Investigation of piezoelectrically generated synthetic jet flow

Abstract

The purpose of this paper is to investigate the compressible turbulent synthetic jet flow characteristics of a dual diaphragm piezoelectric actuator. Experimentally, a flow visualization system was established to obtain the particle streak images scattered from 10-Ǎm red fluorescent spheres for observing the synthetic jet flowfield produced by a dual diaphragm piezo actuator. The centerline velocity of the synthetic jet was also measured by using a hot-wire anemometry system. In the analysis, the computational approach adopted the transient three-dimensional conservation equations of mass and momentum with the moving boundary specified to represent the piezo diaphragm motion. The standard k-dž two-equation turbulent model was employed for turbulence closure. For the actuator operating at the frequency of 648 Hz, the particle streakline images in the cross-sectional plane visualized a turbulent jet flow pattern in the far-field area. The hot-wire anemometry data indicated that the measured centerline velocity of synthetic jets reached 3.8 m/s at y/d= 50. The predictions were compared with the visualized particle streak images and centerline velocity of the synthetic jet in order to validate the computer code. The numerical simulation revealed the time-periodic formation and advection of discrete vortex pairs. Caused by the outward movement of the piezo diaphragms, air near the orifice was entrained into the actuator cavity when the vortex pairs were sufficiently distant from the orifice.

Time-Mean Structure of Axisymmetric Synthetic Jets

“…One of the important new findings resultant from the comparison of the model and experiments was the discovery of discontinuity of the jet character. The change was found to take place at rather large relative axial distance X 1 /d -the data analysed in [2] indicated this to be at about X 1 /d ∼ 30, a distance larger than investigated in previous literature [13,17,25]. A hypothesis formulated in [2] considered this change to be associated with the final disappearance of the organised vortex rings and their role being replaced by differently behaving stochastic turbulence.…”

“…It uses data from three rather extensive experimental projects each consisting of several measurement runs, on the basis of which it is now possible to validate the model and to evaluate the numerical magnitudes of the factors used in the model. No similar database for synthetic jets being available in literature [13,17,22,23,24], the presented material provides, apart from validating the model, a unique information about this type of flow of considerable engineering importance.…”

Smart Actuation for Helicopter Rotorblades

“…The objective is to bring the separation point closer to the trailing-edge and therefore improve laminar flow over a larger portion of the airfoil [23]. Actuators for this application are placed inside a cavity which has a tiny opening [26] or a full slot perpendicular to the flow direction on the top part of the profile [67]. Figures 7 and 8 show these two types of synthetic jet actuator.…”

“…Research on flow control systems has considered piezoelectric diaphragms to deliver enough airflow speed for synthetic jets and achieve proper flow control [31,67].…”

Smart actuation mechanisms for helicopter blades : design case for a Mach-scaled model blade

“…The objective is to bring the separation point closer to the trailing edge and therefore improve flow over a larger portion of the aerofoil [44,45]. Actuators for this application are placed inside a cavity which has a tiny opening [46] or a full slot perpendicular to the flow direction on the top part of the blade [47]. Figures 1.8 and 1.9 show these two types of synthetic jet actuator.…”