Modulation of energetic coherent motions by large-scale topography.

The distinctive characteristics and dynamics of the large-scale coherent motions induced over 2D and 3D large-scale wavy walls were explored experimentally with time-resolved volumetric PIV, and selected wall-normal high-resolution stereo PIV in a refractive-index-matching channel. The 2D wall consists of a sinusoidal wave in the streamwise direction with amplitude to wavelength ratio a/$\lambda $x $=$ 0.05, while the 3D wall has an additional wave in the spanwise direction with a/$\lambda $y $=$ 0.1. The ?ow was characterized at Re \textasciitilde 8000, based on the bulk velocity and the channel half height. The walls are such that the amplitude to boundary layer thickness ratio is a/$\delta $99 $\approx $ 0.1, which resemble geophysical-like topography. Insight on the dynamics of the coherent motions, Reynolds stress and spatial interaction of sweep and ejection events will be discussed in terms of the wall topography modulation.