Experiments on the interactions between a rigid plate and vortices

Abstract

This study provides a quantitative analysis, and subsequent comparison, of flow field behavior under varied experimental parameters for vortex production by, and vortex ring interaction with, a rigid plate. The relationship between the experimental parameters: flapping amplitude and average rotational speed, and flow field characteristics: vorticity, circulation, total kinetic energy, and vortex trajectory, were examined for the cantilevered plate. The relationships between the parameter of plate inclination and the flow field characteristics of vorticity, circulation, and vortex trajectory, were examined for the inclined plate. All experiments involved a particle image velocimetry (PIV) analysis followed by processing of the data to produce quantified flow field data. The cantilevered plate experiments revealed that a flapping cantilevered plate produces two primary vortices: a tip vortex and a plate hugging vortex, and in some cases a stopping vortex above the tip. It was determined that the maximum magnitudes attained, the accumulation rate, and the dissipation rate of both circulation and kinetic energy are speed dependent. However, rate of accumulation and dissipation of either quantity does not vary with total flapping amplitude. It was concluded that flapping amplitude does not influence the shape of vortex trajectory or the trajectory angle relative to the horizontal, though the total distance traveled along the vortex trajectory is dependent on flapping amplitude. In the case of the inclined plate, it was concluded that the levels of vorticity, particularly in the lower part of the vortex ring, and the formation of additional vortices in the flow field are dependent on plate inclination and thus, the degree of asymmetry of the interaction. During the die off phase the circulation of the upper part of the vortex ring is inversely proportional to plate angle, while circulation of the lower part of the vortex ring is proportional to plate inclination. The relationship between plate inclination and vertical displacement of the two parts of the ring was found to be based on the degree of asymmetry.