주기적인 분사/흡입이 난류경계층에 미치는 영향

Abstract

An experimental study was carried out to investigate the effect of periodic blowing and suction on a turbulent boundary layer. Particle image velocimetry (PIV) was used to probe the characteristics of the flow. The local forcing was introduced to the boundary layer via a sinusoidally-oscillating jet issuing from a thin spanwise slot. Three forcing frequencies (f+=0.044, 0.066 and 0.088) with a fixed forcing amplitude (A+=0.6) were employed at $Re_{=690. The effect of the forcing angles (α=60o , 90o and 120o ) was investigated under the fixed forcing frequency (f+=0.088). The PIV results showed that the wall region velocity decreases on imposition of the local forcing. Inspection of phase-averaged velocity profiles revealed that spanwise large-scale vortices were generated in the downstream of the slot and persist further downstream. The highest reduction in skin friction was achieved at highest forcing frequency (f+=0.088) and a forcing angle of α=120o. The spatial fraction of the vortices was examined to analyze the skin friction reduction.