Measurement of breakdown length of supersonic micro jets usinglaser-nduced fluorescence and phosphorescence

近年来，随着推进、发电、MEMS器件冷却等工程应用的不断增加，超声速微射流的研究越来越受到重视，为了提高超声速微射流在各种工程应用中的性能，必须了解其流动特性。特别是，它是重要的是知道的射流的击穿长度，因为湍流强度和射流的增长率在击穿点附近突然变高。本研究利用丙酮分子的激光诱导荧光，测量了不同雷诺数下的击穿长度。结果表明，随着雷诺数的增加，击穿长度变短。这与亚音速微射流的实验结果一致。然而，亚音速射流的破裂长度已知与雷诺数成反比，相反，发现超音速射流的破裂长度不与雷诺数成反比。从这个结果可以预期，有一些参数以外的雷诺数，占主导地位的超音速微射流的击穿长度。

Recently, study on supersonic micro jets has been important due to increase of engineering applications such as propulsion, power generation, cooling of MEMS components, and so on. In order to improve the performance of a supersonic micro jet for each engineering application, the detailed characteristics of this flow has to be understood. Especially, it is important to know the breakdown length of the jet because turbulence intensity and the growth rate of jet become suddenly high near the breakdown point. In this research, the breakdown length is measured changing Reynolds number by using laserinduced fluorescence from acetone molecules. As a result, it is found that the breakdown length becomes short with increase of Reynolds number. This agrees with the experimental results of subsonic micro jets. However, the breakdown length of the subsonic jet is known to be inversely proportional to Reynolds number, in contrast, that of the supersonic jet is found not to be inversely proportional to Reynolds number. It is expected from this result that there are some parameters other than Reynolds number that dominates the breakdown length of the supersonic micro jet.