Large Eddy Simulation of Lock-Exchange Flow in a Curved Channel

Abstract

A lock-exchange density current flowing in a 90° bending channel is investigated using dynamic large eddy simulation. In the middle of the current and far from the head and tail, this type of flow shows common characteristics with the previously studied steady-state submarine currents, e.g., superelevation of the flow near the outer bank of the bending section. The secondary flow direction has been a topic of interest among various researchers lately, and the seemingly contradictory results of these studies have demonstrated both senses of rotation near the channel bed at the bend apex. The simulations in this study show a secondary flow pattern toward the outer bank near the channel bed. A part of the current paper is devoted to discussion of this issue. On the other hand, all previous studies have been conducted in a steady-state setting, and so the flow properties in this work are altered relative to the previous ones because of the lock-exchange nature of the current. Secondary flow changes to different patterns near the tail of the current and is nearly absent in the head section of the flow. Also, the current density distribution does not have any directional preferences in the tail of the current and may oscillate between the outer and inner banks of the section due to the thinning of the density and reduction in the size of the downstream velocity. As the current enters the curve, wall turbulence streaky structures demonstrate an amplified turbulent intensity near the inner bank because of the increased magnitude of the tangential velocity. The tangential velocity decreases near the outside bank due to the presence of an inhibiting outer wall, whereas the reverse occurs near the inner bank of the section. The turbulence structures also show separation of flow parcels from the inner bank toward the outside of the channel section, while advecting the turbulence characteristics with themselves. This phenomenon occurs synchronously with the shifting of the maximum streamwise velocity from the inner bank toward the outer bank. Finally, the effect of the channel mean radius on the flow properties has been investigated. The current study is the first high-resolution numerical study of the density currents in bending channels, and it investigates the flow phenomena that have not been previously addressed.