Modified phase average algorithm for the wake of a propeller

Abstract

In periodic unsteady flow fields of rotating machinery, instability factors such as physical oscillations often appear in instantaneous results. Thus, instantaneous results for flow fields are not representative. The phase average method is often employed in flow field analyses to account for the rotation of machinery. A traditional phase average method uses phase-locked analyses, which average all flow fields that have propeller blades passing through the same angular position. However, wake analyses based on traditional phase average methods are misleading in terms of the interpretation of tip vortex behaviors. This is because the traditional phase-average method tends to present increasingly diffuse traces of downstream tip vortices in vorticity fields, leading to an overestimation of the turbulent diffusion rate, including that of the vorticity spread through the meander and instability motions of the tip vortices. To address this problem, a modified phase average algorithm is proposed that can obtain more realistic vorticity fields and provide a powerful post-processing method of studying the streamwise evolution of the characteristics of propeller tip vortices.