Affiliation:
1. Department of Applied Mechanics and Biomedical Engineering, Indian Institute of Technology Madras , Chennai 600036, India
Abstract
This article is a follow-up research of our recent paper [Charles and Narasimhamurthy, Phys. Fluids, 34(10), 105111 (2022b)] on direct numerical simulation (DNS) of planar turbulent jets with a pintle orifice. In the present study, we compare the DNS results of three different pintle-jet configurations (30°, 45°, and 60°), which vary only by the chamfering angle (α) within the pintle-shaped orifice. Instantaneous flow fields show the large amplitude oscillation of jets and how the oblique shedding of vortical structures correlates with the inlet condition. We found that as α reduces, the jet experiences more flapping, high turbulent intensity in the near-to-intermediate field, and less coherence in Kelvin–Helmholtz (KH) vortices in the near-field. The vortex dynamics are studied using Q-criterion, λ2-criterion, and enstrophy dynamics, and the effects of the pintle wall on the onset of large-scale motions are investigated. Further, the higher order statistics are evaluated, and it shows the inlet-dependent variations in the jet flow characteristics downstream. The energy balance between the large- and small-scale eddies is studied using a turbulent kinetic energy budget. In addition, we employ quadrant analysis of Reynolds shear stresses along three downstream regions of the jet—initial shear layer, interaction region, and similarity region—and show the effect of turbulence behavior on those mixing regions. The small-scale turbulence length scales, such as the Kolmogorov scale and Taylor microscales, are studied. In addition, we compute the turbulent Reynolds number for each case. Furthermore, the invariant analysis using a barycentric map shows the anisotropy behavior of turbulence in large- and small-scales, where it shows 30° case return-to-isotropy faster than 60° case. The above findings can help in the modeling of turbulent jets with varying orifice conditions and may also facilitate the design of pintle-shaped orifices in airblast atomizers.