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Control of the Streaky Structure in Turbulent Boundary Layer by means of Streamwise Vortex Pair

流向涡对控制湍流边界层条纹结构

基本信息

批准号：
14350093
负责人：
OSAKA Hideo
金额：
$ 4.42万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14350093/
关键词：
Turbulent Boundary Layer Streaky Structure Longitudinal Vortex Organized Motion Scaling Law Spatial Averaging

项目摘要

Interaction process between turbulent boundary layer and longitudinal vortex pair was investigated experimentally. Two-types of longitudinal vortex pair, that is, common-flow up and common-flow down, were generated by delta wing located in free stream and introduced into developed turbulent boundary layer. Radius of vortex is comparable with the boundary layer thickness at the start of the interaction. Circulation of the longitudinal vortex is much less than circulation of whole boundary layer, but, of the same order of circulation in the outer layer. In the present study, spanwise oscillation was applied to vortex generator. Amplitude of spanwise oscillation is a half of wing span of the delta wing. Frequencies of sinusoidal oscillation were chosen as 0.5Hz and 1.0Hz.Effect of spanwise oscillation was investigated with behavior of statistical quantities in free stream. Contours of streamwise vorticity becomes to flattened shape by applying spanwise oscillation. Some strong peaks appea … More r in contours of Reynolds stresses. It is expected that Reynolds stresses measured at a given cross-stream position contain apparent components depending on probability distribution of vortex cantor. Circulation generated by the wing was measured by two different ways, that is, integral of longitudinal vorticity and estimation from lift force obtained pressure measurement. The two results prove that spanwise oscillation has no significant effect on the vorticity generating process.In the interaction process, deformation and relaxation of the mean velocity and Reynolds stresses profile were measured in the boundary layer. The longitudinal vortex pair moves away from the wall in faster rate in case of common-flow up. Spanwise spreading rate of two longitudinal vortex path is larger in case of common-flow down. Decay of maximum longitudinal vorticity is slower in case of common-flow down. At symmetrical plane between two vortex, the interaction between longitudinal vortex makes closely distributed mean velocity contour lines and higher skin-friction coefficient in case of common-flow down. Otherwise, in case of common-flow up the interaction makes widely distributed mean velocity contour lines and low skin-friction coefficient. Effect of extra rate of strain involved in momentum integral equation is applied to explain boundary layer behaviors in the two cases.Effect of the extra rate of strain, ∂W/∂z and ∂V/∂y, was examined in the profiles of three turbulent intensity components and Reynolds shear stress profiles. The boundary layer along symmetrical plane is classified into "cross flow" in case of common-flow down and "identifiable streamwise vortices" in case of common-flow up. The extra rates of strain modify magnitude of turbulent intensity and Reynolds shear stress in the inner layer in case of common-flow down. Otherwise, close to the wall in the case of common-flow up, local adverse pressure gradient is deduced from the fact that magnitude of transverse divergence is grater than that of spanwise convergence.Effect of the interaction on the streaky structure was investigated by simultaneous multi point hot-wire measurement and conditional detection technique. The multi point hot-wire sensor has 12 single hot-wire sensors with 2mm spanwise separation that corresponds to 40 times viscous wall length. The Variable Interval Time Averaging method (VITA) was employed as a detection scheme for low speed streaks. Averaged spanwise spacing of the low speed streaks detected by the scheme is about 150 times viscous wall length. In the common-flow down case, the average spacing is larger at wall-ward secondary current and smaller at up-ward secondary current. The comparison shows that the spanwise oscillation makes the effect somewhat weaker. Less

对湍流边界层与纵向涡对的相互作用过程进行了实验研究。三角翼在自由流中产生共流上升和共流下降两种纵向涡对，并将其引入到发展的湍流边界层中。涡流半径与相互作用开始时的边界层厚度相当。纵向涡的环量远小于整个边界层的环量，但与外层的环量数量级相当。本文将展向振荡应用于涡发生器。展向振动幅值为三角翼翼展的一半。正弦振动频率分别为0.5Hz和1.0Hz，通过统计量在自由流中的变化，研究了展向振动的影响。通过施加展向振荡，流向涡量的等值线变得平坦。出现了一些强峰 ...更多信息雷诺应力等值线中的r。可以预料，在给定的横流位置测得的雷诺应力包含明显的成分，取决于概率分布的涡康托。采用纵向涡量积分和压力测量升力估算两种方法测量了机翼产生的环量。结果表明，展向振荡对涡量生成过程没有明显影响，在相互作用过程中，边界层内平均速度和雷诺应力的分布发生了变形和松弛。共流向上时，纵向涡对以较快的速度远离壁面。同向下流时，两条纵向涡路的展向扩展率较大。同向流向下时，最大纵向涡量衰减较慢。在两涡对称面处，纵向涡的相互作用使平均速度等值线分布较密，同向流下时表面摩擦系数较高。而在同向流向上时，这种相互作用使平均流速等值线分布较宽，表面摩擦系数较低。用动量积分方程中的附加应变率效应来解释这两种情况下的边界层行为，并在三个湍流强度分量剖面和雷诺切应力剖面中考察了附加应变率的影响。沿对称面的边界层沿着分为共流下行时的“横流”和共流上行时的“可识别流向涡”。在同向流下，附加应变率改变了内层湍流强度和雷诺切应力的大小。另外，在近壁面处，由横向发散大于展向收敛的特点，推导出了同向流上升时的局部逆压梯度，并采用多点热线同步测量和条件探测技术研究了这种相互作用对条纹结构的影响。多点热线传感器有12个单热线传感器，展向间距为2mm，对应于40倍粘性壁长。采用可变间隔时间平均法（VITA）作为低速条纹的检测方案。该方案检测到的低速条纹的平均展向间距约为150倍粘性壁长。在同向下流的情况下，二次流流向壁面时平均间距较大，而流向上的二次流时平均间距较小。结果表明，展向振动使这种影响有所减弱。少