NUMERICAL-MODEL OF TURBULENT-FLOW OVER SAND DUNE

A two-dimensional numerical model, based on solution of the Reynolds-a veraged Navier-Stokes equations and the k-omega turbulence model, whic h takes into account sand-grain roughness, is developed to describe th e flow in a fixed dune-bed channel. The model predicts the velocity an d turbulence fields, as well as the pressure and friction distribution s along the dune. The details of the flow in the separation eddy are c alculated. The model predictions are in general agreement with existin g detailed experimental data in a rectangular channel with two-dimensi onal dunes of typical but regular shape. The calculated pressure and f riction distributions enable determination of the resistance component s of the channel without further empiricism. However, compared to a we ll-known and representative semiempirical engineering formula for the prediction of resistance of natural dune-bed channels, the two-dimensi onal numerical model predicts significantly different contributions of friction and pressure to the total resistance, and a much larger tota l resistance. The numerical model is general enough to be used for cha nnels with different bed topography. Its extension to model the flow i n ice-covered channels is in a companion paper.