Mixing and Structural Characteristics of Unforced and Forced Jets in Crossflow
Mixing and Structural Characteristics of Unforced and Forced Jets in Crossflow
复制标题
横流中非受迫射流与受迫射流的混合及结构特性
DOI：
10.1063/5.0113987
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发表时间：
2017
影响因子：
4.6
通讯作者：
T. Shoji
中科院分区：
文献类型：
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作者：
T. Shoji
作者：Shoji，Takeshi|顾问：Karagozian，Ann R|摘要：本文对横流中强制射流和非强制射流的结构和混合特性进行了实验研究。对于非受迫实验，针对具有固定射流雷诺数（Rej=1900）的三种替代喷射器，探索了可变射流与横流密度比（0.35≤S≤1.00）和动量通量比（5≤J≤41）。对于强制射流实验，探索了从两个替代冲洗喷嘴（Rej=1900; Rej=1500）发出的等密度射流。采用同步PLIF/立体PIV测量方法研究了JICF射流中心平面标量场和速度场之间的相互作用。POD分析表明，从对流过渡到绝对不稳定的上游剪切层J减少，与热线测量一致。通过Howarth变换从PLIF和PIV数据中提取局部应变率。通过中心平面PLIF图像探索了具有可变混合尺度长度的混合表征。与搅拌以及分子混合相关的混合可以被区分，特别是在冲洗管注入的旋涡结构中。对流不稳定JICF的正弦强迫表明，相对较低的振幅强迫影响射流结构和混合，特别是接近基频。对于绝对不稳定的JICF，需要更高的强迫振幅来改变射流特性，与锁定一致，从而增强分子混合。单脉冲方波强迫产生深入穿透特定冲程比（L/D）的涡结构，即使是绝对不稳定的JICF。L/D产生最大的射流传播和渗透减少J，但L/D为最佳分子混合对应于不同的值和趋势J.双脉冲方波激发，每个时间段内的两个变量脉冲，使射流的近场涡环相互作用和碰撞，与随之而来的影响分子混合。
Author(s): Shoji, Takeshi | Advisor(s): Karagozian, Ann R | Abstract: This dissertation describes an experimental exploration of structural and mixing characteristics of the unforced as well as forced jet in crossflow (JICF). For unforced experiments, variable jet-to-crossflow density ratios (0.35≤S≤1.00) and momentum flux ratios (5≤J≤41) were explored, for three alternative injectors with a fixed jet Reynolds number (Rej=1900). For forced jet experiments, an equidensity jet emanating from two alternative flush nozzles (Rej=1900; Rej=1500) were explored. The interplay between scalar and velocity fields for the JICF was studied using simultaneous PLIF/stereo PIV measurements in the jet’s centerplane. POD analysis showed a transition from convective to absolutely instability in the upstream shear layer as J was reduced, consistent with hotwire measurements. Local strain rates were extracted from both PLIF and PIV data via the Howarth transformation. Mixing characterization with variable mixing scale lengths was explored via centerplane PLIF images. Mixing associated with stirring as well as molecular mixing could be distinguished, apparent especially in vortical structures for flush pipe injection. Sinusoidal forcing of the convectively unstable JICF demonstrated that relatively low amplitude forcing affected jet structures and mixing, especially close to the fundamental frequency. For the absolutely unstable JICF, a much higher forcing amplitude was required to alter jet characteristics, consistent with lock-in, leading to enhanced molecular mixing. Single-pulse square wave forcing created deeply-penetrating vortical structures for specific stroke ratios (L/D), even for the absolutely unstable JICF. L/D producing the greatest jet spread and penetration decreased with decreasing J, but L/D for optimal molecular mixing corresponded to different values and trends in J. Double-pulse square wave excitation, with two variable pulses within each temporal period, enabled the jet's nearfield vortex rings to interact and collide, with attendant effect on molecular mixing.