Shallow mixing layers between non-parallel streams in a flat-bed wide channel

Zhengyang Cheng,George Constantinescu

doi:10.1017/jfm.2021.254

Zhengyang Cheng, George Constantinescu

https://doi.org/10.1017/jfm.2021.254

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Abstract

Highlights

Converging or confluent flows of unequal velocities and different directions occur in many engineering applications including in geophysical systems, mechanical systems and biological systems
For same planform geometry and velocity ratio (VR), comparison of the α = 60°, S-RF, VR = 2.2 simulations conducted with H = D/2 and H = D suggests that the nearly constant value of |lcy| past the end of the transition regime is fairly independent of the flow depth
Similar to the canonical case of shallow mixing layer (ML) developing between parallel streams in a constant-depth, straight channel, the present study showed that the structure of MLs developing between non-parallel streams changes once the average diameter of the cores of the KH vortices becomes much larger than the flow depth and bed friction impedes the pairing of the KH vortices

Summary

Introduction

Converging or confluent flows of unequal velocities and different directions occur in many engineering applications including in geophysical systems (e.g. river networks), mechanical systems (e.g. networks of ducts or pipes) and biological systems (e.g. arterial networks). For environmental fluid mechanics and geo-physical applications, where the ML develops in between a no-slip boundary and the free surface, there is interest in studying the development of the ML and of the exchange of momentum and mass between the two converging flows at large distances from the ML origin where the dynamics of the eddies generated inside the upstream part of the ML via the Kelvin–Helmholtz (KH) instability (Lesieur et al 1988; Liu, Lam & Ghidaoui 2010; Lam, Ghidaoui & Kolyshkin 2016) is strongly affected by bed friction. The dynamics of mixing controls how the different inputs (e.g. contaminant concentration, particle load) or properties (e.g. temperature) of the flows in the incoming channels will evolve toward a uniform (spanwise) distribution in the downstream channel

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