| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 99 === To prevent the overheating and unstable problems, the heat dissipation of electronic products has become a critical and challenging issue due to the demand of dimension reduction. Nowadays, because of its effective heat removing ability and low manufacturing cost, heatsink assembly is the widely-adopted cooling module for handling the thermal- management task. A heatsink assembly is a combination of heatsink and cooling fan; thus the cooling fan plays a vital role and becomes the topic of this thesis. This research focuses on investigating the feasibility of using the flapped airfoil on the small axial-flow fan to enhance its aerodynamic performances, especially the static pressure. The Gurney flap is a small flat plate attached on the trailing edge of airfoil, and it can avoid the unwanted flow from the pressure surface to suction surface for enhancing the lift force substantially.
In this study, the flapped airfoil is utilized in the fan design procedure since the increased lift force on blade may be transferred to the pressure gain, which enables the cooling airflow to overcome the system resistance. Nevertheless, form the simulation results, it is found that some local pressure raises are found on the suction surface of blade, but the total pressure of the discharging air is similar to that of the original fan. To explore the physical mechanism, the comprehensive flow visualization is carried out numerically to identify an unexpected leakage flow, which stems from the pressure surface of one blade to the suction surface of next blade. Evidently, different from the case of single airfoil, this leakage phenomenon is generated by the significant pressure difference caused by the flapped airfoil. It follows that this flow not only diminishes the pressure-raise effect, but also forms an obstacle for the incoming flow near the fan inlet. Consequently, the expected performance enhancement on the axial fan disappears completely. In conclusion, the proposed flapped-airfoil design does not function as expected unless the reversed leakage flow is ceased by proper arrangements based on the flow pattern obtained in this work.
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