An Experimental Investigation of Starting Impinging Jets

Impulsively started impinging jets were experimentally investigated in a water tank utilizing a fluorescent dye technique. The jets were examined prior to and subsequent to impingement. The impingement surfaces included a flat surface and a two-dimensional semicircular concave surface. The normalized jet-to-surface distance and the jet Reynolds number were varied in this study. Using digitized flow visualization images, the jet trajectories, front velocities, growth rates, and convective velocities of large-scale turbulent structures were quantified. A central conclusion of this investigation is that, for all cases studied, the jet-front velocity varies with the square root of time. These results are important to applications that might use starting or pulsed jets for heat transfer enhancement and in combustion processes.