The interaction of jets with crossflow

It is common for jets of fluid to interact with crossflow. This article reviews our understanding of the physical behavior of this important class of flow in the incompressible and compressible regimes. Experiments have significantly increased in sophistication over the past few decades, and recent experiments provide data on turbulence quantities and scalar mixing. Quantitative data at high speeds are less common, and visualization still forms an important component in estimating penetration and mixing. Simulations have progressed from the Reynolds-averaged methodology to large-eddy and hybrid methodologies. There is a general consensus on the qualitative structure of the flow at low speeds; however, the flow structure at low-velocity ratios (jet speed/crossflow speed) might be fundamentally different from the common notion of shear-layer vortices, counter-rotating vortex pairs, wakes, and horseshoe vortices. Fluid in the near field is strongly accelerated, which affects the jet trajectory, entrainment, and mixing behavior. At low speeds, mixing depends more on Reynolds number than the jet trajectory or spatial extent does. Turbulence kinetic energy budgets are discussed that reveal the considerable nonequilibrium nature of the flow and the consequent challenges posed to time-averaged prediction methodologies. The parameter space at high speeds is fairly large, and even experimentally derived correlations for trajectories show significant scatter. Coherent motions in high-speed jets are seen to entrain large amounts of crossflow fluid but do not mix effectively in the near field.