Metodologia de projeto de ventiladores axiais de baixo ruído através de análises aeroacústicas

Abstract

The study and analysis of the sound generated by flows has become increasingly important in several areas of the industry, from household appliances to aeronautical propulsion systems. A particular case is the noise generated by axial fans applied to the cooling systems in the generator sets. These equipment represent considerable noise sources that must be treated so as not to exceed the permissible limits. In this sense, several studies have been carried out with the aim of analyzing and proposing noise control techniques caused by the fan flow. Therefore, aeroacoustics has become an important topic to be considered for the study and identification of noise sources and for the analysis of noise reduction techniques generated by rotor flow that can be incorporated from the design stage. This work presents a methodology for the aeroacoustic design of axial flow fan rotors, considering the lift wing theory, the radial equilibrium condition, the free and non-free vortex condition and the incorporation of the sweep effect based on a cubic function, as an aerodynamic noise control technique. The analysis methodology used is based on the integration of Computational Fluid Dynamics (CFD) techniques and noise prediction models to determine the main performance characteristics of fans and to evaluate the influence of the incorporated geometric variations (sweep) in the acoustic and aerodynamic fields of the fan. Numerical analyzes were performed based on steady-state simulations to obtain fan characteristic curves and identify local noise sources. In a second approach, in transient regime, the sound pressure level was analyzed as a function of frequency for the analysis of the aeroacoustic behavior considering the ISO 13347-3: 2004 standard for the positioning of the receivers. The simulation methodology to obtain the aerodynamic magnitudes was validated through the experimental tests of a fan with constant thickness blades without torsion. The experiments were carried out in the test bench suitable for ASHRAE (Norma 5175) / AMCA (Norma 210-74) standards of the Ventilator Laboratory (LabVent) of IEM/UNIFEI. The main contribution of the methodology proposed in this work is the incorporation of aerodynamic noise control mechanisms from the design stage through an approach with low computational cost that consists of a sensitivity analysis to determine the parameters that allow reducing the local sources of aerodynamic noise without compromising the aerodynamic performance characteristics. The results showed that designs incorporating sweep based on free vortex and forced vortex condition reduce noise sources and improve the aerodynamic performance of the fan compared to the base rotor geometry. It is important to highlight that the designed axial fan rotors present a consistent aerodynamic behavior in terms of hydraulic efficiency and total pressure, since the maximum efficiency values are far from the stall region.