Numerical calculation techniques of turbulent shear flows are classified into two categories : one is the k-ε turbulence model, and the other is the large eddy simulation (LES). The standard k-ε model has been established at present to predict a turbulent structure in jets, boundary layers and closed channel flows, while LES is being developed to predict a coherent eddy structure in simpler channel flows. The standard k-ε model cannot be, however, easily applied to open channel surface flows, because the turbulence near the free surface is more depressed than the closed channel flows. In the present study, a new modified k-ε model is proposed to predict reasonably a turbulent structure in open channel flows with both the low and high Reynolds numbers. The numerical calculations indicate a good agreement with the experimental data which were obtained by making use of hot-film and Laser Doppler anemometers
