Overview of the Self-Preserving Properties of Turbulent Jets and Plumes in Crossflow (Invited)

Abstract

*The self-preserving mixing properties of steady round turbulent nonbuoyant jets and buoyant plumes in uniform crossflows were reviewed and investigated experimentally. The experiments were done in a water channel and they involved steady round nonbuoyant fresh water jet sources injected into uniform and steady fresh water crossflows for the study of jets in crossflow and salt water sources injected into fresh water crossflows for the study of plumes in crossflow. Mean concentrations of source fluid were measured over cross sections of the flow using Planar-Laser-Induced-Fluorescence (PLIF) and mean velocity fields were measured over cross sections of the flow using Particle-Image-Velocimetry (PIV). The selfpreserving structure properties of the flow were correlated successfully based on the scaling analysis of Fischer et al. (1979); the approach involved assumptions of no-slip convection in the cross stream direction and a self-preserving line puff (thermal) for jets in crossflow (plumes in crossflow) having a conserved source specific momentum force per unit length (source specific buoyancy flux per unit length) that moves in the streamwise direction (parallel to the direction of the initial source flow). The resulting self-preserving structure consisted of two counter-rotating vortices having their axes nearly aligned with the crossflow direction that move away from the source in the streamwise (vertical) direction. This alignment was a strong function of the source/crossflow velocity ratio, uo/v∞. Finally, the counter-rotating vortex system was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to axisymmetric round turbulent nonbuoyant jets (buoyant plumes) in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex system were 2-3 times larger than the transverse dimensions of self-preserving axisymmetric jets (plumes) at similar streamwise distances from the source.