Journal article
Flow hydrodynamics, density contrast effects and mixing at the confluence between the Yangtze River and the Poyang Lake channel
ENVIRONMENTAL FLUID MECHANICS, Vol.23(2), pp.229-257
04/2023
DOI: 10.1007/s10652-022-09848-3
Abstract
In this study, eddy-resolving numerical techniques are used to investigate flow hydrodynamics and mixing at the asymmetric confluence between the Yangtze River and the Poyang Lake channel, one of the largest confluences in the world. The model was previously validated for small and medium-size river confluences. The study also investigates the effects of density contrast between the confluent flows due to unequal temperatures in the two tributaries. Simulations are conducted assuming first negligible density-induced effects (no coupling between the momentum and density equations; Richardson number, Ri = 0) and then with a nonzero Richardson number corresponding to the temperature difference |Delta T| = |T-1 - T-2| between the two streams. Given that the Yangtze River of temperature T-1 contains cooler water during the winter and warmer water during the summer compared to the Poyang River channel of temperature T-2, stratified flow simulations are conducted for |Delta T| = 2.5 degrees C with both T-1 > T-2 and T-2 < T-1. As opposed to small-size natural river confluences, no streamwise-oriented-vortical (SOV) cells forms in the vicinity of the mixing interface (MI) in the three scenarios investigated despite the relatively high confluence angle. The secondary flow is driven by the formation of helical cells of cross-flow motions. Similar to what was observed at small and medium-size river confluences with a low level of bed discordance, the main effect of density contrast between the confluent flows is to generate lateral near-bed intrusions of heavier fluid and to strongly tilt the boundaries of the MI. The density contrast is found to affect not only the position and width of the MI, the size of the patches containing energetic eddies shed from the wake region and the turbulent kinetic energy levels inside the MI, but also the position of the curvature-induced cells of secondary flow and the flow structure inside the wake region. The overall effect of density contrast is to increase mixing at large distances from the confluence apex where the near bed and free surface intrusions are relatively large and most of the mixing occurs beneath the free surface. The largest mixing is observed for the case the main tributary (Yangtze River) contains the warmer, less dense fluid. So, despite the absence of SOV cells, density contrast effects on flow structure and thermal mixing at the large-scale confluence investigated in the present study are qualitatively similar to those observed at several small and medium-size confluences.
Details
- Title: Subtitle
- Flow hydrodynamics, density contrast effects and mixing at the confluence between the Yangtze River and the Poyang Lake channel
- Creators
- Chenyu Jiang - University of IowaGeorge Constantinescu - University of IowaSaiyu Yuan - Hohai UniversityHongwu Tang - Hohai University
- Resource Type
- Journal article
- Publication Details
- ENVIRONMENTAL FLUID MECHANICS, Vol.23(2), pp.229-257
- DOI
- 10.1007/s10652-022-09848-3
- ISSN
- 1573-1510
- Grant note
- This research was funded by the National Natural Science Foundation of China (U2040205; 51779080; 52079044), the 111 Project (B17015), and the Fok Ying Tung Education Foundation (520013312). The Authors are grateful to the Hydrology and Water Resources Survey Bureau of the Lower Reaches of the Yangtze River for data support.
- Language
- English
- Electronic publication date
- 03/15/2022
- Date published
- 04/2023
- Academic Unit
- Civil and Environmental Engineering; IIHR--Hydroscience and Engineering
- Record Identifier
- 9984232155002771
Metrics
21 Record Views