Abstract
The molecular tagging velocimetry (MTV) is applied to measure the velocity fluctuation in a supersonic micro jet issuing from the two-dimensional Laval nozzle whose height is 500μm at the exit. This velocimetry uses the forth harmonic of a Nd:YAG laser (266nm) as a light source to excite the acetone molecules seeded in the flow, and fluorescence images are captured by a CCD camera 300ns after the laser illumination. The distribution of root-mean-square (RMS) of velocity fluctuation is obtained from these images. The distribution represents well the characteristics of the turbulent micro jet although unreasonable RMS values due to low fluorescence intensity are recognized around the jet. The distribution of single-time two-point spatial correlations is also obtained from the measured velocity fluctuations and this distribution reveals that the micro jet fluctuates in a flapping mode.
