FEATURES OF THE FLOW STRUCTURE IN A RECTANGULAR TRENCH

Abstract

The study of features of the flow structure in rectangular trenches in a wide range of Reynolds numbers was carried out by means of direct numerical simulation of the flow in the channel and on а plate. Both isothermal and non-isothermal formulations of the problem were considered. Water and air were used as the investigated fluids. The flow structure inside and around the trench in the rectangular channel in the range of Reynolds numbers based on the trench length Re<=9000 was studied in a three-dimensional setting. In the Reynolds numbers range Re>=10000, unsteady flow around a plate with a trench was considered in two-dimensional formulation of the problem. Depending on the Reynolds number, the flow structure in the trench, the influence of geometric parameters on the vortices scales in the trench, their localization and intensity were analyzed. The scale of inhomogeneity of the trench flow in the transverse direction was obtained. The features of non-stationary behavior and interaction of vortex formations with each other and with the external flow at higher Reynolds numbers are considered, development of instability of the vortex structure in the trench and its influence on characteristics of the external flow are shown: from regular oscillations at certain frequency to gradual chaosization of the flow around the trench as the Reynolds number increases, when fractional and multiple frequencies appear. A comparison was made with the vortex structure obtained by other researchers for similar geometric parameters of the trench. The contributions of frictional drag and shape drag to the overall hydraulic drag of the trench, as well as the streamlined surface downstream the trench, are considered. Intensity of heat exchange processes inside the trench, localization of the maximum values of heat fluxes, dependence of heat transfer on the oncoming flow speed were evaluated.