A semi-empirical model for predicting the frequency of profile vortex shedding relevant to low-speed axial fan blade sections

Abstract

This paper extends existing semi-empirical models on the frequency prediction of vortex shedding. Moderate Reynolds numbers are investigated being of interest in low-speed axial fan design. By an extensive literature review, a new parametrization is proposed for the factor establishing a connection between boundary layer properties and vortex shedding characteristics. Measurement data on symmetrical and non-symmetrical NACA profiles, and on flat and cambered plates, are processed. It is found that the value of the factor is influenced by the relative thickness of the profiles and by the angle of attack. Based on the measurement results, an empirical value is given for the vortex spacing ratio for flow past airfoils. With the use of the proposed empirical model, the vortex shedding frequency of various airfoil profiles and operating conditions can be predicted.