Study on the collapse length of compressible rectangular microjets
Study on the collapse length of compressible rectangular microjets
复制标题
可压缩矩形微射流塌陷长度研究
DOI：
10.1007/s00348-020-03030-5
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发表时间：
2020
影响因子：
2.4
通讯作者：
Taro Handa
中科院分区：
文献类型：
--
作者：
Masayuki Anyoji;Fujio Akagi;Yu Matsuda;Yasuhiro Egami;Taro Handa;Taro Handa
摘要本文研究了马赫数在0.3 ~ 1.5之间的矩形可压缩微射流的崩溃长度。微射流是由一个出口高度为500 μm的收敛矩形喷嘴产生的。平面激光诱导荧光（PLIF）和分子标记测速（MTV）技术被用来显示微射流。PLIF图像显示，每个微射流在某个位置突然扩展。从瞬时MTV图像确认，该位置对应于射流开始塌陷的位置。从PLIF图像估计射流塌陷长度，其被定义为喷嘴出口和射流塌陷位置之间的距离。崩溃长度与射流雷诺数的关系图显示，崩溃长度与亚音速和理想膨胀的微射流的雷诺数成反比。另一方面，当射流雷诺数大于一定值（~ 103）时，欠膨胀微射流的崩溃长度几乎是均匀的，尽管在较低雷诺数时，崩溃长度与雷诺数成反比。为了解释欠膨胀微射流中出现这种特性的原因，进行了数值模拟。结果表明，只要发生射流尖叫，崩溃长度保持不变。因此，尖叫射流的塌陷长度与射流中的反馈长度有关。临界雷诺数在层流湍流过渡发生的估计从崩溃长度的微射流没有尖叫和绘制对流马赫数。研究发现，临界雷诺数随对流马赫数的增加而增加。图形摘要
AbstractThe present study focuses on the collapse length of compressible rectangular microjets whose Mach numbers range between 0.3 and 1.5. The microjets are created from a convergent rectangular nozzle whose height is 500 μm at its exit. The techniques of planar laser-induced fluorescence (PLIF) and molecular tagging velocimetry (MTV) are used to visualize the microjets. The PLIF images reveal that each microjet spreads abruptly at a certain location. It is confirmed from the instantaneous MTV images that this location corresponds to the location where the jet starts to collapse. The jet collapse length, which is defined as a distance between the nozzle exit and jet collapse location, is estimated from the PLIF image. The plot of the collapse length versus the jet Reynolds number reveals that the collapse length is inversely proportional to the Reynolds number for subsonic and ideally expanded microjets. On the other hand, the collapse length for underexpanded microjets is almost uniform when the jet Reynolds number is higher than a certain value (~ 103) although the length is inversely proportional to the Reynolds number for the lower Reynolds numbers. To clarify the reason why such peculiarities appear in the underexpanded microjets, the numerical flow simulations are carried out. The results reveal that the collapse length remains constant as long as a jet screech occurs. Consequently, the collapse length of the screeching jet is related to the feedback length in the jet. The critical Reynolds numbers at which laminar-turbulent transition occurs are estimated from the collapse lengths of the microjets without screeching and plotted against the convective Mach number. It is found that the critical Reynolds number increases with the convective Mach number.Graphic abstract