高频吹气扰动影响近壁区拟序结构统计特性的实验研究

EFFECTS OF HIGH FREQUENCY BLOWING PERTURBATION ON A TURBULENT BOUNDARY LAYER

利用恒温热线风速仪测量了零压力梯度平板上施加由合成射流激发的狭缝周期吹气扰动前后不同流向位置湍流边界层的速度信号,展开高频吹气扰动影响近壁区湍流结构的统计特性研究.研究结果表明:高频周期吹气扰动在狭缝下游产生明显的减阻效果.扰动强度在湍流边界层内的发展沿流向呈衰减趋势,其与湍流结构的相互作用也相应衰减.然而,因高频扰动产生运动的展向涡结构与猝发引起的结构变化尺度相当,直接影响了近壁区拟序结构产生与发展的统计,从而使得猝发检测方法 VITA表现出与低频或定常吹气减阻机理相异的现象.

An experimental study is conducted on a zero pressure gradient flat plate for investigating the effects of a periodical perturbation on the turbulent boundary layer over the flat plate. This experiment is focused on studying the effects of high frequency blowing on statistical characteristicss of near wall turbulence. By measuring and analyzing streamwise velocity signals at different streamwise locations with and without a periodical perturbation induced by a synthetic jet actuator, the conclusion of the experiment indicates skin friction reduction can be achieved downstream of the slot by applying high frequency periodical blowing perturbation. Owing to the intensity of the perturbation in the turbulent boundary layer is attenuating along the streamwise, the interaction between the perturbation and turbulent flow structures is attenuating. However, the negative spanwise vortexes induced by the high frequency perturbation are nearly of the same scale as the structures of bursting events, which directly impact the statistics of production and evolution of near wall coherent structures. As a result, the outcomes of bursting detection methods like VITA in the experiment show a contradictory phenomenon to the mechanism of skin friction reduction in low frequency blowing or steady blowing.