Synthetic Jet Actuator Research Articles

Effects of different working parameters on the turbulent drag reduction regulated by annular plasma synthetic jet actuators

Reduction of turbulent drag force is one of important works in the design of airplanes and hypersonic aircrafts. The annular plasma synthetic jet (APSJ) has become an interesting and popular flow control method in reducing the drag of turbulent boundary layers. In this paper, a comprehensive experimental study is carried out on the turbulent drag reduction regulated by an array of annular plasma synthetic jet actuators. The effects of the operating parameters such as the actuation voltage, the pulse frequency and the incoming wind speed on the drag reduction rate are studied and discussed in detail. The performances of the plasma actuator array are evaluated and summarized at multiple working conditions. Finally, the coherent structures of turbulence and the hairpin-like vortices are depicted and discussed. The results show that the optimal drag reduction rate is achieved, as the actuation voltage, pulse frequency and incoming wind speed are Vpp = 7 kV, fp= 50 Hz, and U∞ = 7 m/s, respectively. A resonant coupling phenomenon is observed when the pulse frequency of the actuators approaches the characteristic frequency of the coherent structure. The upward sweep flow induced by APSJ actuators may lead to a reduction of the turbulent drag force, but the downward wash flow leads to an increase in the drag. Present study could provide solid experimental data and a helpful guidance for the drag reduction of an airplane.

Experimental characterization of a modified high-speed plasma synthetic jet actuator with oblique-slot exit

In the field of flow control research, oblique jets are known to offer several advantages over vertical jets. To gain a comprehensive insight into the flow field characteristics of a plasma synthetic jet actuator with an oblique-slot exit, the related experiments are conducted. The experiment employed high-speed schlieren imaging techniques and electrical parameter measurements to acquire the flow field characteristics and discharge properties of the oblique-slot actuator, followed by a comparative analysis with a vertical circular orifice actuator. The oblique-slot plasma synthetic jet exhibits a wall-attaching effect and asymmetric flow characteristics, which differ from those of the vertical circular orifice actuator. The actuator generates a wall jet with an initial velocity of 389.5 ± 15.08 m/s, effectively propelling the fluid within the boundary layer. The Mach number of the precursor shock wave in the direction of the jet reaches 1.59, but decreases to just 1.02 in the opposite direction. Over a period in the range of 10–70 μs, the Froude number of the plasma jet decreases from 1841 to 238. The dominant role of the inertial force gradually weakens, while the influence of buoyancy increases, causing the jet boundary to move upward. The oblique-slot jet configuration represents a typical planar jet, exhibiting superior flow control uniformity compared with the vertical circular orifice jet. The results indicate that the high-speed oblique-slot plasma synthetic jet actuator designed in this study possesses distinct advantages over vertical circular orifice actuators for high-speed fluid flow control.

Virtual deflection with synthetic jet actuators at high angles of attack

Abstract A hybrid drone called a biplane quadrotor operates in both low (during the horizontal flight) and high (transition maneuver) Angle of Attack (AoA). So, this paper focuses on enhancing aerodynamic force during the transition maneuver. Synthetic Jet actuators (SJAs) can modify airfoil shapes virtually, so either the flow reattaches or flow separation will be delayed. This delay can enhance the aerodynamic force. In this paper, CFD analysis is performed using Ansys Fluent to study the impact of SJA on NACA 0015 airfoil at high (30°) AoA. This study aims to find the best location of SJA for high AoA to get maximum lift enhancement. The outcome of this study reveals that at 85 %, we can get maximum enhancement in the lift.

Effects of piezoelectric synthetic jet actuator parameters on synthetic jet formation process and actuator performance

Aiming at the problem that the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude of the piezoelectric synthetic jet actuator (SJA) causes it difficult to obtain the variation laws of the synthetic jet (SJ) velocity accurately, a theoretical model of the whole flow field of the piezoelectric SJA is established and four important parameters (half period jet mean velocity, Reynolds number, effective jet length and energy) for evaluating the performance of the SJ are proposed. Then a two-dimensional axisymmetric numerical simulation is carried out with k-ω turbulence model to study the SJ formation process and the velocity characteristics of the SJ at the orifice. The results show that the fluid pressure in the cavity is the main reason causing the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude, the influence of which decreases with the increase of the orifice diameter. The SJ velocity increases first and then decreases slowly with the increase of excitation frequency. The extreme point occurs at the first resonant frequency of the piezoelectric vibrator and the position of the maximum velocity occurs at 0.5 mm outside the orifice. Other conditions being constant, both the piezoelectric vibrator deflection and jet velocity have a maximum value when the radius ratio of the piezoelectric layer to the elastic layer is 0.75. Smaller piezoelectric layer thickness leads to larger lateral displacement of the piezoelectric vibrator, and the optimum thickness ratio is 0.25. The results of this study have important guiding significance for accurately obtaining the variation laws of the SJ velocity as well as rationally designing the piezoelectric SJA.

Structural–fluidic–acoustic computational modelling and experimental validation of piezoelectric synthetic jet actuators

In this study, coupled structural–fluidic–acoustic modelling of piezoelectric diaphragm driven synthetic jet actuators is conducted computationally for the first time. The aim is to demonstrate the importance of piezoelectric diaphragm structural modelling and the effects of acoustics coupling to compute accurate synthetic jet exit jet velocity. Two different synthetic jet actuator orifice–diaphragm configurations are studied in which the orifice is parallel and adjacent to the diaphragm, namely, opposite and adjacent synthetic jet actuators, respectively. In investigating the aforementioned configurations, cavity acoustic and mechanical resonance frequencies are identified within ± 100 Hz, compared to in-house experimental measurements of laser vibrometry and hot-wire anemometry. The numerical peak jet velocity differs from the experimental value at the diaphragm mechanical resonance by 5.4% and 0.3% for opposite and adjacent synthetic jets, respectively. Further analysis of velocity and vorticity fields showed that no vortex formation is observed in the cavity of the adjacent synthetic jets, despite having similar exit jet velocity of the opposite synthetic jet configuration.

Flight control of a flying wing aircraft based on circulation control using synthetic jet actuators

To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft (FWA), a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders. Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated. Then, flight tests were carried out to verify the control abilities, providing a novel technology for the design of a future rudderless FWA. Results show that synthetic jets could narrow the dead zone area, improve the flow velocity near the trailing edge, and then move the trailing-edge separation point and the leading-edge stagnation point downwards, which make the effective Attack of Angle (AOA) increase, thereby enhancing the pressure envelope area. Circulation control based on synthetic jets could improve the lift, drag and nose-down moment. The variations of lift and nose-down moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency. Finally, synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA, which could realize the roll and pitch control without deflections of rudders during the cruise stage, and the maximum roll and pitch angular velocity are 12.64 (°)/s and 8.51 (°)/s, respectively.

Comparison of Separation Control Mechanisms for Synthetic Jet and Plasma Actuators

This study numerically investigated the mechanisms of separation control using a synthetic jet (SJ) and plasma actuator (PA) around an NACA0015 airfoil at the chord Reynolds number of 63,000. Both SJ and PA were installed on the leading edge with the same order of input momentum (Cμ=O(10−3–10−5)) and the same actuation frequencies in F+=1.0–30. The momentum coefficient Cμ is defined as the normalized momentum introduced from the SJ or the PA, and F+ stands for the actuation frequency normalized by the chord length and uniform velocity. A number of large-eddy simulations (LES) were conducted for the SJ and the PA, and the mechanisms were clarified in terms of the exchange of chordwise momentum with Reynolds shear stress and coherent vortex structures. First, four main differences in the induced flows of the SJ and the PA were clarified as follows: (A) wall-tangential velocity; (B) three-dimensional flow structures; (C) spatial locality; and (D) temporal fluctuation. Then, a common feature of flow control by the SJ and the PA was revealed: a lift-to-drag ratio was found to be better recovered in F+=6.0–20 than in other frequencies. Although there were differences in the induced flows, the phase decomposition of the flow fields identified common mechanisms that the turbulent component of the Reynolds shear stress mainly contributes to the exchange of the chordwise (streamwise) momentum; and the turbulent vortices are convected over the airfoil surface by the coherent spanwise vortices in the frequency of F+.

Attenuation of the unsteady loading on a high-rise building using top-surface open-loop control

With the severity and frequency of significant weather events increasing, methods for alleviating unsteady wind loading for high-rise buildings are gaining interest. This study numerically investigates the three-dimensional flow structures around a canonical high-rise building immersed in an atmospheric boundary layer at different oncoming wind angles, using wall-resolved large eddy simulations. A synthetic jet located on the top surface is used as open-loop active actuation with the aim of suppressing the building's side-force fluctuations when exposed to oncoming wind variations. Three different frequencies of jet forcing are considered, all half an order of magnitude larger than the vortex shedding frequency. The behaviour of the synthetic jet and its effect on the building's unsteady side force, time-averaged flow fields and unsteady flow structures are investigated numerically. The synthetic jet actuation is found to reduce the side-force fluctuation of the building, enhance the downwash flow and successfully attenuate the antisymmetric vortex shedding. This was achieved to different extents across the range of oncoming wind angles considered and may motivate future attempts to explore experimental active control strategies for attenuation of unsteady wind loading.

Investigation of drag reduction mechanism for blunt bodies with plasma spikes

The two main problems in hypersonic vehicles are wave drag and aerodynamic heating. This work proposes a novel method for drag reduction by combining spikes with the plasma synthetic jet actuator (PSJA). Numerical simulations are performed to better understand the drag reduction mechanism with an incoming flow at Mach 6. The results suggest that the flow field is affected primarily by the diffracted wave and synthetic jet. The maximum drag reduction reaches 47.7% with the plasma spike compared with the opposing jet. A better drag reduction effect is achieved when increasing the energy density of the PSJA, while the propagation velocity of the diffracted wave remains constant. A wider and faster jet is obtained with a larger PSJA orifice diameter. However, the control time of the jet shortens. A mode conversion occurs when the orifice diameter is 1 mm. Furthermore, the maximum drag reduction rate increases from 37.6% to 49.0% when the length diameter ratio (L/D) increases from 0.5 to 1.5. The effect of spike length on drag reduction decreases gradually at greater lengths.

Experimental study on convective heat transfer of hybrid impingement configuration by square-array continuous jets and a center-positioned synthetic jet

An experimental investigation is performed to illustrate the heat transfer characteristics for a specific hybrid-jet impingement configuration that is comprised of a square-layout continuous-jet array and a center-positioned loudspeaker-driven synthetic-jet actuator. Herein four continuous-jet Reynolds numbers (ranging from Re=3000 to Re=10,000), three hole-to-hole pitches (X/d = Y/d = 4. 5 and 6), and a series of impinging distances (H/d = 2–10) are considered while the central synthetic jet is operated at f = 250 Hz with a characteristic Reynolds number of about Re0=4500. It is identified that the integration of central synthetic jet in the array-jet unit is indeed an effective means to enhance the overall heat transfer performance, which is more suitable for the practical applications wherein the synthetic jet Reynolds number is greater than or equivalent to the array-jet Reynolds number. By the integration of central synthetic jet, a significant localized heat transfer augment is achieved at the central zone of array-jet unit, especially under small and moderate array-jet Reynolds numbers. In terms of the spatially-averaged Nusselt number, an increase of more than 100% could be achieved by the central synthetic jet integration at H/d ≥ 6 under Re=3000. The benefit of the central synthetic jet integration is also clearly demonstrated under Re=5000, wherein the spatially-averaged Nusselt number could be increased by 30%-60%, taking a monotonous increasing trend along with the impinging distance generally. Under Re=7000, a relative increase among 10%-30% still remains. When the array-jet Reynolds number is increased up to 10,000, only in the sparse continuous-jet array (X/d = Y/d = 6) the benefit of the central synthetic jet integration could behave, with a limited relative increase of less than 20%.

Enhancing Jet Velocity and Power Conversion Efficiency of Piezoelectric Synthetic Jet Actuators

The present work discusses an experimental investigation into the effect of piezoceramic employed to drive a synthetic jet actuator into a quiescent flow. The electromechanical coupling ratio of polycrystalline piezoceramics, lead zirconate–titanate 5A/5H (PZT-5A/5H), conventionally used in synthetic jet actuators, is inherently low. Therefore, this study aims to investigate using more electromechanically efficient piezoceramics, such as single-crystal, lead magnesium niobate–lead titanate (PMN-PT). In addition, two different orifice-diaphragm configurations of synthetic jet actuators, opposite and adjacent, are tested. It is identified that PMN-PT piezoceramic promotes three times higher transverse diaphragm displacement and two times more peak jet velocity compared to the PZT-5A piezoelectric actuator for the same input diaphragm voltage. A peak exit jet velocity of was obtained at 40 V of peak supply voltage, which can be classified as a low voltage supply compared to other studies in the literature that obtained similar exit jet velocity. Also, a power conversion efficiency of 72% was achieved, corresponding to the Helmholtz resonance frequency. A new figure-of-merit, momentum coefficient per power consumption, is defined to evaluate the potential impact for full-scale implementation. A state-of-the-art value of is achieved.

The flow and heat transfer behavior of synthetic jets with star shaped orifice of different lobes

In the present experimental investigation, the flow and heat transfer characteristics of synthetic jet (SJ) issuing from different lobed (3–10) star-shaped orifices are studied. Tests are performed by actuating the SJ actuator at constant input power of 4Vrms, with varied range of orifice to surface spacings (1–16) and numerous values of Reynolds number (8692–10746). The synthetic jet's flow characteristics are studied using hot-wire anemometry, while the thermal characteristics are analyzed using an IR camera. Distinct peaks in turbulence intensity are observed in major and minor planes for different lobed (3–6) star orifices; this may be due to the development of two shear layers in such orifices, which consequently merges into a single shear layer for higher lobed (8–10) star orifice. The 6-lobed star orifice is found to exhibit maximum heat transfer performance at z/d varying between 2 and 14. At z/d = 2, the 6-lobed star orifice exhibit 7.6% and 10.1% improvement in average Nusselt number compared to circular and 10-lobed star orifice respectively, which may be due to formation of vortical structures along the lobed edges and subsequent switching of axes between the major and minor planes. To comprehend the energy associated with the issuing vortices, the power spectral density of the velocity signal at the orifice exit is examined. A unified correlation for the average Nusselt number is also derived for various star-shaped orifices.

Hybrid Lumped-Element and Finite Element Model for Novel Synthetic Jet Actuator Shapes

A modeling approach was developed that combines lumped-element and finite element methods for analysis of synthetic jet actuator (SJA) geometries that deviate significantly from an ideal Helmholtz resonator. The diaphragm was modeled using the finite element method (FEM) coupled to lumped-element equations that govern the fluid flow. The loss coefficient was estimated based on the geometry of the cavity and orifice. A pressure acoustic FEM model of the cavity and orifice was used to determine a characteristic resonance frequency to use in place of the Helmholtz resonance frequency that appeared in the lumped element equations. The results were validated using experimental data for SJAs with geometries that deviate significantly from the Helmholtz resonator idealization. The combination of replacing the Helmholtz frequency with a more accurate characteristic frequency and using a computed value for the loss coefficient was shown to provide more accurate performance predictions for low-profile SJA designs.

Novel yaw effector of a flying wing aircraft based on reverse dual synthetic jets

For achieving the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft (FWA), a novel yaw effector based on Reverse Dual Synthetic Jets (RDSJ) was proposed without the movement of rudders. Effects on aerodynamic characteristics of a small-sweep FWA and control mechanism were investigated by numerical simulations. Finally, reverse dual synthetic jet actuators were integrated into a real FWA and flight tests were firstly carried out. Numerical results show that RDSJ could make drag coefficient increase and weaken lift coefficient, which generate a yawing moment and a rolling moment in the same direction, realizing control of heading attitudes, but strong coupling with the pitching moment occurs at large angles of attack. For control mechanism, RDSJ could produce two reverse synthetic jets out of phases, improve the reverse pressure gradient and hence form alternate recirculation zones or even early large-area separation, which cause the rise of pressures before exits and the dip of pressures behind exits, achieving improvement of drag and the yawing moment. The results of flight tests support that RDSJ could realize control of heading attitudes without deflections of rudders during the cruise stage and achieve the maximal yaw angular velocity of 10.12(°)/s, verifying the feasibility of this novel yaw effector.

Large-Eddy Simulation of a Flow Generated by a Piston-driven Synthetic Jet Actuator

We study the characteristics of a compressible flow generated by a piston-driven synthetic jet actuator by employing large-eddy simulation with OpenFOAM. The actuator consists of a piston and a cylinder with a square orifice on top and produces a compressible synthetic jet with the piston movement. Comparison with experimental data demonstrates that the numerical model constructed with OpenFOAM is useful to examine the performance of the actuator. As the piston frequency increases, the maximum pressure inside the cylinder increases while the minimum pressure decreases. The fluid temperature inside the cylinder also varies similarly to the pressure. The maximum jet Mach number is well represented as a function of the maximum pressure. The phase-averaged velocity field of the synthetic jet confirms that the blowing and suction phases do not perfectly match with the piston movement. The root-mean-square velocity defined with the phase average also shows that a high turbulence level is observed in the region where the flow is decelerated at the furthest location of the jet in the blowing phase

Characterisation of an independently controlled coaxial synthetic jet

This paper presents the hot-wire measurements to characterise the flow field of a novel coaxial synthetic jet (CSJ) actuator. The CSJ actuator is formed by positioning two single-acting synthetic jet (SJ) actuators coaxially (0° orientation angle) along with their own flow actuation mechanism (piezo-electric diaphragms). The CSJ is formed by the periodic suction and expulsion of the fluid into a quiescent medium employing the piezo diaphragms through the inner and annular openings (orifices), which have an equal hydraulic diameter (dh) of 3 mm. This novel configuration facilitates independent control of excitation voltage (V), frequency (f) for inner and annular jets, and additionally, various phase differences (∅s) between the inner and annular jets. The resonance frequency of both the inner and annular cavities are obtained separately as 350 Hz, and 320 Hz, respectively. The inner jet is operated at Reynolds number Re=1100 (V=50 V, and f=350 Hz), which remains fixed for all the test cases. The CSJ flow field is analysed for three mass flux ratios (Mrs) as 0.7, 1.0, and 2.0, which are achieved by operating both the diaphragms independently at various excitation voltages for a fixed f=350 Hz, and at various fs for a fixed excitation voltage of 50 V. Moreover, the effect of ∅s (range: 0° to 180° in the step of 45°) by leading the inner or annular jet is examined while the CSJ is operated at these Mrs. It has been observed that the strength and spreading of the CSJ can be enhanced by providing ∅s between the jets, without investing any additional power for flow excitation. It is important to notice that leading the weaker jet enhances its contribution to the creation of the CSJ, which improves the CSJ's strength and spread. The CSJ flow field is compared with that of the inner SJ, and annular SJ, operated individually, to illustrate the superior performance of the CSJ. The paper conveys that the CSJ’s strength and spreading can be manipulated significantly with the independent control facility, which is feasible with this configuration.

Effect of Synthetic Jet Actuator with Different Pulse Waveforms on Fan Blade Lift

The lift of wind turbine blades is a significant factor influencing the working efficiency of wind turbines. The influence of synthetic jet actuator on the lift of fan blades is studied in this manuscript. The influence of different pulse waveforms (sine wave, square wave and triangle wave) and different action positions (airfoil front end and rudder front end) on fan blades is analyzed. It is found that when the synthetic jet actuator acts on the airfoil front end, the best lift effect on the fan blade exists in the square wave. While when acting on the front end of the rudder, the best lift effect on the fan blade appears in the triangle wave. When two positions are acted on by the synthetic jet actuator at the same time, the square wave is the best relative to the other two pulse forms. At the same time, the effects of three pulse forms on the surface vortex of airfoil are studied, the flow conditions of the three waveforms are investigated when the airfoil is in a steady state of flow. The vortices formed by square waves can better adhere to the airfoil, while the vortex formed by the triangle wave can be separated from the airfoil faster.

Dual Synthetic Jets Actuator and Its Applications Part V: Novel Valveless Continuous Micropump Based on Dual Synthetic Jets with a Tesla Structure

The valveless micropump based on dual synthetic jets is a potential fluid pumping device that has the ability to transport fluid continuously. In order to improve the performance of this device, a novel valveless continuous micropump based on dual synthetic jets with a Tesla structure was proposed by combining a double Tesla symmetrical nozzle and a dual synthetic jets actuator. The mechanism of the novel micropump and its flow field characteristics were analyzed, combined with numerical simulation and a PIV experiment. The performance of the novel micropump was compared with that of a dual synthetic jet micropump based on a traditional shrinking nozzle. The novel micropump achieved continuous flow with a larger and more stable flow rate in one cycle. The maximum pump flow speed reached 12 m/s. Compared with the traditional type, the pump flow rate was increased by 5.27% and the pump flow pulsation was reduced by 214.93%. The backflow and vortex inside the nozzle were prevented and inhibited effectively by the Tesla structure. The velocity and influence range of the pump flow increased with the intensification of driving voltage in a certain range.

Feedforward Harmonic Suppression for Noise Control of Piezoelectric Synthetic Jet Actuators

Piezoelectrically driven Synthetic Jet Actuators (SJAs) are a class of pulsatile flow generation devices that promises to improve upon steady forced cooling methods in air flow generation, surface cleaning and heat transfer applications. Their acoustic emissions and vibrations, an intrinsic by-product of their operation, needs to be mitigated for applications in noise-sensitive contexts. Already used for aerodynamic control [1, 2], thrust vectoring [3], spray control [4], and heat transfer [5, 6], they are increasingly being considered for sensor lens cleaning in automobiles. In this study, the sound generation mechanisms of SJAs are discussed and an active noise reduction method is proposed and evaluated. Driven with a single frequency sinusoidal input, SJAs produce acoustic emissions at harmonic frequencies within the frequency range of speech communication. The sound pressure levels of those emissions are commensurate with that of other automotive subsystems and electronic components. Previous attempts at noise control include passive strategies, such as, nozzle design [7, 8], enclosure design [5], and mufflers. Active strategies, such as out-of-phase actuator pairs [9], and signal modulation have also been considered. Given their relative novelty, further reduction is possible at the source through the tuning of prominent tonal components of their emissions. The present study demonstrates that feedforward active control, achieved through input harmonic tuning, results in significant drops in the loudness of the radiated sound with minimal effects on flow and cleaning performance. Acoustic emissions from all prominent harmonics could be reduced using this method. Tuning is local to the location of the error microphone and further work is required to achieve global tuning. Preliminary performance investigations are presented.

Numerical investigation of aerodynamic characteristics of a flying wing aircraft controlled by reverse dual synthetic jets

In this work, to explore the control potential of reverse dual synthetic jets (RDSJs) in a flying wing aircraft (FWA), reverse dual synthetic jet actuators (RDSJAs) are integrated into a FWA with a hybrid flow mode of rollers and streamers. The aerodynamic characteristics and control mechanism are investigated using numerical simulations. The results show that the aerodynamic loads follow a nonlinear trend, and the overall process can be divided into three stages with an increasing angle of attack (AOA). In the first stage (AOA = 0°–8°), the RDSJs can improve the reverse pressure gradients and form alternate recirculation zones or even a large-area separation. The pressure rises before and falls after the exits, causing an increase in Cd and a drop in CL. The decrease in the leading-edge suction and the pressure envelope area results in a further increase with the increasing AOA, resulting in a reduction in ΔCL and an improvement in ΔCd. In the second stage (AOA = 8°–24°), the energy of the RDSJs is too low to form a strong disturbance over the leeward surface, and the promotion of favorable pressure gradients along the lower surface can weaken the control effects of the RDSJAs, causing a decrease in the narrowing degree of the pressure envelope. The leading-edge vortex (LEV) is weakened, and ΔCL increases as Cd experiences a drop. In the third stage (AOA = 24°–32°), the RDSJs interact with the larger separation and are capable of accelerating the flow over the wing section, elevating the longitudinal velocity of the LEV through entrainments and improving the strength and stability of the LEV. The accelerated flow creates negative pressures behind RDSJAs, causing a further reduction in the decrement of the pressure envelope area. An enhancement of CL and Cd appears under the influence of the above factors.