A MODELING OF SHEAR AND NORMAL TURBULENT STRESSES IN OPEN CHANNEL FLOWS

摘要

The structure of turbulence in open channel flows is anisotropic and very complicated. This structure is described by the turbulent stresses tensor. This tensor can be presented as a sum of two tensors: the normal stress and shear stress tensors. The normal stresses can be known from measurements or some suitable theoretical and empirical approaches. One of them which allows for calculating the main component of the normal stresses is presented in the paper. The shear stresses can be defined by many different models. In the paper the stresses definition is based on a new concept of generic mixing length. It is shown how to define the generic mixing length and how to decompose it into the three main components of the mixing length tensor. To show how the new model works the basic hydrodynamics equations (parabolic approximation of Reynolds equations) together with the turbulence model are solved. The well-known Patankar-Spalding algorithm was used for solving these equations. Some numerical simulations were performed for different components of the mixing length tensor. The results show the role of these components in calculation of 3-D velocity distribution, i.e. the prime velocity distribution and secondary currents. Also, they show that the process of model calibration is simple and very efficient.