Statistics of fluctuating dispersion and penetration of a round jet into a counterflow

Abstract

This paper describes the statistical behaviours of dispersion and penetration of a round jet into a counter-flow. The instantaneous flow patterns are illuminated by a laser sheet and recorded for a range of jet-to-current ratios. The edge of each frame is detected so that the dividing streamline between the counter-flowing jet and the ambient stream can be obtained. The locations of the instantaneous penetration as well as the locations of the largest lateral extent of the dividing streamline are stored for probability density function (pdf) analysis. Large temporal and spatial fluctuations are found in the flow patterns of the counter-flowing jet. The maximum penetration in the axial direction exceeds the time-averaged mean value by approximately 30%. The lateral spreading exhibits an even larger excursion. Both the range and the standard deviation of pdf's increase with the jet-to-current ratio. The statistical results of the instantaneous flow characteristics are found to be more informative than the time-averaged mean flow patterns, especially in the situation like the discharge of toxic or chemical pollutants.