本研究發展出一種利用動態孔達效應而形成交互振盪噴流以調制尾流特性的V型鈍體。面對著V型鈍體的開口，裝置一個特殊設計的新月型曲面標靶物，經適當而技巧的調整幾何安排，使得進入狹縫的噴流產生自激振盪。將產生自激振盪的射流，導入特殊設計的流道，再注入V型鈍體的尾流區中，形成交替而週期性的噴流，能夠有效調制尾流區的特性。影響流體振盪的主要參數包括：新月形曲面曲率半徑、新月形曲面曲率中心與標靶物虛頂點的偏移距離與雷諾數。由於自激振盪而形成交替噴射流體的注入，振盪器在尾流區中可以偵測到兩種型態的不穩定波：一種是高頻率的射流振盪(此一頻率與狹縫噴流的自激振盪頻率相同)，另一種是低頻率的渦旋流逸(此一渦旋流逸與閉口的V型鈍體及前端開口的V型鈍體之尾流區渦旋流逸是相似的)。本研究所發展出來自激振盪器的流體振盪頻率換為史卓數可以達到0.56，為一般利用振盪原理應用在標靶型流量計史卓數的60倍，比用於熱傳增強器的振盪器多約80倍。此史卓數的提升可歸因於振盪器新月形曲面孔穴的特殊幾何設計。流體振盪器尾流區的平均紊流強度會比閉口V型鈍體及前端開口的V型鈍體尾流區分別增加18.6%及5.8%。高頻振盪的狹縫噴流射入低頻的尾流中，射流振盪在流動方向的渦旋長度尺度，只有渦旋流逸長度尺度的5%左右。紊流的時間與長度尺度也會大幅的減小，尾流區中振盪噴流可以增加渦旋的拉伸衍化，有助於紊流動能的增加，由於渦流在剪流層的拉伸增加效應，流體振盪器尾流區的紊流長度尺度比V型鈍體尾流區小約10倍左右。為了更清楚了解射流振盪器的物理機制與發展更高性能的射流振盪尾流混合器，本研究另外進行一個水洞實驗，以質點軌跡視流法與PIV量測，研究強制射流振盪器的振盪行為與射流對尾流流場的影響。強制射流振盪器在曲面腔室中也會產生振盪。基本上兩種振盪的機制是相同的，只是強制射流的控制與用途可以更廣。為了增強尾流區的混合效果，在交替振盪的射流出口處，加裝折射擋板將振盪的噴流導引到尾流流場內部，結果對於尾流流場的動量、紊流強度與剪應力分佈的均勻度皆會有大幅的提昇。經由折射擋板折射角度的調整，可以有效控制尾流迴流長度，紊流的長度尺度也會因折射角增大而變小，證明此一折射擋板技術對尾流紊流特性的調制有很大的功能。

The vee-shaped fluidic oscillator is developed by inserting a target blockage with a specially designed crescent surface into the downstream cavity of a slit vee-gutter. Stable, self-sustained, periodic fluidic oscillations can be induced by the dynamic Coanda effect when the geometric parameters of the target blockage and the Reynolds number are properly tuned. The fluidic oscillations are directed through two slit passageways and injected into the near wake of the vee-shaped fluidic oscillator like the pulsing jets. The oscillation behaviors, frequency selection, streamline patterns, and turbulence properties of the unsteady flows in the near wakes of the vee-shaped fluidic oscillator are studied experimentally in a wind-tunnel by using the smoke-wire flow visualization technique, hot-wire anemometer, and laser Doppler velocimeter. Flow fields of the slit vee-gutter and the closed-tip vee-gutter, which are the counter parts of the vee-shaped fluidic oscillator, are measured as well for comparisons. The Strouhal number of the fluidic oscillation based on the slit width of the presently developed oscillator can attain about 0.56 at large Reynolds numbers, which is about 80 times larger than the previous results for the enhancement of heat transfer and about 60 times larger than that for the fluidic flowmeter. The fluidic oscillations act as an excitation source to the wake. The kinetic energy of the fluidic oscillations is transferred to turbulent fluctuations and therefore causes increases in the size of the recirculation bubble and the turbulence intensity in the wake of the vee-shaped fluidic oscillator. The turbulence intensity in the near wake can be increased by about 7% when compared with that of the closed-tip vee-gutter. In order to further enhance the understanding and to increase the functionality of the developed fluidic oscillator, the particle tracking flow visualization method (PTFV) and the particle image velocimetry (PIV) are employed to diagnose the flow field in the forced fluidic oscillator. The experiments are conducted in a water tunnel. The Reynolds number ranges from 1332 to 2333. The forced fluidic oscillator is made of transparent acrylic so that the flow visualization and the PIV measurements are possible. The time-evolving instantaneous and time-averaged flow and streamline patterns are obtained. The statistical properties of the turbulence, e.g., the probability density function, autocorrelation coefficient, power spectrum density function, time and length scales of the turbulence, turbulence intensity, shear stress, vorticity, are extracted from the measured raw data of the PIV experiments. A technique of jet-deflection-plate is developed to control the injection path and excitation situation of the oscillation jets on the wake flow. The results reveal that the vee-shaped fluidic oscillator with the installation of the jet-deflection-plate can effectively modulate both the small-scale, large-scale flow structure and the turbulence.

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