Mean flow, turbulence structure, and bed form superimposition across the ripple-dune transition

摘要: [1] This paper describes a laboratory study of the dynamics flow associated with three different stages bed form amalgamation across ripple-dune transition. Measurements velocity were obtained over simplified fixed forms, designed to simulate conditions at ripple:dune transition, using 2D laser Doppler anemometer. This yielded information detailing mean field, turbulence statistics, local production, deviations from pressure caused by dynamic effects, turbulent kinetic energy and contributions total Reynolds stresses coherent events. The results broadly confirm previous hypotheses that as proceeds superimposed bedstate can induce series critical changes structure, higher being produced near downstream reattachment. In particular, quadrant 4 events (turbulent structures greater than average, directed towards bed) dominate vertical diffusion longitudinal momentum in near-bed regions close crest next ripple, thus providing potential for increased erosion sediment transport. These experiments simple beds also provide support recent measurements document suspended concentrations transition (Schindler Robert, 2004, 2005), largest forms are not necessarily those most intense shear layer activity 2005). Bed superimposition may significantly alter field compared without superimposition.