Session: 10-03 Fan Design and Optimization

Paper Number: 123991

123991 - Enhanced Modelling of the Phenomenon of Vortex Shedding From a Low-Speed Axial Flow Rotor Blade Profile 

Vortex shedding (VS) from the airfoil sections of low-speed axial rotor blades may occur as a significant source of rotor noise, and may contribute to blade vibration via the resultant fluctuation of the blade forces. For engineering judgment of the noise-generating effect of VS, the proper modelling of the velocity and vorticity distribution represented by the shed individual vortices is of especial importance. A practically important further feature of VS is the VS frequency, to be considered in preliminary rotor design and analysis from the perspectives of both noise and vibration. As the literature [1] suggests, an empirical, universal Strouhal number exists that can be used for estimation of VS frequency. The universal Strouhal number is scaled with the transversal distance between the vortex rows shed from the suction as well as pressure surfaces. The authors of the present paper explored that the transversal position of the shed vortices is not constant but exhibits a variance. Therefore, the formerly established empirical universal Strouhal number definition is to be critically overviewed and further developed. The above imply the following research objectives, being of practical, engineering relevance. a) Elaborating a suitable model for description of velocity distribution within the shed vortices. b) On this basis, modelling the noise generation effect of VS. c) Establishment of a model for describing the distribution of transversal location of the shed vortices. d) On this basis, further development of the universal Strouhal number definition, enabling a more realistic empirical estimation of VS frequency.

The case study in the present paper aims to contribute to the fulfilment of the aforementioned aims, as logical continuation of research carried out by the authors in association with former ASME Turbo Expo conferences, resulting in journal publications [2][3]. A Computational Fluid Dynamics (CFD) tool was developed, experimentally validated, and applied for a low-speed RAF6-E airfoil blade profile for resolving the VS phenomenon in a two-dimensional approach for various operating conditions. The location of the vortex centers as well as the boundaries of the vortices were identified using the Lagrangian-averaged vorticity deviation (LAVD) approach. Various rotationally symmetric vortex models – e.g. Rankine, Scully, Vatistas models – have been tested for properly describing the velocity and vorticity distributions within the vortices. The noise generation effects related to the various vortex models have been modelled and comparatively assessed. A mathematical formulation has been elaborated for describing the distribution of transversal location of centers of vortices passing through fixed streamwise positions downstream of the blade trailing edge. On this basis, the literature-based formula for the universal Strouhal number has been revised and further developed, in context of the estimated VS frequency. The above results aid the development of engineering guidelines for estimation and moderation of noise and vibration due to VS related to low-speed axial-flow rotors used in industrial air technology (e.g. ventilating fans) and in propulsion (e.g. drone technology).

References

[1] Yarusevych, S., Boutilier, M. S. H., 2011, “Vortex Shedding of an Airfoil at Low Reynolds Numbers,” AIAA Journal, 49(10), pp. 2221-2227.

[2] Daku, G., Vad, J., 2021, „Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding from Low-Speed Axial Fan Blades,” Journal of Turbomachinery - Trans ASME, 143(6), 061014, 10 p.

[3] Daku, G., Vad, J., 2023, „A Comprehensive Analytical Model for Vortex Shedding from Low-Speed Axial Fan Blades,” Journal of Turbomachinery - Trans ASME, 145(7), 071008, 11 p.

Presenting Author: Janos Vad Budapest University of Technology ad Economics

Presenting Author Biography: 1997 PhD in Mechanical Engineering, 3D flow field investigation on axial fans using LDA
2013 Academic Doctor of Sciences (DSc) in axial fan design and analysis

Authors:

Gabor Daku Budapest University of Technology and Economics
Janos Vad Budapest University of Technology ad Economics