基于仿生学原理的射流表面减阻性能研究

针对仿生射流表面减阻问题,建立仿生射流表面模型,利用SST k-ω湍流模型对其进行数值模拟,所得射流速度曲线与实验数据吻合良好。研究射流流体对边界层厚度的影响规律,探讨仿生射流表面的减阻机理。利用4因素3水平的正交试验,对射流表面和光滑表面摩擦阻力进行对比分析,得到了射流模型参数对减阻效果和节能效果的影响规律:在不考虑外加射流能量的情况下最大减阻率达50.41%;射流速度对节能效果的影响最大,主流速度对节能效果的影响其次,节能效率与主流速度成正比,最大节能效率为276。射流改变了边界层内的流场结构,使得射流表面的边界层厚度增大,垂直于射流表面的速度梯度减小,摩擦阻力减小。     

多孔仿生射流表面减阻特性数值模拟

利用RNGk-ε湍流模型对流体在多孔仿生射流表面上的流动特性进行了数值模拟。结果表明:减阻率和流速比呈线性关系,流速比越大减阻效果越好,最大减阻率为59.02%;单孔射流表面中心线上的摩擦阻力系数先减小后增大,局部减阻率最大为111.8%;射流孔越多,减阻效果越好。探讨了仿生射流表面减阻机理:射流通过改变其表面附近的流场结构,使得边界层黏性底层的厚度增加,垂直于壁面的法向速度梯度减小,达到了显著的减阻效果;同时产生稳定的流向涡结构,并在壁面处形成小的二次涡,抑制了流体间的动量交换,减小了摩擦阻力。     

气动灭火炮弹体橡胶圈仿生凹坑表面减阻特性

针对气动灭火炮炮弹发射过程中弹体橡胶密封圈与炮管之间摩擦阻力大的问题,将仿生凹坑表面减阻技术应用于弹体橡胶密封圈上。建立气动灭火炮橡胶密封圈仿生凹坑减阻运动模型,采用数值模拟方法,研究弹体橡胶密封圈仿生凹坑特征直径及弹体速度对橡胶密封圈与炮管之间摩擦阻力的影响。结果表明:在相同的弹体速度下,当灭火炮弹体橡胶密封圈仿生凹坑特征直径为2mm时,减阻效果最佳,凹坑特征直径为4mm时,减阻效果最差;最大减阻率为17.191%,最小减阻率为3.158%。仿生凹坑中存储的润滑油在弹体运动时,润滑油产生拖拽泼洒而溢流到炮管内壁,对炮管内壁和橡胶密封圈起到润滑作用,达到减小摩擦阻力以及提高炮弹发射速度的目的。     

35°Ahmed模型气动射流减阻主动控制

使用CFD仿真软件STAR-CCM+,对类车体35°Ahmed模型的尾流场进行仿真,采用主动控制减阻技术,用定常射流的方法研究射流孔的位置、速度等因素对尾部流场的影响。在尾部各个可能减阻的位置布置射流孔,针对不同的射流速度进行分析,并对不同位置采用逐步优化减阻的方法,找到最好的减阻工况。研究结果表明:与原始工况相比,采用射流减阻方案的模型尾流结构得到了明显改善;控制了模型尾部的分离涡;改变了车体的压力变化;降低了模型的压差阻力,使其阻力系数明显降低;实现了超过6%的减阻效果,达到了减阻的目的。     

外旋立式射流减阻测试平台研制及实验

以同轴圆筒旋转黏度计测量原理为基础,研制了一台适用于测量射流表面阻力的小型实验平台。通过数值模拟技术对外旋立式同轴旋转筒间环流流场进行分析,获取湍流流场中各点速度及压强分布规律,并对流场稳定性予以理论验证;依靠实验平台完成射流减阻测试实验。研究表明:湍流状态下外旋立式环流运动具有较强规律性;实验减阻效果与仿真结果趋势相近,验证了该实验平台的可行性;该实验平台具有体积小、成本低且易于实现样件表面射流等功能。此外,针对两类孔形样件实验研究表明:当外筒转速为3000r/min,射流速度为2.5m/s时,代号为a2b10的孔形取得了高达12.78%的减阻率。     

沟槽非光滑表面流场的数值分析

利用有限体积法对三角形仿生非光滑沟槽表面流场进行了数值计算。近壁面区采用B-L两层模型,外区采用雷诺应力模型。分析了沟槽表面的流场特性,对计算域中心Z=3 mm平面的速度场和湍流统计量进行了研究。顶点间距s+≈20,h+≈17.3的沟槽减阻率为5.2%;s+≈40,h+≈34.6的沟槽增阻率为12.3%。从速度场、剪应力及湍流统计三方面对沟槽表面减阻、增阻机理进行了分析讨论。与风洞和油槽实验数据定性对比的结果表明,理论计算与实验结果一致。     

射流孔入射雷诺数对循环射流混合槽内流场特性影响研究

采用计算流体力学方法对循环射流混合槽内多孔耦合射流流动特性进行研究,分析射流轴截面内纵向速度分布、中心线速度衰减及其自相似性在不同射流孔入射雷诺数下的变化规律.结果表明:随着射流孔入射雷诺数的增大,三股射流在汇聚区相互卷吸与掺混,逐渐提升纵向速度,导致三股发展为两股射流;射流孔入射雷诺数的增大,减弱了射流中心线速度与初始速度比值的衰减趋势,同时增强了射流轴截面内纵向速度的自相似分布特性.     

横向淹没射流和表面射流问题

本文对淹没射流和表面射流问题进行了较系统地分析和研究。在建立控制方程的基础上以大量数据验证其正确性,并得出几种不同边界条件下的扩展率,扩展系数及附加质量系数的数值,其中深水断面横向表面射流的扩展率是最新的数据。     

形态/柔性材料二元仿生耦合增效减阻功能表面的设计与试验

通过研究水生生物在流体介质运动中,皮肤可随着流体载荷的变化而发生动态变化,并与皮下组织特有的非光滑结构形成动态耦合,形成具有特定功能的表面的现象,并依据仿生学相似原理,提出一种形态/柔性材料二元耦合功能表面设计的新思想,称之为仿生耦合功能表面(BCFS),该功能表面由不同属性的双层材料构成,利用面层材料的弹性变形以及面层材料与基底材料表面上仿生非光滑结构的耦合,对流体进行主动控制,实现增效减阻功能。探索了将这种仿生耦合功能表面(BCFS)在典型流体机械-泵上面的实现方法,并以效率为目标,进行了仿生耦合功能表面增效减阻功能的试验,试验结果表明,采用这种耦合功能表面的仿生耦合水泵,效率提高了5%以上。     

基于仿鸽子翼型的风力机叶片结构气动性能分析

对风力机轻风启动,有效利用风能进行研究。利用仿生耦合技术通过对鸽子翼型数据提取,建立仿生模型。基于NACA0015翼型及鸽子数据特征,将优缘凸起、后缘凸起及前后缘凸起三类翼型与NACA0015翼型进行对比,分析得到翼型上下表面压力分布、表面流场变化、剪切应力分布及增升减阻各气动系数,当失速攻角为16°、马赫数为0.073条件下,仿生翼型在提高升力方面比NACA0015提高了31.98%、降低阻力达到了10.62%,仿生翼型对表面流体起到了有效改善,改变结构的翼型对提高升力,降低阻力有了很大的提高。     

Numerical exploration on jet oscillation mechanism of counterflowing jet ahead of a hypersonic lifting-body vehicle

Numerical investigation of a supersonic jet from the nose of a lifting-body vehicle opposing a hypersonic flow with the freestream Mach number being 8.0 at 40 km altitude was carried out by solving the three-dimensional, time-accurate Navier-Stokes equations with a hybrid meshes approach. Based on the analysis of the flow field structures and aerodynamic characteristics, the behaviours relevant to the LPM jet were discussed in detail, including the drag reduction effect, the periodic oscillation and the feedback loop. The obtained results show that the flow oscillation characteristic of the LPM jet is low-frequency and high-amplitude while that of the SPM jet is high-frequency and low-amplitude. Compared with the clearly dominant frequencies of the LPM jet, the SPM jet exhibits a broad-band structure. The LPM jet can sustain drag reduction effect until the angle of attack is 8°, and the lift-to-drag ratio of the vehicle is effectively improved by 6.95% at angle of attack of 6°. The self-sustained oscillation process was studied by a typical oscillating cycle of the drag force coefficient and the variation of the instantaneous pressure distribution,which reveals an off-axial flapping motion of the conical shear layer. The variation of the subsonic recirculation zone ahead of the vehicle nose strengthens the understanding of the jet behavior including the source of instability in the long penetration mode and the mechanism of the feedback loop. The aim of this paper is to advance the technology readiness level for the counterflowing jet applied as an active control technology in hypersonic flows by gaining a better insight of the flow physics.     

快背式MIRA模型射流主动控制气动减阻研究

利用CFD仿真软件STAR-CCM+,对类车体MIRA模型的尾流场进行仿真研究。采用主动控制减阻技术的流动控制方式, 应用定常射流的方式控制尾流场的流动结构,探讨射流减阻的减阻措施。使用雷诺时均法SST k-w湍流模型对快背式MIRA模型尾部流场进行数值仿真,对尾部各个可能减阻的位置做了研究,找到最好的减阻工况,并分析了尾部涡流的变化,发现通过控制模型尾部的分离涡,可以改变车体的压力大小,从而减小模型的压差阻力,实现减阻的目的。     

Water-trapping and drag-reduction effects of fish Ctenopharyngodon idellus scales and their simulations

In the last decades, surface drag reduction has been re-emphasized because of its practical values in engineering applications,including vehicles, aircrafts, ships, and fuel pipelines. The bionic study of drag reduction has been attracting scholars' attentions. Here, it was determined that the delicate microstructures on the scales of the fish Ctenopharyngodon idellus exhibit remarkable drag-reduction effect. In addition, the underlying drag-reduction mechanism was carefully investigated. First,exceptional morphologies and structures of the scales were observed and measured using a scanning electron microscope and3-dimensional(3D) microscope. Then, based on the acquired data, optimized 3D models were created. Next, the mechanism of the water-trapping effect of these structures was analyzed through numerical simulations and theoretical calculations. It was determined that there are many microcrescent units with certain distributions on its surface. In fact, these crescents are effective in generating the "water-trapping" effect and forming a fluid-lubrication film, thus reducing the skin friction drag effectively.Contrasting to a smooth surface, the dynamics finite-element analysis indicated that the maximum drag-reduction rate of a bionic surface is 3.014% at 0.66 m/s flow rate. This study can be used as a reference for an in-depth analysis on the bionic drag reduction of boats, underwater vehicles, and so forth.     

鸮翼前缘非光滑形态消声降噪机理

长耳鸮扑翼噪声测量试验表明,其翼前缘圆弧齿状非光滑形态对其飞行降噪影响显著。应用逆向重构技术,对长耳鸮翼前缘非光滑形态特征几何信息进行量化,并建立仿生类比模型。采用计算气动声学方法,对仿生前缘非光滑模型的降噪特性进行了数值模拟,并通过分析仿生非光滑形态对模型表面流场的影响,对仿生非光滑形态气流噪声控制机理进行了研究。结果表明,仿生非光滑模型与光滑模型相比,可降低气流噪声5～10 dB,且具备一定的增升作用;仿生前缘非光滑形态具有整流及控制气流分离的特性,可减少由于翼表面气流压力脉动及涡流脱离引发的气流噪声。     

Water-trapping and drag-reduction effects of fish <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis> scales and their simulations

In the last decades, surface drag reduction has been re-emphasized because of its practical values in engineering applications, including vehicles, aircrafts, ships, and fuel pipelines. The bionic study of drag reduction has been attracting scholars’ attentions. Here, it was determined that the delicate microstructures on the scales of the fish Ctenopharyngodon idellus exhibit remarkable drag-reduction effect. In addition, the underlying drag-reduction mechanism was carefully investigated. First, exceptional morphologies and structures of the scales were observed and measured using a scanning electron microscope and 3-dimensional (3D) microscope. Then, based on the acquired data, optimized 3D models were created. Next, the mechanism of the water-trapping effect of these structures was analyzed through numerical simulations and theoretical calculations. It was determined that there are many microcrescent units with certain distributions on its surface. In fact, these crescents are effective in generating the “water-trapping” effect and forming a fluid-lubrication film, thus reducing the skin friction drag effectively. Contrasting to a smooth surface, the dynamics finite-element analysis indicated that the maximum drag-reduction rate of a bionic surface is 3.014% at 0.66 m/s flow rate. This study can be used as a reference for an in-depth analysis on the bionic drag reduction of boats, underwater vehicles, and so forth.     

浅水流动环境中垂向缝隙射流的数值模拟

为探求浅水流动环境中缝隙射流的流动规律,提出射流的影响范围公式与流动转变条件.应用体积率（VOF）方法跟踪处理自由水面,利用重组化群（RNG）紊动动能-紊动耗散率（k-ε）模型,对浅水流动环境中垂向缝隙射流进行数值模拟.研究流速分布和自由水面位置,对比数值模拟与物理模型试验结果,分析流动转变条件.结果表明,计算结果与试验结果吻合较好,射流出口断面垂向流速分布符合半无限域中射流流速的衰减规律,流速场分布及自由水面位置在小流速比、临界流速比及大流速比下存在不同特性,自由水面隆起高度和流速比、水深比有关,射流对上游的影响距离随流速比增大而增大.     

针头表面改性及穿刺阻力实验

基于非光滑表面减阻理论,采用化学刻蚀的方法在不锈钢针头上构建微观结构。利用光学视频测试仪和超景深三维扫描系统分别对试样表面的润湿性和微观结构进行了检测与表征。通过测量接触角和穿刺阻力试验研究其疏水性和减阻特性关系,并对其穿刺减阻机理进行了分析。试验结果表明：试样接触角越大,减阻效果越明显。研究其机理发现,化学刻蚀形成的微观结构增加了针头表面的疏水性能,降低了针头表面的摩擦系数,从而达到了减阻效果。因此,经化学刻蚀方法可以在一定程度上调控不锈钢针头表面的疏水性进而控制其减阻特性。     

凹槽内剪切流动特性对滑动减阻的影响

为了揭示凹槽内部剪切流动特性对滑动减阻效果的影响,利用静、动滑动摩擦因数测试系统和计算流体力学方法,理论、实验和数值模拟研究了凹槽高宽比(e=0.5、1.0、2.0、3.0)、凹槽几何尺寸、壁面运动速度等因素,对凹槽内的剪切流动特性及壁面滑动减阻效果的影响.研究发现,凹槽结构增加了润滑油滑动减阻效果,凹槽几何结构对减阻效果有明显影响,当凹槽宽度L、深度H均为2 mm时,凹槽的减阻效果相对较好,且壁面运动速度对其剪切力减小率fτ的影响较小.此外,凹槽尺寸、壁面滑动速度对凹槽内流场特性有重要影响,不同工况下凹槽内部存在上下2个涡或者1个大涡和2个边角涡.结果表明:凹槽内的剪切流动特性对滑动减阻效果有重要影响,并可为滑块表面凹槽结构设计提供重要的指导.