Simulations of high Reynolds number transverse jets and analysis of the underlying vortical structures

Transverse jets arise in many applications, including propulsion, effluent dispersion, oil field flows, V/STOL aerodynamics, and drug delivery. This study seeks a fundamental, mechanistic understanding of the underlying vortical structures of the transverse jet. We develop a massively parallel 3-D vortex simulation of a transverse jet at large Reynolds number and formulate vorticity flux boundary conditions that reflect the boundary generation of vorticity around the jet nozzle. We then analyze the structure and evolution of vorticity in jets with jet-to-crossflow velocity ratios r ranging from 5 to 10. Transformation of the cylindrical shear layer emanating from the nozzle, initially dominated by azimuthal vorticity, begins with axial elongation of its lee side to form sections of counter-rotating vorticity aligned with the jet trajectory. Periodic roll-up of the shear layer accompanies this deformation, creating arcs carrying azimuthal vorticity of alternating signs, curved toward the windward side of the jet. Following the pronounced bending of the trajectory into the crossflow, we observe a sharp breakdown of near-field vortical structures into a dense distribution of smaller scales. Spatial Altering of this region reveals the persistence of counter-rotating streamwise vorticity initiated in the near field.