ABSTRAKT

Direct numerical simulation (DNS) of open-channel flow in the presence of an air-water interface was performed to examine the effects of interface deformation on the turbulence structures. In the water-driven turbulence, flows characterized by either of two Froude numbers (Fr=.2 and 0.8) were examined and compared. A coupled level-set and volume-of-fluid (CLSVOF) method was employed to track the interface. The air that contacted the water was entrained into the turbulent flow. At high Fr, all turbulent normal stresses on the air side of the interface were high near the sidewall. Moreover, all terms of the Reynolds shear stress were intensified at the mixed-boundary corner on the air side of the interface. Two-point correlations between the streamwise vortex and the velocity fluctuations provided structural information about the near-wall streaky structures and the inner secondary flows in the cross-stream plane. Linear stochastic estimates of the conditionally averaged flow field showed that the inner secondary flow consisted of not only in-plane velocity components but also streamwise velocity components.