Experimental investigation of combination degree effects on characteristics of twin round impinging jets

Abstract

The present study investigates the velocity distribution of impinging twin jets at various spacing distances, heights, and Reynolds numbers using particle image velocimetry (PIV). The results indicate that the velocity on the symmetry line can be used to determine the positions of the merging point (MP) and the combined point (CP), independent of the Reynolds number. For round jets, the position of MP varies linearly with spacing, facilitating the assessment of twin jets development. Furthermore, the mean velocity increase along the symmetry line in the merging region follows a modified exponential-Gaussian distribution. Three specific degrees of combination are defined based on the interaction of the twin jets with the impingement plate: combined, incompletely combined, and separated. Additionally, three distinct flow field structures in the impinging jet region may emerge depending on the degree of combination. In the case of incompletely combined twin jets with a relatively low combination degree, a pair of counter-rotating vortices exists above the plate in the impinging region. There exists a critical height and spacing that results in the disappearance of vortices. This study is expected to provide guidance for predicting the degree of combination and the flow field characteristics of the impinging twin jets.