涡流发生器对细长体侧向力的控制研究

细长体在大攻角情况下会出现很大的侧向力. 在10°半顶角细长旋成体头部安置涡流发生器（微型三角翼）,通过调节涡流发生器相对模型轴线的滚转安装角,实现了对大迎角状态下旋成体侧向力的近似比例控制.研究了涡流发生器半展长、后掠角和攻角等参数对侧向力控制效果的影响. 研究发现半展长为6mm、后掠角为45°的涡流发生器具有较好的控制效果,在一系列攻角下均能够实现侧向力的近似比例控制. 由于该机构非常简单,在工程中具有一定的应用前景.      

支杆-钝头体带攻角流场和“军刺”挡板作用研究

通过三维N-S方程的数值求解, 研究了支杆-钝头体结构在10o攻角M∞=6.0飞行条件下的流场结构和特点, 指出其气动力特性恶化的原因, 提出采用``军刺'挡板改善流场和气动力特性, 并通过对比两种不同挡板作用下的流场和气动力特性变化分析其作用机理, 发现``军刺'挡板结构分割流场抑制三维效应形成的周向流动, 迎风面形成稳定的回流区和剪切层结构, 将迎风面锥激波推离轴线, 降低钝头体肩部流动结构相互作用强度, 并在一定程度上缓解背风面流动干扰, 明显改善支杆-钝头体带攻角飞行时的气动力特性.      

Dynamics of single and twin circular jets in cross flow

2D-PIV is used to investigate the near field jet dynamics of a single and a tandem twin jet in cross flow at a blowing ratio of 3. The flow characteristics that were studied included jet trajectory and penetration, windward and leeward jet spread, and the size, location and magnitude of the reverse flow region. The tandem jet setup resulted in configuration where the rear jet was shielded by the front jet that allowed the rear jet to penetrate deeper into the cross stream. The penetration of front jet was found to be comparable to that of the single jet in the near field. Asymmetric jet spread was observed both in the windward and leeward side with higher jet spread in the leeward side for both the single and tandem jet configuration. Furthermore, for the tandem jet condition, the presence of rear jet was found to affect the windward spread of the front jet minimally. The windward and leeward spreads of the rear jet were observed to be decreased by the presence of the front jet. Reverse flow zones confined between the front and rear jets in tandem setup was also observed to be stronger than that of a single jet. A turbulent kinetic energy (TKE) analysis indicates that the behavior of a jet in tandem setup follows the same trend as that of an axisymmetric turbulent jet with low turbulence in the jet core and higher turbulence in the jet shear layer that subsequently transitions to high turbulence production in the jet core as the jet shear layers on windward and leeward side of the jet coalesce.     

内孤立波作用下潜深对潜体运动响应和载荷特性的影响研究

内孤立波常发生于海洋密度跃层, 因其峰高谷深、携带能量巨大, 在传播过程中会导致跃层上下的海水流动呈现剪切状态, 并引起突发性的强流. 潜体在水下悬停时极有可能会遭遇内孤立波, 由于内孤立波的流场特性, 置于跃层上下的悬浮潜体所产生运动响应和水动力载荷变化不尽相同, 甚者会出现掉深现象. 为探究潜深对波体耦合作用的影响, 基于不可压缩N-S方程和mKdV理论, 采用速度入口造波, 结合重叠网格技术和流固耦合方法, 建立了分层流中内孤立波耦合水下潜体多自由度运动的数值模型, 通过该模型分析了不同潜深下悬浮潜体的运动响应和载荷特性. 结果表明: 在内孤立波作用下, 位于密度跃层上方和跃层中的潜体顺着波的前进方向运动, 先下沉后抬升, 位于跃层下方的潜体则会逆流持续下沉; 潜体与波面的垂向距离越小, 对其纵荡、垂荡和速度的影响越显著, 而位于密度跃层中的潜体在分界面处沿着波形运动, 其运动响应和载荷变化受影响较小; 潜体在跃层上、下流体中所受水平力的方向相反, 水平力峰值小于垂向力峰值, 且位于跃层下方的潜体一直受到低头力矩, 最终导致掉深.      

Analysis of slender bodies of revolution with curved-ground effect and waving-water effect

The classical slender body theory is generalized to the problems of a slender body of revolution moving with an angle of attack, in very close proximity to curved-ground and waving-water surfaces. The flow problems are reduced to the two-dimensional flow problem of double, circular cylinders, which is then solved by the method of complex variables and Fourier series. The attractive force and pitching moment, and the lateral force and yawing moment acting on the body are derived in terms of integrals over the body length. For a horizontal translation of the body near the curved ground, the attractive force will increase as the body is brought closer to the ground or as the absolute value of the angle of attack increases, and a convex (concave) ground will strengthen (weaken) the ground effect. However, for a horizontal translation of the body near a waving-water surface, the periodic attractive force is nearly in phase with the wave height beneath the body's centre, and its amplitude increases with the relative velocity between the body and the water wave motion.     

Experimental investigation of some singularities of the supersonic flow around V-shaped wings

Some results are presented of an experimental investigation of the stream configuration in a supersonic flow over the windward and leeward sides of V-shaped wings.     

Effects of drift angle on model ship flow

The effects of drift angle on model ship flow are investigated through towing tank tests for the Series 60 C_B=0.6 cargo/container model ship. Resistance, side force, drift moment, sinkage, trim, and heel data are procured for a range of drift angles β and Froude numbers (Fr) and the model free condition. Detailed free-surface and mean velocity and pressure flow maps are procured for high and low Fr=0.316 and 0.16 and β=5° and 10° (free surface) and β=10° (mean velocity and pressure) for the model fixed condition (i.e. fixed with zero sinkage, trim, and heel). Comparison of results at high and low Fr and previous data for β=0° enables identification of important free-surface and drift effects. Geometry, conditions, data, and uncertainty analysis are documented in sufficient detail so as to be useful as a benchmark for computational fluid dynamics (CFD) validation. The resistance increases linearly with β with same slope for all Fr, whereas the increases in the side force, drift moment, sinkage, trim, and heel with β are quadratic. The wave profile is only affected near the bow, i.e. the bow wave amplitude increases/decreases on the windward/leeward sides, whereas the wave elevations are affected throughout the entire wave field. However, the wave envelope angle on both sides is nearly the same as β=0°, i.e. the near-field wave pattern rotates with the hull and remains within a similar wave envelope as β=0°. The wave amplitudes are significantly increased/decreased on the windward/leeward sides. The wake region is also asymmetric with larger wedge angle on the leeward side. The boundary layer and wake are dominated by the hull vortex system consisting of fore body keel, bilge, and wave-breaking vortices and after body bilge and counter-rotating vortices. The occurrence of a wave-breaking vortex for breaking bow waves has not been previously documented in the literature. The trends for the maximum vorticity, circulation, minimum axial velocity, and trajectories are discussed for each vortex. Received: 16 September 1999/Accepted: 8 November 2001     

Experimental investigation of side force control on cone-cylinder slender bodies with flexible micro balloon actuators

Side forces on slender bodies of revolution at medium to high angles of attack (AOA > 30°) has been known from a large number of investigations. Asymmetric vortex pairs over a slender body are believed to be the principle cause of the side forces. Under some flight conditions, this side force may be as large as the normal force acting on the slender body. In this paper, experimental results are presented for side force control on a cone-cylinder slender body by using microfabricated balloon actuators. The micro balloon actuators are made of polydimethylsiloxane (PDMS) elastomer by using micro molding techniques. They can be packaged on curve surfaces of a cone-cylinder slender body. As actuator is actuated, the micro balloon actuator inflates about 1.2 mm vertically, which is about 2.4% of the cylinder diameter D (=50 mm) of the cone-cylinder slender body. Micro balloon actuators are actuated at different roll angles of a cone-cylinder slender body. Aerodynamic force measurement results indicate the effects of micro balloon actuators vary at different actuation locations on the cone-cylinder slender body. The side forces can be significantly reduced if the actuators are actuated in the weak vortex side (the side corresponding to the asymmetric vortex which is far from the surface) and actuation angles are located at about 50–60° (the actuation angle here is measured from stagnation line of the incidence plane toward weak vortex side direction). Significant changes are noticed from the surface pressure, as well as leeside vortex flow field, measurement. Micro balloon actuators change nose shapes of the slender body which decide adverse-pressure-gradient values and directly influence the origin of the separation lines and characteristics of the separated vortices over the leeside surface.     

ON SHOALING PROPERTY OF A SET OFFOURTH DISPERSIVE BOUSSINESQ MODEL

Boussinesq 类水波模型在港口、海岸以及海洋工程领域应用广泛,但以前对这类模型的变浅性能的研究不够充分. 针对Madsen 和Schäffer 提出的一组四阶Boussinesq 方程,从理论和数值两个方面对这一问题进行了探讨. 理论分析了其变浅性能,指出该文献中参数α₂ 和β₂ 的取值是不合理的,并重新确定其取值. 在交错网格下建立了基于混合4 阶Adams-Bashforth-Moulton 格式的预报-校正数值模型. 数值模拟了两个典型算例： 一是缓变平坡地形上波浪的传播变形,二是波浪在淹没梯形潜堤上的波浪演化过程. 计算结果分别与解析结果、物理模型实验结果进行了比较,发现变浅系数的取值对数值结果影响很大,新参数比原文参数模拟结果的吻合程度更高,这佐证了理论分析.     

矢量喷流对细长体大迎角非对称流动影响研究

采用测压方法研究了矢量喷流对细长旋成体大迎角非对称流动的影响特性.实验结果表明:矢量喷流对细长旋成体大迎角非对称侧向力有明显的抑制作用,该抑制作用是通过喷流诱导作用,改变其空间绕流涡系结构的分布来实现的,但是矢量喷流的存在并不能改变大迎角机身空间绕流涡系的本质结构;随着迎角的增大,矢量喷流对细长旋成体大迎角非对称流动的影响区域不断前移,甚至影响到头部;随着喷流落压比的增加,矢量喷流对细长旋成体大迎角非对称侧向力的抑制作用加强,但当喷流落压比达到临界落压比后(即喷管出口处达到设计马赫数时),喷流影响作用将不会随喷流落压比的增加而改变.     

EFFECT OF TWO-DIMENSIONAL MICROPILLAR ARRAYED TOPOGRAPHY ON SPREADING OF INSOLUBLE SURFACTANT-LADEN DROPLET

针对二维微柱阵列壁面上含不溶性活性剂液滴的铺展过程,采用润滑理论建立了液膜厚度和浓度演化模型,采用数值计算方法得到了液滴的铺展特征及相关参数的影响. 研究表明：活性剂液滴在微柱阵列壁面上铺展时,在壁面凸起处衍生出隆起结构,壁面凹槽处衍生出凹陷结构,随时间持续,隆起和凹陷均向两侧移动,且数量不断增加. 活性剂液膜流经凸起时,隆起高度呈驼峰形变化. 增大预置液膜厚度或活性剂初始浓度,铺展区域隆起和凹陷数量增多,液滴铺展速度加快. 增加凹槽深度或减小斜度会使毛细力作用增强,液膜破断可能性加大;增大凹槽宽度可加速活性剂液滴的铺展,加剧液膜表面波动幅度.     

Numerical Study of the Aerodynamic Performance of a Train with a Crosswind for Different Embankment Heights

A numerical study using improved delayed detached eddy simulation (IDDES) was used to investigate the influence of the embankment height on the aerodynamic performance of a high-speed train travelling under the influence of a crosswind. The results of the flow predictions were used to explore both the instantaneous and the time-averaged flows and the resulting aerodynamic forces, moments and slipstreams. An increase of the aerodynamic drag and side forces as well as the lift force of the head and middle cars were observed with rising embankment height. While the lift force of the tail car decreased with the increasing embankment height. Furthermore, the height of the embankment was found to have a strong influence on the slipstream on the leeward side of the train. The correlation between the embankment height and the slipstream velocity on the windward side, was rather small. The flow structures in the near-wake of the leeward side of the train, responsible for the aerodynamic properties of the train were analyzed, showing strong dependency on the embankment height.

     

A numerical study of the load on cylindrical piles exerted by internal solitary waves

A continuously stratified nonlinear model is employed to simulate the generation of internal solitary waves (ISWs) over a sill by tidal flows, and it is shown that the simulated ISW-induced current field basically agrees with that observed. Then the force and torque on a supposed small-diameter vertical cylindrical pile exerted by the simulated ISW packet are calculated. According to the calculation, it is found that, no matter whether the direction of the ISW-induced current is the same as that of the tidal current or not, the force exerted by the ISW would be much larger than that by only the tidal current; if the direction of the ISW-induced current is the same as that of the tidal current, then the torque exerted by the ISW would also be much larger than that by only the tidal current; whilst if the direction of the ISW-induced current is against that of the tidal current, then the torque exerted by the ISW has the same order as that exerted by only the tidal current. It is shown that, under the same conditions, the maximum force on the cylindrical pile is 6.58×10² kN, which is larger than that by the modal separation method of Cai et al., whilst the maximum torque is 2.46×10⁵ kN m, which is less than that given by Cai et al. During the passage of the ISW, the time series of the force and torque on the cylindrical pile can also be shown. Finally, the effect of the characteristics of the Gaussian sill on the force is studied, and the resulted empirical formulas on the force with the wave amplitude and the non-dimensional variable of the sill parameters are put forward.     

RESEARCH ON THE COLLISION EFFICIENCY OF NANO-PARTICLE-TO-WALL WITH EXTERNAL ELECTRIC FIELD

着重考虑了电场作用下,壁面排斥力对颗粒-壁面碰撞效率的影响. 采用Matlab 中的龙格库塔方法,对颗粒-壁面碰撞的压缩阶段及回弹阶段的动力学方程组进行求解,并对Maxwell 速度分布进行积分获得不同速度方向下的碰撞效率. 研究表明,颗粒的碰撞效率随着碰撞角度的增加而增大,并最终达到一个临界值,即完全凝并时的碰撞效率;且颗粒的碰撞效率将因壁面排斥力的影响而减小,即壁面排斥力在一定程度上阻碍了颗粒的凝并.     

Inviscid vortex structures in the shock layers of conical flows around V wings

The applicability of the criteria of existence of inviscid vortex structures (vortex Ferri singularities) is studied in the case in which a contact discontinuity of the corresponding intensity proceeds from the branching point of the λ shock wave configuration accompanying turbulent boundary layer separation under the action of an inner shock incident on the leeward wing panel. The calculated and experimental data are analyzed, in particular, those obtained using the special shadow technique developed for visualizing supersonic conical streams in nonsymmetric, Mach number 3 flow around a wing with zero sweep of the leading edges and the vee angle of 2π /3. The applicability of the criteria of existence of inviscid vortex structures is established for contact discontinuities generated by the λ shock wave configuration accompanying turbulent boundary layer separation realized under the action of a shock wave incident on the leeward wing panel. Thus, it is established that the formation of the vortex Ferri singularities in a shock layer is independent of the reason for the existence of the contact discontinuity and depends only on its intensity.     

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.     

超音速流动中侧向喷流干扰特性的实验研究

在超音速流动中，进行了侧向喷流干扰特性的实验研究，研究了喷流压力、 攻角、迎风侧及背风侧喷流对侧向喷流干扰特性的影响. 结果表明，随喷流压力增大，喷流 前的高压区向前扩展，喷流的包裹作用加强. 有攻角时，背风侧喷流前的高压区更大，喷流 包裹作用的影响区域前移，喷流的控制效果更好，这一趋势随攻角的增大更加明显.     

SIMULATION OF TRANSVERSE VIBRATION OF SLENDER ROD STRING IN THE VERTICAL CYLINDER UNDER BUCKLING DISPLACEMENT EXCITATION1)

对于铅直圆筒内受交变拉压轴向载荷作用的细长杆柱,当杆柱底端所受到的轴向压力大于杆柱屈曲的临界载荷时,细长杆柱在圆筒内将产生螺旋屈曲,杆柱的屈曲变形将激励杆柱在圆筒内产生横向振动。以细长杆在圆筒内的瞬时屈曲构型作为杆柱横向振动的位移激励,建立了屈曲位移激励下的细长杆在圆筒内横向振动与杆管碰撞规律的仿真模型。采用有限差分法对井深进行离散,Newmark 法对时间进行离散,以恢复系数法建立了细长杆和圆筒的碰撞条件,对细长杆在圆筒内的横向振动数学模型进行了数值仿真。仿真结果表明,细长杆和圆筒内壁的碰撞现象主要发生在细长杆底端受压发生屈曲后,且几乎沿整个圆筒都有发生,从圆筒顶部至底部的碰撞力峰值逐渐增大;而在杆柱底端受拉时碰撞现象很少,碰撞力也较小。     

EXPERIMENTS ON EVOLUTION CHARACTERISTICS FOR THE MUSHROOM-LIKE VORTEX STRUCTURE GENERATED BY A SUBMERGED LAMINAR ROUND JET

利用溢流恒压装置产生具有稳定出流速度的层流圆管潜射流,结合染色液流态显示方法,在多种射流时间和雷诺数组合下,实验研究了该射流动量在密度均匀黏性流体中的演化机理及其表现特征,定量分析了蘑菇型涡结构的无量纲射流长度L^*、螺旋型涡环半径R^*及其包络外形长度d^*等几何特征参数随无量纲时间t^*的变化规律。系列实验结果表明,蘑菇型涡结构的形成与演化过程可分为3个不同的阶段,分别为启动阶段、发展阶段和衰退阶段。在启动阶段,L^*和d^*随t^*线性变化,而R^*则近似为一个常数。在发展阶段,蘑菇型涡结构的演化具有自相似性,在各种射流时间和雷诺数组合下,L^*,R^*和d^*与t^*1/2均为同一正比关系,而且实验结果与基于斯托克斯（Stokes）近似的理论解结果一致。在衰退阶段,蘑菇型涡结构会发生两类形式的演化,第1类衰退出现在射流结束之后,其间L^*和R^*与t^*1/5相关,而d^*近似为一个常数;第2类衰退出现在射流结束之前,当射流动量达到某个临界值后,蘑菇型涡结构就会发生破碎等现象。     

EXPERIMENTAL INVESTIGATION ON LIFT INCREMENT OF A PLASMA CIRCULATION CONTROL AIRFOIL

利用等离子体激励器发展了新型的环量增升技术,并对二维NACA0012翼型绕流实施控制。由于NACA0012翼型为尖后缘构型,环量增升装置由2个非对称型介质阻挡放电等离子体激励器构成。一个等离子体激励器贴附于翼型吸力面靠近后缘处,其诱导的壁面射流沿来流方向指向下游;另一个等离子体激励器贴附于翼型压力面靠近后缘处,其诱导的壁面射流与来流方向相反指向上游。在风洞中通过时间解析二维PIV系统对翼型绕流流场进行了测量,基于翼型弦长的雷诺数Re=20 000。结果表明在等离子体激励器的控制下,翼型压力面靠近后缘处可以形成一个定常回流区,从而起到虚拟气动外形的作用,因此翼型吸力面的流场得到加速,压力面的流场得到减速,使得翼型压力面的吸力以及压力面的压力都得到增加,进而增加了翼型的环量。风洞天平测力实验进一步验证了该环量增升技术的有效性。在整个攻角范围内,施加控制的翼型的升力系数相比没有控制的工况有明显的提高。