Direct Numerical Simulation of Open Channel Flow with Buoyancy

Free surface flow is important in chemical reactions, heat exchange, atmospheric science and industrial technology. In terms of fundamental research, turbulence near a free surface is important in transport phenomenon. However, free surface effects exhibit some nonlinear behavior, so that numerical methods are usually employed instead of analytical approaches. In this investigation, direct numerical simulation is applied to turbulent channel flow with a free surface. The Navier‐Stokes equations are solved using a finite difference method, and an interpolation scheme is applied to the convective term. Grid resolution is 128x65x128 and Reynolds number based on the friction velocity and channel elevation is 150. Slip wall approximations have been used extensively. This means that the free surface has no stress, velocity or deformation. In order to solve such problems, low Froude number approximations have recently been presented and these are used to calculate the free surface flow. In turbulent flow, dissipation and production are essential qualities, Reynolds‐stresses balances and pressure‐strain correlations are examined numerically. It is shown that the main difference between free surface and slip wall approximations is in pressure‐strain correlations near the surface.