Wall Turbulence

摘要CTS-9500518伊利诺伊州汉拉蒂大学这项提议涉及到固体边界上的流动所产生的湍流。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。这项研究的一个重要特点是使用了直接数值模拟(DNS)、脉冲图像测速仪(PIV)、双分量激光多普勒测速仪(LDV)以及专门为湍流光学研究而建造的设备。主要目的是开发一个壁面湍流的概念框架，可以用来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旋的结构和动力学。我们将研究(1)“简单”的壁面湍流，如槽道或Couette流中充分发展的流动，(2)波状固体边界上的流动，(3)减阻聚合物溶液的流动。PIV和DNS将用于研究外流中的大尺度涡流。将特别注意它们的起源以及它们与靠近壁面的流动导向涡的相互作用，这些涡流是产生湍流的非常大的因素。适当的正交分解将区分大尺度和小尺度的湍流。波状边界上的流动与光滑边界上的流动根本不同，因为靠近壁面的湍流产生与分离的剪切层有关，而不是与壁涡有关。加入低至3ppm的长链聚合物，通过改变粘性壁区的结构大大减少阻力，但人们对此知之甚少。

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.