Numerical Research on the Jet-Mixing Mechanism of Convergent Nozzle Excited by a Fluidic Oscillator and an Air Tab

Unsteady numerical simulations, coupled with the SST (Shear Stress Transport) k-ω turbulence model, were conducted to study the mixing-enhancement characteristics of the excited jet generated by the fluidic oscillator and the air tab in a single channel convergent nozzle with an inlet total pressure of 140–200 kPa. Compared with the steady air-tab jet, the sweeping jet generated by the fluidic oscillator has roughly the same penetration in the main flow, but it can induce streamwise vortices and planar vortices of larger scale and longer duration, which is beneficial to enhance jet mixing efficiency in the range of 1.0 DN (DN represents the diameter of the main nozzle outlet) downstream from the main nozzle. When x > 1.0 DN, the jet mixing is mainly dominated by the shear layer between the main jet and the ambient. As the sweeping jet suppresses the expansion of the main jet, which reduces the contact area between the main jet and the ambient, its mixing efficiency is less than that of the air tab in this region. With the increasing inlet total pressure of the fluidic oscillator, the influence range of the sweeping jet is increased, but its mixing efficiency does not increase significantly. In general, the fluidic oscillator can use a small jet flow (<5%) to achieve a high mixing efficiency (i.e., 60% at x = 2.0 DN) at the expense of low total pressure loss (<2.3%), which indicates that it has good engineering applicability.