Experimental observation of impinging jet breakup utilizing laser-sheet illuminated photography

Observation of impinging jets in the near-injector region has been accomplished with laser-sheet luminated photography to determine the spray characteristics and geometry as a function of jet Reynolds number. This method produces high resolution photographs with 30 to 60 nanosecond laser pulses. An exposure from a single laser pulse produces a instantaneous picture of the injection and subsequent breakup processes while a multiple-exposure picture provides a time averaged representation of the spray. A 60° total impingement angle injector was tested at Reynolds numbers ranging from 3000 to 107,000 (1.5 to 55 m/s). Instantaneous photographs of light scattered by the spray from two-dimensional cuts of the flow-field in the plane of the two impinging jets and perpendicular to this plane are presented. In addition to the four previously documented spray regimes, the data suggest the inclusion of a higher Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. This spray regime is characterized by the presence of many fine droplets and the disappearance of the well-defined liquid breakup wave pattern in the post-impingement region. Multiple-exposurephotographs revealing the overall spray shape are mapped to the equation of a conic section yielding a characteristicshape parameter which varies as a function of jet Reynolds number. This shape parameter was found to increase rapidly at low Reynolds numbers, reach a maximum, drop off slightly, and then increase gradually to an asymptotic value.