柔性管与紊流耦合的减阻特性

BEHAVIOR ON DRAG REDUCING BY COUPLING FLEXIBLE TUBES WITH TURBULENT FLOW

为探讨柔性管与紊流耦合的减阻特性和初步机理，使用双重管结构，对柔性管的减阻特性进行试验研究，采用激光传感测位仪对柔性管外壁的位移脉动特性及其与柔性管减阻率之间的相关性进行研究。结果表明，壁厚越小，雷诺数越大，柔性管减阻率越大；在双重管结构及雷诺数约为3×10^4时，壁厚为2mm、3mm及4mm柔性管的减阻率依次约为16％、11％、9％；管外壁位移脉动的低频方均根值与减阻率存在正相关关系；在高雷诺数下，由于使用理论模型计算的管径膨胀引起的减阻率偏低，单重管的减阻率比实际值偏高。

In order to probe into the mechanism and behavior of drag reducing by coupling flexible tubes with turbulent flow, experimental investigation is performed on behavior of turbulent drag reduction using flexible tubes with sleeve-structure, and the fluctuating displacement characters of tubes at the outer wall and their relations with the drag reduction rates are studied by using laser displacement sensor. The results are found as follows. The thinner the flexible tubes are or the bigger the Reynolds number is, the bigger the drag reduction rates by coupling flexible tubes with turbulent flow are. At the Reynolds number of about 3×10^4 , the rates of drag reduction of the sleeve-structured flexible tubes with thickness of 2, 3, 4 mm are about 16%, 11%, 9% respectively. A positive correlation exists between the drag reduction rates and the root mean square of fluctuating displacement in low frequency band at the outer wall of simple tubes. With simple tubes and at the big Reynolds number, the rates of drag reduction of the flexible tubes are bigger than their true values, as the drag reduction rates, which are caused by the inside expansion of the tubes and obtained by using the theoretical formula, are much lower.