Investigation of flow characteristics and velocity fields of excited two parallel plane jets

Abstract

An experimental investigation was conducted to study the flow characteristics and velocity fields of excited two parallel plane jets. The experiments were carried out at a jet Reynolds number of 200. A loudspeaker system was used to create the jets pulsation and to vary the intensity of jet pulsations at a constant excitation frequency of 40 Hz. A hot-wire anemometer was used to measure the velocities of the jets as they exited. The flow patterns were visualized using a laser-light sheet technique combined with smoke flow visualization. The jet spread widths were determined from images taken with a long-exposure method using binary edge detection. A particle image velocimetry measurement technique was used to render the flow field behaviors of the parallel jets. The introduction of jet pulsation by the speaker led to the roll-up of coherent vortices along the shear layers of the jets. These vortices became more prominent as the intensity of jet pulsations increased. These coherent vortices broke apart into turbulent eddies, resulting in wider jet spread with higher pulsation intensities. Two counter-rotating vortices were detected at the jet exit. These vortices moved closer to the jet exits as the jet pulsation intensity was increased. The intensity of turbulence and the presence of vortices were both influenced by the magnitude of the jet pulsation. Greater jet pulsation led to higher turbulence levels, a more pronounced vorticity field, and a more efficient transfer of momentum, consequently enhancing the mixing process.