On intermittency in the turbulent asymptotic suction boundary layer

Abstract: This thesis presents a series of direct numerical simulations (DNS) performed in order to understand the discrepancy in the literature regarding turbulent asymptotic suction boundary layers (TASBLs) at low Reynolds numbers. The hypothesis to be tested is that the main reason for higher turbulence intensities observed in experiments compared to DNS is that the latter exhibits intermittent patches of laminar flow, developing both temporally and spatially. This hypothesis is confirmed here by comparing simulations with and without tripping, where the former removed patches of laminar flow thereby establishing a fully developed turbulent state with higher turbulence intensities compared to its naturally developing counterpart. The DNS were performed at different suctions rates corresponding to Reynolds numbers above the critical value of 270. The statistics taken from the simulations at different streamwise positions also support the developing character of the flow with increasing intermittency further downstream. Thus, it can be concluded that the actual flow state at these marginal Reynolds numbers is indeed an intermittent one, with lower fluctuation values as the experimental data would indicate.