Flow Analysis of a Jet Emanating from a Flexible Membrane Nozzle Using Particle Image Velocimetry

Abstract

The study of flow control using pulsatile jets has been a prominent area of research in the recent years due to its many applications. The current study aims to study the near-field characteristics of flow field associated with an incompressible circular jet generated by a self oscillating flexible membrane nozzle. The jet was self-excited and produced a pulsatile flow due to the motion of the flexible membrane. The dynamic characteristics of the jet are studied using time-averaged and phase-locked 2D PIV measurements in different planes relative to the flexible membrane nozzle in an attempt to study the complex three dimensional features of the jet. As illustrated in Reference 1, two different kinds of flow could be excited depending on the tension applied to the flexible nozzle that is pointed as nozzle parameter or strain % (change in length/original length) of the flexible nozzle and mass flow through it. The first was a flapping mode that is related to the alternate shedding of vortices and the second was a symmetric mode that is related to the generation of counter rotating vortex pairs. The first mode initiates a strong steering of the jet to either side and turbulence was much larger in the measured plane for the first mode compare to the second mode. The experiments were conducted by attaching strings at the flexible nozzle’s exit to impart tension to the nozzle. This allows a certain length of the flexible nozzle upstream of the string location to conform flexibly to the jet. In the current study, focus has been on the three dimensionality of the jet in the near field of a symmetric mode. The formation of counter rotating vertical structures is symmetrical in the middle plane compared to the other planes as the flow is extremely sensitive to the initial conditions at the exit of the nozzle.