Effect of Blade Curvature on Fan Integration in Engine Cooling Module

Abstract

Two blade curvatures representative of those found in automotive fans are compared.Measured performances are analyzed for forward and backward curved blades, either with orwithout heat‐exchangers placed in front of them. The backward fan demonstrated good efficiencybut poor acoustics, whereas it is the contrary for the forward fan. Investigations are completed by anumerical analysis of the flow in the cooling module. Different integration effects are highlighteddepending on the blade curvature, showing variation in pressure, torque and efficiency. Analysesof blade loadings show that the flow is more homogeneous with a forward curved fan and itproduces less unsteadiness at the blade tip. Post‐processing of detached eddy simulations (DES)shows density fluctuations on the blade wall and confirms the correlation between the large vorticalstructures and the acoustic sources for both fans. In addition, with the forward fan, the soundpropagation is less directed towards the axis of rotation and it yields up to −3.6 dB of sound pressurelevel (SPL) measured in front of the cooling module. As a conclusion, any choice for a fan mustresult from a compromise between aerodynamics and aeroacoustics, and the final performancesmust be carefully checked on the module.

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

“…More details on the mesh geometry and on the inlet and outlet boundary conditions are given in [18]. Furthermore, a similar simulation strategy, despite the use of an unsteady approach in that case, can be found in [7] where the analyzed forward-skewed fan is a slightly bigger sample of the same rotor family produced by Valeo. The RANS-based numerical results show similar azimuthal features over the 7 non-equally-distributed fan blades, making it possible to deal with them separately: in (a), the relative velocity is illustrated on a plane normal to the fan rotating axis, showing higher velocities at the blade trailing-edge tips; in (b), the distribution of pressure indicates that the most loaded zones are the blade leading-edge tips.…”

“…The limitations of the methodology proposed in the following work mainly consist in the lack of modeling of sound-source mechanisms governed by large vortical structures that are particularly dominant sources in the low-frequency range and that require higher-order CFD methods to be simulated. For these systems, in fact, the secondary flow passing through the gap between the ring and the shroud can reach 6% of the nominal flow rate [7]. As shown by an unsteady detached-eddy computation of the same fan in Figure 1, the Q-criterion technique depicts complex vortical structures developing all around the rotating ring.…”

“…Blade sweep is considered as a classical technique in order to mitigate the far-field emissions as well as to enhance the aerodynamic efficiency [5]. In the automotive field, low-speed cooling fans [6] are used to cool down the engine of the car by extracting hot air out of heat exchangers [7]. Several noise-generating mechanisms of tonal and broadband nature occur in this application [8], where backward-swept and forward-swept propellers are often employed [9].…”

Sound localization and quantification analysis of an automotive engine cooling module

“…In modern automotive applications, the low-speed cooling fan has been identified as one of the major contributors to the total radiated sound field [1,2], especially for certain operating conditions such as, for instance, at traffic lights and in traffic jams, where the gear and wind noise are negligible. The axial fan is integrated into the engine cooling module and is placed downstream of a heat exchanger or radiator [3]. The whole automotive cooling module is installed in the under-hood compartment of the car.…”

“…Tip-clearance or tip-leakage noise is produced by recirculating vortical structures that are formed due to the pressure difference between the pressure and suction sides in the tip region of the blades. Here, the recirculating flow can reach up to 6 % of the nominal flow rate [3], producing turbulence that interacts with the blade leading and trailing edges, increasing the low-to-mid frequency region of the noise spectrum [12,13]. It has been found that, in this region, the generated large vortices rotate at a slower speed than the rotor: the frequency of the impact is thus lower than the blade passing frequency (BPF), emitting subharmonic broadband or quasi-tonal noise [7].…”