使用實驗方法研究噴流雙平行平面噴流受到聲波激擾時的流場與混合特性。藉由揚聲器產生聲波激擾；使用綠光雷射光頁輔助流場可視化技術擷取瞬時與長時間煙霧流場照片；透過二位元邊緣偵測技術，計算噴流煙霧的擴散寬度；利用一維熱線風速儀探針量測噴流出口的速度振盪、剪流層不穩定性、時間平均速度、紊流強度以及紊流渦漩的時間與長度尺度；使用質點影像速度儀檢測時間平均速度場、渦度分佈以及雷諾剪應力；利用追縱氣體偵測技術量測噴流混合特性。當噴流在低雷諾數時，受聲波激擾之雙平行平面噴流在噴流擾動強度及擾動史卓數的域面上，可識別出四個流場特徵模態：分離型層流凝聚性渦漩、接觸型層流凝聚性渦漩、渦漩提前破碎、橫向擴散。當噴流雷諾數增加至600以上時，層流凝聚性渦漩轉變為紊流凝聚性渦漩。雙平行平面噴流在分離型凝聚性渦漩及接觸型凝聚性渦漩模態時，剪流層上的渦漩緩慢地破碎，形成少量的噴流擴散與紊流擾動，因此噴流的擴散效率較低。在渦漩提前破碎模態時，渦漩破碎引致大的紊流擾動及噴流擴散。在橫向擴散模態時，隨著噴流沿著軸向高頻率的前後流動行為，軸向動能明顯地降低並且轉換至橫向，因此噴流的橫向擴散增加。當噴流擾動強度增加時，在中心線上之紊流渦漩時間與長度尺度隨著往下游的距離增加而遞減。廻流區、合併點及結合點的軸向長度隨著噴流擾動強度及擾動史卓數的增加而減小。在匯合點處，噴流動量由軸向主導轉變為橫向主導，且在中心線上的雷諾剪應力較大。聲波激擾有效的改變雙平行平面噴流之流動型態，產生主導性渦漩並提前破碎，因而增強紊流強度、改善混合特性。

The flow and mixing characteristics of dual parallel plane jets subject to acoustic excitation were studied experimentally. The acoustic excitation was generated by a loudspeaker. The green laser-light sheet assisted flow visualisation technique was used to render the instantaneous smoke flow patterns and long-exposure smoke flow patterns. A binary edge-detection technique was used to calculate the jet spread width by processing long-exposure flow images. The jet velocity pulsation at the jet exits, shear layer instability, time-averaged velocity, and turbulence intensity, Lagrangian time scales, and length scales of turbulence eddies in the centerline were measured by a one-component hot-wire anemometer. The time-averaged velocity, vorticity fields, and Reynolds shear stress were examined by employing Particle Image Velocimetry. The tracer-gas concentration detection method was used to study the dispersion and mixing characteristics. Four characteristic flow modes (discrete coherent vortices, contiguous coherent vortices, early vortex breakup, and lateral dispersion) were identified in the domain of the jet pulsation intensity and excitation Strouhal number at low jet Reynolds numbers. The laminar coherent vortices changed into turbulent vortices when the pulsation intensity was increased at jet Reynolds numbers greater than about 600. The discrete and contiguous coherent vortices appearing in the jet shear layers broke up slowly and caused small jet expansions and turbulent intensities, thus inducing a low efficiency of jet fluid dispersion. Early vortex breakup induced large turbulence fluctuations caused by the early vortex breakup increased the jet dispersion significantly. In lateral dispersion mode, the axial momentum reduced drastically with high-frequency back-and-forth flow motions thus, lateral jet expansion and jet dispersions were increased. The instability in the coherent vortices was roll up at the excitation frequencies. Lagrangian time scales and length scales of turbulent eddies reduced in the centerline with an increase in the jet pulsation intensity. The axial length of the recirculation zone, merging point, and the combined point was reduced with the increase in pulsation intensity and excitation Strouhal number. The momentum transfer was large in the merging region, thus, the Reynolds shear stress was large in the centerline. The acoustic excitation effectively modulated the flow patterns, generated near-field coherent flow structures, inducing advanced vortex breakup, and therefore substantially enhanced turbulence intensities and mixing capability.

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