计算实际机翼湍流边界层流动的积分法

本文采用一种拟坐标变换掺混方法,计算任意外形机翼的三维边界层流动,亦适用于边界层外流为位流或非位流情况。对C-5A机翼的计算结果表明,该方法具有同微分方法可以比拟的计算精度。并分析了在亚音速情况下粘性对机翼升力和力矩的干扰影响。     

直方管内充分发展湍流的大涡模拟 第二部分

本文第一部分用大涡模拟的方法对直方管内Ｒｅ＝４．９×１０￣４的充分发展湍流运动进行了数值模拟。所得结果证实大涡模拟是高雷诺数复杂湍流运动数值模拟的一个有效手段。在本文第二部分用所得的数据库对湍流运动的结构和形态进行了分析，并且用流体质点运动图形显示了湍流运动的二次流。     

翼型尾缘噪声源空间分布与辐射特性关系

详细研究了翼型湍流边界层尾缘宽频噪声源空间分布与辐射特性的关系.采用基于雷诺平均流场的翼型尾缘宽频预测方法研究了NACA0012翼型湍流边界层尾缘宽频噪声在4种不同工况下的噪声源空间分布与辐射特性.首先计算了NACA0012翼型湍流边界层尾缘噪声源在不同频率下的空间分布.计算结果发现:边界层中湍流是翼型湍流边界层尾缘噪声声源.随着频率的增加,噪声源强度和噪声源空间尺寸都是先增加后减小,噪声源位置不断靠近翼型尾缘.同时也计算了边界层内不同位置处的噪声源对远场噪声的辐射特性,结果表明:边界层内层区域,其噪声频谱能量集中在高频;边界层外部区域,其噪声能量集中在中低频;攻角增大或者来流速度减小,噪声能量向低频转移.      

“大涡破碎”的紊流减阻实验研究

本文对当今国外曾提出的紊流表面摩擦减阻新概念——“大涡破碎”(LEBU)进行了初步的风洞实验探索。将具有对称流线型剖面的二元小肋,沿垂直于气流的方向安置在平板表面的紊流附面层内某一高度处,收到了不同程度的减阻效果。实验中分别考察了小肋的安置位置L,安置高度H,迎角θ及相对厚度b等参数对减阻效果的不同影响。从紊流附面层涡结构的观点出发,提出紊流的“细化”作用是小肋对平扳减阻的根本原因,并认为改善紊流附面层的速度型是研究紊流减阻的一种手段。实验使用自制的高灵敏度摩擦天平,测得的减阻效果与Ludwieg—Tillman公式的计算结果基本一致。     

A new two-scale model for large eddy simulation of wall-bounded flows

A new hybrid approach to model high Reynolds number wall-bounded turbulent flows is developed based on coupling a two-level simulation (TLS) approach (Kemenov and Menon, 2006 [1], 2007 [2] in the inner region with conventional large eddy simulation (LES) away from the wall. This new approach is significantly different from previous near-wall approaches for LES. In this hybrid TLS–LES approach, a very fine small-scale (SS) mesh is embedded inside the coarse LES mesh. The SS equations capture fine-scale temporal and spatial variations in all three Cartesian directions for all three velocity components near the wall. The TLS–LES equations are derived using a new scale separation operator that allows a smooth transition between the two regions, with the equations in the transition region obtained by blending the TLS large-scale and LES equations. New terms in the hybrid region are identified. The TLS–LES approach is used to study the near-wall features in canonical turbulent channel flows for a range of Reynolds number using relatively coarse large-scale (LS) grids. Results show that the TLS–LES approach is able to capture the effect of both the LS and SS features in the wall region consistently for the range of simulated Reynolds number.     

Macroscopic Transport Large-scale advection, turbulent diffusion, wave transport

While the solar convection zone is very well mixed by its turbulent motions, chemical composition gradients build up in the radiative interior due to microscopic diffusion and settling, and to nuclear burning. Standard models, which ignore any type of macroscopic transport, cannot explain the depletion of lithium in solar-type stars, as they evolve; neither do they account for the observed profile of molecular weight at the base of the solar convection zone. Such macroscopic transport can be achieved through thermally driven meridian currents, through turbulent diffusion generated by differential rotation and possibly through gravity waves. These processes transport also angular momentum, and therefore the internal rotation profile of the Sun provides a crucial test for their relative importance. So does also the behavior of tidally locked binaries, which appear to destroy less lithium than single stars of the same mass. This revised version was published online in June 2006 with corrections to the Cover Date.     

特型钝体绕流动态特性的低速实验研究

在低速自由射流风洞上 ,利用热线及相关设备对由半球头部、颈部及旋成体构成的特型钝体周围非定常流动的基本特性、联合特性及湍流度分布进行了测试与分析 ,实验工况为迎角α=- 1 5°～ 1 5°、侧滑角 β =0°～ 1 0°。结果表明 ,在上述工况范围内 ,该钝体周围流场中速度脉动的能量分布平坦 ,属宽频带随机信号 ,流场中没有发生明显的流动分离 ,流场动态品质良好 ;凹陷区内气流的脉动以不同的速度向下游空间传播 ;在上述α、β变化范围内 ,钝体颈部凹陷区的最大湍流度高达 1 0 .9～ 2 4.8%。     

求解最小费用最大流问题的一种方法

介绍了最大流问题的多解，提出了通过调整圈来求解最小费用最大流的方法。     

用非线性k-ε-k_p两相湍流模型模拟旋流两相流动

建立了两相湍流的代数应力模型 ,并由此出发 ,导出非线性k ε kp 两相湍流模型 ,目的是合理地模拟各向异性较强的旋流两相流动 ,保持二阶矩模型的优点 ,同时比二阶矩模型简单 .文中得到了气相、颗粒相的雷诺应力和两相脉动速度关联的非线性应力应变关系式。这些代数式和两相各自的湍动能k ,kp,以及两相脉动关联湍动能kpg的方程联立 ,就构成非线性k ε kp 模型 .将该模型用于模拟旋流两相流动 ,给出两相时均速度场及雷诺应力各分量 ,并且将模拟结果和实验数据以及二阶矩模型的模拟结果对照 .研究结果表明 ,该模型预报旋流两相流动的能力和二阶矩模型的能力相差不多 ,但计算量比二阶矩模型的小     

定常可压缩无粘流非线性方程解的完全边界积分表示式

 本文以ρV为因变量将可压缩等熵无粘流非线性方程的解表示成完全边界积分形式,从而将问题的计算维数降低一维。