PIV計測による再層流化を目指した脈動円管内乱流の実験的研究

抄録

An experimental study of pulsation control for reducing frictional drag in turbulent pipe flow was conducted. Some numerical studies have demonstrated that relaminarization was observed during the entire period of acceleration and deceleration. Although turbulence suppression is observed, it is challenging to achieve relaminarization in experiments. Our aim is to consider pulsation control to settle the flow into a completely laminar flow. PIV measurements were performed to reveal the difference between the enhancement and suppression of turbulence corresponding to acceleration and deceleration. In this study, we measured turbulent flow fields subjected to a pulsation that exhibited a sufficiently high drag reduction effect. The results showed that the Reynolds shear stress decreased in the pulsating flow compared to the uncontrolled flow except near the wall in the time-averaged statistics, which indicates that the turbulence was suppressed. In addition, from the coefficient of frictional drag in the uncontrolled and controlled conditions, it is possible to show that the turbulence decreased during acceleration and during deceleration, and there was a tendency for re-laminar flow. However, the turbulence did not completely disappear and increased again in the late deceleration phase. These results suggest that turbulence decreases during the acceleration phase and tends to relaminarize in the early deceleration phase, leading to a drag reduction.