Direct Numerical Simulation (DNS) is performed to investigate turbulence and momentum exchange in an asymmetric compound open channel flow with a rigid lid approximation. The simulations employ a high order spectral h/p element method combined with a homogeneous Fourier expansion in the streamwise direction to resolve three dimensional flow structures efficiently. A systematic convergence assessment (spatial discretization, Fourier modes, and time step), together with a dedicated statistical sampling strategy, is used to ensure that dynamically relevant scales and turbulent statistics are reliably captured. The flow attains a global friction Reynolds number of approximately 160, defined using the main channel (MC) height as the characteristic length. Spectral analyses indicate a spatially heterogeneous regime: the MC exhibits a weakly turbulent state, whereas the floodplain (FP) remains transitional. The external corner at the MC-FP junction induces pronounced anisotropy of the Reynolds normal stresses, which drives secondary currents and produces a strong cross sectional redistribution of streamwise momentum. In particular, the mean advective contribution to momentum transport becomes comparable in magnitude to the turbulent transport, highlighting the importance of secondary motion induced redistribution in compound channel hydraulics. To characterize coherent structures and their lateral variability, instantaneous fields are analyzed using the streamwise vorticity component and two vortex identification criteria. These complementary diagnostics reveal a pronounced cross sectional inhomogeneity: coherent rotational activity is sparse near the floodplain corner, whereas vortical motions concentrate near the floodplain center and in the junction region, with strong intermittency. Overall, the results demonstrate that combining vortex criteria with vorticity visualization provides a robust description of lateral variations in turbulence organization in transitional compound open channel flows.     «

Direct Numerical Simulation (DNS) is performed to investigate turbulence and momentum exchange in an asymmetric compound open channel flow with a rigid lid approximation. The simulations employ a high order spectral h/p element method combined with a homogeneous Fourier expansion in the streamwise direction to resolve three dimensional flow structures efficiently. A systematic convergence assessment (spatial discretization, Fourier modes, and time step), together with a dedicated statistical sam...     »