A Comprehensive Analytical Model for Vortex Shedding From Low-Speed Axial Fan Blades

Abstract

The paper presents a comprehensive analytical model for the characterization of von Karman vortex shedding in the wake of models of low-speed axial fan blades. The elaborated minimal model is based on the Reynolds-averaged Navier–Stokes and continuity equations. For validation purposes, hot-wire measurements have been carried out in a wind tunnel on representative blade profiles. The measurement data obtained for various streamwise positions downstream of the blade trailing edge, i.e., transversal profiles of mean velocity as well as root-mean-square of fluctuating velocity, are evaluated. As the experimental validation demonstrates, the minimal model fairly localizes the transversal position of the vortex centers and represents the motion of the vortices along the wake. The validated minimal model serves the following benefits: (a) an extensive understanding of the underlying physics related to the flow field featuring vortex shedding in the near-wake region (easy-to-use quantitative correlation among the characteristics of wake flow affected by the shed vortices); (b) extension of the literature-based methodology for determination of the transversal distance between the shed vortex rows, being used as a scaling parameter for the Strouhal number utilized in calculation of vortex shedding frequency; and (c) modeling the behavior of rows of shed vortices farther away from the trailing edge. Such behavior may influence the acoustic signature of VS, and, as such, it is to be considered in fan noise modeling.