涡轮叶栅尾迹对二次流影响的试验研究

本文利用运动圆柱排模拟上游叶片尾迹,在平面涡轮叶栅上研究了上游尾迹与叶栅通道内二次流相互作用,初步讨论了尾迹与二次流相互作用的机理,研究发现利用这种相互作用可以控制二次流的强度、减小二次流损失,进而可实现提高涡轮效率的目的.     

叶顶布置蜂窝的涡轮平面叶栅间隙泄漏流动研究

本文提出一种将蜂窝结构直接布置在涡轮动叶顶部的抑制涡轮径向间隙泄漏流动新措旌,数值研究了有/无蜂窝叶对涡轮平面叶栅间隙泄漏流场的影响。结果表明,蜂窝叶顶使得进入蜂窝腔的间隙流体形成旋涡运动,对间隙流具有能量耗散的作用,形成的径向射流类似于"气动栅栏",增加间隙内流体的运动阻力,进而对间隙泄漏流产生有效的抑制效果。与常规无蜂窝平顶叶栅相比,蜂窝叶顶叶栅的相对泄漏流量减低了约10%,形成的泄漏涡尺寸减小,叶栅出口下游总损失降低了4%。     

DES模型在压气机亚音转子中的应用探讨

本文运用分离涡模拟(DES)方法研究了不同工况下压气机亚音转子的流动情况,分析了其时均与瞬时流场中顶部间隙泄漏流动和根部角区的流动分离.通过与S-A模型计算结果的对比表明,DES模型在模拟顶部泄漏流动及二次泄漏、泄漏流在转子下游与尾迹的干涉时能够捕捉到更强的旋涡结构,在模拟转子根部角区的分离时也能获得更为丰富的流动现象.对不同工况的DES计算表明负荷的上升会使泄漏涡形成的位置向上游移动,从而导致并加剧二次流动,并对叶栅下游泄漏涡与尾迹的干涉产生影响.对设计工况下瞬时流场的分析表明,泄漏涡在叶栅下游体现出周期性的强弱变化,近叶根分离区也体现出明显的非定常性.     

离心压缩机级内静叶时序效应的数值研究

本文采用三维粘性非定常数值模拟的方法研究了离心压缩机级内静叶的clocking(时序)效应,研究结果表明,当两级静叶相对周向位置改变时最大效率变化为0.175%.另外,通过对非定常计算叶根,叶中和叶尖处流场图的分析,发现非定常环境下上游周期性尾迹对下游叶片边界层、尾迹以及叶尖泄漏流的相互作用.     

串列平板叶栅尾迹速度场的LDA实验研究

绕流叶栅的尾涡脱落是诱发水力机械振动噪声的重要因素。本文以串列布置平板叶栅为研究对象,进行雷诺数Re=5000与10000下的叶栅绕流尾迹速度场的LDA测量实验,分析不同雷诺数下绕叶栅流场速度分布,探究涡脱频率特性。实验结果表明:同一雷诺数下平板尾迹区中心线上速度分布可分为回流区、快速增长区、缓慢增长区三个区域;双平板绕流场,下游平板的存在明显抑制了上游平板尾迹的发展,与单平板模型比回流区流向长度减小;雷诺数从5000增大到10000时,平板尾迹回流区的流向长度变小,但最低流速分布升高;下游平板的存在抑制了上游平板的涡脱,使其频率降低,上、下游平板涡脱频率一致。     

串列平板叶栅尾迹速度场的LDA实验研究

绕流叶栅的尾涡脱落是诱发水力机械振动噪声的重要因素。本文以串列布置平板叶栅为研究对象,进行雷诺数Re=5000与10000下的叶栅绕流尾迹速度场的LDA测量实验,分析不同雷诺数下绕叶栅流场速度分布,探究涡脱频率特性。实验结果表明:同一雷诺数下平板尾迹区中心线上速度分布可分为回流区、快速增长区、缓慢增长区三个区域;双平板绕流场中下游平板的存在明显抑制了上游平板尾迹的发展,与单平板模型相比回流区流向长度减小;雷诺数从5000增大到10000时,平板尾迹回流区的流向长度变小,但最低流速分布升高;下游平板的存在抑制了上游平板的涡脱,使其频率降低,上、下游平板涡脱频率一致。     

带冠喷气涡轮叶栅气动性能研究

多种控制技术耦合应用是涡轮叶栅间隙泄漏流动研究的趋势之一。结合围带与喷气两种控制方法,本文通过实验与数值模拟研究了喷气对带冠涡轮叶栅气动性能的影响机理,探讨了测量截面上的损失分布以及叶栅通道内涡系的演变规律。研究发现,与带冠无喷气叶栅相比,喷气改变了泄漏流体的流动方向,使泄漏涡尺寸有所增加。但喷气改善了叶顶附近总压分布,因而0.3%主流流量喷气使叶栅气动性有所提高。喷气可以降低间隙入口流量,且由于喷气量小于减小的间隙入口主流流量,因而带冠叶栅中,喷气使间隙出口流流量减小。     

沟槽面对扩压叶栅表面流态的影响

采用油流显示技术研究了沟槽面扩压叶栅表面流动的拓扑结构,通过与光滑叶栅壁面流动拓扑图像的比较,发现沟槽面能抑制叶背附面层的发展,减小附面层内低速流体的展向流动,减弱叶背附面层与叶背角区旋涡的相互作用.随后用总压耙对栅后流场进行了测量,和光滑叶栅测量结果相比,沟槽面叶栅端壁区总压损失低,主流区沟槽面叶栅尾迹宽度变小、损失降低,证实该非光滑面能减小叶栅二次流损失.     

具有叶尖小翼的压气机叶栅间隙流动分析

采用数值模拟方法对利用不同安装方式叶尖小翼控制压气机叶栅间隙流动进行研究。结果表明,不同安装方式叶尖小翼都可以有效降低叶顶泄漏流速,削弱泄漏涡强度。叶尖小翼改变了叶尖负荷及泄漏涡运行轨迹,进而影响了叶尖流场不同涡系之间的相互作用。吸力面小翼削弱了泄漏涡,抑制了通道涡的发展,使得叶栅总损失降低。压力面小翼及组合小翼削弱了泄漏涡,但增强了通道涡及其与泄漏涡之间的相互作用,叶栅总损失增加。     

间隙大小对高负荷压气机叶栅流动特性的影响

在低速平面叶栅风洞中,对不同间隙大小条件下的高负荷压气机叶栅流动特性进行了实验研究。实验采用五孔气动探针测量了叶栅出口截面参数,得到了该截面的二次流速度矢量分布,并对叶栅下端壁和叶片表面进行了墨迹流动显示.结果表明,叶顶间隙的增加加剧了间隙泄漏流动与通道涡的相互作用和掺混,导致叶栅流道内的二次流结构和形态发生改变;增加叶顶间隙可完全抑制吸力面角区分离,但被间隙泄漏流动带走的低能流体被带到尾缘及其下游位置,加剧了相应位置的流动分离;间隙泄漏流动将引起叶栅总损失的显著下降,损失的大小并不一定与间隙大小成正比.     

轴流压气机转子叶尖泄漏涡和尾迹在静子尖区的传播

用三维激光多普勒测速系统测量了轴流压气机设计状态转子叶尖泄漏涡和尾迹在静子尖区的传播过程。结果表明,转子叶尖泄漏涡和转子尾迹周期地扫过静子通道尖区,导致该区出现周期性的流动阻塞和脉动。转子尾迹在静子通道内追赶上从前一转子叶片通道内下来的叶尖泄漏涡,二者的相互作用和掺混导致静子尖区更为复杂的二次流动。同转子尾迹相比,转子叶尖泄漏涡对静子尖区的影响更为明显和深远。静叶尾部吸力面出现流动分离,分离流同低能物质之间发生相互作用和掺混。     

空间飞行器近尾区内场和密度空腔的研究

在静态极限下,通过傅里叶变换,研究了空间飞行器近尾区内等离子体与场之间的非稳态非线性相互作用,并进行了数值求解。数值模拟结果表明,在飞行器近尾区内会产生电磁孤波和密度空腔,由电场的塌缩现象可以探测到它们。因而通过探测电磁孤波和密度空腔的形状和强度,能够探寻具有隐身特性的飞行器。     

Flow patterns of cross-flow around a varicose cylinder

The near wake of a varicose cylinder has been experimentally investigated using Laser Induced Fluorescence (LIF) and Digital Particle Imaging Velocimetry (DPIV). The work aims to provide understanding to the mechanism of the cross flow around varicose cylinder as well as to comprehend why the introduction of relatively small degrees of spanwise waviness can have a significant effect on drag reduction and suppression of the cylinder vibration. The evolution of the flow patterns and the corresponding vortex interactions are obtained. The experimental results indicated that the wake width and the formation length vary along the span of the varicose cylinder. A wider wake and a longer formation length were observed in the saddle plane. In addition, an interpretation of the three-dimensional wake structures is postulated and conceptually shown. The numerical simulation by 3-D finite volume method is successful in predicting the flow features found by the experiments.     

Numerical simulation and flow visualization using soap film of the self-organized vortex structure in the wake of an array of cylinders

Abstract  

With the aid of computational fluid dynamics (CFD) and simple flow visualization technique using flowing soap-film, we present here the wake structures behind an array of cylinders for Reynolds numbers corresponding to both laminar and turbulent flow regimes. The image results illustrate interesting vortex interactions past these equally spaced cylinders; for low Reynolds number flow, well-organized wake pattern persists and manifests unsteadily to different symmetry states. An increase of free stream flow velocity causes the wake transition, resulting in the formation of asymmetric flow wake with chaotic mixing at the far wake. Observations from both the numerical simulations and soap-film are in good agreement at least qualitatively.     

Spatiotemporal measurements of flame stretch and propagation rates for lean and rich CH4/air premixed flames interacting with a turbulent-wake

A 1.5 m long turbulent-wake combustion vessel with a 0.15 m × 0.15 m cross-sectional area is proposed for spatiotemporal measurements of curvature, strain, dilatation and burning rates along a freely downward-propagating premixed flame interacting with a parallel row of staggered vortex pairs having both compression (negative) and extension (positive) strains simultaneously. The wanted wake is generated by rapidly withdrawing an electrically-controlled, horizontally-oriented sliding plate of 5 mm thickness for flame–wake interactions. Both rich and lean CH₄/air flames at the equivalence ratios  = 1.4 and  = 0.7 with nearly the same laminar burning velocity are studied, where flame–wake interactions and their time-dependent velocity fields are obtained by high-speed, high-resolution DPIV and laser-tomography. Correlations among curvature, strain, stretch, and dilatation rates along wrinkled flame fronts at different times are measured and thus their influences on front propagation rates can be analyzed. It is found that strain-related effects have significant influence on front propagation rates of rich CH₄/air (diffusionally stable) flames even when the curvature weights more in the total stretch than the strain rate does. The local propagation rates along the wrinkled flame front are more intense at negative strain rates corresponding to positive peak dilatation rates but the global propagation rate averaged along the rich flame front remains constant during all period of flame–wake interaction. For lean CH₄/air (diffusionally unstable) flames, the curvature becomes a dominant parameter influencing the structure and propagation of the wrinkled flame front, where both local and global propagation rates increase significantly with time, showing unsteady flame propagation. These experimental results suggest that the theory of laminar flame stretch can be applicable to a more complex flame–wake interaction involving unsteadiness and multitudinous interactions between vortices.     

Non-steady interaction of plasma with aircraft in its near wake region

Non-steady interactions between plasmas and aircraft in its near wake region are investigated in detail. Under the non-static limit, a set of equations that describe these interactions are obtained. The results of the numerical simulation show that the cavitons of transverse plasmas are excited and density cavitons appear when the envelope of plasma becomes sufficiently intensive. This is very important for detecting the moving body that has a `stealth' characteristic.     

New expressions for the surface roughness length and displacement height in the atmospheric boundary layer

An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness obstacles. The experiments are carried out by the use of the hot wire anemometry in the simulated atmospheric boundary layer in a wind tunnel. Based on the experimental data, a new expression for the zero-plane displacement height is proposed for the square arrays of roughness elements, which highlights the influence of free-stream speed on the roughness length. It appears that the displacement height increases with the wind speed while the surface roughness length decreases with Reynolds number increasing. It is shown that the calculation results based on the new expressions are in reasonable agreement with the experimental data.     

尾迹流中大尺度涡的三维理论模型

根据流动稳定性理论,在边界层外区大尺度涡理论模型的基础上提出了一种解释尾迹流中大尺度涡产生机理的三维理论模型。采用该模型对NACA0012翼型尾缘后0．1到0．3倍弦长区域的流动进行计算,得出的流场结构及大尺度量的等值线等与实验符合一致,说明该理论模型能够很好地捕捉到尾迹流中大尺度结构的主要特征。该模型的提出为开展尾迹型流动的实验和数值模拟研究提供理论支持,同时为研究尾迹对流动的影响,特别是叶轮机内部的流动前一级叶栅尾迹对下一级叶片边界层的干扰提供了很大的简化。     

舰船尾迹光学信号特征的直方图提取方法

现有舰船尾迹光学信号特征提取方法普遍存在运算复杂、处理速度不快等问题,研究基于直方图分析的舰船尾迹光学信号特征快速提取方法。根据舰船尾迹图像直方图具有明显的双峰特征,提出用峰值点分布密集程度kdd和尾迹区与海水背景区像素灰度值均值比Ci2个参数来表征舰船尾迹光学信号特征强度,通过专门研制的海上特征提取实验装置进行特征提取实验分析。分析结果表明:这2个参数能定量可靠地描述舰船尾迹光学信号特征强度的变化规律,并且在特征提取中具有简单快速的优势,从读进一张舰船尾迹图像到利用MATLAB软件计算出其特征参数值,电脑处理时间约为0.07 s。     

基于多重散射强度和偏振特征的舰船尾流气泡激光探测方法

研究多重散射效应对舰船尾流气泡群光散射强度和偏振特征的影响是舰船光尾流探测以及新型光自导鱼雷研究的基础. 基于矢量Monte Carlo方法建立了舰船尾流气泡群激光后向探测仿真模型, 重点研究了尾流气泡群的多重散射机理,分析了多重散射效应、尾流气泡群密度对回波信号强度和偏振特征的影响规律. 基于粒子碰撞重要性抽样的基本思想, 在传统能量接收方法的基础上, 提出了回波光子偏振贡献接收方法和回波信号偏振信息统计方法, 解决了小视场系统光子返回概率低无法形成回波能量的难题. 构建了模拟尾流气泡群激光散射强度和偏振探测实验平台, 从实验的角度验证了模拟结果的准确性. 实验和模拟结果的一致性表明, 利用回波强度、偏振信息可表征气泡群距离、密度信息, 从而可对舰船尾流特别是低密度尾流进行高精度的探测和辨识. 关键词： Monte Carlo 偏振 多重散射 气泡