A detailed numerical solution of the fluid flow patterns engendered by a synthetic jet has been carried out. The synthetic jet is caused by a reciprocating piston assembly which is attached to a large, stationary cavity. It was found that a significant momentum efflux is produced by the synthetic jet assembly. Also, fluid entrainment by the synthetic jet causes a coincident flow around the exterior of the cavity (selfinduced co-flow). Numerical solutions allow the investigation of the effect of reciprocation stroke length and piston speed on the resulting flow patterns and momentum flows. For all investigated cases, the contribution made by the co-flow to the momentum flowrate is found to be small. In order to account for the simultaneous existence of both laminar and turbulent regions, two numerical approaches were taken. One approach used the Shear Stress Transport (SST) turbulence model while the other used a newly devised transitional turbulence model. Of particular interest was a comparison between the predicted locations of the laminar-to-turbulent transition based on the two independent models. The excellent agreement between the two models reinforces the use of the SST model throughout the domain.