Computation of strongly swirling axisymmetric free jets

Finite-difference computations have been performed for strongly swirling circular free jets operating at swirl numbers 1.18 and 1.3. These values are sufficiently high for recirculation to occur near the jet nozzle. The study focuses on the response of the computed flowfield to the introduction of swirl-related modifications into the k-epsilon model of turbulence, and to changes in the boundary conditions for the dissipation rate (epsilon) and the radial velocity (V) at the computational jet-inlet plane. It is shown that the inlet conditions for V and epsilon, usually considered of subordinate importance, play as crucial a role in achieving predictive accuracy as turbulence-modeling details. In particular, it is found that, with a realistic V distribution prescribed at the jet-inlet plane, satisfactory predictions can be obtained without any swirl-specific modifications to the k-epsilon model. While it is not argued that such modifications are generally redundant and inappropriate, it is suggested that any attempt to identify and rectify turbulence-model defects is bound to be frustrated unless comprehensive experimental data for all flow properties at the jet exit become available.