Rib in Turbulent Boundary Layer

Abstract

Experimental and theoretical investigations of the flow structure, with the flow over a variety of protrusions and depressions on the initially smooth surfaces are of considerable practical interest, since the there are constructive or random occurring depressions and cavities found on many different convective surfaces. With the flow over the depressions and protrusions, the boundary layer separation and its reattachment can lead to occurring specific phenomena, which have a significant impact on drag and heat transfer. These phenomena, which are encountered in the course of experimental studies and obtaining adequate mathematical models, are complicated and hard-to-understand.The paper presents experimental results of hydrodynamics and heat transfer in the separation zone before and after a single rectangular rib and a round corner rib with the height of approximately y+ = 100, which are placed on the flat plate that is heated according to the law of qw=const. Experimental studies were conducted using a Pitot-Prandtl microprobe and a hot-wire Dantec Dynamics anemometry system, which allowed us to obtain both the mean and the fluctuating characteristics of the turbulent boundary layer and determine the boundaries of the vortex and separation zones.It is shown that the structure of vertex zones before and after the rib has a strong dependence on the rib shape and size. New experimental data on the mean and fluctuating characteristics in the turbulent boundary layer with the flow over the rectangular ribs with and without round top corners are obtained. Also, the fluctuations of temperature and especially velocity in the boundary layer after the rib are significantly higher than in the layer on the flat plate. The changing characteristic of the friction and heat transfer coefficients indicates that the increase of the heat transfer coefficient exceeds the growth of the friction coefficient after the ribs with the size 30 < y+ < 100.