Measurements of aerodynamic noise and wake flow field in a cooling fan with winglets

Abstract

The aerodynamic noise and the wake flow field in a cooling fan under actual operating conditions are studied with and without winglets on the fan blades. In order to understand the influence of the winglet, the aerodynamic noise and the wake velocity distribution are measured. The results indicated that overall noise level decreased and the noise spectrum was changed in a low frequency range when the winglet was installed. It was found from the flow visualization and PIV measurement that the influence of the winglet appeared in the traces of the tip vortices and the magnitude of vorticity was reduced in the near wake region, which suggest the observed reduction in aerodynamic noise.

Flow driven by a stamped metal cooling fan – Numerical model and validation

“…Early effort by Campbell presented a theoretical analysis on the effects of engine temperature on the engine performance [8]. Various investigations focused on the cooling fan geometric designs for automobile and turbine engines, including the blade angle, blade dimensions, and the radial clearance between the fan and the shroud [9][10][11][12][13][14]. Sheu [9] presented a set of formulas to predict axial flow turbine propeller parameters when the blade profile, shroud and tip diameter, and the number of blades, are known.…”

“…They found that the axial position of the fan relative to the shroud had significant effects on the fan performance. Nashimoto et al [14] experimentally measured the wake flow after the blades of an axial flow cooling fan and related the wake flow structure to the fan noise level. They reported that a winglet generated vortices changed the structure of the vortices born at the leading edge of the blade and the overall noise level of the fan was reduced.…”

Visualization of aerodynamic noise source around a rotating fan blade

“…Note that the tip vortices are generated from the upstream blade due to the roll-up flow from the pressure side to the suction side of the blade. For details, see the flow visualization study by Nashimoto et al (2004). The trailing edge vortices are Karman vortices shed alternatively from pressure and suction surfaces of the trailing edge of the blade.…”

“…With this method, however, it is impossible to identify the flow structure regarding the noise generation with high spatial resolution. On the other hand, as for the flow field around the fan blade, the flow field is visualized by oil film and smoke (Nashimoto et al, 2000), and the velocity field is measured by laser doppler velocimetry (Nash, 1999;Cai et al, 2002) and particle image velocimetry (Nashimoto et al, 2004). Although these studies on flow field around the fan blade allow for the understanding of flow phenomena, such as separation, reattachment and vortex shedding, these techniques are not suitable for identifying the noise source distribution.…”

Optimization design of annular axial cooling fan based on circumferential vorticity analysis

“…[2][3][4] tended to performed the structure optimization of fan by traditional method of Computer Dynamic Fluid (CFD), the calculation model of fan-flow-field was built and then the distribution of pressure and vortex were further analyzed, and finally the optimization design of structure was performed by their engineering experience. The optimization procedure mentioned above is blind for uncertain of the really source of decreasing of flow-field quality.…”