Array Of Synthetic Jet Actuators Research Articles

Experimental investigation of synthetic jet control of wing rock for a flying wing aircraft

Flying wing aircraft easily experience wing rock due to the lack of lateral-directional stability, which causes serious challenges to flight control and safety. Thus, it is necessary to reduce the wing rock amplitude or reduce the mean roll angle by additional control. For a flying wing model with a 65° leading-edge sweep, we propose a strategy using an array of synthetic jet actuators to control the wing rock. The control effect and mechanism are studied by attitude measurement and particle image velocimetry measurement in a wind tunnel; the results confirm that the synthetic jet can effectively change the trim position of the wing rock. The control effect is affected by the angle of attack, Reynolds number, actuation position, actuation voltage, and frequency. In general, downstream actuators perform better at low angles of attack, while upstream actuators perform better at high angles of attack; the actuators positioned at the downward rolling side have a better effect than those positioned at the upward side. Furthermore, continuously variable control of the trim position can be achieved by changing the actuation voltage or modulation frequency, which provides a base for attitude manipulation by using active flow control instead of a mechanical control surface. Quantitative analysis of the flow field indicates that the leading-edge vortex on the upward side provides a rolling moment, while the recirculation zone on the downward side also contributes to the wing rock. This is a dynamic process, causing the flying wing to balance at a nonzero mean roll angle. The synthetic jet positioned at the downward rolling side can transport high-momentum fluids to the near-wall region, thereby suppressing flow separation and reducing the size of the recirculation zone. This enhances the lift on the control side and thus reduces the mean roll angle of the wing rock.

Numerical study of flow separation control over a circular hump using synthetic jet actuators

This study deals with the wall resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation of boundary layer flow separation over a circular hump model and its active control. An array of Synthetic Jet Actuators (SJAs) is implemented in the hump model to introduce a train of vortex rings into the boundary layer to control flow separation. The OpenFOAM solver is used to numerically simulate and analyze the fluid flow using the k–ω shear stress transport model. Hot wire anemometry and particle image velocimetry measurements are carried out to evaluate the accuracy of the URANS technique as well as the effectiveness of SJAs by comparing numerical predictions to experimental data. The time-averaged results are in a good agreement with experimental results and demonstrate a successful application of SJAs to delay the flow separation by the interactions of vortical structures with the separated shear flow. The three-dimensional simulation also reveals that near wall coherent flow structures (streamwise and spanwise vortices) are responsible for the wall shear stress components. The results can be used to better understand the performance of SJAs and to further improve future actuator configurations.

Application of synthetic jet arrays for flow separation control on a circular “hump” model

This research investigates the effectiveness of a spanwise array of synthetic jet actuator (SJA) for the control of boundary layer separation over a circular “hump” model. The influence of geometrical and operational parameters – including actuator position, velocity ratio (i.e., the ratio of the peak exit jet velocity of actuators to the freestream velocity of cross flow, VR) and the actuation waveform – on the flow separation control are investigated using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. The effect of the position of SJA array on flow separation control has been studied experimentally over a considerable length of the hump chord (from the “apex” of the model to near the “trailing edge”) for the first time. The investigation looks in more detail into the mechanisms behind the alleviation of adverse pressure gradient as a key factor controlling the flow separation. The investigation of the effect of VR on the performance of SJAs shows the importance of the momentum injection in the mitigation of the momentum deficiency as another important factor in turbulent boundary layer flow separation. A holistic overview of the control parameters allowed to reveal a considerable change in the separation flow patterns. The results show that the best performance of SJA array from the viewpoint of separation control occurs at the velocity ratio of 1.85 with a reduction of the length of recirculation region of around 42.6 and 44.2% by using sine and square waves excitation of SJAs, respectively.

Experimental Study of a NACA0015 Circulation Control Airfoil Using Synthetic Jet Actuation

Wind tunnel testing is conducted on a NACA0015 airfoil with a rounded trailing edge, known as a circulation control airfoil, at the chord Reynolds number of and at the angles of attack of 0–15°. An array of synthetic jet actuators is installed next to the rounded trailing edge to produce synthetic jet at the excitation frequency range of 150–600 Hz and the momentum coefficient range of 0.00021–0.0134 across the airfoil span length. For the circulation control airfoil at prestall angles of attack, the current study suggested that the reduced excitation frequency of a synthetic jet should approximately be on an order of the Strouhal number based on the diameter of the Coanda surface to achieve optimal lift augmentation.

Experimental research on the shock wave control based on one power supply driven plasma synthetic jet actuator array

The interaction between a ramp induced shock wave and a plasma synthetic jet actuator (PSJA) array was experimentally investigated using high-speed schlieren imaging technique. The PSJA array consisting of 10 actuators was driven by only one power supply. To enhance the actuation intensity, the actuators were located along the streamwise direction to form an accumulation effect. Experimental results showed that the plasma synthetic jet can penetrate into the supersonic flow field with a depth of more than 10 mm. Both the induced shock and the controlling gas bulbs generated by PSJA array can affect the shock wave. The separation shock wave bifurcates when interacting with the shock induced by the actuator. The foot portion of the separation shock wave disappeared when the controlling gas bulbs passed through the interaction region. What's more, as the actuators were located in streamwise direction, the controlling gas bulbs were completely emerged as a much larger gas bulb. As a result, the effective control time was longer than the single actuator and the control effect is also much better.

Effect of Synthetic Jets Spacing on Flow Separation over Swept, Flapped Airfoils

An experimental study was performed on flow field interactions and aerodynamic performance enhancement due to the activation of an array of synthetic jet actuators on a swept, flapped, modified NACA 0012 airfoil model at two angles of attack (0° and 5°) and two control surface deflection angles (20° and 30°) at a chord-based Reynolds number of 720,000 and sweep angle of 20°. The focus was on understanding the mechanisms for separation reduction and lift enhancement due to the application of the flow control. Activating all the jets resulted in up to increase in the sectional lift, which was measured via an array of surface-mounted pressure ports. Stereoscopic particle image velocimetry revealed the presence of trains of pinched, skewed vortical rings that were created by the synthetic jets and that caused flow reattachment over the control surface. The characteristics of the train of these vortical rings varied with the spacing between active jets, where smaller spacing resulted in the largest modification to the flow field. The proposed mechanisms for separation reduction in a swept cross flow via pinched vortex rings are discussed, revealing further potential for how to leverage synthetic jets for separation postponement and lift enhancement over control surfaces.

Experimental characteristics of a two-electrode plasma synthetic jet actuator array in serial

Plasma Synthetic Jet (PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a two-electrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial, the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.

Computational Evaluation of Flow Control for Enhanced Control Authority of a Vertical Tail

A computational method for predicting the aerodynamic performance of a vertical tail due to active flow control has been developed. Enhanced directional control using flow-control technology can potentially result in reduced fuel consumption and improved airplane performance. The numerical method is based on the unsteady Reynolds-averaged Navier–Stokes formulation for overset grid systems. The flow control is modeled for an array of synthetic jet actuators mounted at the trailing edge of the stabilizer. Results of the validation for various flow conditions, actuation parameters, and port layouts are used to establish the accuracy of the numerical tool. The side-force increments on the tail due to flow control at various sideslip conditions are presented. Sensitivities to flow-control layouts, especially with respect to spanwise flow development, are also investigated. A practical approach to facilitate preliminary evaluations of active flow control with quick computational turnaround is proposed. It is shown that constant actuation can be used as proxy for predicting the effects of the unsteady actuation from synthetic jets. Its confirmation in the context of the current application has been invaluable for developing practical flow-control implementations. Aspects of integration are presented, and guidelines for preferred modes of actuation are put forth.

Load control on a dynamically pitching finite span wind turbine blade using synthetic jets

AbstractThe feasibility of active flow control, via arrays of synthetic jet actuators, to mitigate hysteresis was investigated experimentally on a dynamically pitching finite span S809 blade. In the present work, a six‐component load cell was used to measure the unsteady lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch and to correlate these effects with the forces and moment measurements. It was shown that active flow control could significantly reduce the hysteresis in lift, drag and pitching moment coefficients during dynamic pitching conditions. This effect was further enhanced when the synthetic jets were pulsed modulated. Furthermore, additional reduction in the unsteady load oscillations can be observed in post‐stall conditions during dynamic motions. This reduction in the unsteady aerodynamic loading can potentially lead to prolonged life of wind turbine blades. Copyright © 2014 John Wiley & Sons, Ltd.

On the use of synthetic jet actuator arrays for active flow separation control

Present study highlights the flow control effectiveness of newly designed synthetic–jet–actuator (SJA) arrays placed at 23% and 43% of the chord from the leading edge of a low-speed wing model. First, the characteristics of a single SJA were investigated under the quiescent-flow condition. It was found that the jet velocity attains a peak between 400Hz and 500Hz, which corresponds to the SJA’s Helmholtz resonance frequency. The SJA arrays were then implemented on the wing model and investigated under the cross-flow condition. Both force balance and hot-wire measurements showed that the SJA arrays are able to effectively delay the flow separation and hence improve the aerodynamic performance of the wing model. The highest improvement in the lift coefficient is 27.4% and the average reduction in the drag coefficient is 19.6%. It was also found that the front (upstream) SJA array is more effective than its rear (downstream) counterpart. Tomographic-PIV measurements were also performed to unravel the three-dimensional flow details over the suction surface of the wing model with and without the SJA actuation. The time-averaged results showed that the introduction of synthetic jets substantially changes the flow structures of the separated shear layer, brings the outer high-momentum flow into the near-wall region, and delays the flow separation. In the end, the power consumption of a single SJA array was measured and found to be less than 5W.

Investigation of Phasing on Synthetic Jet Actuator Arrays

Unsteady computations of laminar flow have been performed for two-dimensional configurations of micro-channel equipped with two synthetic jets. The effect of phasing has been investigated at in-phase and 180̊ out-of-phase of the synthetic jet actuators at a fixed operating frequency and oscillating amplitudes. It was shown that the 180̊ out-of-phase configuration of the synthetic jets promotes better and more continuous flow mixing within the channel during the oscillation. This was due to the discrete pattern of vortex forming which disrupts the main channel flow. The 180̊ out-of-phase jet configuration exhibits higher cooling performance compared to the in-phase jet configuration in terms of the reduction in the maximum temperature in the silicon wafer.

Performance recovery of a thick turbulent airfoil using a distributed closed-loop flow control system

This paper describes an experimental study aimed at controlling the performance of a thick airfoil, typical to the root section of a wind turbine blade. The main purpose is recovering decreased performance due to degraded surface quality, leading to decreased lift and increased drag. Since wind turbines are designed to operate for decades, the blades’ surface quality degradation due to environmental effects is unavoidable. This process promotes early transition to turbulent flow, leading to premature boundary layer separation in the post-transitional regime. In addition, non-uniform and unsteady wind speeds cause dynamic loads on the blade and on the overall turbine structure. Controlling unsteady and non-uniform loads by changing the blades’ (or its cross-section) performance will allow building larger, lighter and more durable to aging wind turbines. Active flow control (AFC) is a possible remedy to boundary layer separation, including rough surface effects. Currently, three arrays of synthetic jet actuators are controlled based on state estimation provided by feedback from hot-film and pressure sensors. The unsteady pressure sensors’ data are used to estimate the lift while the unsteady and un-calibrated hot-films data are used to determine the flow separation location and define the relative magnitude of actuation imparted by each of the three actuator rows. The aerodynamic results demonstrate that the “clean” turbine blade performance, with lift-based controller, is recovered by the closed-loop active flow control system at Reynolds numbers around half a million and excitation at Strouhal numbers larger than 10. The total closed-loop AFC system energy efficiency was measured and shown to increase by up to 60 % compared to the airfoil with degraded surface quality. The current results indicate the potential of a closed-loop AFC system to provide significant increase in the net energy harvesting capability of a wind turbine blade with degraded surface quality over a wide range of incidence angles and Reynolds numbers.

Hybrid Liquid Immersion and Synthetic Jet Heat Sink for Cooling 3-D Stacked Electronics

This paper focuses on the design and parametric numerical study of a hybrid heat sink combining a liquid thermal interface with an array of synthetic jet actuators for 3-D chip stack cooling. The air-side heat sink exploits enhanced localized heat transfer achieved via a central array of synthetic jet actuators. The key focus of this paper is the numerical simulation of the dielectric liquid interface used to efficiently transmit the heat from the high-power 3-D stacked electronics to the hybrid heat sink base. The coupled natural convection in the fluid and conduction in solid spreaders sandwiched between the tiers of the stack form a novel efficient, passive, and scalable thermal management solution for 3-D stacked die structures. It is shown that this heat sink with a footprint of 76-mm square × 51-mm height can dissipate a total of 41 W of heat/power from the stack for a 44°C average chip temperature rise above ambient (an Rja of ~ 1.06 K/W obtained passively).

Development of design methodology for a synthetic jet actuator array for flow separation control applications

This article documents the development of synthetic jet actuator array hardware to augment high-lift system effectiveness in a wind tunnel model. The study involved the design, manufacture and bench test of a synthetic jet actuator array based on an inclined actuator configuration to reduce volume installation requirements without a loss in jet velocity relative to a non-inclined baseline model; incorporation of proper synthetic jet actuator systems wiring and internal synthetic jet actuator chamber pressure-sensing for actuator health monitoring. The peak velocity obtained from the inclined synthetic jet actuator array was 100 m/s, which favourably compares to the baseline array (∼90 m/s), while reducing the usable depth requirements by 50%. The final outcome of this study has been to apply the design lessons learned to develop a methodology for designing a synthetic jet actuator array with the constraints of using piezoelectric-based actuator technology for flow separation control applications.

Active Vibration Control of a Wind Turbine Blade Using Synthetic Jets

Active vibration control via an array of synthetic jet actuators was investigated experimentally in a wind tunnel. Using synthetic jets the flow over a small scale S809 finite wind turbine blade was controlled, resulting in reduction of the blade's structural vibrations. The effectiveness of the synthetic jets was explored for a range of post-stall angles of attack at Reynolds numbers between 7.1 × 104 and 2.38 × 105. The blade vibrations were measured and quantified using a pair of strain gauges mounted at the root of the model. Using flow control, significant vibration reduction was observed for some post-stall angles of attack. A correlation between vibration reduction and the degree of flow reattachment, measured using Particle Image Velocimetry, was found.

Active Flow Control at Low Angles of Attack: Stingray Unmanned Aerial Vehicle

Active flow control using fluidic actuators, via arrays of synthetic jet actuators, was used to provide control power for the Stingray unmanned aerial vehicle in the longitudinal (pitch) and lateral (roll) directions at low angles of attack. Using this technique, the pitch and roll moments were altered such that the effect is similar to that of a deflection of conventional control effectors. The control effectiveness of the synthetic jets on the aerodynamic performance of the Stingray unmanned aerial vehicle was investigated experimentally in a wind tunnel. Global flow measurements were conducted, where the moments and forces on the vehicle were measured using a six-component sting balance. The effect of the actuation was also examined on the surface static pressure at two spanwise locations. In addition, a particle image velocimetry technique was used to quantify the flowfield over the model, both the global flowfield as well as the localized interaction domain near the synthetic jet orifice. The synthetic jets were able to alter the local streamlines and displace the boundary layer through the formation of a small quasi-steady interaction region on the suction surface of the Stingray unmanned aerial vehicle's wing. Phase-locked particle image velocimetry data were acquired to provide insight into the growth, propagation, and decay of the synthetic jets impulse and their interaction with the crossflow. Furthermore, the changes induced on the moments and forces can be proportionally controlled by either changing the momentum coefficient or by driving the synthetic jets with a pulse modulation waveform. This can lead the way for future development of closed-loop control models.

Active Flow Control on the Stingray Uninhabited Air Vehicle: Transient Behaviour

The application of leading-edge separation control on an uninhabited air vehicle (UAV) with 50-deg leading-edge sweep is investigated experimentally in a full-scale close-return wind tunnel using arrays of synthetic jet actuators. Active flow control is used to enhance vehicle control at moderate and high angles of attack for takeoff and landing activities or gust load alleviation. The surface-mounted synthetic jet actuators are operated in various waveforms where the carrier frequency is at least an order of magnitude higher than the characteristic shedding frequency of the UAV. Actuation yields a suction peak near the leading edge, however, while excitation with a sinusoidal waveform results in a sharp suction peak near the leading edge; pulse modulation yields a larger and wider suction peak. The flow transients associated with controlled reattachment and separation of the flow over the UAV are investigated using amplitude modulation of the actuation waveform by measuring the dynamic surface pressure at different locations on the upper surface of the UAV’s wing. Phase-locked measurements show that the transients, associated with the onset of reattachment and separation, at high angles of attack are accompanied by the shedding of large-scale vortical structures and oscillations of the surface pressure. However, no oscillations are observed when the baseline flow is attached.

Separation Control in Duct Flows

Active control of separation in a duct flow is achieved using an array of fluidic actuators based on synthetic-jet technology. A two-dimensional serpentine duct model is designed to produce controlled separated flow in two configurations, in which the flow is either completely separated or has a separation bubble. An array of synthetic-jet actuators is placed within the separated flow domain in the diffuser section downstream of the onset of separation. Actuation leads to complete flow attachment up to U in =75 m/s (M≃0.2) and to partial reattachment up to U in = 105 m/s (M≃0.3)