Design Optimization of Micro Synthetic Jet Actuator for Flow Separation Control

2006 ◽  
Vol 128 (5) ◽  
pp. 1053-1062 ◽  
Author(s):  
Oktay Baysal ◽  
Mehti Köklü ◽  
Nurhak Erbaş
Keyword(s):  
Design Methodology ◽  
Moving Boundary ◽  
Stokes Equations ◽  
Wall Slip ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Recirculation Region ◽  
Flow Separation Control ◽  
Analysis And Design ◽  
Design Variables

A computational analysis and design methodology is presented for effective microflow control using synthetic jets. The membrane is modeled as a moving boundary to accurately compute the flow inside the jet cavity. Compressible Navier-Stokes equations are solved with boundary conditions for the wall slip and the temperature jump conditions encountered for a specific range of Knudsen numbers. For validation, microchannel flow and microfilter flow are successfully computed. Then, flow past a backward-facing step in a microchannel is considered. Analysis is coupled with a design methodology to improve the actuator effectiveness. The objective function is selected to be the square of the vorticity (enstrophy) integrated over a separated region. First, from a design of experiments study, orifice and actuator cavity widths are identified as the most effective design variables. Then, a response surface method is constructed to find the improved control of the flow. This optimization results in more than 83% reduction of the enstrophy of the recirculation region.

Effective Range of Micro and Synthetic Jets for Flow Control

2005 ◽  
Author(s):  
Mehti Koklu ◽  
Nurhak Erbas ◽  
Oktay Baysal
Keyword(s):  
Flow Control ◽  
Moving Boundary ◽  
Rarefied Gas ◽  
Oscillation Amplitude ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Rarefied Gas Flows ◽  
Design Variables ◽  
Primary Focus

Effectiveness of two-dimensional synthetic jet is studied using numerical simulations. A Navier-Stokes (NS) solver for moving and deforming meshes has been modified to investigate numerically the diaphragm-driven flow in and out of two synthetic jet cavity geometries. Compressible flow simulations are required for rarefied gas flows to accurately predict the micro flow field. The solver is modified to accommodate slip wall boundary condition proposed in literature for micro scale flow problems. The piezoelectric-driven diaphragm of the cavity is modeled in a realistic manner as a moving boundary to accurately compute the flow inside the jet cavity. The primary focus of the proposed paper will be on the analysis of the design space determined by the geometric and flow-type design variables that identify the effectiveness of the synthetic jet by means of the orifice jet velocity and local jet momentum rate. The design variables are the membrane oscillation frequency (f), membrane oscillation amplitude (A), orifice width (d), and membrane width (W). The present computations for jet discharging into quiescent medium reveal that these variables have determining effects on the flow control parameters, which are the jet exit velocity, local momentum rate, as well as vortex shedding from the orifice.

Computing Micro Synthetic Jet in Slip Regime With Moving Membrane

2002 ◽  
Author(s):  
A. Rustem Aslan ◽  
Oktay Baysal ◽  
Firat O. Edis
Keyword(s):  
Moving Boundary ◽  
Pressure Field ◽  
Wall Slip ◽  
Synthetic Jet ◽  
Navier Stokes ◽  
Rarefied Flows ◽  
Flow Simulations ◽  
Slip Regime ◽  
Velocity Magnitude ◽  
Primary Focus

A Navier-Stokes (NS) solver for moving and deforming meshes has been modified to investigate numerically the diaphragm-driven flow in and out of two synthetic jet cavity geometries. The piezoelectric-driven diaphragm of the cavity is modeled in a realistic manner as a moving boundary to accurately compute the flow inside the jet cavity. The primary focus of the present paper is to describe the effect of cavity geometry and the wall slip, resulting from the relatively larger Kn number flows associated with micro sized geometries, on the exit jet velocity magnitude. Compressible flow simulations are required for rarefied flows to accurately predict the pressure field. The present computations for the quiescent external flow condition reveal that cavity geometry and the wall slip has an increasing effect on the magnitude of the average jet exit velocity as well as vortex shedding from the orifice.

Computational Study of the Synthetic Jet on Separated Flow Over a Backward-Facing Step

2010 ◽  
Author(s):  
Koichi Okada ◽  
Kozo Fujii ◽  
Koji Miyaji ◽  
Akira Oyama ◽  
Taku Nonomura ◽  
...  
Keyword(s):  
Shear Layer ◽  
Reynolds Stress ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Frequency Characteristics ◽  
Synthetic Jet ◽  
Recirculation Region ◽  
Backward Facing Step ◽  
Freestream Velocity ◽  
Jet Control

Frequency effects of the synthetic jet on the flow field over a backward facing step are investigated using numerical analysis. Three-dimensional Navier-Stokes equations are solved. Implicit large-eddy simulation using high-order compact difference scheme is conducted. The present analysis is addressed on the frequency characteristics of the synthetic jet for understanding frequency characteristics and flow filed. Three cases are analyzed; the case computing flow over backward facing step without control, the case computing flow with synthetic jet control at F+h = 0.2, and the case computing flow with synthetic jet control at F+h = 2.0, where non-dimensional frequency F+h is normalized with the height of backward-facing step and the freestream velocity. The present computation shows that separation length in the case of the flow controlled at F+h = 0.2 is 20 percent shorter than the case without control. Strong two-dimensional vortices generated from the synthetic jet interact with the shear layer, which results in the increase of the Reynolds stress in the shear layer region. These vortices are deformed into three-dimensional structures, which make Reynolds stress stronger in the recirculation region. Size of the separation length in the case of the flow controlled at F+h = 2.0 is almost the same as the case without control because the mixing between the synthetic jet and the shear layer is not enhanced. Weak and short periodic vortices induced from the synthetic jet do not interacts with the shear layer very much and diffuse in the recirculation region.

Experimental and numerical studies of synthetic jets driven by a dual-diaphragm piezoelectric actuator

2009 ◽  
Vol 223 (6) ◽  
pp. 1393-1400 ◽  
Author(s):  
A-S Yang ◽  
J-J Ro ◽  
W-H Chang
Keyword(s):  
Moving Boundary ◽  
Active Flow Control ◽  
Vortex Pair ◽  
Ambient Air ◽  
Lateral Spreading ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Visualization System ◽  
Air Jet ◽  
Centre Line

The applications of piezoelectric synthetic jet actuators have shown great potential as active flow control devices. The objective of this study is to investigate the flow phenomenon of a synthetic jet generated by a dual-diaphragm piezo-driven actuator. In this analysis, the computational approach adopted unsteady three-dimensional conservation equations of mass and momentum for examining the development process of synthetic jets. The moving boundary was also treated to represent the motion of the piezo diaphragm. Experimentally, a flow visualization system was employed to acquire the particle-streak images scattered from red fluorescent spheres for observing the synthetic jet flow. The jet velocity along the centre-line was also measured by using a hot-wire anemometer. The system test results demonstrated a satisfactory functioning of the actuator for producing synthetic jets. The predictions were then compared with the visualized particle-streak images and the measured centre-line velocity of the synthetic jet to validate the computer software. In the near-field, both simulation results and experimental observations revealed the time-cyclical formation and advection of a vortex pair in a full sinusoidal actuation cycle at an operating frequency of 4 Hz. When the vortex pair travelled well downstream, the ambient air from the vicinity of the slot was entrained into the cavity of the actuator. However, the overall far-field flow pattern, characterized by longitudinal decay of the centre-line velocity and lateral spreading, resembled a conventional continuous air-jet in essence.

DETACHED-EDDY SIMULATION FOR SYNTHETIC JETS WITH MOVING BOUNDARIES

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1429-1434 ◽  
Author(s):  
HAO XIA ◽  
NING QIN
Keyword(s):  
Boundary Layers ◽  
Moving Boundary ◽  
Turbulent Boundary Layers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Moving Boundaries ◽  
Time Dependent ◽  
Jet Flows ◽  
Detached Eddy Simulation ◽  
Eddy Simulation

A Detached-Eddy Simulation (DES) with moving boundaries has been developed and applied to synthetic jet flows. Complex unsteady flow patterns of the flows were revealed from the simulation. Comparisons between the simulation and experiments showed reasonably good agreements, which indicates that, as a hybrid RANS/LES method, DES is capable of handling unsteady separations with turbulent boundary layers and time-dependent moving boundary conditions.

A New Class of Synthetic Jet Actuators—Part I: Design, Fabrication and Bench Top Characterization

2005 ◽  
Vol 127 (2) ◽  
pp. 367-376 ◽  
Author(s):  
J. L. Gilarranz ◽  
L. W. Traub ◽  
O. K. Rediniotis
Keyword(s):  
Flow Separation ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Separation Control ◽  
Synthetic Jet Actuators ◽  
New Class ◽  
Momentum Coefficient ◽  
Jet Actuators ◽  
In Series ◽  
Exit Slot

Although the potential of synthetic jets as flow separation control actuators has been demonstrated in the existing literature, there is a large gap between the synthetic jet actuators (SJA) used in laboratory demonstrations and the SJAs needed in realistic, full-scale applications, in terms of compactness, weight, efficiency, control authority and power density. In most cases, the SJAs used in demonstrations are either too large or too weak for realistic applications. In this work, we present the development of a new class of high-power synthetic jet actuators for realistic flow control applications. The operating principle of the actuator is the same as that of crankshaft driven piston engines, which makes a significant part of the technology necessary for the actuator development available off-the-shelf. The design of the actuator is modular and scalable. Several “building block” units can be stacked in series to create the actuator of the desired size. Moreover, active exit slot reconfiguration, in the form of variable exit slot width, decouples the actuator frequency from the actuator jet momentum coefficient and allows the user to set the two independently (within limits). Part I of this paper presents the design, fabrication and bench top characterization of the actuator. Several versions of the actuator were designed, built and tested, leading up to the development of a six-piston compact actuator that has a maximum power consumption of 1200 W (1.6 hp) and can produce (for the tested conditions) peak exit velocities as high as 124 m/s. In Part II, the actuator was housed in the interior of a NACA0015 profiled wing with a chord of 0.375 m (14.75 inches). The assembly’s performance in controlling flow separation was studied in the wind tunnel.

Separation Control of Axial Compressor Cascade by Fluidic-Based Excitations

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Xinqian Zheng ◽  
Yangjun Zhang ◽  
Weidong Xing ◽  
Junyue Zhang
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Separated Flow ◽  
Synthetic Jet ◽  
Separation Point ◽  
Navier Stokes ◽  
Separation Control ◽  
Compressor Cascade ◽  
Navier Stokes Equations ◽  
Flow Separation Control

Flow separation control was investigated on a compressor cascade using three types of fluidic-based excitations: steady suction, steady blowing, and synthetic jet. By solving unsteady Reynolds–averaged Navier–Stokes equations, the effect of excitation parameters (amplitude, angle, and location) on performance was addressed. The results show that the separated flow can be controlled by the fluidic-based actuators effectively and the time-averaged performance of the flow field can be improved remarkably. Generally, the improvement can be enhanced when the amplitude of excitation is increased. The optimal direction varies with each type of excitations and is related to physical mechanisms underlying the separation control. For two types of steady excitations, the most effective jet location is at a distance upstream of the time-averaged separation point and the synthetic jet is just at the separation point.

Convective Heat Transfer in an Impinging Synthetic Jet: A Numerical Investigation of a Canonical Geometry

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Luis A. Silva ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Stokes Equations ◽  
Heated Surface ◽  
Vortex Pair ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Scaling Analysis ◽  
Dependent Flow

Synthetic jets are generated by an equivalent inflow and outflow of fluid into a system. Even though such a jet creates no net mass flux, net positive momentum can be produced because the outflow momentum during the first half of the cycle is contained primarily in a vigorous vortex pair created at the orifice edges; whereas in the backstroke, the backflow momentum is weaker, despite the fact that mass is conserved. As a consequence of this, the approach can be potentially utilized for the impingement of a cooling fluid onto a heated surface. In previous studies, little attention has been given to the influence of the jet's origins; hence it has been difficult to find reproducible results that are independent of the jet apparatus or actuators utilized to create the jet. Furthermore, because of restrictions of the resonators used in typical actuators, previous investigations have not been able to independently isolate effects of jet frequency, amplitude, and Reynolds number. In the present study, a canonical geometry is presented, in order to study the flow and heat transfer of a purely oscillatory jet that is not influenced by the manner in which it is produced. The unsteady Navier–Stokes equations and the convection–diffusion equation were solved using a fully unsteady, two-dimensional finite volume approach in order to capture the complex time dependent flow field. A detailed analysis was performed on the correlation between the complex velocity field and the observed wall heat transfer. Scaling analysis of the governing equations was utilized to identify nondimensional groups and propose a correlation for the space-averaged and time-averaged Nusselt number. A fundamental frequency, in addition to the jet forcing frequency, was found, and was attributed to the coalescence of consecutive vortex pairs. In terms of time-averaged data, the merging of vortices led to lower heat transfer. Point to point correlations showed that the instantaneous local Nusselt number strongly correlates with the vertical velocity v although the spatial-temporal dependencies are not yet fully understood.

Computational Study of Frequency and Amplitude Effects on Separation Flow Control With the Synthetic Jet

2009 ◽  
Author(s):  
Koichi Okada ◽  
Kozo Fujii ◽  
Koji Miyaji
Keyword(s):  
Shear Layer ◽  
Reynolds Stress ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Frequency Characteristics ◽  
Synthetic Jet ◽  
Recirculation Region ◽  
Separation Flow ◽  
Control Case ◽  
Backward Facing Step

In order to investigate the frequency and amplitude effects of the synthetic jet on the flow field, numerical simulation is carried out. Even though the final objective of this study is to understand mechanism of separation control for various objects, streamline and bluff bodies, the configuration of backward-facing step is chosen as the first step because of the simplicity. Three-dimensional Navier-Stokes equations are solved. Implicit large eddy simulation using high-order compact difference scheme is applied. The present analysis is addressed on the frequency characteristics of the synthetic jet for understanding frequency characteristics and flow-filed. Three cases are selected, No-control, F+h = 0.2 and F+h = 2.0, where non-dimensional frequency F+h is normalized with the height of backward-facing step and the free stream velocity. The present computation shows that at F+h = 2.0, separation length is 20 percent shorter than the No-control case. Strong two-dimensional vortices generated from the synthetic jet interact with the shear layer, which results in the increase of the Reynolds stress in the shear layer region. These vortices are deformed into three-dimensional structures, which make Reynolds stress stronger in the recirculation region. At F+h = 2.0, size of the separation length is almost same as the No-control case because the mixing between the synthetic jet and the shear layer is not enhanced. Weak and short periodic vortices induced from the synthetic jet do not interacts with the shear layer very much and diffuse in the recirculation region.

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