Direct computation of zero-net-mass-flux synthetic jets

Abstract

Axisymmetric direct numerical simulations (DNS) are performed to study the formation criterion and evolution of zero net mass-flux synthetic jets. Jet formation is defined by an oscillating streamwise jet centreline velocity, showing net momentum flux away from the orifice. This momentum flux away from the orifice takes the form of a series of vortical structures, often referred to as a vortex train. Modelling of the jet actuator consists of a modified oscillating velocity profile applied to a wall boundary. The jet issues into quiescent air, and the Reynolds numbers used vary from 85 < Re < 1000. Variations to the input simulation parameters are carried out in order to determine the overall effects on the flow field. From these results the conditions necessary for the formation of the synthetic jet along with the input parameters that provide an optimal jet output are deduced. Jet optimisation is defined by both the vortical strength and longevity of the vortex train as it travels downstream. This study examines both the vortical structures, the jet centreline velocities along with other external flow characteristics in order to deduce and visualise the effects of the input parameters on the jet performance. The results attained on altering the oscillation amplitude and frequency of the jet actuator are in good agreement with previous studies. Further details on the jet centreline velocity for all cases are also presented; along with a study on the effects on the vortical structures of altering the Reynolds number of the flow