本文主要目的是要探討平面銳角狹縫噴流之流場結構和其渦流動力機制。研究的方法是以熱線量測為主，並且配合視流法及直角狹縫噴流和傳統噴嘴噴流的比較。針對於流場結構和渦流的研究，雷諾數定於10300；而初始條件對其流場結構影響之探討的雷諾數範圍則介於 5150 ~ 20600。實驗結果表明，狹縫噴流是受到出口起始條件的影響。同時，也證明vena contracta 效應出現於近出口處，且和初始速度有關。它也會造成動量厚度、剪切層寛度等在流場初始發展階段呈現出內凹的現象。另外，推斷這效應會抑制噴流的擴散和延遲流場相干性結構的成長。實驗發現狹縫噴流有較好的混合效果，而且銳角狹縫噴流在等勢核區域後的混合效果優於直角狹縫噴流。本實驗也發現流體經過斜角後產生分離的現象，同時此不穩定的分離層會對流場有激擾的效果，誘導了流場產生負的turbulent energy production。因此，相干性結構的結合過程能量是源自於turbulent energy advection。從頻譜的分析結果，證明這個分離層確實是和相干性結構共存且相互影響。銳角狹縫噴流有偵測到兩種不同頻率的初始不穩定波，且流場中主導的頻率是沿下游而減小，這說明了狹縫噴流是非常不穩定的。

The dynamics of coherent structures in jet column region of a sharp-edged orifice plane jet was extensively studied by means of hot-wire technique. The present study was conducted in a sharp-edged orifice plane jet (i.e. 450 beveled edge) and the height of orifice is set to 15mm, therefore, the aspect ratio is 20. The investigation of the flow structures and intrinsic dynamics of vortex interaction are defined in the fixed operating velocity at and the corresponding Reynolds number based on the orifice height is . However, the study of initial flow properties of sharp-edged and right angle orifice plane jet are undertaken within operating velocity of .
It is found that jet flow is sensitive to initial conditions, particularly nozzle exit with irregular geometry. Due to the sudden contraction of the orifice jet, the vena contracta effect is formed and plays a crucial role at immediate exit of orifice of sharp-edged and right angle orifice plane jet as well. The vena contracta effect depends upon the jet exit velocity, i.e. the vena contracta effect will be more prominent at lower jet exit velocity. This effect leads the flow to accelerate.
Due to the forming of vena contracta at the initial stage, the initially contract inward in momentum thickness, flow entrainment rate and shear layer width is discovered in sharp-edged orifice plane jet. It is found that the vena contracta effect will suppress the flow to spread and delays the development of the coherent structures. In addition, the orifice plane jets perform well in the mixing characteristic than that to the smooth contraction nozzle plane jet.
The existence of the shedding frequency due to the separation on the sharp-edged walls is confirmed in study of Fourier and Wavelet power spectra. Meanwhile, the higher formation rate of sharp-edged orifice plane jet is found in flow visualization and spectral analysis. The frequency of the instability waves in the present case are varying as well as decreasing along the downstream direction. Moreover, two initial instability frequencies exist in tandem within the shear flow. It is expected that these two instability waves will compete to each other to extract energy from the mean flow or separation as well. On the other hand, the ‘forking of structures’ in wavelet coefficient indicates to the vortex pairing at former portion of merging process. The location of the vortex formation in present case is locate somewhere near X/H=0.8., and the occurrence of first and second vortex merging are believed at vicinity of X/H=1.2 and X/H=2.3, respectively. No apparent interchange between and at former and latter portion of vortex formation and merging.
The presence of the negative Reynolds shear stress or energy production prompts the existence of the unstable boundary layer and oscillation of separation zone, which excites the shear flow under high amplitude. This behavior is presumed as self-oscillation in sharp-edged orifice plane jet. Experimental results show that kinetic energy contributes by mean energy advection term at initial flow development and the fluctuation kinetic energy increases drastically during the vortex formation and interaction.

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