Numerical Study of Momentum Exchange in Compound Open Channel Flow

Compound open channel flow is studied numerically with a new nonlinear low-Reynolds \ik-ω model, capable of predicting the turbulence anisotropy and the turbulence-driven secondary currents. The cross-diffusion term in the exact ω-equation is included in the modeled one and when combined with the proposed model coefficients, produces the correct asymptotic behavior near walls. Free surface modeling is also included, based on an empirical approach. Emphasis is given in conditions of low relative depths \ih\i\dr, where the main channel-flood plain interaction is significant. The velocities follow the logarithmic law in the interaction region even for \ih\i\dr as low as 0.1. Secondary currents are reproduced well by the model when compared with available measurements. Turbulent shear stresses, especially –\iū\iw¯, which is indicative of the strength of the lateral momentum transfer, are predicted satisfactorily. Turbulent intensities are captured sufficiently with a slight underestimation of \iu′. With the decrease of \ih\i\dr from 0.5 to 0.1 the lateral shear and turbulence are enhanced at the interface, and the secondary flow in the flood plain is reduced.