Turbulence characteristics of a round offset jet with different offset ratios in a counterflow

Abstract

A round jet entering a counterflow with different jet-to-current velocity ratios and different offset ratios was experimentally investigated using particle image velocimetry. Turbulence characteristics, including axial and radial turbulence intensity, Reynolds stress, and skewness in the radial direction, were analyzed based on the measured data. When a round free jet enters a counterflow, the axial or radial turbulence intensity increases to a maximum value rapidly after the jet exit and then generally decreases to a small value. Near the stagnation point, the axial turbulence intensity reaches a second local maximum value, while radial turbulence intensity does not appear the second local maximum value. The ratio of axial to radial turbulence intensity is 0.5 inside the penetration length. The axial and radial turbulence intensities do not present self-similarity in the radial direction. The skewness is negative on the axis, increases continuously as the radial distance increases, and reaches a maximum near the zero-velocity half-width and then gradually decreases. When an offset round jet enters a counterflow, the ratio of axial to radial turbulence intensity is less than 0.5 when the offset distance is less than 10D (where, D is the diameter of jet exit), while it is equal to 0.5 when the offset distance is greater than 10D. However, the other features of the jet are similar to that of a free jet entering a counterflow.