Experimental Study on Drag Reduction Using Flexible Tubes.

Abstract

Friction drag reduction of pipe flow using a flexible tube was experimentally investigated and compared with a rigid tube. It was found that the coefficient of friction of the flexible tube was lower than that of the rigid tube. Furthermore, when the thickness of the flexible tube was decreased and the Reynolds number was increased, the rate of drag reduction increased, except when using a very thin flexible tube. To clarify these phenomena more precisely, the fluctuating velocity on the center axis of the tube, the fluctuating pressure on the inner wall surface of the tube and the fluctuating displacement on the outer wall surface of the tube were measured. From the power spectrum distribution and the overall band energy obtained by analyzing these waves, it was clarified that there exists an interrelation between the turbulent energy and the drag reduction and a negative correlation between the fluctuating pressure and the fluctuating displacement.