Wall Turbulence

这一提议处理的是固体边界上的流动产生的湍流。目标是确定湍流是如何产生的，如何控制湍流，如何预测雷诺应力和小尺度湍流的性质。该研究的一个重要特点是它使用了直接数值模拟（DNS）、脉冲图像测速（PIV）、双分量激光多普勒测速（LDV）和专门建造的湍流光学研究设施。主要目的是发展一个壁面湍流的概念框架，该框架可用于分析复杂的流动并确定如何修改湍流。所采取的方法是考虑产生应力的涡流的结构和动力学。研究将包括：(1)“简单的”壁面湍流，如沟道中完全发育的流动或库埃特流；(2)在波浪状固体边界上的流动；(3)减阻聚合物溶液的流动。PIV和DNS将用于研究大尺度外流涡旋。将特别注意它们的起源以及它们与靠近壁面的流动导向旋涡的相互作用，这些旋涡是非常大的湍流生产者。适当的正交分解可以分离大尺度和小尺度湍流。波浪边界上的流动与光滑边界上的流动有着根本的不同，因为靠近壁面的湍流产生与分离的剪切层有关，而不是与壁面涡有关。长链聚合物的添加量小至3ppm，通过改变粘壁区域的结构显著降低阻力，其方式尚不清楚。

ABSTRACT CTS-9500518 HANRATTY UNIVERSITY OF ILLINOIS This proposal deals with turbulence generated by flow over a solid boundary. The goals are the determination of how turbulence is produced, of how to control turbulence, of how to predict Reynolds stresses and the properties of small scale turbulence. An important feature of the research is that it uses direct numerical simulations (DNS), pulsed-image velocimetry (PIV), two-component laser-Doppler velocimetry (LDV), and a specially constructed facility for optical studies of turbulence. The chief thrust is to develop a conceptual framework for wall turbulence which can be used to analyze complex flows and to determine how turbulence can be modified. The approach taken is to consider the structure and dynamics of stress producing eddies. Studies will be made of (1) "simple" wall turbulence, such as fully developed flow in a channel or Couette flow, (2) flow over a wavy solid boundary, (3) flow of a solution of drag-reducing polymers. PIV and DNS will be used to study large scale eddies in the outer flow. Particular attention will be given to their origin and to their interaction with the flow oriented vortices close to the wall which are very large producers of turbulence. Proper orthogonal decomposition will separate large and small scale turbulence. Flow over a wavy boundary is fundamentally different from flow over a smooth boundary in that turbulence production close to the wall is associated with a separating shear layer rather than wall vortices. The addition of a long chain polymer, in amounts as small as 3 ppm, dramatically decreases drag by changing the structure in the viscous wall region, in ways which are poorly understood.