Abstract:
A large eddy simulation study of mixing and intermittency of a coaxial turbulent
jet discharging into an unconfined domain has been conducted. The work aims to
gain insight into the mixing and intermittency of turbulent coaxial jet
configurations. The coaxial jet considered has relatively high jet velocities
for both core and annular jets with an aspect ratio (core jet to annular jet) of
1.48. The computations resolved the temporal development of large-scale flow
structures by solving the transport equations for the spatially filtered mass,
momentum and passive scalar on a non-uniform Cartesian grid and employed the
localized dynamic Smagorinsky eddy viscosity as a sub-grid scale turbulence
model. The results for the time-averaged mean velocities, associated turbulence
fluctuations and mean passive scalar fields are presented. The initial inner and
outer potential cores and the shear layers established between two cores have
been resolved, together with the establishment of high turbulence regions
between the shear layers. The passive scalar fields developing from the core and
the bypass flow were found to exhibit differences at near and far field
locations. Probability density distributions of instantaneous mixture fraction
and velocity have been created from which intermittency has been calculated and
the development of intermittency from the probability density distributions for
instantaneous velocity follows similar variations as for the passive scalar
fields.
