Analysis of Vortices in Three-Dimensional Jets Introduced in a Cross-Flow Boundary-Layer

The aim of this work is to numerically investigate the different vortical structures present in the flow generated by a jet in crossflow. The test case which is relevant to an hydraulic experiment consists of a single jet ejecting normally into a laminar main stream.The computation is performed using a stationary three-dimensional Navier-Stokes code. A multi-block technique is used to compute the flow in the injection pipe. In addition high resolution is achieved in the region of jet-mainstream interaction.The flow analysis relies on the visualization of particle trajectories. These particles are introduced into vortex cores that are located by the secondary velocity field they induce. The three-dimensional behavior of these structures is enlightened. This provides us with the origin of the fluid of which they are comprised. The mixing between the jet and the incoming viscous layer appears to begin on the windward side of the jet boundary.Up to five types of vortices are identified including the well known counter rotating vortices that dominate the downstream flow. They clearly result from the stretching and warping of the annular vorticity rings issuing from the pipe. At the jet exit, they each split into two sub-structures with different growth and downstream development. Less prominent structures are also seen. The “horse shoe” vortex has been captured which is typical of the near wall effects due to blockage induced by the jet in the main stream. Its downstream legs are sucked through the jet boundary. Another weak structure located on the upstream jet boundary is the “lip” vortex which results from the upstream part of the flow specific topology. It is shown that viscous effects play an important role in both the generation and interaction between vortical structures.Copyright © 1997 by ASME