The paper presents hot wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds-number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt-trailing-edge VS based on Strouhal numbers obtained from the measurements in a case specific manner. Utilizing the experimental results, the semiempirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.

This paper presents an overview of the characteristics potentially influencing the profile vortex shedding (PVS) phenomenon being relevant in noise and vibration of low-speed axial fan rotor blades. Dimensional analysis has been applied to explore the essential dimensionless quantities in a systematic and comprehensive manner. On this basis, limitations have been established, and simplifying assumptions have been set up in terms of PVS investigation. Groups of dimensionless characteristics playing a role in the semi-empirical model for predicting the PVS frequency were identified. The available semi-empirical model and its unique features related to the measurement evaluation methodology and Reynolds number dependence have been outlined. The presented comprehensive analysis provides guidelines from the perspective of transferability of the literature data on PVS from steady, isolated blade profile models to low-speed axial fan rotors. It also results in the formulation of objectives of future research related to PVS.

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 centres, and represents the motion of the vortices along the wake. The validated minimal model serves with 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 scaling parameter for the Strouhal number utilized in calculation of vortex shedding frequency. c) Modelling 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 modelling.

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 centres, and represents the motion of the vortices along the wake. The validated minimal model serves with 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 scaling parameter for the Strouhal number utilized in calculation of vortex shedding frequency. c) Modelling 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 modelling.

The paper presents hot wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds-number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt-trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.