Transient flow characteristics of single and twin circular impinging jets using particle image velocimetry and proper orthogonal decomposition

This study experimentally investigated the transient flow characteristics of single and twin parallel circular impinging jets using Particle Image Velocimetry (PIV) and Proper Orthogonal Decomposition (POD). High spatiotemporal resolution data were collected to analyze and visualize the distribution and interactions of multi-scale vortex structures. The experimental data were evaluated for PIV uncertainty and statistical convergence. The flow field distribution of the fountain that may occur in the twin impinging jets was also discussed. The results revealed that, for the oblique single jet, high-energy large-scale structures primarily concentrate in downhill regions and gradually decompose into smaller-scale structures. In the combination of twin jets, vortices in the shear layers merge in an alternating pattern. The frequencies of the inner and outer shear layers are sensitive to jet spacing with different characteristic interaction patterns repeatedly observed based on varying spacings. Three distinct cases are defined based on the interaction of the twin jets with the impingement plate. Additionally, three distinct flow field structures of fountain are defined to facilitate, indicating the degree of combination as well. The velocity profiles of the fountain are similar and adhere to a Gaussian distribution. Furthermore, a semi-empirical equation was developed to describe the centerline velocity of the fountain.