Amplification of turbulence by sharp meanders on thermally stratified open channel flow

Abstract

In order to unravel the effects of meander bends on the mechanism by which the turbulence kinetic energy (TKE) is produced, redistributed and dissipated in a thermally stratified curved open-channel flow, Direct Numerical Simulation (DNS) was carried out through an idealized sharp meander with and without an internal heat source. The heat source models radiative heating from above and varies with height due to progressive absorption. In both cases, we find a pronounced local increase in TKE starting in the region approximately 25% of the distance through the bend. Here a local extremum of TKE is found near the channel bed at the inner bank and close to the free surface at the outer bank. This grows to a more generalised increase in turbulence that starts at a location approximately 35% of the distance through the bend and peaks at the meander apex before gradually weakening in the downstream part of the bend. However, while only showing a marked increase in the mid-depth region near the inner bank in the neutral case, turbulence is amplified more strongly in the stratified case with the high TKE values spread out across the whole channel width. This is due to the two observed separated shear layers converging in the bend apex in this case. There is only one SSL observed in the neutral case. An investigation of the TKE budget terms for the stratified case at the turbulence amplification location was undertaken to elucidate the mechanisms leading to the production, dissipation and transport of TKE in these regions.