Using an eddy-resolving technique to assess the effects of reservoir operation on the bend flow in Yangtze River, China

摘要

With increasing computing power over the last decade, eddy‐resolving methods inhydraulics engineering have been widely used to investigate the turbulence structurein natural rivers, where accurate field measurements were difficult to conduct andinvestigate. A detached eddy simulation (DES) model was developed on the basis ofthe k‐ω‐SST (shear stress transport) eddy‐viscosity model within the framework of anunstructured‐mesh Semi‐implicit Eulerian–Lagrangian Finite Element (SELFE) hydrodynamicmodel. The DES model was then applied to simulate the bend flow in theupper Yangtze River, and the calculation efficiency was enhanced through parallelizedcomputation to mitigate the high computation costs involved in the DES modelling.The time‐averaged velocity, turbulent intensity and Reynolds stress werecompared, using DES modelling and acoustic Doppler current profiler (ADCP) measuringresults, indicating good agreement, especially in the near‐bed region. The coupledrelationship between the turbulent flow and riverbed terrain was alsoinvestigated through extracting and analysing the high‐order statistical variables reflectingthe turbulence structure, including non‐hydrostatic pressure, vorticity andhelicity, indicating the fluctuated amplitude of non‐hydrostatic pressure can reach to100 Pa, and the stripe distribution of non‐hydrostatic pressure and vorticity had anorthogonality relation. At the same time, the streamwise velocity at the middle of theHLM bend was found to be decreased at least 0.7 m/s because of unsteady processsmoothing and backwater effects attributable to water releases and storage of thereservoirs located upstream and downstream of the HLM bend. The developed unstructured‐mesh DES model will provide a new tool to study turbulent flows in anatural river and assess the effect of reservoir operations on river flows.