CAJ | 학술논문

The calculation of the mechanical energy loss is one of the fundamental problems in the field of Hydraulics and Enginee- ring Fluid Mechanics. However, for a non-uniform flow the relation between the mechanical energy loss in a volume of fluid and the kinematical and dynamical characteristics of the flow field is not clearly established. In this paper a new mechanical energy equation for the incompressible steady non-uniform pipe flow of homogeneous fluid is derived, which includes the variation of the mean tur- bulent kinetic energy, and the formula for the calculation of the mechanical energy transformation loss for the non-uniform flow bet- ween two cross sections is obtained based on this equation. This formula can be simplified to the Darcy-Weisbach formula for the uniform flow as widely used in Hydraulics. Furthermore, the contributions of the mechanical energy loss relative to the time avera- ged velocity gradient and the dissipation of the turbulent kinetic energy in the turbulent uniform pipe flow are discussed, and the con- tributions of the mechanical energy loss in the viscous sublayer, the buffer layer and the region above the buffer layer for the turbu- lent uniform flow are also analyzed.