Numerical investigation of the turbulence characteristics and energy dissipation mechanism of baffle drop shafts.

Qinghua Yang,Qian Yang

doi:10.2166/wst.2021.137

Abstract

The baffle drop shaft is widely used in deep tunnel drainage systems due to its fine applicability and high energy dissipation. To fully study the turbulence characteristics and energy dissipation mechanism of baffle drop shafts, a 1:25 scale physical model test and a numerical simulation based on the Realizable k-ε model and Volume of Fluid (VOF) method were performed. The results showed that a baffle spacing that is too dense or too sparse is not conducive to energy dissipation and discharge. The minimum baffle spacing is the optimal structural design at the design flow rate when the flow regime is free-drop flow. The energy dissipation calculation model established in this paper has high accuracy for calculating the energy dissipation rate on the baffles in free-drop flow. The energy dissipation modes of the shaft can be divided into inlet energy dissipation, baffle energy dissipation, and shaft-bottom energy dissipation. Baffles play a major role in the energy dissipation at low flow rates, and the proportions of inlet and shaft-bottom energy dissipation increase with the increase in flow rate.

Highlights

Since the construction of the ‘sponge city’ was proposed by the Chinese government in 2013, the deep tunnel drainage system has gradually become the main way for big cities to solve flood disasters and overflow pollution in old urban areas (Liu et al )
The calculation error was less than 5.7%, which shows that Equation (10) had a better ability to predict the energy dissipation rate of the baffle drop shaft in the free-drop flow regime
Using fitting formulas of the second baffle specific energy and energy loss ratio, this model could accurately calculate the energy dissipation rates of each baffle in the free-drop flow regime, and the calculation error was less than 5.7%

Summary

INTRODUCTION

Since the construction of the ‘sponge city’ was proposed by the Chinese government in 2013, the deep tunnel drainage system has gradually become the main way for big cities to solve flood disasters and overflow pollution in old urban areas (Liu et al ). An experimental investigation on the hydraulic characteristics inside stacked drop manholes was carried out by Camino et al ( ), and the mechanism of energy dissipation with different flow regimes was analyzed. Liu et al ( ) designed a novel internal energy dissipation vortex shaft, and experimentally and numerically investigated the energy dissipation characteristics and movement mechanism of the new shaft This kind of shaft is only suitable for hydraulic engineering due to the necessary conditions of stable water head and large inflow area during operation. The flow regime and hydraulic characteristic of the stepped drop shaft with different central angles were investigated, but the air entrainment characteristics and energy dissipation performance of stepped drop shafts need further research. Numerical simulations were performed to analyze the flow regimes and baffle functions, establish expressions for the energy dissipation on the baffles, and explore the energy dissipation mechanism in baffle drop shafts

EXPERIMENTAL SETUP

RESULT

Findings

CONCLUSIONS AND RECOMMENDATIONS