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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

实验研究了湍流边界层与纵向涡对的相互作用过程。自由流动中的三角翼引入发达的湍流边界层后，产生了共流向上和共流向下两种类型的纵向涡对。涡旋半径与相互作用开始时的边界层厚度相当。纵向涡旋的环流远小于整个边界层的环流，但在外层属于同一量级的环流。本研究将展向振荡应用于涡发生器。展向振荡的振幅是三角翼翼展的一半。正弦振荡频率分别为0.5Hz和1.0Hz。利用自由流中统计量的行为研究了展向振荡的影响。施加展向振荡后，流向涡度轮廓变得扁平。在雷诺应力的轮廓中出现了一些强峰。根据涡旋康托的概率分布，期望在给定的横流位置测量的雷诺应力包含表观分量。采用纵向涡度积分和升力估算两种不同的方法对机翼产生的环流进行测量。这两个结果证明了展向振荡对涡度产生过程没有显著影响。在相互作用过程中，测量了边界层内平均速度和雷诺应力的变形和松弛。在共流上升的情况下，纵向涡对以更快的速度远离壁面。在共流下行的情况下，两个纵向涡通道的展向扩展速率较大。在共流下降的情况下，最大纵向涡度的衰减速度较慢。在两涡之间的对称平面上，纵向涡之间的相互作用使得共流下行时平均速度轮廓线分布紧密，摩擦系数较高。而在共流向上的情况下，相互作用使平均速度轮廓线分布广泛，摩擦系数较低。采用动量积分方程中额外应变率的影响来解释两种情况下的边界层行为。在三种湍流强度分量剖面和雷诺数剪切应力剖面中考察了额外应变速率∂W/∂z和∂V/∂y的影响。沿对称面边界层分为共流向下时的“横流”和共流向上时的“可识别的流向涡”。在共流向下的情况下，额外的应变率改变了内层湍流强度和雷诺剪切应力的大小。反之，在近壁面共流向上的情况下，根据横向散度的大小大于展向辐合的大小，可以推导出局部逆压梯度。采用多点热线同步测量和条件检测技术，研究了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，间隔2mm，相当于粘性壁长度的40倍。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粘壁长度的150倍。共流下行情况下，沿壁面的二次电流时平均间距较大，沿壁面的二次电流时平均间距较小。对比表明，向展向振荡使这种效应有所减弱。少