The Structure of Turbulence in the Near-wall Area of a Channel Flow

Abstract

Fluid dynamics plays an essential role in the paper manufacturing process. The quality of paper is affected by the turbulence properties in the headbox and jet. In this paper the structure of turbulence in the wall area of a two-dimensional converging channel is studied experimentally. The measurements are performed with Particle Image Velocimetry, which provides instantaneous two-dimensional velocity fields. The structure of turbulence is studied by analysing both instantaneous and time-mean velocity fields. As a result several kind of flow structures can be identified close to the channel walls. The most prominent are streamwise elongated structures, which manifest themselves as a spatial modulation of the streamwise velocity component. Substantial activity in the near-wall region is related to the mean-shear close to the surface. The mechanisms of the wall-turbulence are discussed in a short review of the main concepts found in the literature. The results of this study are expected to improve the understanding of the significance of the headbox slice boundary layers in the paper-making process.