Study On Effect Of Rotor Structures On Fan's Performance And Internal Flow

With the continued miniaturization and higher performance of electronic products, the demand for efficient small fans for heat dispersion, has been increasing. Such fans affect both the performance and life span of these products'. Therefore, the main aim of this research is how to design a small fan with the characteristics of low noise, high flux and compactness.The AC fan series models SF23092A and SF23080AT from Sunon Company were studied in this paper. The general static and internal flow characteristics of small axial fans were obtained by numerical analysis. The total pressure performance curve of model SF23092A was verified by experiment to ensure the reliability of the numerical simulation methods. Thus the static characteristics, internal flow field and sound distributions of the fan models derivatives with different hub ratios and blade numbers were analyzed. Results indicated little or no improvement in aerodynamic performance or noise increase, which did not meet the requirements, hence further study continued with dual-rotor fans, and the good characteristics of counter rotating fans could meet the requirements well .Geometric models of the fans were obtained using Reverse Technology using Unigraphics (UG) on the blade data obtained by 3D Laser ScanArm. The fans'flow channel and mesh were established, using the Turbo module of Gambit software. Then the steady flow simulation was carried out using the RNG k-εturbulence model, whose reliability was verified by comparing the total pressure performance curve by experiment. The general static characteristics and internal flow performances of small axial fans were obtained by comparative analysis which provide the basis for next study.The effect of hub ratio and blade number on the aerodynamic performance of model SF23092A was researched. The numerical calculations involved in the analysis of hub ratio was processed in three steps. First the steady flow field was simulated by adopting the standard k-εturbulence model, which was then used as the initial field of the large eddy simulation (LES) to calculate the unsteady pressure field. Finally when the kinetic energy stablized, the sound field would be completed by LES precisely calculating Ffowcs Williams Hawkings equation, and the sound pressure signals are of accuracy and reliability by the application of Fast Fourier Transform (FFT) on the time-domain spectrum. For the different hub ratios the numerical results for the static characteristics, sound power spectral density, sound pressure level and its attenuation trend were comparatively analyzed. While the steady flow simulation was carried out using the RNG k-εturbulence model, the analysis for the effect of blade number on the performance concluded that five blades was the best choice considering the fixed speed, stagger angle and chord.Finally, counter rotating fans, which could achieve higher pressure ratio, efficiency and flow in a smaller space, were preliminary studied. According to numerical analysis, the pressure of counter rotating fans is double that of single-rotor fans, while the efficiency is not lowered, so their adoption to obtain more powerful fluid to get a higher ventilation rate is feasible.This paper provides significant theoretical support in the optimal design of small axial flow fans with the characteristics of low noise, high flux and compactness.