本研究分別以熱線測速法及粒子影像測速法量測二維平板混合紊流之流
場速度分布。平板混合紊流場中有兩種不同類型之流場，分別為在流場離開分
隔板末端後形成之剪力紊流與在兩外側之高、低速自由流，而剪力層隨著流向
逐漸自發展區域至完全發展 (自我保持)區域。
本研究以熱線測速法量測的速度時域 (temporal)資訊分析偏態係數與峰態
係數在流場中分布的極值發生位置定義新的混合層範圍 (ySL 與ySH、yFL 與yFH)。
峰態係數極值位置yFL、yFH 可視為剪力紊流最遠能影響的位置，其包含區域可
視為真實受剪力紊流所影響之區域，因此可作為中央剪力紊流區與外圍均值紊
流區之分界。須注意到進行高階統計量值如偏態係數、峰態係數之分析，須有
較長的取樣時間以得到較多的取樣數量方可達到統計穩定值。
藉由分析流場對稱軸位置的聯合概率密度傾斜角判定流場到達自我保持
狀態之位置，對照以平均速度定義之兩位置間距離 (y0.05 與y0.95)及高階的統計
量值ySL 與ySH、yFL 與yFH 包含區域呈現線性速率擴張之位置，ySL 與ySH、yFL
與yFH 呈現線性速率擴張更適合作為判定流場到達自我保持狀態的充分且必要
條件。
以粒子影像測速法得到的速度平面分布經由空間差分得到流場的渦度及
形變量分布，並且運用三重分解法區別在渦度項中受剪力紊流誘發的渦度及純
粹剛體旋轉的渦度，以及在形變項中受剪力紊流誘發的形變及無旋形變，將剪
力誘發渦度在各量測截面中量測誤差範圍 (80 s-1)以下之位置視為不受剪力紊
流影響之區域 (高速側邊界為yωH，低速側邊界為yωL)，在剪力誘發渦度區域呈
現線性擴張速率後流場到達自我保持狀態。
本研究分別比較以熱線測速法得到yFL 與yFH、y0.05 與y0.95，以及以粒子影
像測速法得到yωL 與yωH、y0.05 與y0.95，訂定以峰態係數極值發生位置yFL、yFH寬度作為混合層之特徵長度lF，將lF 沿流場方向呈線性成長趨勢作為判定流場
到達自我保持狀態之判斷依據。

This thesis investigates the velocity distribution of two-dimensional planar turbulent mixing layer by hot-wire anemometry (HWA) and particle image velocimetry (PIV). A turbulent mixing layer is composed of two different flow types within its flow fields, namely a shear layer in the central region and two free streams in each outer high- and low-speed side. Shear layer is formed after the trailing edge of the splitting plate and developing through successively distinct regions, namely the near-field region and fully-developed (self-preserving) region.
The cross-type hot-wire anemometry is capable of measuring the temporal velocity information and analysing profile distributions of skewness factor and flatness factor. The positions of flatness extreme values (yFL and yFH) are the farthest positions where the shear turbulence can reach. It can be viewed as the actual sectional range of shear turbulence. Hence the positions of flatness extreme values
(yFL and yFH) are the interfaces of central shear turbulence and outer high- and low-speed homogeneous turbulence. Note that analysis of high-order turbulent statistics such as skewness or flatness needs more sampling data, in other words, longer sampling time to achieve statistical stationary.
The linear growth rate of regions bounded by ySL and ySH, yFL and yFH are necessary and sufficient conditions and more appropriate for justifying the achievement of self-preserving state.
Particles image velocimetry is used to measure planar velocity information of mixing layer. The spatial derivative of planar velocity distribution can be split into vorticity part and straining part. Furthermore, with new decomposition method, namely the triple decomposition method (TDM), the vorticity part is futher split into the shear-induced vorticity and rigid body rotation, while the straining part is split into the shear-induced strain and irrotational strain. The region which the shear-induced vorticity drops below 80 s-1 is defined as the interfaces shear and free-stream regions. After the width between the two interfaces between the shear layer and high-speed as well as low-speed free streams growths linearly, the flow reaches its self-preserving state.
After comparing the width defined by positions with yFL, yFH and y0.05, y0.95 by HWA, and the interfaces of shear-induced vorticity (yωL and yωH) and y0.05, y0.95 by PIV, one concludes that the range bounded by extreme flatness factor values can be taken as the actual range of shear turbulence layer. The linear growth rate of lF along stream-wise direction can serve as a criterium to justify whether or not
self-preserving state of the flow is achieved.

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