Fluid Dynamics & Aerodynamics

Biography

Biography: Leonardo P. Chamorro

Abstract

Systematic experiments were carried out to uncover the physical processes modulating the onset of instability and development of turbulence over 2D and 3D sinusoidal roghness/walls. High-resolution particle image velocimetry in a refractive-index-matching flume was used to quantify high-order statistics. The 2D wall is described by a wave in the streamwise direction with amplitude to wavelength a/λx=0.05. The 3D wall is defined with a a/λy=0.1 spanwise wave superimposed on the 2D wall. The flow was characterized at roughness Reynolds numbers Rek=320-340 to capture the onset of transition; while the developing and developed flows were quantified at Re=4000 and 40000, based on the bulk velocity and the flume half height. Instantaneous velocity fields, turbulence quantities and POD reveal strong coupling between the topography and the turbulence dynamics. The spanwise superimposed mode on the 2D roughness topology is found to play a dominant role on the location of the flow instability and the dynamics leading to turbulence. In the developed flow, turbulence statistics show the presence of a well-structured shear layer that enhances the turbulence for the 2D wavy wall, whereas the 3D wall exhibits different flow dynamics and significantly lower turbulence levels, where turbulent shear stress shows 30% reduction. The likelihood of recirculation bubbles, levels and spatial organization of turbulence, and the rate of the turbulent kinetic energy production are shown to be severely affected in the 3D wall.