湍流边界层中固体颗粒运动的数值模拟

根据Ｌａｇｒａｎｇｅ颗粒运动微分方程及不可压缩湍流边界层中流体的壁面速度分布规律，数值求解了颗粒在湍流边界层中的运动，考虑了Ｓａｆｆｍａｎ升为对颗粒运动的影响，壁面对运动阻力的影响，给出了固体颗粒沉积边壁，在边界层外缘上所需的最小速度和最小入射角，计算结果还表明边界层对固体颗粒撞击边壁的速度和入射角有较大影响，从数值结果可可以发现一个重要现象。     

对流边界层大涡自组织过程的数值研究

利用简化的边界层日变化干对流模式,结合非线性热力学观点,数值模拟并分析了日间对流边界层中大涡形成、发展及衰亡的动力和热力学特征.结果表明,对流边界层中大涡始终处于不稳定状态,大涡的自组织合并和破碎串级输送过程同时并存,前者与边界层系统的局部减熵相对应,后者与对流边界层的总体增熵效应对应;大涡的演变是对流边界层总体增熵这一稳定因素和局部减熵这一不稳定因素相互竞争的结果.     

自然对流边界层中湍流的发生

自然对流边界层中从层流到湍流的转捩经历了浮力振型、无摩擦振型和黏性振型的三重流动不稳定性相继产生的前转捩过程,以及近壁迅速出现强湍流源,随之平缓地向自模拟的湍流边界层过渡的热转捩过程.浮力振型在修正Grashof数G>40时开始失稳并成为主要振型,在振幅分布中3种振型的临界层位置处出现3个峰值;在G>100时浮力振型消失,无摩擦振型失稳并成为主要振型,振幅分布中在近壁区还出现黏性振型的峰值;在G>170时无摩擦振型经非线性演化在外层形成较弱的湍流,但内层黏性应力仍远高于湍流应力,振幅分布中仅有与黏性振型相应的峰值,在频谱中黏性振型的基频、第一、第二、第三阶亚谐频随G的增加相继出现,此时黏性不稳定波的高频成分已转化为湍流,但低频成分仍按线性规律增长,直至湍流惯性子区开始形成;至G>800时黏性振型消失,并在G=850附近时近壁区出现强湍流源,湍流应力、湍能产生项和近壁湍流热流率剧增.在热转捩后期,湍流应力和湍能产生项明显下降,流动在内外层趋于平衡.     

数值研究平板方舵激波-湍流边界层干扰

数值研究了平板方舵激波-湍流边界层干扰流场。模拟出了分离激波与弓型激波砬撞后形成的“λ”激波结构;消晰地显示了分离区中的旋涡结构,发现流场中会出现二次分离涡,并从理论上分析了流场对称面涡心形态与非定常的关系,得到了涡心为不稳定螺旋点或出现极限环是非定常流动特征的新结论。     

高超声速激波湍流边界层干扰直接数值模拟研究

高超声速激波与湍流边界层干扰会导致飞行器表面出现局部热流峰值,严重影响飞行器气动性能和飞行安全. 针对高马赫数激波干扰问题,以往数值研究多采用雷诺平均方法,而在直接数值模拟方面的相关工作较为少见. 开展高超声速激波与湍流边界层干扰的直接数值模拟研究,有助于进一步提升对其复杂流动机理认识和理解,同时也将为现有湍流模型和亚格子应力模型的改进提供理论依据. 采用直接数值模拟方法对来流马赫数6.0,34°压缩拐角内激波与湍流边界层的干扰问题进行了研究. 基于雷诺应力各向异性张量,分析了高超声速湍流边界层在压缩拐角内的演化特性. 通过对湍动能输运方程的逐项分析,系统地研究了可压缩效应对湍动能及其输运的影响机制. 采用动态模态分解方法,探讨了干扰流场的非定常运动历程. 研究结果表明,随着湍流边界层往下游发展,近壁湍流的雷诺应力状态由两组元轴对称状态逐渐演化为两组元状态,外层区域则由轴对称膨胀趋近于各向同性. 干扰流场内存在强内在压缩性效应(声效应),其对湍动能输运的影响主要体现在压力--膨胀项,而对膨胀--耗散项影响较小. 高超声速下压缩拐角内的非定常运动仍存在以分离泡膨胀/收缩为特征的低频振荡特性,其物理机制与分离泡剪切层密切相关.      

低Pr数流体自然对流边界层流动的直接数值模拟

在太阳能采暖通风系统中,空气在太阳辐射作用下于吸热壁上所形成的非稳态自然对流边界 层流动是决定系统热性能的关键所在. 对于线性分层的低普郎特数($Pr<1$)流体而言,标度分 析表明在起始阶段边界层的发展是与高度无关而只依赖于时间的,而处于稳态时,各项标度 关系与处于起始阶段终结时刻的大不相同,且都与高度和时间无关,而只与$Pr$数和线性分 层度相关. 直接数值模拟计算结果表明由标度分析所得的各项标度关系揭示了流动的特性参 数与控制参数之间的决定性内在联系. 但同时也表明标度关系并没有充分体现出 对$Pr$数的所有依赖关系,这一不足可利用直接数值模拟计算结果得到弥补.     

对管内湍流边界层结构与流动阻力特性的数值研究

在研究紊流边界层的过程中,本文考虑了分子粘性对紊流产生的作用、雷诺数以及壁面附近脉动动能的耗散不是各向同性对紊流产生的影响,采用Jones-Launder模型对管内紊流流动边界层厚度、边界层内的脉动动能K,动能耗散ε,管壁切应力τ0以及由此可得的管内流动摩擦阻力系数λ进行了数值计算,计算结果与实验值、理论计算值得具有较好的一致性。     

微型射流涡流器对湍流边界层控制的数值研究

运用数值方法,模拟出展向分布的同向倾斜微型射流列与平板湍流边界层相互作用形成流向涡列的流场结构,验证了利用其来对湍流边界层进行控制的可能性.随射流间距减小,流向涡列控制作用流向渗透能力增强,但作用区域减小;随射流速度提高,流向涡列控制作用增强,但过大的射流速度反而会导致流向涡列在局部区域内控制作用的下降;随射流俯仰角减小、倾斜角增大,流向涡列初始控制作用增强,但过小的俯仰角、过大的倾斜角会导致流向涡列流向控制区域明显缩小.要保证流向涡列具有较强的湍流边界层控制作用,必须通过合理配置射流列各主要参数,在保证各流向涡具有一定强度的同时,还要确保各流向涡在形成时部分嵌入边界层内部.     

受对流边界层影响的过山气流

建立了一个自由大气与对流边界层相耦合的解析模式，利用该模式系统地讨论了对流边界层对过山气流的影响。     

稳定分层流动中湍流特性的研究综述

本文总结了近60 年来分层流动中湍流特性研究的成果. 主要从两个方面进行了综述:(1) 分层流动中湍流场的演变和混合. 在这方面主要分析稳定分层对湍流混合和湍流结构的影响, 以及混合层内湍流结构的特性和混合层的演化规律. (2) 分层流动中湍流的扩散和输运. 动量和标量的逆梯度输运特性是分层湍流研究的一个重要方向;分析分层对湍流扩散的影响. 并指出了一些值得今后进一步研究的方向.     

Three-dimensional Turbulent Boundary Layer in a Shrouded Rotating System

A thre-dimensional direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed annular rotor-stator cavity characterized by a large aspect ratio G = (b − a)/h = 18.32 and a small radius ratio a/b = 0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Ω considered is equivalent to the rotational Reynolds number Re = Ωb ²/ν= 9 .5 × 10⁴ (ν the kinematic viscosity of water). This corresponds to a value at which experiment has revealed that the stator boundary layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the computed solution with velocity measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence by comparing the turbulence properties with available data in the literature (Lygren and Andersson, J Fluid Mech 426:297–326, 2001). An approximately self-similar boundary layer behavior is observed along the stator. The wall-normal variations of the structural parameter and of characteristic angles confirm that this boundary layer is three-dimensional. A quadrant analysis (Kang et al., Phys Fluids 10:2315–2322, 1998) of conditionally averaged velocities shows that the asymmetries obtained are dominated by Reynolds stress-producing events in the stator boundary layer. Moreover, Case 1 vortices (with a positive wall induced velocity) are found to be the major source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson (J Fluid Mech 426:297–326, 2001).     

Eddy Structures in a Simulated Low Reynolds Number Turbulent Boundary Layer

Coherent structures in a tripped turbulent boundary layer havebeen analysed by applying a new conditional sampling algorithm tolarge-eddy simulation (LES) data. The space-time development of theevents and structural characteristics were examined. The new conditionalsampling scheme is shown to be very effective in the eduction of thecoherent eddy structures, allowing the simultaneous detection, trackingand averaging of several three-dimensional (3-D) structures. Alignmentof the triggering events in all spatial directions and flip-averaging(spatial reflection of the samples) enhance significantly the extractionof detailed features of the structures. The detection method minimisesthe smearing of the spatial details and avoids imposing artificialsymmetry, which is often intrinsic to other conditional samplingschemes.The results show the existence of cigar-shapedstreamwise vortices which are directly associated with negative pressurefluctuation peaks (positive source term of the pressure Poissonequation). They are inclined at 12^° to the wall andtilted laterally at an angle of 7^° to the streamwisedirection. The streamwise vortices induce ejections and sweeps throughan advection mechanism due to the tilting or inclination of thevortices. There is no evidence of hairpin vortices in either theconditional averages or instantaneous flow fields. Near-wall shearlayers are found to be related to the positive pressure fluctuationpeaks as a result of complex interactions between ejection and sweepevents. The shear layer structure has an inclination of10^°, being located between two tilted, streamwisevortices of opposite direction of rotation.The presentresults are very close to other Direct Numerical Simulation studiesusing different conditional sampling schemes. Conceptual models for thestreamwise vortices and shear layer structures are proposed to accountfor the results.     

平板湍流边界层的声辐射

基于平板湍流边界层的壁压起伏波数—频率谱 ,给出了一种湍流边界层声辐射的估算方法 ,并对光滑平板湍流边界层和平板表面粗糙度引起的湍流边界层声辐射进行了分析。结果表明 :湍流边界层声辐射是一种四极子声辐射 ,且其辐射声能集中于平板表面粗糙度引起的湍流边界层声辐射 ;光滑平板湍流边界层的声辐射也不可忽略。     

二维平板湍流边界层减阻研究

利用一套以位移传感器为主的弹性平衡装置,测量几种不同表面形状设计的平板在充分发展的二维湍流边界层中的减阻效果,并对其减阻机理进行研究。结果表明,大涡破碎器 LEBU(Large Eddy Break-up)和其它减阻装置的形状和布置对表面摩擦阻力有较大影响,在有些设计状态下的平板得到了净减阻。     

湍流边界层流场与噪声实验研究

在重力式水洞中进行了水翼及半翼湍流边界层流场与噪声的实验研究。测量了水翼及半翼边界层附近的湍流脉动速度场;测量了半翼翼型表面三点处的压力脉动及其辐射噪声,测量了水翼内部测点的噪声及外部辐射噪声,在不同流速、不同攻角、光滑和粗糙翼面的情况下都进行了测量分析。试验结果发现,上述因素对模型的边界层湍流速度场有显著影响,15度攻角时,翼面附近湍流强度要比0度时大得多,粗糙翼面附近的湍流强度比光滑的大,而湍流强度随来流速度的变化不大,u(来流）方向和v方向的湍流强度量级相当;一般地,翼面压力脉动、翼内部噪声及外部噪声都是随来流速度的增大而增大,随攻角的增大而增大,粗糙翼面时的结果要比光滑翼面的大。从压力脉动与噪声测量结果与相应的流场测量结果比较可知,可以从湍流区域的湍流强度来判断出声源强度的定性变化。     

Effect of a Short Roughness Strip on a Turbulent Boundary Layer

The response of a turbulent boundary layer to a short roughness strip is investigated using laser Doppler velocimetry (LDV) and laser induced fluorescence (LIF). Skin friction coefficients are inferred from accurate near-wall measurements. There is an undershoot in , where is the undisturbed smooth wall skin friction coefficient, immediately after the strip. Downstream of the strip, overshoots before relaxing back to unity in an oscillatory manner. The roughness strip has a major effect on the turbulent stresses ; these quantities increase, relative to the undisturbed smooth wall, in the region between the two internal layers originating at the upstream and downstream edges of the strip. The increase in the ratio suggests a decrease in near-wall anisotropy. From the flow visualizations, it is inferred that streamwise vortical structures are weakened immediately downstream of the strip. Consistently, streamwise length scales are also reduced; direct support for this is provided by measured two-point velocity correlations.     

Permissible Height of the Surface Roughness in a Turbulent Boundary Layer with a Streamwise Pressure Gradient

The results of an experimental investigation of the effect of the streamwise pressure gradient in a turbulent boundary layer on the permissible height of the surface roughness of bodies in an incompressible fluid flow are presented. The permissible roughness Reynolds number for which the characteristics of the turbulent boundary layer remain the same as in the case of flow past a smooth surface is determined.     

Universal Velocity Defect Law for the Turbulent Boundary Layer

Turbulent plane boundary layer flows of an incompressible fluid are considered. A refinement of the known Coles wake law is proposed. This refinement makes it possible to ensure the smooth matching of the turbulent boundary layer velocity profile with the outer flow and to extend the range of validity of the law to the case of large positive pressure gradients. The accuracy of the analytical approximation obtained is verified by comparison with the known experimental equilibrium velocity profiles. Using the approximation proposed, a relation for calculating the cross-sectional distribution of the Reynolds stress in the equilibrium boundary layer is derived. The pressure distributions for which the equilibrium turbulent boundary layer flows are single- and two-valued are distinguished.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 89–101.Original Russian Text Copyright © 2005 by Mikhailov.     

基于雷诺应力模型的平衡大气边界层模拟

基于雷诺应力湍流模型（简称RSM模型）,研究了平衡大气边界层风场数值模拟问题．假设流体不可压,且不计雷诺应力输运方程中的对流项、浮力产生项、系统旋转产生项和扩散项,在准各向同性的条件下,推导出RSM模型湍动能k的表达式是标准k-ε模型k常数表达式的0.893倍．考虑k沿高度变化的修正,根据在标准k-ε模型中满足水平均匀性的湍流来流边界条件,提出在RSM模型中产生平衡大气边界层的湍流来流边界条件．基于空风洞的数值模拟结果表明,与工程上常用的湍流来流边界条件相比,基于本文提出的湍流来流边界条件得到的风场水平均匀性更优,且在整个流域内,得到的雷诺应力剖面更合适．从而验证了该湍流来流边界条件的适用性．