Numerical and experimental investigation of aerodynamic noise from a cooling fan in a turbulent flow

Abstract

The investigation into aerodynamic noise arising from rotating surfaces bears significant practical implications. Among these, engine cooling fans have persistently been identified as primary contributors to vehicle noise. This study aims to provide a deeper comprehension of the complex unsteady flow dynamics surrounding an automotive cooling fan and its consequential impact on the generation of aerodynamic noise. Prediction of sound generated from fluid flow, despite its difficulty, can be simulated using modern numerical techniques and computational fluid dynamics (CFD). This research undertakes both numerical and experimental investigations. The experiment involves evaluating fan pressure against mass flow rate at 1500 rpm, while aerodynamic noise assessment transpires at two rotational speeds of 1500 rpm and 2500 rpm. Empirical sound pressure level data of the fan is meticulously captured using the requisite measurement apparatus. In addition, numerical investigations of the aerodynamic noise of an automotive cooling fan based on computational fluid dynamics and computational aeroacoustic (CAA) method have been performed. Initially, a steady-state aerodynamic simulation is carried out, followed by the simulation of the flow field through the application of the improved delayed detached eddy simulation (IDDES) formulation. The pressure rise of the fan versus the mass flow rate is obtained. The satisfactory concurrence observed between the simulation outcomes derived from the numerical method and the experimental dataset stands as notable validation. For the aeroacoustic computation, the Ffowcs Williams-Hawkings model is invoked to deduce sound pressure levels at specific flow points. The broadband noise sources model is also used to obtain the sound power level on the blade surface. Conclusively, it emerges that maximal noise manifestation occurs at a 90° degree angle, corresponding to the hub’s frontal orientation, with discernible dominance of tonal noise within lower frequency ranges (sub-1000 Hz).