Effect of Strouhal Number and Stokes Number on the Flow Behaviour of an Axisymmetric Synthetic Jet: A Numerical Study

Abstract

Abstract The study focusses on the response of a round synthetic jet (SJ) towards the Strouhal number and Stokes number An SJ is formed by issuing a stream of fluid into a low momentum region with the help of an oscillating boundary. The nature of the jet can be controlled by controlling the actuation frequency and amplitude of oscillation, and these two operating parameters are associated with the Strouhal number (St) and Stokes number (S) of the jet respectively. These non-dimensional numbers play a significant role in the effective utilization of SJs in controlling the flow, and heat transfer. The purpose of this article is to numerically investigate the flow behaviour of an SJ issued into a quiescent medium based on these two non-dimensional parameters. For analysis, a two-dimensional axisymmetric SJ is modelled using a finite volume solver integrated with openFOAM. The oscillating boundary resembles the motion of a diaphragm, and deforming mesh is enforced in the flow domain. Range of parameters within which the jet is operated: St – 0.13 to 0.16, and S – 23 to 36. The study highlights the strength, and spreading of the SJ based on St and S. Effect of St and S on the mean jet parameters such as centreline velocity decay, jet half-width, jet momentum flux, and entrainment rate are studied in detail, which can enhance the idea of operating an SJ effectively for better heat transfer and flow control. Time evolution of saddle point, and mean jet centreline decay profiles suggest the spacing between the orifice and a heated plate to be maintained for effective heat transfer. The jet should be operated at a low Strouhal number and high Stokes number for better impingement on a heated plate to be cooled. Low Strouhal number should be maintained to get high-velocity output, which is desirable for better flow control. These results are useful for the effective utilization of SJs for heat transfer, flow control, and other similar applications.