Effect of momentum flux distribution on multiple round jets

Abstract

Purpose This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics. Design/methodology/approach The nozzle configuration consists of a central nozzle surrounded by four nozzles. All nozzles have the same diameter and constant separation between nozzles. OpenFOAM® is used for simulating the jet flow. Reynolds-averaged Navier-Stokes (RANS) equations are solved iteratively with a first-order closure for turbulence. Pitot-static tube with differential pressure transducer is used for mean velocity measurements. The comparison of computed results with experimental data shows similar trend and acceptable validation. Findings According to the results, the momentum flux distribution significantly alters the near field of multiple turbulent round jets. Highly non-linear decay region in the near field is found for the cases having higher momentum in the outer jets. As a result of merging, increased positive pressure is found in the mixing region. Higher secondary flows and wider mixing region are reported as a result of momentum transfer from axial to lateral directions by Reynolds stresses. Research limitations/implications The present study is limited to isothermal flow of air jet in air medium. Social implications Optimum momentum flux distribution in multijet injector of a combustor can reap better mixing leading to better efficiency and lesser environmental pollution. Originality/value As summary, the contributions of this paper in the field of turbulent jets are following: simulations for various momentum distribution cases have been performed. In all the cases, the flow at the nozzle exit is subsonic along with constant velocity profile. To simulate proper flow field, a large cylinder-type domain with structured grid is used with refinements toward the nozzle exit and jet axis. The results show that the non-linearity increases with increase in momentum of outer jets. Longer merging zones are reported for cases with higher momentum in outer nozzles using area-averaged turbulent kinetic energy. Similarly, wider mixing regions are reported using secondary flow parameter and visualizations.

Effect of aspect ratio on mean flow characteristics of cruciform orifice jet

“…The cruciform or cross-shaped jet is a noncircular jet and said to have better mixing than circular jets (Azad and Quinn, 2012; Quinn and Azad, 2013; Fujita and Osaka, 1992). Because of its mixing characteristics, it can be used as a nozzle in fuel injectors (Kannan and Panchapakesan, 2018), aircraft cabin air-conditioning systems and thrust augmentation devices in aircraft (Bandopadhyay et al , 2022). The turbulent jets issuing from pipes, orifices/slots and nozzles are studied for their mean flow and turbulent characteristics.…”