Passive Drag Reduction of Wall-Turbulent Flows

本计画的目的是发展一种有效的壁面紊流被动减阻装置。为此，提出了两种模型来模拟聚合物的作用，在减阻中起着重要作用，称为汤姆斯效应。第一种模型是静电沉积在平板上的细纤维丝。用专门设计的装置测量了“羊毛状”平板的阻力，采用平衡法将微小的阻力转化为微小的流向位移。然而，测量结果表明，由于难以获得足够细的纤维丝以满足目的，模型没有阻力减少。第二个模型，然后进行测试，其中包括放置在一个平板上的钓鱼线和aligned在流向方向。对于最佳构型，观察到约7%的阻力减小。这种情况下的突起的高度比肋的情况下要小得多。

The objective of the project is to develop a devise effective for passive drag reduction of wall-turbulent flows. For this purpose two models are proposed to simulate roles of polymers which plays important roles in drag reduction known as Toms' effect. The first model is fine fibre-filament deposited on a flat plate by means of electrostatic method. The drag of the 'woolly' flat plate is measured by a specially designed apparatus using a ballancing method which edtects minute drag force as slight streamwise displacement. The measurements show, however, no drag reduction for the model because of difficulty in obtaining fibre filament fine enough to meet the purpose. The second model is then tested which consists of fishing lines placed on a flat plate and alligned in streamwise direction. For optimum configuration the drag reduction of about 7 % is observed. The height of protuberance for this case turns out to be much smaller than the riblets case.