Effect of momentum flux distribution on multiple round jets (original) (raw)

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 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 towards 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.

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