IDENTIFICATION AND BREAKDOWN OF NEAR-WAKE VORTEX STRUCTURES

The process of vortex breakdown, while studied extensively at a fundamental level, is not well characterized for propeller-driven flows behind a self-propelled vehicle. In the wake of a self-propelled vehicle, flow transitions from the complicated near-wake directly behind the propulsor to the fully mixed far-wake in which distinct propulsor features can no longer be recognized. Vortical structures generated by the propulsor may be identified using several techniques. It is hypothesized that the behavior of these vortical structures can be used to predict vortex breakdown and show the transition to the far-wake. In this study, data from an unsteady Reynolds-Averaged Navier-Stokes simulation is examined for the scaled, axisymmetric Iowa Body geometry with two propulsion configurations: single-propeller and contra-rotating propellers, which are simulated using an actuator-line model. Analysis of the data for each configuration identifies and characterizes propeller hub- and tip-vortical paths to show coupling among these vortices in an attempt to predict breakdown. Stationary flow structures in the wake are identified to show the transition from near- to far-wake.