Simultaneous measurements of time-resolved velocity and concentration fields behind a sand dune-inspired jet in crossflow

Abstract

The flow field and scalar concentration behind a sand dune-inspired jet-in-crossflow were measured to quantify the characteristics of flow and scalar mixing. The velocity was resolved from particle image velocimetry measurements, and the time-resolved concentration was simultaneously captured by planar laser-induced fluorescence. During the experiments, the velocity ratio was set to 0.4, 0.6, 0.8, 1.0, and 1.2. The corresponding jet flow statistics, concentration statistics, and flow-concentration dynamics were comparatively analyzed. Aided by the dune, all jets were found to discharge tangentially into the mainstream, forming an energetic shear layer in the dune upper region that not only affects the jet attachment but also influences the flow mixing dynamics. The measured turbulent flow statistics (vorticity, turbulent kinetic energy, and Reynolds stress), concentration statistics (scalar standard deviation and turbulent scalar flux), and dynamics of the flow-concentration fields (instantaneous evolutions, scalar dissipation, and strain rate) revealed not only the complex nature of the generated shear layer but also the significant correlations between the shear flow and scalar mixing. Proper orthogonal decomposition (POD) analysis successfully decomposed the instantaneous velocity and concentration fields into a series of energetic POD modes, vividly demonstrating the modulating effect of the energetic shear layer on the flow and scalar mixing.