Turbulence structural changes for a three-dimensional turbulent boundary layer in a 30° bend
Turbulence structural changes for a three-dimensional turbulent boundary layer in a 30° bend
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30°弯曲处三维湍流边界层的湍流结构变化
DOI：
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发表时间：
1994
影响因子：
3.7
通讯作者：
P. Bradshaw
中科院分区：
文献类型：
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作者：
W. Schwarz;P. Bradshaw
在低速风洞底部，通过横流压力梯度在水平面上施加30°弯曲，形成了三维湍流边界层。地表流线相对于局部隧道中心线偏转多达22°。在弯道下游，3DTBL逐渐向2DTBL放松；这是一个专注于外层的冲动和恢复实验。用三孔偏航仪测量平均速度，用交叉线热线风速仪测量湍流量，包括雷诺应力张量和三重积。该实验将横流的影响从逆流压力梯度的影响中分离出来，这可能会使以前3DTBL实验的解释变得模糊。特别是，横向剪切应力和应力/能比的详细发展变得更加清晰。随着横流的发展，剪切应力矢量滞后于速度梯度矢量；然而，这两个矢量在弯曲的下游变得更加紧密。应力/能量比的减小意味着横流降低了剪切应力的产生效率。三维的另一个影响是边界层内部湍流对湍流动能垂直输送的符号变化。
A three-dimensional turbulent boundary layer (3DTBL) was generated on the floor of a low-speed wind tunnel by the imposition of a cross-stream pressure gradient using a 30° bend in the horizontal plane. The surface streamlines were deflected by as much as 22° relative to the local tunnel centreline. Downstream of the bend, the 3DTBL gradually relaxed towards a 2DTBL; this was an impulse-and-recovery experiment which focused on the outer layer. Mean velocities were measured with a three-hole yawmeter and turbulence quantities, which included the Reynolds-stress tensor and the triple products, were measured with a cross-wire hot-wire anemometer. The experiment isolated the effects of crossflow from those of adverse streamwise pressure gradients, which may have clouded interpretations of previous 3DTBL experiments. In particular, the detailed developments of the cross-stream shear stress and of the stress/energy ratio become clearer. The shear-stress vector lagged behind the velocity-gradient vector as crossflow developed; however, the two vectors became more closely aligned downstream of the bend. Reductions in the stress/energy ratio implied that crossflow made shear-stress production less efficient. Another effect of three-dimensionality was a change of sign in the vertical transport of turbulent kinetic energy by turbulence, in the inner part of the boundary layer.