Reynolds number effects on transition, turbulence intensity and axial-velocity decay rate of turbulent round jets

Abstract

Numerical simulations of turbulent round jets, using explicit-filtered LES technique, are performed, for three different Reynolds numbers(Re = 3600, 88000, 400000), to understand the Reynolds number effect on subsonic jets with Mach number 0.9. Eigth-order compact schemes are used for spatial derivative estimation. Second order Runge-Kutta method is used for Time evolution of flow. One-parameter fourth-order compact filter is used for low-pass explicit filtering of transported variables. Decreased centreline axial velocity decay rate and reduced turbulence intensities are observed as jet Reynolds number increases. Jet spread-rate is observed to be independent of the Reynolds number. An early potential-core collapse and transition to turbulent regime is observed in jets with high Reynolds number, for same inflow turbulence seeding. Role of increased smaller length scales with increase in Reynolds number is analyzed. It is observed that behavior of turbulent round jets is similar to that of plane jets, irrespective of gain in dimensional freedom. Detailed discussions of the observations made from numerical experiments are presented.