Session: 35-03/10-03 Joint session: Fan Noise

Paper Number: 153711

Minimal Modelling for Noise and Vibration Propensity of Low-Speed Axial Flow Rotor Blades Due to Vortex Shedding 

The subject of the paper is the phenomenon of shedding of vortices from the region being upstream of the trailing edge (TE) of sections of blade profiles being characteristic for low-speed axial flow rotor blades. The chord-based Reynolds number is typically less than or equal to 100 000, and therefore, the studies presented herein can be adopted to small-scale, low-speed cooling fans as well as to the propulsor rotors of unmanned aerial vehicles such as drones. The vortex shedding phenomenon is termed herein as profile vortex shedding (PVS). PVS is associated with vortex shedding noise at the TE. Furthermore, the shed vortices correspond to pressure fluctuations taking an effect over the suction and pressure surfaces of the blade, thus resulting in lift force fluctuations, and causing temporarily fluctuating bending moments on the blade. Therefore, PVS may remarkably contribute to the noise and vibration propensity of the blading. Minimal models have formerly been established for characterising the lift force fluctuation and noise related to PVS. Such substantially simplified models aim at capturing the main qualitative trends and giving order-of-magnitude quantitative estimates on PVS-related noise and vibration, by the possibly most simple analytical means. The shed vortices are modelled as circular, rotationally symmetrical coherent structures. The model parameters are retrieved from simplified computational fluid Dynamics (CFD) case studies. The present paper gives a synthesis on the results of PVS investigations on a classic RAF-6E profile [1] and on a circular-arc cambered plate profile of 8 % relative camber [2], both considered as being representatives for low-speed axial flow rotors. The flow field related to the various CFD scenarios has been surveyed in detail, for comprehension of underlying physics of PVS. The results of minimal models have been processed in a merged way for the two blade profiles, they have been generalized, and compared to literature data for validation purposes. By such means, straightforward and yet effective analytical minimal modelling tools have been made available for assessing the noise and vibration effects due to PVS. Such modelling toolkit has been proposed for inclusion in the preliminary design methodology of low-speed axial flow rotors, serving for reducing rotor noise and for improving operational safety.

[1] G. Daku and J. Vad. “Enhanced modelling of the phenomenon of vortex shedding from a low-speed axial flow rotor blade profile.” ASME Paper GT2024-123991, 2024.

[2] G. Daku and J. Vad. “A comprehensive analytical model for vortex shedding from low-speed axial fan blades.” In: Trans ASME, J Turbomachinery 145.7 (2023), 11 p.

Presenting Author: Janos Vad Budapest University of Technology and Economics

Presenting Author Biography: 1997 PhD in Mechanical Engineering / Fan aerodynamics and measurements
2013 Doctor of Sciences in fan aerodynamics

Authors:

Marton Mizsei Department of Fluid Mechanics, Faculty of Mechanical Engineering, Budapest University of Technology and Economics
Esztella Balla Department of Fluid Mechanics, Faculty of Mechanical Engineering, Budapest University of Technology and Economics
Janos Vad Budapest University of Technology and Economics