本研究針對受聲波激擾之雙旋轉噴流，以實驗方法探討特徵流場模態、衍化過程、噴流擴散、混合性能及紊流特性。藉由雷射光頁輔助之煙霧流場觀察技術搭配高速攝影機擷取瞬時流場影像;利用熱線風速儀記錄噴流速度的不穩定性;透過影像邊界辨識技術量測噴流的擴散特性;使用追蹤氣體濃度測試法診斷噴流的消散情況。應用高速質點影像速度儀量測流場速度。分析流場結構之連續衍化照片，在振盪強度比對聲波激擾史卓數的域面上，可劃分出兩種流場的特徵模態，分別為「同步環狀渦漩」與「同步泡芙狀紊亂噴流」。同步環狀渦漩形成在低振盪強度的區域(振盪強度低於1)，而同步泡芙狀紊亂噴流形成在高振動強度的區域(振盪強度高於1)。在高振盪強度區域，噴流出口形成「回吸」的現象，因此引致管內混合。激擾史卓數低於0.85時，噴流在高振盪強度區域產生大的噴流擴散寬度及紊流強度值。激擾史卓數高於0.85時，高頻的效應造成噴流延遲破碎及消散，噴流擴散寬度及紊流強度明顯地降低，並且在比較高的激擾史卓數時，結果與未受聲波激擾之雙環噴流相似。當雙環噴流被激擾在高振盪強度時，泡芙狀渦漩的形成及管內混合的效應，使得渦漩結構的紊流時間尺度及長度尺度變小，因此造成噴流的擴散特性增強。噴流的擴散特性主要受到兩項機制支配: (1)環狀渦漩破碎形成小尺度的紊流渦漩引致擴散及(2)噴流出口附近的環狀渦漩結構引致擴散。前者主要發生在振盪強度低於0.5，而後者主要形成在振盪強度高於0.5。藉由分析質點影像速度儀量測的渦度、紊流強度、剪應力、紊流動能，進一步說明流場可視化及濃度量測的實驗結果。

Characteristic flow modes, flow-evolution processes, jet spread width, turbulence properties, and dispersion characteristics of the acoustically excited swirling double-concentric jets were studied experimentally. Streak pictures of smoke-flow patterns, illuminated by a laser-light sheet, were recorded by a high-speed digital camera. A hot-wire anemometer was used to digitize instantaneous velocity instabilities in the flow. Jet spread width was obtained through a binary edge identification technique. Tracer-gas concentrations were measured for information on jet dispersions. A high-speed particle image velocimeter (PIV) was used to acquire velocity field data. Two characteristic flow patterns were observed in the domain of excitation Strouhal number and pulsation intensity: (1) synchronized vortex rings appeared in the low pulsation intensity regime (the pulsation intensity less than one) and (2) synchronized puffing turbulent jets appeared in the high pulsation intensity regime (the pulsation intensity greater than one). In the high pulsation intensity regime, the “suction back” phenomenon occurred and therefore induced in-tube mixing. The jet spread width and turbulent fluctuation intensity exhibited particularly large values in the high pulsation intensity regime at the excitation Strouhal numbers smaller than 0.85. At the excitation Strouhal numbers greater than 0.85, the high frequency effect caused significant decay of jet breakup and dispersion—the jet spread width and fluctuation intensity decreased sharply and may, at very high Strouhal numbers, asymptotically approach values almost the same as the values associated with unexcited jets. Exciting the jets at the high pulsation intensity regime, the effects of puffing motion and in-tube mixing caused breakup of the jet in the near field and therefore resulted in a small Lagrangian integral time and length scales of fluctuating eddies. This effect, in turn, caused drastic dispersion of the central jet fluids. The dispersion and mixing were simultaneously dominated by two mechanisms: (1) the breakup of the induced vortex ring into turbulent eddies, and (2) the near-field entrainment of the induced vortex rings. The former was more important at excitation intensities smaller than about 0.5, whereas the latter was more prominent at pulsation intensity larger than approximately 0.5. The jet half width, vorticity, turbulence intensity, shear stress, and fluctuation kinetic energy characteristics measured by PIV supplement the behaviors of the flow observed in flow visualization and dispersion measurement results.

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