Influence of Swept Blades on Low-Order Acoustic Prediction for Axial Fans

Abstract

The low-speed fans used for automotive engine cooling contribute to a significant part of the global noise emitted by the vehicle. A low-order sound-prediction methodology is developed considering the blade sweep-angle effect on the acoustic predictions of the turbulence-impingement and the trailing-edge noise-generating mechanisms. We modeled these through the application of a semianalytical method based on Amiet’s airfoil theory, appropriately adapted via a strip-theory approach accounting for rotation and modified to include the blades forward curvature. Sweep was already shown in the literature to reduce the noise emitted by isolated airfoils, but its effect on rotating machines was not yet well understood. In this study, we show that the effect of the sweep-angle is to globally reduce the emitted noise by the fan and to change the sound distribution of the sources along the blade span. Thus, the sweep-angle must be considered not only because it yields a better comparison with experimental results but also because wrong conclusions on the dominating noise-generating mechanisms can be drawn when this effect is not taken into account. The investigation is finally complemented by a sensitivity analysis focusing on some of the key parameters characterizing the acoustic prediction.

Sound localization and quantification analysis of an automotive engine cooling module

“…The sound maps at this frequency band for other operating points are not shown here for the sake of conciseness, but this trend is always observed with and without the heat exchanger. For the studied axial fan, the importance of this blade region in terms of sound emissions was highlighted in [53], especially for frequencies below 3 kHz, where a dominance of the leading-edge noise mechanism was attributed to the high turbulent-kinetic-energy development in such a loaded blade area.…”

Aeroacoustics research in Europe: The CEAS-ASC report on 2020 & 2021 highlights

“…VKI is pursuing research for a better understanding, modelling, and eventually mitigation of the noise emitted by lowspeed axial fans used for automotive engine cooling. A low-order sound-prediction methodology has been developed considering the blade sweep-angle effect on the acoustic predictions of the turbulence-impingement and the trailing-edge noise-generating mechanisms [110]. The prediction method implemented in the VKI in-house aeroacoustic solver BATMAN is based on a semianalytical framework following Amiet's theory, via a strip decomposition of the blade modified to include the blade forward curvature (Fig.…”

Aerodynamic and Acoustic Interaction Effects of Adjacent Propellers in Forward Flight

“…The tip-on-tip interaction would induce non-uniform inflow conditions leading to periodic loads that radiate tonal noise [14]. Broadband noise related to turbulence interactions is also enhanced, by both the trailing-edge scattering of the turbulent boundary layer [15] and the mixing of tip vortices causing eddy dissipation, yielding random fluctuations on the blades [9]. Hence, we intend to quantify the noise generation and directivity variations caused by the aerodynamic installation of the adjacent three propellers with respect to the isolated-propeller case.…”