壁湍流周期性吹吸减阻的实验研究

为了研究局部周期性吹吸小扰动对湍流边界层的影响和湍流相干结构减阻控制机理,用实验方法研究了局部周期性吹吸小扰动与湍流边界层的相互作用.采用热线测速技术精细测量了施加吹扰动前后平板湍流边界层不同法向位置的流向、法向和展向速度分量的时间序列信号;通过测量扰动源下游近壁区域平均速度剖面的变化,发现在扰动下游一定空间范围内,粘性底层增厚和壁面减阻;通过对湍流度变化的分析,发现扰动影响猝发的发生;此外通过对展向平均涡量变化的分析发现,在扰动下游形成了2个定常的、强度相似的、大尺度的展向涡,它们起到流体滚动轴承的作用,减小了壁面摩擦阻力.

Drag reduction by periodic pressure/suction perturbations of wall turbulence

In order to investigate the effect of local periodic pressure/suction perturbations on turbulent boundary layers and the drag reduction mechanism of coherent structures in turbulent flows, experimental research was carried out to investigate the interaction between local periodic pressure/suction perturbations and the turbulent boundary layer. Hot-wire anemometry was used to measure the time sequence signals of instantaneous longitudinal, normal and transverse velocity components at different vertical locations over a flat plate, before and after local periodic pressure/suction perturbations were introduced into the turbulent boundary layer. By measuring the mean velocity profiles of downstream perturbations in the near wall region, it was found that special regions exist downstream from the spanwise slot where the viscous sub-layer tends to become thick and surface friction has been reduced. Variation of turbulence intensity implies that the perturbation influenced the occurrence of a burst event. Through the analysis of variation of the mean spanwise vorticity component, two steady, large-scale spanwise vortexes with similar strength have been found in the downstream region after introducing pressure/suction periodic perturbations. These vortexes behaved as fluid rolling bearings, causing the drag reduction.