Three-dimensional interactions of a free jet with a perpendicular synthetic jet

Three-dimensional interaction of an axisymmetric free jet with a single synthetic jet that is oriented perpendicular to the free jet was investigated experimentally using PIV. The main objective was to investigate the effect of the upstream location of the synthetic jet, inside the nozzle of the main jet (Re-Ue = 6600). The interaction location of the synthetic jet (for a range of momentum coefficients) was varied from 0.4 to 1.4 orifice diameters upstream of the main jet exit plane. The synthetic jet was driven at a frequency of 1000 Hz, which corresponds to a Strouhal number of 0.16 (within the range of unstable modes of the free jet). To better explore the complex flow field resulting from the interaction, a reduction technique was used where 3D flow renderings were calculated from multiple 2D measurement planes. The interaction is affected by two mechanisms: (1) direct impact of the synthetic jet into the main jet, and (2) amplification of unstable modes of the main jet. When the momentum coefficient is increased, the synthetic jet penetrates deeper into the main jet flow creating larger streamwise vortical structures and increasing the main jet width. Increasing the distance between the synthetic jet exit and the main jet nozzle exit the effectiveness of the synthetic jet's impulse decreases, resulting in smaller jet vectoring, weaker streamwise vortical structures, and decreased turbulence levels. When compared to a continuous control jet of the same momentum coefficient and upstream location, the effects are significantly different.