The Structure of Turbulence Across the Sediment-Water-Interface

An increasing body of literature indicates that turbulence is
a major contributor to the exchange of mass and momentum
across the sediment-water-interface (SWI). The permeability
Reynolds number ReK=√Ku∗/υ s a key parameter describ-
ing the flow at the SWI, where K is the permeability of the
porous medium. The dynamics of turbulence around the SWI
are determined by the intricate interaction between the hydro-
dynamics and the sediment characteristics, however, traditional
experimental techniques are hindered in accessing this region
properly, making experimental data rare. In this work we de-
scribe novel experimental results, which combines refractive in-
dex matching (RIM) and particle tracking velocimetry (PTV),
and capture the instantaneous velocity fields across the SWI,
for two different values of ReK he measurements enable us
to evaluate the TKE budget, a key tool for understanding tur-
bulent processes. The results show that for low ReK the TKE-
budget is in good agreement with DNS results for an imperme-
able boundary. For the same permeability but larger ReK, the
flow penetrates the interface and the TKE-budget shows turbu-
lence is both produced and transported beyond the SWI and into
the permeable medium. Unlike the low ReK case where at the
interface only viscous diffusion and dissipation are dominant,
in the high ReK case all terms in the TKE-budget are of impor-
tance.