress on the study of asymmetric vortex flow over slender bodies

The investigations of forebody vortex flow and its flow control have great importance in both academic field and engineering application areas. A large number of papers and many review papers have been published. However in this research field of forebody asymmetric vortices, three problems such as tip perturbation effect, Reynolds number effect and flow instability are less studied and thus not understood completely. So many researches are still working on the issues in recent years. The present paper attempts to provide a review of recent research progress on first two problems. The first problem is mainly concerned with how the vortex flow evolves after tip perturbation; how to solve the problem of repeatability and reproducibility of wind tunnel testing data; how to develop a conception of active flow control technique with tip perturbation based on the study of vortex flow response to tip perturbation. For the second problem one is mainly concerned that how the asymmetric vortices are developed with the increase of Reynolds number; how to classify the vortex flow patterns in different Reynolds number regimes; how to develop an appropriate boundary layer transition technique to simulate flows at high Reynolds number in the convention wind tunnels. Finally, some important ques- tions that deserve answers are proposed in the concluding remarks.

Experimental Investigation of the Characteristics of an Artificial Cavity During the Water-Exit of a Slender Body

Experimental studies are carried out with slender bodies vertically exiting out of the water using a high-speed camera. The mechanisms for the formation, development, and collapse of the cavity around the slender body are explored. The dynamic characteristics of the shoulder cavity and the trail cavity during the water-exit of low-speed bodies are analyzed for various water depths and initial velocities. The results show that the initial velocity has a great influence on the formation, development, and collapse of the cavity. The length and the thickness of the shoulder cavity vary non-linearly with the depth.

AN ANALYTIC SOLUTION ON HYPERSONIC FLOW OVER AN ARBTTRARY SLENDER BODY WITH NEAR POWER-LAW PROFILE

On the basis of a self-similar solution as well as of the assumption of the 'Transserse Motion',a general linear theory on hypersonic flow over a general slender body is set up in this paper By means of this theory, the problem concerned can he put into a universal system of O.D Eqs .which can be integrated manerically in adyance

Proof of Concept MFD Optimization of the Aftbody Geometry of Axisymmetric Slender Body Based on Wave Drag Considerations

A comprehensive, universally valid, elegant and yet simple method to design slender axisymmetric body of minimum wave drag in transonic and supersonic flows is developed. Computational aerodynamics is also used as a tool for numerical experiments in gaining physical understanding of the drag mechanism due to the geometry of the aftbody, such as the correlation between wave drag and wave distribution of the aftbody geometry. The method utilizes MFD （modified feasible direction） based optimization program, along with the linear slender body aerodynamics, for its elegance and generic optimization convenience. The efforts are focused on inviscid flow. A practical method of reducing the wave drag of a given body is developed for both bodies with pointed end and with base area, using shock wave generator at a particular location on the aftbody. The results show that the MFD optimization program can be effectively utilized in an aerodynamic optimization problem.

高速条件下细长旋成体背风区流动特性试验研究

导弹全方向攻击时会产生由旋涡主导的复杂流动,发生转捩和流动分离,对导弹的机动性和控制能力具有重大影响。为探索攻角及马赫数对弹体流动形态的影响,针对某细长旋成体在FD-12风洞开展高速粒子图像测速及荧光油流试验,来流Ma分别为0.4、0.6、0.8,攻角范围α为0°~180°,获取了细长体背风区的流场特性演化规律。研究结果表明:当攻角α<90°时,随着攻角的增大,模型背风区流场从附着流变化为分离流,且分离涡从对称变为非对称,最终演化为非定常流动;当攻角α>90°时,情况有所不同,α=100°及α=120°时背风区存在非定常涡脱落现象,时均流场具有明显的非对称性;当攻角α=150°时,迎风面分离区出现不对称偏移,初始分离区下边界已越过模型端面,在模型中后部形成分离线;当攻角α=180°时,时均流场没有明显的特征,在模型头部位置出现了环形分离区及再附区,表明由于底部扰动的影响,该截面流场呈现局部的非定常、非线性流动状态;在攻角相同情况下,增大流场的来流Ma,不但会使分离涡的影响范围变大,也会导致分离涡的位置抬高。

船舶阻力预测几种理论的深度探讨

随着世界经济的全球化发展,海运运输成为一种经济实用的运输方式。海运运输的发展离不开各种各样的船舶。船舶在水中行驶时,由于海水是黏性液体,因此会受到阻碍作用,故而会产生船舶阻力。为了提高船舶在海水中行驶的速度,同时降低燃油消耗,因此需要对船舶阻力进行计算。船舶的种类不同,其型线就不同。型线不同自然导致其与水的接触面积不同。因此,针对不同船型的种类,其船舶阻力的计算方法也是不同的。预测船舶阻力的计算方法可以按照船体类型划分为不同的计算类型,分别有适用于滑行艇阻力预测的算法、适用于排水型船舶阻力预测的算法、适用于游艇阻力预测的算法以及细长体理论。探讨结果说明,不同算法和理论适用于不同的船体类型,也有其特定的适用范围。

火星大气环境下发动机喷流对飞行器气动特性的影响分析

本文采用计算流体力学(CFD)方法模拟火星大气参数和发动机喷流,研究火星大气对飞行器气动特性的影响,针对发动机喷流对火星大气环境下细长体飞行器的气动特性影响开展了研究。计算结果表明:相较地球大气,火星大气环境计算出的轴向力系数更大,压心系数在跨声速段波动更小。为了进行精细化的火星飞行器气动外形设计,需要进一步优化火星大气计算模型,更加真实地模拟火星大气环境带来的影响。火星大气环境下的发动机喷流也会显著改变上升飞行器的全箭气动特性,影响飞行器表面的压力分布和下游流场区域。火星飞行器受到喷流影响,轴向力系数在Ma=5前变小,在Ma=5后变大,法向力系数以及压心系数在跨声速段会突然减小。

基于放宽静稳定度空空导弹重定向研究

采用放宽静稳定度设计,利用空空导弹静不稳定性产生的气动力矩,设计了空空导弹重定向使用流程,提出了空空导弹完成重定向的运动学标志。根据细长体理论和粘性横流理论分析了空空导弹重定向过程中的气动力和力矩,认为无控细长旋成体无法满足本文提出的完成重定向的运动学标志,必须增加气动舵面或直接力等控制方式。以大长细比鸭式舵身的简单组合体为研究对象,采用工程理论方法获取0°~180°攻角范围内气动特性,并计算了重定向过程中空空导弹轨迹和姿态。结果表明,本文提出的基于放宽静稳定度的重定向技术能够在1.15 s内实现空空导弹安全、快速、稳定的重定向。最后,分析了空空导弹重定向过程中应该注意的关键设计问题。

细长体分布式载荷的缩聚及其在气动伺服弹性地面模拟中的应用

气动伺服弹性地面模拟试验是近年发展出的一种新型气动弹性地面试验技术,其中的一个关键问题就是非定常气动力的缩聚,即将飞行器所受的分布式气动载荷缩聚为少数几个集中载荷。传统缩聚方法以简单的力、力矩平衡准则对分布力进行处理,或者是通过求解静不定问题,把支反力作为缩聚力,均存在一些缺点。本文提出一种基于一维样条插值的细长体分布式载荷缩聚方法,采用关键模态相似准则来优化缩聚点位置,以达到细长体在缩聚点集中式载荷作用下的动响应与分布式载荷作用下的动响应最为接近的效果。利用简支梁、悬臂梁两个算例验证了所提出的分布式载荷缩聚方法的精度,并将该方法应用于一个细长体导弹的气动伺服弹性地面模拟中。数值仿真表明,所提方法能够快速准确将导弹的非定常气动力缩聚成实时的集中力,满足气动伺服弹性地面模拟试验的精度和快速性要求。

基于回归分析方法的船舶阻力估算

阻力预测是船舶设计的重要环节。本文采用多种阻力预测方法对KCS船舶、KVLCC2船舶、Wigley船型以及NPL圆舭艇的阻力进行估算,验证多种阻力预测方法的计算精度和可靠性,探究各种阻力预测方法的适用范围。结果表明,基于回归分析方法计算常规排水型船舶阻力和基于细长体方法计算瘦长船型和方尾船阻力的方案可行。船型特征是选择阻力预测方法的首要因素。细长体理论计算的自由面波形结果基本令人满意。本文对船舶阻力估算方法的研究起到一定的借鉴和参考作用,同时也提供了一系列阻力计算的验证算例。

等离子体激励控制细长体分离流动研究

为研究等离子体激励对细长体大迎角分离流场的控制作用,运用了模拟等离子体激励作用效果的唯象学模型,将等离子体对流动的控制作用简化为对流场的能量注入,数值模拟研究了等离子体放电能量密度、放电位置对控制效果的影响。结果表明:在细长体头部施加等离子体激励,能够控制细长体背涡结构,实现对细长体大迎角下产生的侧向力进行控制;当等离子体激励位置不变时,放电功率越大,对细长体大迎角分离流场的影响越大;当等离子体激励越远离头部时,对细长体分离流场的控制作用越弱;当等离子体激励与低位涡同侧并且远离迎风面对称面附近时,才能实现对细长体分离流场的控制。

固体火箭发动机随动推力作用下细长体亚临界试车及动力学失稳临界推力预示

设计了随动推力作用下细长体模拟件试车试验系统,开展固体火箭发动机试车;理论推导了耦合模态频率差-推力关系的多项式,结合亚临界试车数据外推预示失稳临界推力。研究结果表明:理论分析与地面试验结果吻合,只需开展少数几次安全可控的亚临界试车试验,获取系统的振动响应数据,即可准确预测临界推力;亚临界试验验证了随动推力横向分量引起模态间的刚度耦合,对于弯曲振动明显的细长体飞行器,推力对结构的影响应视为随动载荷。

随动推力作用下细长体结构振动模态特性及稳定性分析

引入随动推力横向分量的细长体结构的振动模态特性与稳定性进行对比分析。分析结果表明:随动推力轴向分量作为保守力,引起细长体结构轴向刚度的削弱;随动推力横向分量为非保守力,使系统的动力学失稳临界值高于静态屈曲的临界值。在失稳临界点,细长体结构的1、2阶频率重合,说明随动推力横向分量引起细长体结构模态间的刚度耦合。因此,对于弯曲振动明显的细长体结构,随动推力横向分量的影响不可忽略。

系列头型空泡特征及其对细长体阻力特性影响的试验研究

为了了解不同头型的空泡特征及其对轴对称体阻力特性的影响,在高速水洞中试验研究了6种典型头体在不同空泡数下,轴对称体上空泡的几何特征以及相对应的阻力特性,分析了空泡数对轴对称体空泡特征与阻力的影响.

伴随超空泡产生的高速细长体入水实验研究

介绍了几种不同工况下高速细长体入水过程的实验研究工作.用高速摄影仪实时记录了细长体高速入水时与自由液面之间的瞬态相互冲击作用,清晰地观察了细长体高速入水后诱导生成的水中空泡流的形态及其演化过程.具体分析了几种工况下高速细长体入水瞬间自由面的波动特性和细长体入水后运动的不稳定性.从实时记录的照片中,测量出相邻2帧图片之间的细长体的位移差之后,计算出细长体在入水过程中以及在水中的瞬时速度.通过分析物体速度的变化趋势,了解了超空泡流动的复杂过程.

分层流体中细长体生成内波的试验研究

在密度连续分布的3层流体中,对细长体运动生成的内波问题进行了模型试验研究.采用多通道电导率阵,测量分析了拖曳模型产生内波的相关速度、垂向位移场及其波形结构.结果表明,拖曳模型产生的内波可以分为两类:一类是由定常源激发的Lee波;另一类是由非定常源激发的尾迹波,而且Lee波转换为尾迹波的临界内Fr=4.

小攻角带空泡细长体的试验研究

本文对小攻角带空泡细长体进行了较为细致的试验研究。其中包括水洞三分力天平的研制与测力系统的建立 ,空泡起始、发展空泡形态观测 ,空泡几何特征的测量和定常来流中空泡水动力的测量 ,对试验结果进行深入的研究和分析 ,以揭示其中某些内在的规律性 ,同时为进一步的研究提供经验。

细长体大迎角非对称涡流的数值研究

通过数值方法对大迎角细长体低速湍流流场的模拟,探讨头部顶端极小扰动对细长体非对称绕流形成与发展的影响.结果表明在细长体顶端附近施加极小扰动可以模拟出实验观测到的非对称流场,非对称的涡系结构沿轴向是逐步发展的,截面侧向力沿轴向的分布呈现正弦型曲线的变化特征,扰动能量经过指数增长后达到饱和,有效扰动的规模影响涡流非对称性的大小及分布,单侧扰动产生的流场非对称性随扰动周向位置的变化呈现单周期性规律.小扰动诱发非对称的数值算例表明非对称绕流的形成是源于流场的空间不稳定性机制.