In order to clarify the mechanical characteristics on friction reduction by coupling flexible tubes with turbulent flow,experimental investigation was performed on effects of turbulent drag reduction by using sleeve structured flexible tubes.The speciality of pressure fluctuating on inner wall surface of the flexible tubes and the speciality of the displacement fluctuating on the external wall surface are studied, by using the strain gauge and pressure sensor. The results are as following. The thinner the flexible tubes and the bigger the Reynolds numbers, the bigger the turbulent drag reduction rates are, and at the Reynolds numbers of about 18000, the rates of drag reduction of the sleeve structured flexible tubes with thickness of 2 mm, 3 mm, 4 mm are about 12%, 10%, 9%. The intensity of the pressure fluctuation on the inner wall surface is greatly weakened in comparison with the rigid tube, the displacement fluctuation phase on the outer wall surface of the tubes is the same as the pressure fluctuation on inner wall, so the greatly weakened intensity of pressure fluctuation can be supposed to be the main cause of drag reducing.
