VORTEX CONTROL BY THE SPANWISE SUCTION FLOW ON THE UPPER SURFACE OF DELTA WING

The numerical investigation has been performed to explore the feasibility of vortex control by leading edge sucking excitation on a delta wing. The results reveal that the flow on the upper surface of the delta wing changes significantly in a wide range of the angle of attack. For the vortical flow at moderate angle of attack, the secondary and tertiary vortices are weakened or suppressed, and the total lift is almost unchanged. For the stalled flow at high angle of attack, the leading edge concentrated vortex is recovered, and the lift is enhanced with increasing suction rate. For the bluff-body flow at even high angles of attack, the lift can still be improved. The concentrated vortex disappears on the upper surface, and the load increment is nearly unchanged along the chordwise direction.

Study on Forms of Vortex Breakdown over Delta Wing

Visualization test is performed at the water channel of BUAA. The vortex coreis visualized by dye injection from a small tube located upstream the apex of a delta wing. Thetest results are recorded by a video camera connected to a computer and processed by Photoshop^(^R)software. The test shows new findings in the following respects: (1) Besides the well known spiraland bubble forms of vortex breakdown, there are 3 other forms of vortex breakdown over delta wingfound in the test. They are the frog-jump form, the double spiral form and the filiform spiral form.(2) It has also been found that there is a transition from the spiral form to the bubble form andthen back to the spiral form in the test. Therefore it shows that the spiral form vortex breakdownover delta wing is often observed. (3) In a certain sense it can be said that the bubble form ofvortex breakdown is a special case of the spiral form type. There is no essential difference betweenthem. For the bubble form of vortex breakdown , there are branches of the vortex core and manyelements carrying vorticity separated from the vortex core. However, there is at least one vortexfilament that forms a spiral or a complex warping shape.

Conceptual Design Optimization of Fighter Trainer Aircraft with Double-delta Wing Configuration

Compared with a delta wing aircraft, the double delta wing configuration has better aerodynamic performance at high angles of attack. An operational analysis was introduced as a method for evaluating training effectiveness of trainer aircraft. Approaches to the engineering estimation of aerodynamic characteristics for aircraft with a double delta wing configuration were studied, and the procedures for determining aircraft performance indices formulated. Taking training effectiveness as the objective function and geometric parameters of the wing platform as design variables, through a numerical multivariate optimization arithmetic, the conceptual design optimization for a certain fighter trainer aircraft with double delta wing configuration was carried out under the constraints of tactical and technical requirements and interrelated geometry. Agreement of a calculation example with engineering practice indicates that the optimal design has higher training effectiveness than the baseline design, and in addition, improves the structural force bearing conditions.

EXPERIMENTS AND ANALYSIS OF HYSTERESIS OF VORTEX BREAKDOWN OVER PITCHING-UP DELTA WINGS

An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is the time or phase lag due to the ini-tial suPerPOsition of linearized small disturbance, which enlarges the range of the incidenceof keeping attached flow and postpones the initial incidence of vortex breakdown. Theother is the reduction of adverse pressure gradient due to the periphery centrifugal instabil-ity after the concentrated vortex has come into being, which is the key reason of hystere-sis of vortex breakdown- The structure of vortex over a pitching up delta wing can be di-vided into three layers, which is not a significant a1teration compared with that of vortexover a static delta wing.

Aerodynamic improvement of a delta wing in combination with leading edge flaps

Recently, various studies of micro air vehicle （MAV） and unmanned air vehicle （UAV） have been reported from wide range points of view. The aim of this study is to research the aerodynamic improvement of delta wing in low Reynold＇s number region to develop an applicative these air vehicle. As an attractive tool in delta wing, leading edge flap （LEF） is employed to directly modify the strength and structure of vortices originating from the separation point along the leading edge. Various configurations of LEF such as drooping apex flap and upward deflected flap are used in combination to enhance the aerodynamic characteristics in the delta wing. The fluid force measurement by six component toad ceil and particle image velocimetry （PIV） analysis are performed as the experimental method. The relations between the aerodynamic superiority and the vortex behavior around the models are demonstrated.

Piezoelectric energy harvesting from flexible delta wings

The potential for harvesting energy from a flexible delta wing using a piezoelectric bimorph is experimentally investigated.Different configurations of the proposed harvesting system were tested in a wind tunnel over a broad range of airspeeds.In addition to evaluating the level of harvested power,an analysis is performed to extract critical aspects for the relation between speed,flexibility,geometry and the potential power that can be harvested from a clamped,cantilevered flexible delta wing at low angles of attack and low speeds.This analysis provides an insight into parameters that impact energy harvesting from flexible membranes or elements.

Mechanism of Generation and Collapse of a Longitudinal Vortex System Induced around the Leading Edge of a Delta Wing

The purpose of the paper is to clarify the mechanism of generation and collapse of a longitudinal vortex system induced around the leading edge of a delta wing. CFD captured well characteristics of flow structure of the vortex system. It is found that the vortex system has a cone-shaped configuration, and both rotational velocity and vorticity have their largest values at the tip of the vortex and reduce downstream along the vortical axis. This resulted in inducing the largest negative pressure at the tip of the delta wing surface. The collapse of the vortex system was also studied. The system can still remain until the tip angle of 110 degrees. However, between 110 degrees and 120 degrees, the system becomes unstable. Over 120 degrees, the characteristics of the vortex are considered to have converted from the longitudinal vortex to the transverse one.

Experimental Study on Aerodynamic Noise Radiated from Delta Wing

Aerodynamic noise has been impairing the comfort of passengers in automobiles.Studies have shown that the aerodynamic noise is generated by the separation of the flow and the generation of the longitudinal vortex at the front pillar(A-pillar)and the door mirror.To remove the effects of the door mirror and extract the longitudinal vortex from A-pillar,studies employ the delta wing model.This research also employed the model and observed relations between the generated sound from the vortex at the A-pillar and the surface pressure fluctuation of the wing.The experiment was carried out in a wind tunnel of the Japan Aerospace Exploration Agency(JAXA)wind tunnel using the delta wing model.The radiated sound was measured using a far-field microphone to characterize the sound,and microphone array to conduct sound source exploration.Distribution of surface pressure fluctuation was measured using electret condenser microphones.Results showed that the radiated sound has a characteristic of dipole sound,and broadband sound from 1 kHz is radiated from the apex of the wing.Those indicate that sound generated from the apex of the delta wing was scattered at the surface of the delta wing,which follows the Lighthill-Curle theory.Surface pressure fluctuation with high fluctuation was distributed following the cone-like shape of the longitudinal vortex.Their peaks moved to the apex with the frequency increase.Coherence between far-field sound and surface pressure fluctuation was calculated.The point which is 70 mm inward from the apex showed higher value than those at the apex.As the diameter of the longitudinal vortex grows at the downstream,it is considered that a certain vortex scale radiates the most noise.

Aerodynamic Sound Radiated from Longitudinal and Transverse Vortex Systems Generated around the Leading Edge of Delta Wings

Flow around the front pillar of an automobile is typical of a flow field with separated and reattached flow by a vortex system. It is known that the vortex system causes the greatest aerodynamic sound around a vehicle. The objective of the present study is to clarify the relationship between vortical structures and aerodynamic sound by the vortex system generated around the front pillar. The vortex system consists of the longitudinal and the transverse system. The characteristics of the longitudinal vortex system were investigated in comparison with the transverse one. Two vortex systems were reproduced by three-dimensional delta wings. The flow visualization experiment and the computational fluid dynamics (CFD) captured well the characteristics of the flow structure of the two vortex systems. These results showed that the longitudinal with the rotating axis along mean flow direction had cone-shaped configuration whereas the transverse with the rotating axis vertical to mean flow direction had elliptic one. Increasing the tip angles of the wings from 40 to 140 degrees, there first exists the longitudinal vortex system less than 110 degrees, with the transition region ranging from 110 to 120 degrees, and finally over 120 degrees the transverse appears. The characteristics of aerodynamic sound radiated from the two vortex systems were investigated in low Mach numbers, high Reynolds number turbulent flows in the lownoise wind tunnel. As a result, it was found that the aerodynamic sound radiated from both the longitudinal and the transverse vortex system was proportional to the fifth from sixth power of mean flow velocity, and that the longitudinal vortex generated the aerodynamic sound larger than the transverse.

Steady vortex force theory and slender-wing flow diagnosis

The concept vortex force in aerodynamics is sys- tematically examined based on a new steady vortex-force theory （Wu et al., Vorticity and vortex dynamics, Springer, 2006） which expresses the aerodynamic force （and moment） by the volume and boundary integrals of the Lamb vector. In this paper, the underlying physics of this theory is explored, including the general role of the Lamb vector in non- linear aerodynamics, its initial formation, and its relevance to the total-pressure non-uniformity. As a typical example, the theory is applied to the flow over a slender delta wing at a large angle of attack. The highly localized flow structures with high Lamb-vector peaks are identified in terms of their net contribution to various constituents of the total aerody-namic force. This vortex-force diagnosis sheds new light on the flow control and configuration optimization.

Longitudinal Aerodynamic Characteristics of the Novel Wing-Body

The Longitudinal Aerodynamic Characteristics （LACs）of a wing-body without tail unit is computed and tested in wind tunnel. The empirical formulas of Datcom and some other authors are applied to estimate the basic Aerodynamic Coefficients. Two wing options are covered as analysis space, namely, the double-delta wing and streak wing, getting two analysis groups respectively. Good agreement between the computation results and the wind tunnel tests shows that the methodology presented is a simple and reliable way to calculate this kind of novel wing-body configurations.

涡流发生器选择性布置方式对换热器性能影响

为提高换热器性能,在雷诺数Re为500~3000范围内,通过数值模拟方法研究三角翼涡流发生器的15种不同布置方式对平直翅片管式换热器的传热和流阻特性影响。结果表明:在涡流发生器布置排数相同时,涡流发生器越靠近迎风侧,换热因子j提升幅度越大;所研究的15种排列j/j_(R)均随Re数的增大而增大。大部分情况下的f/f_(R)随着Re数的增大而增大。换热器迎风侧前两排加装涡流发生器(即case B1布置方式)的翅片管式换热器的α_(JF)(评价系数JF)提高了10.15%~11.12%,综合性能最佳。

低背鳍对细长平板三角翼大迎角空气动力的影响

对细长体平板三角翼和加上两个不同高度背鳍后的组合体在低速风洞进行了六分量天平测力实验，三角翼后掠角82．5°，背鳍当地高度与模型当地半展长比值分别为0．3和0．6，实验迎角范围12°～32°，包括1．66×10^6和2．33×10^6两个雷诺数。实验结果表明：0°侧滑角下，在翼面上发生旋涡破裂前，单独细长平板三角翼的横向力及横向力矩在实验迎角范围内始终为零；加上两个不同高度的低背鳍后，在一定的迎角下，三角翼的横向力及横向力矩开始不为零，流场定常；在更大的迎角下，流场变得非定常。实验结果初步验证了前人关于细长锥体分离涡的稳定性理论，并给出了旋涡失稳后，随着迎角的增大，流场进一步发展的状态。

带背鳍平板三角翼分离涡流场的显示与测量

对后掠角82.5°的平板三角翼和在其对称面分别加低、高背鳍后的组合体在低速风洞进行了烟粒子/激光片光流场显示与测量实验,实验迎角29°,侧滑角为0°。结果表明:对于单独平板三角翼和加高背鳍组合体,其流场是对称、锥型和稳定的;而加上低高度背鳍后,涡变得非对称、非锥型和不稳定。实验结果直接验证了前人关于细长锥体分离涡的稳定性理论,并给出了旋涡失稳后流场的具体表现特性。

大攻角运动时的机翼摇滚问题研究综述

机翼摇滚是现代战斗机、导弹设计中普遍遇到的横向不稳定现象之一,属于典型的大攻角动态特性问题.20多年来,机翼摇滚问题在国内外航空工业界、学术界都引起了极大的重视和兴趣,并在实(试)验、计算方面发表了许多文章,对机翼摇滚问题的认识也取得了较大的进展.本文对自1981年Nguyen、Yip及Chambers最早研究机翼摇滚现象以来,在该问题研究方面的近100多篇有代表性的论文进行了综述,内容涉及实(试)验研究、计算研究的各个方面,并对今后的发展趋势提出了自己的看法.

低背鳍对细长平板三角翼分离涡稳定性影响的研究

对细长锥体分离涡稳定性判据进行了介绍,并应用该判据对细长体平板三角翼和加上两个不同高度背鳍组合体分离涡流场的稳定性进行了分析。为了验证理论分析的有效性,并观察气动力随迎角的变化,根据理论分析模型设计了实验模型,并在低速风洞进行了六分量天平测力实验,三角翼后掠角为82.5°,实验迎角范围12°～32°,侧滑角范围-10°～+10°,实验雷诺数1.66×106。实验结果表明:在翼面上发生旋涡破裂前,单独细长平板三角翼的横向力/力矩在实验迎角范围内始终为零;加了两个不同高度的背鳍后,在一定迎角下,三角翼的横向力/力矩变得不为零。理论分析结果和实验结果在定性上吻合得很好,初步验证了有关文献关于细长锥体分离涡的稳定性理论。

三角翼布局气动特性及流动机理研究

采用流场解算器TRIP2.0(Trisonic Platform version 2.0),在与风洞测力试验比较的基础上,研究了多种跨超声速来流状态下某三角翼布局基本外形气动特性以及前缘涡的产生和发展。数值模拟结果揭示了在不同马赫数、攻角、侧滑角条件下,前缘涡的产生、发展和破裂过程及其对气动特性的影响。在背风区旋涡结构随马赫数的变化关系上,数值模拟结果显示,亚声速旋涡破裂发生在逆压区,破裂从涡轴上开始,超声速旋涡不易破裂,除非在激波的作用下变为亚声速旋涡,该结果在定性上与理论分析结果取得来了较好的一致。对有侧滑角状态下,背风区旋涡的流动特性进行了研究,得到一些有价值的结论。

双三角翼飞机气动力工程计算研究

双三角机翼比三角机翼气动布局具有更优越的升阻特性.飞机空气动力的工程计算是用数值方法寻求飞机最优设计方案的基础.采用基于面积比思想的半经验工程算法计算了双三角翼飞机的升力系数曲线斜率、零升阻力系数和诱导阻力因子.结果经风洞试验数据校验,精度完全能满足飞机方案设计要求.

高阶精度格式WCNS在三角翼大攻角模拟中的应用研究

采用5阶精度的加权紧致非线性格式(WCNS-E-5)数值模拟了65°三角翼的大攻角绕流流场,主要目的是考核高阶精度格式WCNS在大攻角旋涡流动方面以及跨声速流场的激波附面层干扰、涡破裂位置的模拟能力,重点研究不同网格规模和湍流模型对尖前缘三角翼涡系之间的相互作用的影响。通过求解任意坐标系下的雷诺平均N-S方程,采用5阶精度的加权紧致非线性格式(WCNS-E-5)和多块对接结构网格技术,两种湍流模型分别是一方程SA和两方程SST湍流模型,在与相应试验结果对比的基础上,详细研究了WCNS-E-5格式在跨声速大攻角旋涡流动中的表现,以及不同网格规模、两种湍流模型对主涡二次涡相互作用、涡破裂位置和表面压力分布的影响。本文的研究结果表明,高阶精度格式WCNS-E-5能成功应用于三角翼的跨声速大攻角流动,网格规模的增加进一步提高流场分辨率,SST湍流模型相对SA湍流模型在三角翼大攻角流动中具有更好的适用性。

三角翼微秒脉冲等离子体流动控制的试验研究

为改善三角翼在大迎角下的气动特性,进行了微秒脉冲表面介质阻挡放电(SDBD)激励在静止空气中的纹影试验、不同迎角下的PIV测速试验以及不同试验参数下的测力试验。试验结果表明:微秒脉冲SDBD可产生快速温升,快速温升在流场局部诱导产生压缩波;微秒脉冲SDBD激励可有效地控制低速三角翼大迎角下的流动分离,且随迎角增大,流动控制效果逐渐减弱直到消失;存在最佳激励频率,此时流动控制效果最好,当来流风速30 m/s时,最佳激励频率为80 Hz,无量纲频率为1,可将三角翼最大升力系数提高4.3%,失速迎角推迟2°;在同一迎角下,来流速度45 m/s时,流动控制效果较30 m/s时有所降低。