Flow features of underexpanded microjets emerging from a round convergent nozzle
Flow features of underexpanded microjets emerging from a round convergent nozzle
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圆形收敛喷嘴产生的欠膨胀微射流的流动特征
DOI：
10.1007/s00348-023-03603-0
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发表时间：
2023
影响因子：
2.4
通讯作者：
Y.
中科院分区：
文献类型：
--
作者：
Tashiro;T.;Fukunaga;R.;Ustunomiya;D.;Nakao;S.;Miyazato;Y.;and Ishino;Y.
用彩虹纹影偏转仪测量了出口内径为1 mm的圆形收敛喷嘴中喷出的欠膨胀微喷流密度，以非侵入性地捕捉到从喷嘴出口到喷嘴出口直径20倍的下游的大范围区域。在喷嘴压力比(NPR)分别为3.0、4.0、5.0、6.0和7.0，以及相应的完全膨胀射流马赫数(Mach)分别为1.36、1.56、1.71、1.83和1.93的条件下，进行了微射流的流动显示，其中NPR可以定义为喷嘴上游的滞止压力与背压之比。在轴对称密度场假设的基础上，采用Abel反演技术重建了空间分辨率约为4m的微射流三维密度场。用包括射流中心轴在内的密度场俯视图显示了每个核反应堆的近场激波结构的流动拓扑。实验首次给出了沿射流中心轴的密度分布中第一个局部极小值的位置和流动马赫数作为NPR的函数，并提出了经验关系式。给出了射流中心轴上从喷嘴出口到建立等熵过程的位置的流动马赫数与流向距离的近似表达式。此外，从射流中心线上的密度分布得到了含激波微射流的超音速长度，并与以往的Pitot探头实验数据和经验关系式进行了定量比较。此外，将彩虹纹影偏转仪测量的微射流密度场与以前的马赫-曾德尔干涉法在同一喷嘴下的密度场进行了对比，考察了非侵入式技术对射流中心线、中间线和边界线三个有代表性位置的密度分布的影响。
Density measurements of underexpanded microjets that emerge from a round convergent nozzle with an inner diameter of 1 mm at the exit are taken using rainbow schlieren deflectometry to nonintrusively capture an extensive region from the nozzle exit to a downstream location of twenty times the nozzle exit diameter. Flow visualizations of the microjets are carried out at nozzle pressure ratios (NPRs) of 3.0, 4.0, 5.0, 6.0, and 7.0 and corresponding fully expanded jet Mach numbers () of 1.36, 1.56, 1.71, 1.83, and 1.93, where the NPR can be defined as the ratio of the stagnation pressure upstream of the nozzle to the back pressure. The three-dimensional density fields of the microjets are reconstructed at a spatial resolution of approximately 4m by the Abel inversion technique based upon the assumption of axisymmetric density fields. The flow topology of the near-field shock structure for each NPR is demonstrated with an elevated view of the density field, including the jet central axis. The location and flow Mach number of the first local minimum in the density profile along the jet central axis are experimentally provided for the first time as a function of the NPR to propose an empirical relation. An approximate expression for the flow Mach number on the jet central axis from the nozzle exit to the location where the isentropic process is established is also derived against the streamwise distance. In addition, the supersonic length of a shock-containing microjet, which is defined as the distance along the jet central axis from the nozzle exit to the location farthest downstream at which there exists a local flow Mach number of unity, is acquired from the density profile along the jet centerline and compared quantitatively with the experimental data from previous Pitot probe surveys as well as previous empirical relations. Furthermore, the microjet density fields from rainbow schlieren deflectometry are mutually compared with those from previous Mach–Zehnder interferometry under the same nozzle to investigate the effects of nonintrusive techniques on the density profiles along three representative locations: the jet centerline, intermediate line, and lipline.
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