近年來空汙問題日趨嚴重，汙染物會透過空調與窗戶進入室內，而空氣清淨機在維持室內空氣品質中扮演重要的角色；市面上空氣清淨機常見的為前傾式離心風機，而離心風機有前傾、徑向與後傾三種類型；因此本研究將各式離心風機應用在空氣清淨機來探討其性能差異，同時為抑制其衍生之窄頻帶噪音，選用亥姆霍茲共振器來進行降噪工作。首先透過數值模擬工具進行改良設計，藉由系統化更動整體外形、葉片入口角與葉片數，優化性能後的前傾、徑向與後傾式之最大流量為28.1、22.9及14.2 CFM；接著把最適化離心風機應用於原始空氣清淨機裡，藉由模擬計算繪製壓力-流量之性能曲線，於特定限制下分析三種離心空氣清淨機，選用評比限制包括相同轉速、消耗扭矩不變與最大流量輸出一樣。結果顯示相同轉速下，效率優劣依序為前傾式、徑向式與後傾式，其值依序為25.3、25.1與6%；而消耗扭矩不變與最大流量輸出結果相同，效率優劣依序為徑向式、前傾式與後傾式，其中消耗扭矩不變之值為32.5、25.3與23.5%，而相同流量輸出依序為30.7、25.3與21.4%。
至於濾網之高阻抗對輸出流量的影響，本研究將不同型式的空氣清淨機加入濾網後，發現和不同型式風機關連不大，其最大流量皆是未加濾網時的85%左右。接著將針對前傾離心式空氣清淨機做聲場模擬分析，且加入亥姆霍茲共振器針對特徵頻率做降噪工作，彙整其模擬結果顯示，針對第一特徵頻率設計的共振器，可降低第一特徵頻率噪音0.3~9.7 dB、且第二特徵頻噪音降低0.6~13.4 dB；而針對第二特徵頻率設計的共振器，能降低第一特徵頻噪音0.1~9.1 dB 、第二特徵頻噪音降低0.7~12.5 dB。綜合性能分析發現，徑向式風機在消耗扭矩不變與最大流量輸出一樣之條件下，無論噪音和性能皆較前傾式與後傾式為佳；而在同轉速下，前傾式離心風機則是較佳之選項。

With the increasing air-pollution concerns, the compact air cleaner has drawn significant research attentions to develop a high-performance product to improve the air quality inside the vehicle. Hence, this study proposes a rational arrangement on filter and forward-curved (FC) centrifugal fan to minimize total resistance along airflow path for enhancing its flow rate. Also, a comprehensive parametric study on the rotor, the guiding rib, and the spiral housing is carried out in sequence to optimize its aerodynamic performance. Moreover, the radial and the backward-inclined (BI) centrifugal fans are designed and installed inside this new configuration for identifying the appropriate type. Consequently, the CFD results show that the best flow rates and static efficiencies generated by FC, radial, and BI centrifugal fans operating at 2,000 rpm are 28.1, 22.9, and 14.2 CFM and 25.3, 25.1, and 6%, respectively. Also, for thorough evaluating these centrifugal fans, their static efficiencies are calculated under the same power-consumption and flowrate-generation conditions. It is illustrated that radial centrifugal fan performs more effective than other two types. However, FC centrifugal fan is the appropriate choice for producing the best air-cleaning effect under these geometric and operating constraints.
With regard to the noise-reduction effort, the acoustic field of the air cleaner equipped with an optimized FC centrifugal fan is calculated and analyzed carefully via the transient CFD simulation. Thus, an in-depth understanding on the acoustic features of this air cleaner is achieved and utilized to design several Helmholtz resonators, which are installed on the cut-off and the high-pressure region over the spiral housing for evaluating the associated noise-reduction outcomes via CFD tool. The calculated results demonstrated that the resonator aimed at the 1st harmonics can reduce the noise of 1st and 2nd harmonic frequencies by 0.3~9.7 dB and 0.6~13.4 dB, respectively. Also, the resonator aimed at 2nd harmonics produces the noise reduction ranging around 0.1~9.1 dB and 0.7~12. dB on the first two characteristic frequencies. In conclusion, the accomplishment of this study provides a systematic design and noise-reduction scheme for the vehicular air cleaner with the implement of Helmholtz resonator.

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