以葉輪扭轉角進行橫流扇噪音減量與葉輪內部流場觀測之實驗與探討

本文提出以葉輪扭轉角(rotor-skew-angle, RSA)設計之策略進行橫流扇噪音減量工作與研究，重點在於降低風扇運轉時產生之單頻突出噪音，並藉流場觀測之技術，探討葉輪旋轉角對橫流扇內部流場之影響。實驗中分別進行0度、5度與10度三種葉輪扭轉角之設計，在橫流扇出風口以聲學人偶進行噪音量測，評估不同葉輪扭轉角在操作轉速下之風扇噪音、並分析其聲音品質；另外在舌端上不同的軸向位置擷取其壓力擾動頻譜進行相干性分析，探討舌端上因不同葉輪扭轉角對週期性壓力擾動之破壞之探討。從聲場分析之結果中，應用葉輪扭轉角對降低風扇噪音中葉片通過頻率峰值有明確之效果，從舌端壓力頻譜相干性分析亦提供葉片通過單頻音降低機制有利的佐證。在風扇內部流場之觀測上，本文克服前人慣用的二維雷射切面單一橫斷面觀測盲點，將煙線切面組合為三維視流之流場觀測，成功地觀察到葉輪扭轉角所造成的軸向流線分歧現象。在本研究結果中顯示RSA-5能有效降低橫流扇之葉片通過頻率與其諧頻(harmonics)，並且能確保風扇保持原設計之性能(performance)。

關鍵字

橫流扇；風扇噪音；流場觀測；葉輪扭轉角

並列摘要

The rotor-skew-angle design was proposed in this research for lowering the cross-flow-fan emitted noise, especially for the significantly narrow band noise accompanying with the blade operation. Following 0, 5, and 10 degree of rotor-skew-angle designs, the cross-flow fan radiated noise and its sound quality were evaluated. The pressure fluctuations were measured at different positions along the axial direction on the tonge. The coherence analysis was utilized for illustrating the blade passing frequency cancellation mechanism. A 3-D flow visualization method, which overcame the blind slight from LDV and PTV, was used to present the differences of internal flow patterns. The experimental results indicated that RSA-5, which was a rotor with a nearly a pitch skewed within impeller’s two end shrouds, had a lower sound emission and little pressure drops relative to that of no skew-angle case, RSA-0. RSA-10, two pitches twisting case, also had a better acoustics quietness than that of RSA-0, but it exited undesired noise in high frequency components around 2 – 4 kHz (3rd and 4th harmonics of the blade passing frequency). In this research, for a compromise between flow and acoustics performance, RSA-5 showed the most suitable design for cross-flow fan rotor.

並列關鍵字

Cross Flow Fan ； Fan Noise ； Flow visualization ； Rotor-Skew Angle

參考文獻

[12] Yang-Chang Shih, Hung-Chi Hou and Hsucheng Chiang, “Numerical Study of the Similarity Law for the Cross-Flow Fan of a Split-Type Air Conditioner,” ASHRAE Transactions; vol. 110, 2004, pp 378-388.

[6] Go-Long Tsai, Tsung-Hsien Tu, Tung-Chen Li and Kuang-Hsieng Wang, “Flow Style Investigation and Noise Reduction of a Cross-Flow Fan with Varied Rotor-Skew-Angle Rotor,” JSME International Journal, Series B, nol. 49, no. 3, 2006, pp. 695-703.

[11] Young J. Moon, Youg Cho and Hyun-Skin Nam, “Computation of Unsteady Viscous Flow and Aeroacoustic Noise of Cross Flow Fan,” Computers & Fluids, vol. 32, 2003, pp. 995-1015.

[13] A. Toffolo, A. Lazzaretto and A. D. Martegani, “An Experimental Investigation of the Flow Field Pattern within the Impeller of a Cross-Flow Fan,” Experimental Thermal and Fluid Science, vol. 29, 2004, pp. 53-64.

[15] M. J. Lighthill, “On Sound Generated Aerodynamically, I. General Theory,” Proc. Royal Soc. (London), Ser A:211, 1952, pp. 564-587.

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以葉輪扭轉角進行橫流扇噪音減量與葉輪內部流場觀測之實驗與探討

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