Pressure-velocity measurements of a small automotive fan at different working conditions. A noise generation perspective.

Although noise from large fans has been extensively studied by the scientific community, few experimental studies have been performed on small-scale fans, where aerodynamic effects due to low Reynolds numbers needs be taken into account. For this reason, some preliminary experimental investigations have been carried out on cooling fans for automotive applications. The experimental campaign has been focused on the characterization of the flow outlet first, using a static Pitot on a 5.5-inch five-bladed fan, with and without its protective grid. After this preliminary phase, simultaneous measurements of velocity with hot-wire anemometry (HWA) and pressure fluctuations with microphones have been also carried out, the HWA probe being located downstream and two microphones positioned in the nearfield and far-field of the fan. The fan has been also studied at different working conditions, varying the rotational speed and applying specific fine grids at the intake, in order to well reproduce the presence of the cooler. Analyses in the time and frequency domain have been performed on the measured data, including cross-correlation between pressure and velocity signals, in order to find the main driving mechanisms that are related to the noise generation.