scholarly journals Frequency Response of Synthetic Jets Emanating From an Array of Circular Orifices

2021 ◽  
Author(s):  
Nadim Arafa ◽  
Pierre Sullivan ◽  
Alis Ekmekci
Keyword(s):  
Frequency Response ◽  
Excitation Frequency ◽  
Acoustic Mode ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Mode Shapes ◽  
Long Span ◽  
Jet Actuators ◽  
The Mean ◽  
Jet Velocity

Abstract The effect of the excitation frequency of synthetic jet actuators on the mean jet velocity of synthetic jets issuing from an array of circular orifices is investigated experimentally. Herein, the focus is placed on an array of circular orifices, rather than a single orifice, as it brings the advantage of covering long-span airfoils. The array consists of 16 circular orifices, each having a diameter of 3.42 mm, distributed over a span of 300 mm. The jets are generated by the excitation of a single cavity via 16 piezoelectric elements. Localized velocity measurements at the exit of the orifices show that the mean jet velocity varies with the excitation frequency. Several distinct resonant peaks were observed in the frequency response. Acoustic simulations of the cavity showed that these peaks correspond to acoustic mode shapes of the cavity. Due to the high-aspect ratio of the cavity, several acoustic mode shapes exist in the excitation frequency range aside from the Helmholtz resonance frequency. Moreover, the mean jet velocity emanating from the array shows a variation from orifice to orifice, depending on the excited acoustic mode.

The performance of round synthetic jets in quiescent flow

2006 ◽  
Vol 110 (1108) ◽  
pp. 385-393 ◽  
Author(s):  
M. Jabbal ◽  
J. Wu ◽  
S. Zhong
Keyword(s):  
Near Field ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Stroke Length ◽  
Synthetic Jet Actuators ◽  
Macro Scale ◽  
Jet Actuators ◽  
The Impact

AbstractPIV measurements in the near-field region of a jet flow emanating from a round synthetic jet actuator into quiescent air were conducted over a range of operating conditions. The primary purpose of this work was to investigate the nature of synthetic jets at different operating conditions and to examine the jet flow parameters that dictate the behaviour of synthetic jet actuators. The effects of varying diaphragm displacement and oscillatory frequency for fixed actuator geometry were studied. It was observed that the characteristics of synthetic jets are largely determined by the Reynolds number and stroke length. An increase in the former is observed to increase the strength of consecutive vortex rings that compose a synthetic jet, whereas an increase in the latter results in an increase in relative vortex ring spacing and for further increases in stroke length, shedding of secondary vortices. Correlations were also made between the operating parameters and the performance parameters most effective for flow control and which therefore determine the impact of a synthetic jet on an external flow. Relations of time-averaged dimensionless mass flux, momentum flux and circulation with the jet flow conditions were established and found to widely support an analytical performance prediction model described in this paper. It is anticipated that the experimental data obtained in this study will also contribute towards providing a PIV database for macro-scale synthetic jet actuators.

Analytical and Experimental Investigation of Different Synthetic Jet Actuator Configurations

Aerospace ◽  
2004 ◽  
Author(s):  
Sandra Ugrina ◽  
Alison Flatau
Keyword(s):  
Resonant Frequency ◽  
Smart Materials ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Laser Vibrometer ◽  
Synthetic Jet Actuator ◽  
Exit Nozzle ◽  
Geometry Configuration ◽  
Jet Velocity ◽  
Constant Temperature Anemometer

The ultimate goal of this project is to actively control the flow over a micro air vehicle using smart materials. MAVs are a new type of aircraft operating at Reynolds numbers of about 50,000 that are one to two orders of magnitude lower than encountered in larger aircraft. The intention is to implement smart structures and couple them with fluids to improve the deteriorated aerodynamics of MAVs and help improve efficiency, stability and maneuverability of such vehicles. The actuators used in this work for artificially controlling the boundary layer are piezoelectrically driven synthetic jets. We theoretically investigated and predicted the behavior of the synthetic jet as we changed the geometry and material property parameters of the actuator. Analytical results were then compared to the results obtained from the experiments. It is crucial to be able to accurately design a strong unimorph to be implemented as an active component of a synthetic jet actuator and design the geometry configuration of the cavity that will best couple with the chosen membrane. A condenser microphone, a constant temperature anemometer (CTA) and a laser vibrometer were used to quantify actuator performance. It was observed that the size of the cavity and the size and shape of the exit nozzle were related and the performance of the actuator increased when the structure was tuned such that the resonant frequency of the diaphragm and that of the cavity were close to matching. A square unimorph made of PZT-5H and bonded to a 0.20- mm brass shim maximized jet velocity for the actuators studied. Optimum direction of change in the volume and the dimensions of the nozzle will strongly depend on the resonant frequency of the membrane in use. In this situation, increasing either the volume of the cavity or the thickness of the nozzle made the two frequencies move away from each other producing reduction in jet velocity. Increasing the area of the nozzle, made the structure behave more as needed and was taken as a key parameter for tuning the base geometry of the device.

THE MECHANISM OF JET VECTORING USING SYNTHETIC JET ACTUATORS

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1619-1622 ◽  
Author(s):  
ZHEN-BING LUO ◽  
ZHI-XUN XIA
Keyword(s):  
Static Pressure ◽  
Deflection Angle ◽  
Control Mechanism ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Control Mechanisms ◽  
Synthetic Jet Actuator ◽  
Synthetic Jet Actuators ◽  
Jet Actuators ◽  
Main Factors

The control mechanism of jet vectoring using synthetic jet actuators is investigated. The final deflection angle of the primary jet is a result of the primary jet controlled by synthetic jets at three different regions. The lower static pressure near the primary jet exit induced by the synthetic jet, the entrainment and absorption of the primary jet fluid by the synthetic jet during the blowing and the suction stroke, the coupling and interaction between the vortices of synthetic jet and the shear layer of the primary jet are the main control mechanisms for the synthetic jet actuator vectoring a primary jet. The main factors influencing jet vectoring are analyzed and summarized, and a preparatory model for jet vectoring using synthetic jet actuator is presented.

Accuracy Investigation of Active Flow Control Using Synthetic Jets

2015 ◽  
Vol 741 ◽  
pp. 475-480
Author(s):  
Na Gao ◽  
Chen Pu ◽  
Bao Chen
Keyword(s):  
Flow Control ◽  
Velocity Distribution ◽  
Active Flow Control ◽  
Flow Fields ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Experimental Results ◽  
Center Line ◽  
Mean Velocity ◽  
The Mean

2nd order implicit format is implemented in the Navier-Stokes code to deal with instantaneous item unsteady flows. Three simulations are made to testify the method on flow control. First, the external flow fields of synthetic jets are simulated, the mean velocity on the center line, the jet width and velocity distribution are compared well with experimental results. Secondly, the flow fields of synthetic jet in a crossflow are simulated, orifice slot, the mean velocity on the center line and velocity distribution are compared well with experimental results. Finally, the flow control experiments on separation of airfoil are simulated, control methods include steady suction and synthetic jets. Both methods show their ability to favorably effect the flow separation, shortening the length of separation bubble and improving the pressure levels in separation areas in different degrees.

Examination of a Variable-Diameter Synthetic Jet

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Spencer O. Albright ◽  
Stephen A. Solovitz
Keyword(s):  
Particle Image Velocimetry ◽  
Vortex Ring ◽  
Mass Flux ◽  
Particle Image ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Variable Diameter ◽  
Constant Diameter ◽  
Image Velocimetry ◽  
Jet Actuators

Synthetic jet actuators are used to produce net axial momentum flow without net mass flux. Through strategic application, such devices can be used for flow control, propulsive thrust, and cooling. A novel application uses a variable-diameter orifice to constrict the exiting flow, and the motion can be synchronized with the pulse of the jet. This device is examined using phase-locked particle image velocimetry (PIV), permitting investigation of the flow fields and momentum flow. When compared to fixed-diameter synthetic jets, the variable-diameter actuator produces a larger vortex ring that lingers nearer the aperture. In addition, the experiments show increased momentum when the aperture is contracted in phase with the pulsing jet, with peak levels more than twice that of a constant-diameter jet.

Flow characteristics of two-dimensional synthetic jets under diaphragm resonance excitation

2019 ◽  
Vol 91 (4) ◽  
pp. 575-581 ◽  
Author(s):  
Chi-Yu Lin ◽  
Jih Lung Lin
Keyword(s):  
Flow Field ◽  
Flow Characteristics ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Hot Wire ◽  
Content Type ◽  
Velocity Response ◽  
The Mean ◽  
Excitation Waveform ◽  
40 Hz

Purpose This paper aims to experimentally study the external flow characteristic of an isolated two-dimensional synthetic jet actuator undergoing diaphragm resonance. Design/methodology/approach The resonance frequency of the diaphragm (40 Hz) depends on the excitation mechanism in the actuator, whereas it is independent of cavity geometry, excitation waveform and excitation voltage. The velocity response of the synthetic jet is influenced by excitation voltage rather than excitation waveform. Thus, this investigation selected four different voltages (5, 10, 15 and 20 V) under the same sine waveform as experiment parameters. Findings The velocity field along the downstream direction is classified into five regions, which can be obtained by hot-wire measurement. The first region refers to an area in which flow moves from within the cavity to the exit of orifice through the oscillation of the diaphragm, but prior to the formation of the vortex of a synthetic jet. In this region, two characteristic frequencies exist at 20 and 40 Hz in the flow field. The second region refers to the area in which the vortices of a synthetic jet fully develop following their initial formation. In this region, the characteristic frequencies at 20 and 40 Hz still occur in the flow field. The third region refers to the area in which both fully developed vortices continue traveling downstream. It is difficult to obtain the characteristic frequency in this flow field, because the mean center velocities (ū) decay downstream and are proportional to (x/w)−1/2 for the four excitation voltages. The fourth region reveals variations in both vortices as they merge into a single vortex. The mean center velocities (ū) are approximately proportional to (x/w)0 in this region for the four excitation voltages. A fifth region deals with variations in the vortex of a synthetic jet after both vortices merge into one, in which the mean center velocities (ū) are approximately proportional to (x/w)−1 in this region for the four excitation voltages (x/w is the dimensionless streamwise distance). Originality/value Although the flow characteristics of synthetic jets had reported for flow control in some literatures, variations of flow structure for synthetic jets are still not studied under the excitation of diaphragm resonance. This paper showed some novel results that our velocity response results obtained by hot-wire measurement along the downstream direction compared with flow visualization resulted in the classification of five regions under the excitation of diaphragm resonance. In the future, it makes valuable contributions for experimental findings to provide researchers with further development of flow control.

Compressibility Effects in Micro Synthetic Jets

2004 ◽  
Author(s):  
Victoria Timchenko ◽  
John Reizes ◽  
Eddie Leonardi
Keyword(s):  
Compressible Flows ◽  
Incompressible Flows ◽  
Pressure Rise ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Synthetic Jet Actuators ◽  
Jet Actuators ◽  
The Face ◽  
Compressibility Effects ◽  
Numerical Modeling Of Flows

Effects of including compressibility in the numerical modeling of flows produced by and in synthetic jet actuators — consisting of an oscillating diaphragm in a cavity with a small circular orifice in the face opposite the diaphragm — has been studied for axisymmetric configurations. Numerical results obtained on the assumption of incompressible and compressible flows with orifice diameters of the 20 and 40 μm and with an orifice length of 50 μm are compared. There are significant differences between compressible and incompressible flows for the 20 μm orifice, in that the jet velocity is greatly reduced when compressible flow is assumed, whereas the differences are much smaller in the 40 μm case. For both orifices the pressure rise upstream of the orifice is smaller when the fluid is compressible. It follows that results obtained on the assumption of incompressible flow cannot be extrapolated for micro-synthetic jet actuators handling compressible fluids.

Experimental Study of the Incidence of Changing a Synthetic Jet Orifice in Heat Transfer Using a Taguchi Method Approach

2019 ◽  
Vol 11 (3) ◽  
Author(s):  
Juan Sebastian Cano ◽  
Gustavo David Cordova ◽  
Christian Narvaez ◽  
Luis Segura ◽  
Luis Carrion
Keyword(s):  
Heat Transfer ◽  
Steel Plate ◽  
Excitation Frequency ◽  
Acoustic Resonance ◽  
Synthetic Jet ◽  
Cooling Time ◽  
Coefficient Of Performance ◽  
Resonant Frequencies ◽  
Jet Velocity ◽  
Method Approach

The current study allows the recognition of the most optimal combination of excitation frequency, kind of orifice, and synthetic jet-to-surface spacing in order to obtain the fastest cooling time using a Taguchi experimental design. To this end, the heat transfer and synthetic jet velocity behavior using different kinds of orifices are obtained experimentally. A piezoelectric diaphragm has been selected as a vibrating actuator. Four kinds of orifices have been studied: circular, rectangular, triangular, and square. First, the study consists of recognizing the excitation frequency in which each orifice produces the highest flow velocity. A hotwire anemometer has been used in order to measure the synthetic jet velocity. Additionally, a steel plate has been heated and then cooled using the synthetic jet set at the excitation frequency in which the jet velocity was the largest for each orifice. For the statistical analysis, the input study variables are the type of orifice and jet-to-surface spacing. The output variable has been the cooling time. The results show that using a combination of a rectangle orifice, 20 mm of jet-to-surface spacing and an excitation frequency of 2000 Hz, it is obtained the fastest cooling time. In addition, using these parameters, a mean heat transfer coefficient of 11.05 (W/m2K) with a coefficient of performance (COP) of 49.21 has been obtained. Finally, for each kind of orifice, there is the presence of two resonant frequencies, the Helmholtz (acoustic resonance) frequency and piezoelectric diaphragm natural frequency.

Vortex Shedding Control on a Three-Dimensional Ground Vehicle With Synthetic Jets

2016 ◽  
Author(s):  
Wenshi Cui ◽  
Zhigang Yang ◽  
Guojun Wang ◽  
Hua Zhou
Keyword(s):  
Vortex Shedding ◽  
Excitation Frequency ◽  
Three Dimensional ◽  
Synthetic Jet ◽  
Space Distribution ◽  
Ground Vehicle ◽  
Synthetic Jet Actuators ◽  
Synchronization Phenomenon ◽  
Momentum Coefficient ◽  
Jet Actuators

The study is mainly focused on the influence of the vortex shedding control of a three-dimensional ground vehicle by using synthetic jet actuators based on Large-eddy simulation. Excitation parameters for synthetic jet actuators, such as the excitation frequency, momentum coefficient and jet location, have an influence on vortex shedding control process, which lead to different unsteady flow phenomenon, vortex shedding frequency value and space distribution in the wake. Vortex shedding suppression and vortex-synchronization phenomenon have an influence on the pressure. Under present momentum coefficient, the excitation frequency plays an important role in the occurrence of vortex-synchronization phenomenon behind vertical base. As the momentum coefficient increase, the vortex-synchronization zone expands.

Pressure Loading of Piezo Composite Unimorphs

2005 ◽  
Vol 888 ◽  
Author(s):  
Poorna Mane ◽  
Karla Mossi ◽  
Robert Bryant
Keyword(s):  
Active Flow Control ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Synthetic Jet Actuator ◽  
Active Pressure ◽  
Average Maximum ◽  
Non Local ◽  
Jet Velocity ◽  
Active Flow ◽  
Jet Velocities

ABSTRACTOver the past decade synthetic jets have emerged as a promising means of active flow control. They have the ability to introduce small amounts of energy locally to achieve non-local changes in the flow field. These devices have the potential of saving millions of dollars by increasing the efficiency and simplifying fluid related systems. A synthetic jet actuator consists of a cavity with an oscillating diaphragm. As the diaphragm oscillates, jets are formed through an orifice in the cavity. This paper focuses on piezoelectric synthetic jets formed using two types of active diaphragms, Thunder® and Lipca. Thunder® is composed of three layers; two metal layers, with a PZT-5A layer in between, bonded with a polyimide adhesive. Lipca is a Light WeIght Piezo Composite Actuator, formed of a number of carbon fiber prepreg layers and an active PZT-5A layer. As these diaphragms oscillate, pressure differences within the cavity as well as average maximum jet velocities are measured. These parameters are measured under load and no-load conditions by controlling pressure at the back of the actuator or the passive cavity. Results show that the average maximum jet velocities measured at the exit of the active cavity, follow a similar trend to the active pressures for both devices. Active pressure and jet velocity increase with passive pressure to a maximum, and then decrease. Active pressure and the jet velocity peaked at the same passive cavity pressure of 18kPa for both diaphragms indicating that the same level of pre-stresses is present in both actuators even though Lipca produces approximately 10% higher velocities than Thunder®.

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