Structure and mixing of a meandering turbulent chemical plume: concentration and velocity fields

This study presents simultaneous particle image velocimetry (PIV) and laser-induced fluorescence (LIF) measurements of a phase-locked meandering chemical plume, the motion of which is forced by the periodic oscillation of a diverting plate. The plume evolves in a turbulent boundary layer in a moderate-Reynolds-number open channel flow. For the meandering plume, the centerline phase-averaged concentration decreases more rapidly with downstream distance and the plume width increases more rapidly with downstream distance (as x 1 ) compared to the straight plume (as x 3 / 4 ). Furthermore, the concentration fields and transverse profiles are asymmetric about the plume centerline in the meandering plume. Nevertheless, the transverse profiles can be modeled by a Gaussian shape in a segmented manner. The velocity fields indicate that the large-scale alternating-sign vortices induced by the diverting plate are the dominant feature of the flow. The vortices induce the plume to meander and govern the spatial distribution of the phase-averaged concentration. The induced fluid motion by the vortices also helps in explaining the increased mixing and dilution of the concentration field. Further, a phenomenological model of chemical filament transport by the vortical motion explains local peaks in the phase-averaged concentration along the plume centerline. Graphical abstract