Penetrative Convection in Stratified Fluids: Velocity Measurements by Image Analysis Techniques

Abstract

The flux through the interface between a mixing layer and a stable layer plays a fundamental role in characterizing and forecasting the quality of water in stratified lakes and in the oceans, and the quality of air in the atmosphere. The evolution of the mixing layer in a stably stratified fluid body is simulated in laboratory when “Penetrative Convection” (CP) occurs. The laboratory model consists in a tank filled with water and undergone to controlled and reproducible boundary conditions. Laser Induced Fluorescence (LIF) allows the mixing layer evolution to be visualized. Pollutant dispersion phenomena are naturally described in the Lagrangian approach as the pollutant acts as a tag of the fluid particles. To this aim, Particle Tracking Velocimetry (PTV) and Feature Tracking (FT) are used to reconstruct the velocity field through detection of tracer particle trajectories moving within the measurement volume. Fig. 1. Time evolution of features tracked through the technique Feature Tracking. The mixing layer is almost at the top of the test section. Internal waves are visible in the remaining stable layer