Abstract
Low-speed axial cooling fans are frequently used to manage engine temperature by ensuring that adequate quantities of air pass through heat exchangers, even at low vehicle speeds or in the idle condition. This study aims to provide a better understanding of the unsteady flow behavior around an automotive axial cooling fan with seven blades and its impact on the aerodynamic noise generation. Large Eddy Simulation (LES) near the near-field region and the Ffowcs-Williams and Hawkinbygs (FW-H) method were performed to analyze the flow characteristics around the fan and predict the aerodynamic noise emitted from the fan under a constant rotational speed of 2100 rpm. The simulation results for the velocity distributions and aerodynamic noise were compared with the experimental data measured by single hot-wire probe and in a dead-sound room. The results showed a comparatively good agreement upstream and downstream from the fan and at two different receivers of 0.5 m and 1.0 m. When the fan was rotating, a strong tonal noise numerically existed near the leading edge of the blades at the tip and amounted to 110 dB sound pressure level (SPL) caused by the increasing angles of attack with the increasing radial velocity near the ring, which caused the entire air foil to emit a low-frequency noise. Furthermore, the different SPL decay characteristics of approximately 5 dB in the near-field region and 6 dB in the far-field region were observed each time the distance from the fan doubles. The findings of this research can provide important insights into the design of axial fans with low noise and high performance.
Highlights
Low-speed axial cooling fans are frequently used to manage engine temperature by ensuring that adequate quantities of air pass through heat exchangers, even at low vehicle speeds or in the idle condition (Figure 1) [1,2]
The flow characteristics over the fan must be understood because the aerodynamic noise was generated by an unsteady flow
The fan blades generated a wide range of vorticities over the blades after a laminar separation of the bubbles on the surface of each blade consisting of slender airfoils from the root at tip
Summary
Low-speed axial cooling fans are frequently used to manage engine temperature by ensuring that adequate quantities of air pass through heat exchangers (radiators), even at low vehicle speeds or in the idle condition (Figure 1) [1,2]. An important constraint on fan usage is the generation of a flow-induced noise, called aerodynamic noise, which is emitted to the motors’ cabin and causes much annoyance for passengers. This problem poses a significant challenge for noise enhancement of axial fans. Compared to other sources, such as the engine and transmission, mechanical, and exhaust contributions, the cooling fan is a major contributor to overall noise. Reducing the axial fan noise in a cost-effective manner necessitates
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