Turbulence organization in isolated roughness flow

¹ Power System Engineering, Faculty of Mechanical Engineering, University of West Bohemia in Pilsen, Univerzitní 22, 306 14 Pilsen, Czech Republic.
² Department of Fluid Dynamics, Institute of Thermomechanics, Czech Academy of Sciences, Dolejškova 5, 182 00, Prague, Czech Republic.

Abstract

The primary goal of this investigation was to analyze the specific evolution of the boundary layer over an isolated roughness. A specific surface consisting of rectangular elements of the same height arranged in a checkerboard pattern was used for the experiments. Throughout the experiment, the measuring cross-sections were positioned at various distances from the inlet, while maintaining a constant flow velocity of 15 m·s^-1. To investigate the boundary layer topology in the streamwise directions, a 55P14 miniature hot-wire probe was employed. It is worth mentioning that the measuring position was situated at the midpoint between the roughness elements. Through the analysis of the gathered data, we identified the distribution patterns of the mean velocity profile at different measuring positions. Additionally, we estimated the integral scale of the turbulence by applying different approaches, such as the zero-crossing method (based on autocorrelation analysis), and the Roach and Karman methods (based on spectral density function). The data obtained from our experiments demonstrate that the presence of isolated roughness leads to a pronounced alteration of the velocity profile. This phenomenon is likely due to the shear layer, which typically contains the largest and most energetic vortices in the flow.