预应力钢筒混凝土管（PCCP）的阻力系数与粗糙度研究

在长距离输水工程的设计中,水力阻力系数的计算选取是一个关键因素。由于PCCP在我国起步较晚,关于其阻力系数及糙率的研究较少,特别是超大口径PCCP,采用传统水力学试验方法在室内测量其阻力系数有较大困难。本文提出了一种新方法：采用表面形貌仪测量PCCP内壁的表面粗糙度,并以水力学试验为依据,获得当量粗糙度及修正系数,据此可以进行Re已知情况下的阻力系数计算,并推算出水流进入阻力平方区的糙率值,从而避免了超大口径PCCP进行室内水力学试验的不可行性。研究得出,南水北调中线工程DN4000的PCCP糙率值约为0.00979～0.01132,可为南水北调中线京石段应急供水工程的运行提供参考;综合考虑多种因素,认为国产PCCP的糙率范围约在0.010～0.0125之间。利用本文所提出的方法,可方便获得任意管径PCCP的阻力系数。

Study on drag coefficient and roughness of prestressed concrete cylinder pipe

Drag coefficient of pipe is a crucial design factor of long-distance water diversion project.Study of drag coefficient and roughness of prestressed concrete cylinder pipe(PCCP) is quite little in China because of its late application,particularly PCCPs of large diameters,and measurement of the drag coefficient in conventional hydraulic test is much difficult.This paper presents a new method to avoid this difficulty.In this method,surface roughness of PCCP is measured with a surface topography and converted into equivalent roughness that can be used to calculate the drag coefficient if the value of Re is known,and then the roughness coefficient of fully-turbulent flow is obtained.Application of the method to the middle route of South-to-North Water Transfer Project shows that the roughness coefficient of PCCP with DN4000 is in the range of 0.00979~0.01132,which provides reference for design of the Beijing PCCP of this project.With a comprehensive consideration,this paper suggests a roughness coefficient range of 0.010~0.0125 for the PCCPs manufactured in China.The surface topography method is convenient to use for evaluating the drag coefficients of PCCPs produced by any maker.