2D numerical study of circular synthetic jets in quiescent flows

2005 ◽  
Vol 109 (1092) ◽  
pp. 89-97 ◽  
Author(s):  
H. Tang ◽  
S. Zhong
Keyword(s):  
Experimental Data ◽  
Numerical Study ◽  
Initial Study ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Neutral Position ◽  
Computational Results ◽  
Synthetic Jet Actuator ◽  
Field Velocity ◽  
Turbulent Models

Abstract2D numerical simulations of flows generated by a synthetic jet actuator with a circular orifice were conducted at two different diaphragm displacement settings, one representing a typical laminar case and the other a fully turbulent case. The flow in the cavity was included in the computation in order to provide more accurate predictions. A velocity boundary condition was applied at the neutral position of the diaphragm to account for its temporal deformation. Comparisons were made between the computational results and existing PIV and hot-wire data in terms of the time sequence of the velocity vector field, velocity variations in space and with time. It is found that computational results for the laminar case agree well with the experimental data. Four turbulent models were tested for the fully turbulent case. It was found that the predictions using the RNG κ-ε and Standard k-ε models were reasonably close to the experimental data. This initial study has produced some encouraging evidence for the capacity of FLUENT in simulating the key features of synthetic jets.

A Criterion for the Formation of Micro Synthetic Jets

2004 ◽  
Author(s):  
V. Timchenko ◽  
J. Reizes ◽  
E. Leonardi ◽  
G. de Vahl Davis
Keyword(s):  
Numerical Study ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Frequency Range ◽  
Jet Formation ◽  
Synthetic Jet Actuator ◽  
Computational Data ◽  
Flow Device ◽  
New Criterion

A synthetic jet actuator is a zero net mass flow device, which under appropriate conditions generates a continuous jet always directed away from the orifice. Because of limited experimental and computational data on micro-sized jets, there is a need for a criterion to determine the onset of the sustained jet regime. A numerical study of axisymmetric micro synthetic jets for a frequency range from 250 to 50,000 Hz, orifice diameters range from 20 to 200 μm, and Reynolds numbers from 6.5 to 35 has been performed in order to identify a general jet formation criterion. The parametric study has allowed us to develop a new criterion for the onset of micro synthetic jets with Stokes numbers less than 7.

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.

On the Modeling of a Rectangular Synthetic Jet

2008 ◽  
Author(s):  
Gopi Krishnan ◽  
Kamran Mohseni
Keyword(s):  
Kinematic Viscosity ◽  
Turbulent Jets ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Axial Distance ◽  
Periodic Excitation ◽  
Hot Wire ◽  
Laminar Jets ◽  
Field Velocity ◽  
Self Similar

The flow field of a rectangular synthetic jet is studied in this paper. It is known that synthetic jets exhibit similarities to continuous turbulent jets in that the far field velocity profile of synthetic jets displays self-similar behavior as well. In this paper we systematically model the a rectangular synthetic jet by applying the argument that synthetic jets can be described by the same equations used to describe continuous laminar jets, with the replacement of the kinematic viscosity of laminar flow, with the virtual kinematic viscosity obtained from the experiments on a synthetic jet. The virtual kinematic viscosity is obtained through experimental measurements of the time average velocity profiles using hot wire anemometry. The virtual kinematic viscosity of the synthetic jet under study was found to exceed that of a turbulent jet of equivalent momentum. The inherent periodic excitation of the synthetic is attributed to the increased virtual kinematic viscosity, which results in the faster spreading and increased entrainment observed in experiments. It is observed that the variation in the centerline velocity and jet width with axial distance, for various actuator stroke lengths collapse onto single curves when scaled appropriately.

scholarly journals NUMERICAL STUDY OF COOLING BY TANGENTIAL SYNTHETIC JET

2015 ◽  
Vol 14 (1) ◽  
pp. 47
Author(s):  
F. Munhoz ◽  
C. Y. Y. Lee ◽  
F. L. D. Alves
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Conventional Technique ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Jet Cooling ◽  
Processing Power ◽  
Equivalent Mass ◽  
Heated Element

Modern electronics are becoming more compact and with higher processing power, which translates into a demand for higher heat dissipation. Current electronic "coolers," which are based on the combination of fans and heat sinks, are becoming unable to provide sufficient heat dissipation since they rely primarily on generating large volumetric flowrates of air to achieve their results. As an alternative, synthetic jets are under consideration due to their known property to enhance turbulence and heat transfer. Synthetic jets are produced by the oscillation of a membrane in a sealed cavity equipped with an orifice. For this study, a numerical model of channel mounted with a heating element on one surface and a synthetic jet directed to blow along the wall was constructed on ANSYS CFX. Heat dissipation provided by the synthetic jet was analyzed with respect to changes in Reynolds number, pulsing frequency and placement of the heated element. Results were compared to a conventional technique represented by a steady channel flow of equivalent mass flow rate to the average flow induced by the synthetic jet. Results showed that the synthetic jet formed a thin layer of intense vorticity along the targeted surface with cooling greatly outperforming conventional techniques. Synthetic jet cooling was also determined to be most affected by jet velocity and Reynolds number while pulsing frequency and placement of the heated element were not as influential.

Effects of inlet and outlet boundary conditions on the flow field of synthetic jets

2016 ◽  
Vol 231 (2) ◽  
pp. 107-118 ◽  
Author(s):  
Farzad Bazdidi-Tehrani ◽  
Mohammad Hatami ◽  
Ahmad Abouata
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Vortex Rings ◽  
Mean Velocity ◽  
Synthetic Jet Actuator ◽  
Velocity Magnitude ◽  
Wall Boundary Conditions ◽  
Significant Difference

The present work provides the computations of unsteady 3D synthetic jet ejected into a quiescent ambient. The [Formula: see text] turbulence model is employed for numerical simulations of flow field and the problem is considered under incompressible and axisymmetric assumptions. The pressure-implicit with splitting of operators algorithm is used for coupling of continuity and momentum equations. In order to accurately simulate the synthetic jet actuator, the dynamic mesh method is employed to model the flow field. In different simulations, pressure inlet, pressure outlet and wall boundary conditions at the orifice outlet of the synthetic jet are investigated. Changes in the boundary conditions at the orifice outlet affect the flow field such that mean velocity magnitude is higher for unconfined synthetic jets than confined ones. Moreover, form of vortex rings is dissimilar for confined and unconfined jets. Also, the actuator is modelled with two types of inlet boundary conditions, namely, moving piston and moving diaphragm boundaries. Results show that they have no significant difference and can be used interchangeably.

An Experimental and Numerical Study of a Micro-Synthetic Jet in a Shallow Cavity

2008 ◽  
Author(s):  
Alexander Sinclair ◽  
Victoria Timchenko ◽  
John Reizes ◽  
Gary Rosengarten ◽  
Eddie Leonardi
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Numerical Results ◽  
Transfer Rates ◽  
Micro Scale ◽  
Shallow Cavity

By disrupting laminar flow, micro-scale synthetic jets have the potential to significantly increase mixing and heat transfer rates in micro-devices. Due to the difficulty involved in performing measurements on the micro-scale, few experimental studies of micro-synthetic jets exist. In this paper we describe instantaneous velocity fields obtained by μPIV measurements in the vicinity of a synthetic jet orifice 24 μm in diameter issuing into a confined geometry. Numerical results for a synthetic jet operating under similar conditions have been used to help validate and clarify the experimental results. Comparisons between the experimental and numerical results during the expulsion phase of the actuator cycle for a synthetic jet with a Reynolds number (based on maximum velocity), Re = 239 and Stokes number, S = 9, indicate there is good agreement, thereby demonstrating that the μPIV technique can be used successfully for future studies. Experimental difficulties encountered are presented and methods of overcoming them discussed.

Experimental Study on the Effect of Synthetic Jets on Flow Boiling Heat Transfer in Microchannels

2012 ◽  
Author(s):  
Ruixian Fang ◽  
Jamil Khan
Keyword(s):  
Heat Sink ◽  
Flow Boiling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Driving Voltage ◽  
Micro Channel ◽  
Two Phase ◽  
Synthetic Jet Actuator ◽  
Micro Channels ◽  
Boiling Flow

Two-phase flow instabilities in micro-channel exhibit pressure and temperature fluctuations with different frequencies and amplitudes. An active way to suppress the dynamic instabilities in the boiling micro-channels is to introduce synthetic jets into the channel fluid. Thus the bubbles can be condensed before they clog the channel and expand upstream causing flow reversal. The present work experimentally investigated the effect of synthetic jets on the suppression of flow boiling instabilities exhibited in a micro-channel heat sink. The heat sink is consisted of five parallel rectangular microchannels measured 500 μm wide, 500 μm deep each. An array of synthetic jets was placed right above the micro-channels with each channel corresponds to 8 jet orifices. The strength and frequency of the jets are controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. Tests were performed with synthetic jets operating at 80 Hz and 150 Hz respectively. It is found that the bubbles were effectively condensed inside the jet cavity. The boiling flow reversals were notably delayed by the synthetic jets. Meanwhile, the pressure fluctuation amplitudes were substantially reduced. Test results were analyzed and discussed in detail.

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