Turbulent and advective mass transfer at the border separation vortex zone behind the bottom thresholds and benches of hydraulic structures

by

A.E. Shchodro1, S.M. Sidorov2, Yu.E. Shishkin1

1Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28

E-mail: ashodro@ya.ru

2Sevastopol State University, RF, Sevastopol, Universitetskaya St., 33

DOI: 10.33075/2220-5861-2024-2-104-116

UDC 532.54                                                                

EDN: https://elibrary.ru/nogxwc

Abstract:

The paper examines the issues of mass transfer and flow dynamics in the region of separated flow behind a bottom plate oblique relative to the flow or behind a bottom step. It is the helical flows that arise behind the sharp edges and ridges of special plates and structures due to mass transfer in the flow, that make it possible to capture a large amount of solid and suspended matter from the transit flow and ensure the transport of sediment in the desired direction. In addition to the previously discussed issues of the helical flow formation behind such plates flown around by a calm water flow, the issues of mass transfer between the transit flow and a separate region of a closed helical flow behind the plate are considered in more detail. Two main types of components of mass exchange between the transit flow and the closed region of the helical separated flow are considered: turbulent and convective types of water exchange. Issues of exchange of suspended sediments are also considered. We propose a mathematical model for the formation of a stationary flow within a region, along its axis; the flow rates of this flow are determined both from the dynamic conditions of the flow movement and as the difference between the integral characteristics of water capture into the region of the helical flow and its release from it. Then we find conditions for the most optimal formation of the structure of the helical flow, when the convective components of the exchange significantly exceed the turbulent ones; the flow velocity components are of greatest importance and provide all the functions assigned to them for sediment transport and self-flushing of the helical flow region.

Keywords: bottom thresholds, helical currents, flow separation, mass transfer, turbulent and convective water exchange, free turbulence.

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