Turbulent length scales and budgets of Reynolds stress-transport for open-channel flows; friction Reynolds numbers R_eτ = 150, 400 and 1020

Abstract

Turbulence in open channel flows is ubiquitous to hydro-environmental applications and has recently increased in importance with the deployment<br/>of tidal stream turbines, as turbulence impacts both the turbine performance and the blade fatigue life. Tidal turbine analysis requires fully developed<br/>turbulence characteristics at the inlet of numerical simulations where generally the length scale information is limited. In this study, fully resolved<br/>large eddy simulations (LES) with flat beds were undertaken using an open source code at friction Reynolds numbers (Reτ) of 150, 400 and 1020. It<br/>was found that the effects of the free surface on turbulence length scales were felt in approximately the uppermost 10% of the channel only, although<br/>the influence on Reynolds stresses extended further downwards. Furthermore, the cross-correlation length scales of both streamwise and spanwise<br/>velocities were found to be significantly affected by the free surface where turbulent eddies were flattened to the two-component limit.