Synthetic Jet Actuator Research Articles

CFD Investigation of Dual Synthetic Jets on an Optimized Aerofoil's Trailing Edge

In fluid dynamics, a flow control device is used to control, manage, or modify the behavior of a fluid flow. Jet actuators work by releasing high-velocity jets of fluid, usually air or gas, into the surrounding environment to control or manipulate the flow of fluids. In this study, the flow control device, which was a dual synthetic jet actuator (DSJA), acted as a lift enhancement device over an optimized NACA 0012 aerofoil with a rounded trailing edge (TE) (Coanda surface approximately 9% of the trailing edge was modified) to enhance the lift at various angles of attack (AOAs). Fluctuating pressure inlets were introduced in two slots. When the dual synthetic jets were in control, the out-of-phase jets from the upper and lower trailing edge jets helped to boost the lift coefficient. The suction stroke from the lower half of the jet made the Coanda effect stronger in the upper half. The upper trailing edge jet deflected downwards merged with the lower one and helped to deflect the flow field closer to the bottom half. An unsteady CFD analysis was performed on optimized airfoils with and without a DSJ, with a driving frequency of 40.6 and a reduced frequency of 0.025 at a Reynolds number of 25000. The results obtained at different angles indicated that the L/D ratio was improved by 13.5% at higher angles of attack in the presence of the DSJA.

Impact of annular nanosecond plasma actuators on drag reduction in transonic flow

During the last few decades, plasma actuators have emerged as promising devices for aerodynamic flow control. This study focuses on the use of nanosecond plasma actuators for such purposes. A thermal phenomenological model is employed to simulate the effects of these actuators. The propagation of shock waves and their interactions for two specific geometries of plasma actuators, linear and annular plasma synthetic jet actuators, are examined here. A comparative analysis of the performance of these two configurations is presented. Furthermore, the geometric characteristics and temperature model are analyzed to provide insights that can be applied to practical problems. The influence of the actuators on a projectile in the transonic flow is also investigated. The results of the present study show that actuators placed in the conical and cylindrical regions of the object do not contribute to drag reduction. Conversely, actuators positioned at the boat-tail and base of the object effectively reduce drag. This drag reduction is primarily attributed to thermal disturbances in the separation area. Additionally, it is observed that the effects of shock waves and their interaction with stationary waves around the projectile are negligible in terms of drag force reduction.

A novel resonant mode drives the dynamics of a large-cavity synthetic jet actuator

A novel resonant mode drives the dynamics of a large-cavity synthetic jet actuator

Control of the von Kármán vortex street with focusing and vectoring of jet using synthetic jet array

In the present study, a novel flow control technique based on jet focusing and vectoring from a synthetic jet array (SJA) for controlling the wake of a bluff body is proposed and demonstrated. A numerical investigation into the flow past a square cylinder modified by the SJA has been carried out at a free stream Reynolds Number of 100. The SJA consists of four independently controlled synthetic jet actuators operating at a peak velocity of eight times the free stream and fifteen times the natural vortex shedding frequency of the square cylinder. The SJA is operated in two different regimes; a focusing regime involving phase delay (Δφ) with non-linear variation between the actuators and a vectoring regime with a linear phase delay without changing the geometric or operating parameters of the SJA. It has been found that jet focusing is able to reduce the coefficient of drag by as much as 43% for Δφ=90°. Focusing is also observed to reduce the fluctuations in the wake velocity with the maximum reduction in fluctuations also corresponding to Δφ=90°. Jet vectoring is able to deflect the von Kármán vortex street in a singular direction along with shifting of the front stagnation point with maximum deflection for Δφ=60°. Furthermore, vectoring leads to an asymmetry in the wake velocity field with the shifting of the velocity deficit region in the direction of the vectoring along with an asymmetry in the wake velocity fluctuations. This novel approach toward synthetic jet induced active flow control allows for greater manipulation of the flow field characteristics of bluff bodies than present methods with applications in areas of underwater and micro air vehicle maneuvering, automobile, and building aerodynamics among others.

Enhancing heat transfer with a synthetic jet for thermal management applications

AbstractThis article explores the utilization of a synthetic jet as an approach to cool microelectronic devices, addressing their thermal management needs. The study includes both experimental measurements and numerical simulations to gain a comprehensive understanding of the heat transfer characteristics and fluid flow patterns generated by the synthetic jet actuator. The average Nusselt number (Nu) of the synthetic jet impinging flow with the dimensionless separation distances of the orifice to the heated surface (H/D) is investigated at different Reynolds numbers. A dynamic mesh scheme is employed in performing the simulations of the fluid domain to showcase the diaphragm's vibration and its deformation over time. The velocity profiles exhibit that the synthetic jet flow prompts the formation of two countervortices during every vibrating cycle of the diaphragm. The experimental results align closely with the predicted outcomes, indicating that the synthetic jet significantly enhances heat transfer by 3.1 times relative to the natural convection in the case of (H/D = 8.4) across different Reynolds numbers while maintaining low power consumption, a compact size, and a noise‐free operation.

Effect of synthetic jets actuator parameters on deep reinforcement learning-based flow control performance in a square cylinder

We conduct an active flow control study on the mass flow rate of synthetic jets on the upper and lower surfaces of a square cylinder using a deep reinforcement learning algorithm, with a focus on investigating the influence of the position and width of the synthetic jets on the flow control performance. At Reynolds numbers (Re) of 100 and 500, it is found that our proposed method significantly reduced the lift and drag coefficients of the square cylinder and completely suppressed vortex shedding in the wake. In particular, at Re = 100, placing the synthetic jets near the tail corner was beneficial for reducing drag, with a maximum drag reduction rate of 14.4%. When Re = 500, positioning the synthetic jets near the leading edge corner resulted in a maximum optimal drag reduction effect of 65.5%. This indicates that locating the synthetic jet at the main flow separation point can achieve optimal control. Furthermore, we notice that when the synthetic jets are positioned near the tail corner, vortex shedding can be completely suppressed. Additionally, a narrower width of the synthetic jets can enhance flow instability and increase the cost of flow control.

Genetically-Based Active Flow Control And PIV Measurements Of A Circular Cylinder Wake

In the field of flow manipulation, considerable attention is devoted to controlling the wake of bluff bodies, which are characterized by the phenomenon of vortex shedding. Specifically, the control of the wake behind a single circular cylinder has garnered substantial research interest due to its engineering applications, such as reducing aerodynamic drag in the automotive and aerospace industries. Therefore, in the current work, through the application of the planar PIV technique, the fluid dynamic behavior of a circular cylinder wake controlled via synthetic jets (SJ) and Machine Learning (ML) methods is analyzed and discussed. ML algorithms are used to determine the optimal voltage signal for the loudspeaker, which effectively minimizes the aerodynamic drag of the cylinder. This approach overcomes the limitations associated with the a priori assumption of a parametric waveshape. In particular, the gradient-enriched machine learning control (gMLC) algorithm is chosen as optimization tool to search the best open-loop control policy for aerodynamic drag reduction. The cost function for this problem has been defined considering both the drag reduction contribution and the electrical power spent for the actuation. Initial optimization tests are performed by minimizing a cost function considering only the reduction in aerodynamic drag. Subsequently, a term related to the electrical power consumption for actuation is incorporated into the cost function. Once obtained the optimal control policies for these cases (hereinafter renamed CC1 and CC2, respectively), the physical mechanism responsible for reducing the aerodynamic drag is investigated more closely by analyzing the effect of the control laws on the turbulent flow statistics. Figure 1 reports a comparative assessment of the CC1 and CC2 with the baseline configuration and the configuration controlled by a sinusoidal law (CCS). The baseline configuration is characterized by an extended region of localized turbulent fluctuations in the far wake, where the time-averaged signature of von Kármán vortices is found. In contrast, all the controlled configurations show a global reduction in wake turbulence, with a peak of turbulent energy at the rear stagnation point due to the momentum injection from the SJ actuator. Notably, the CCS and CC2 configurations share similar flow field morphologies, while the CC1 configuration shows a greater reduction in turbulent fluctuations compared to the other controlled cases. This control law also achieves the largest drag reduction among all configurations studied reporting a 9.7% of drag reduction, compared to CCS and CC2, which exhibit similar reductions of 8.4% and 8.5%, respectively. Therefore, the optimization procedure has proven the capability of finding control policies able to outperform the traditional sinusoidal control widely studied in literature.

Three-dimensional Flow Field Characteristics of a Normal Slot Plasma Synthetic Jet Actuator

Three-dimensional Flow Field Characteristics of a Normal Slot Plasma Synthetic Jet Actuator

Large eddy simulation study on drag reduction performance of array-based plasma synthetic jet actuators

Large Eddy Simulation (LES) is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators (PSJAs) on a hemisphere in supersonic inflow, and analyze the effect of energy allocation and array angle on the drag reduction performance of opposing Plasma Synthetic Jet (PSJ) in this paper. Numerical simulation results have been compared with experimental data, confirming the validity of the simulation method. The results show that different energy allocations have a significant effect on the drag of the hemisphere. However, the effect of the change in array angle on the drag of the hemisphere is not as noticeable as the effect caused by energy allocation. Interference regions between the two PSJAs occur, which undermine the effectiveness of drag reduction. High Turbulent Kinetic Energy (TKE) regions primarily concentrate on the core region of the jet and downstream of the bow shock. The influence of the array angle on TKE is most evident in the downstream region of the exits of the PSJs on both sides. Temporal evolution of the coherent structures reveals that as the PSJ intensity decreases, the large-scale vortices progressively break up into smaller-scale vortices, and energy is also transferred from large-scale structures to small-scale structures.

Model refinements with experimental validation in piezoelectric plate actuators

The axisymmetric vibration analysis of circular plates with piezoelectric layers and step changes in plate thickness is conducted. For the chosen configurations, it is necessary to solve a coupled system of differential equations for extensional and flexural vibration to obtain accurate modal results. The adopted computational approach is based upon the classical transfer matrix method. Instead of employing analytical solutions in the form of e.g. Bessel functions, matrix exponentials of the system matrix are directly computed in the transfer matrices for finding highly accurate solutions. The developed approach has enabled the complete quantitative modal analysis in piezoelectric actuators. The procedure is firstly verified against available analytical results for natural frequencies and modes shapes in circular homogeneous plates, and by using finite element simulations for plates with asymmetric step changes in thickness. Ultimately, the developed approach is validated against experimental results of relevance to applications in piezoelectric synthetic jet actuation. The obtained numerical results for modal parameters and frequency response functions are in excellent agreement with the available analytical results, and with previous and newly presented in the paper experimental data, when considering the inherent uncertainty in parameter values. Based on extensive experimental results, realistic damping is introduced in the model of piezoelectric plate actuators. Importantly, it is shown that solutions of high accuracy can be obtained by a more general coordinate system than that traditionally linked to the plate neutral plane(s).

Breaking the limitation of thermodynamic cycle efficiency of the plasma synthetic jet actuator: Noble gases

The low thermodynamic cycle efficiency of the plasma synthetic jet actuator (PSJA) limits its application in flow control of supersonic aircraft. To improve the thermodynamic cycle efficiency of the PSJA, the energy conversion process of the PSJA under single discharge has been investigated by thermodynamic theory analysis and numerical simulation. The relations between thermodynamic cycle efficiency, specific heat ratio of gas medium, non-dimensional energy deposition and heating efficiency are established by theoretical deduction. Employing the three-dimensional nonconstant electrode center energy deposition model, energy conversion processes in the PSJA with six different gas mediums have been investigated. The simulation results show that the thermodynamic cycle efficiency of the PSJA with noble gas medium can exceed 3.2 %, which is 1.92 times of the PSJA with air medium due to their low volume specific heat. The maximum jet x-velocity of helium can reach 493.11 m/s, which is 3.3 times higher than that of air. Consequently, noble gases prove to be effective in improving the thermodynamic cycle efficiency of the PSJA and enhancing the strength of the synthetic jet. The advancement in the performance of the PSJA contributes to their enhanced capabilities in the field of active flow control.

An experimental investigation on the influence of Strouhal number and amplitude on the flow and heat transfer behavior of synthetic jet impingement

ABSTRACT Here, tests are performed to analyze the effect of Strouhal number (St) and amplitude on thermo-fluid characteristics of synthetic jet (SJ) impingement for varied range of Reynolds numbers (Re = 3000–6000) and three different SJ actuation amplitudes (Vrms = 4, 6, 8 V). The hot wire anemometer and the infrared thermal imaging camera are used to measure the flow velocity and surface temperature, respectively. At a constant amplitude of the SJ actuation, discrete pairs of Strouhal numbers, i.e. low St ( S t L ) and high St ( S t H ), are found to exhibit the same Re. The heat transfer characteristics are expressed in three different regions such as the region of recirculation, the region of high Strouhal number dominance, and the region of low Strouhal number dominance. At lower orifice-to-surface spacings (z/d < 6), the thermal efficacy of SJ with S t H is found to be lower compared to the SJ with S t L . At z/d = 2, SJ with S t H exhibits the decrease in the average Nusselt number upto 53.4% corresponding to S t L at Re = 4000 and 4 Vrms. However, at intermediate spacings (z/d ≥ 6 ), the SJ with S t H tends to outperform the S t L , which may be due to vortex pairing at high St synthetic jets. At larger z/d, the dominance of S t L is reestablished due to matching of the SJ actuation frequency with the natural frequency of a steady jet. Correlations have been proposed for the average Nusselt number at both S t L and S t H as a function of Re, St, and z/d. The results of the study provide information on the selection of the operating frequency of SJ to achieve higher heat transfer at varied orifice-to-surface spacings.

Torque generation using synthetic jet actuators

This article presents a novel method of utilizing the thrust generated by synthetic jet actuators to generate torque. Piezoelectric-based synthetic jet actuators were used to create a device with two isolated cavities and orifices. Weight balance and hotwire anemometry were used to quantify the thrust generated by the synthetic jet actuator. Each orifice provides a maximum thrust of 0.15gf, thereby generating a net maximum torque of 17.17gf mm. The torque generated can be used to produce a rotary motion. Such a novel device may be useful where a high-momentum rotary jet may be employed for heat transfer and mixing enhancement.

Multiphysics Modeling of a Synthetic Jet Actuator in Operation

Active flow control is a promising technology for reducing noise, emissions, and power consumption in various applications. To better understand the performance of synthetic jet actuators, a computational model that couples structural mechanics with electrostatics, pressure acoustics, and fluid dynamics is needed. The model presented here was validated against experimental data and then used to investigate the fluid behavior inside and outside the synthetic jet actuator cavity, the impacts of thermoviscous losses on capturing the acoustic response of the actuator, and the viability of different modeling methods of diaphragms in computational simulations. The results capture the feedback from the fluid onto the diaphragm and highlight the need for careful acoustic modeling.

Vortex ring breakdown dominating the entrainment of a synthetic jet

The understanding of the entrainment mechanism of synthetic jets can help optimise the synthetic jet actuators in engineering applications. It is generally believed that vortex rings or strong velocity fluctuations in the near field of the synthetic jet are responsible for its enhanced entrainment. However, in recent years, it has been found that the enhanced entrainment of the synthetic jet may be caused by the instability or the vortex ring breakdown in the transition region. To shed new light on this issue, synthetic jets with different Reynolds numbers and dimensionless stroke lengths are investigated with time-resolved two-dimensional particle image velocimetry. Based on the analyses of velocity triple-decomposition, Fourier mode decomposition and phase-averaged $\lambda _{ci}D/U_0$ field, the streamwise positions of the vortex ring breakdown are determined for the synthetic jets, and the entrainment coefficient can be divided into three components, i.e. the coherent turbulent kinetic energy production, the random turbulent kinetic energy production and the shape of the velocity profile. It is found that the entrainment coefficient is dominated by the component related to the random turbulent kinetic energy production, and reaches its peak value at the position of vortex ring breakdown. The results obtained in different cases show a strong correlation between vortex ring breakdown and entrainment enhancement. From the perspective of instantaneous snapshot, the mechanism of vortex ring breakdown enhanced entrainment is revealed, that is, vortex ring breakdown enhanced the small-scale vortex near the turbulent/non-turbulent interface, resulting in an increase of enstrophy production, and thus enhanced local entrainment.

Experimental study on shock interaction control of double wedge in high-enthalpy hypersonic flow subject to plasma synthetic jet

The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.

Plasma synthetic jet actuator array driven by a programmable triggered Marx high-voltage generator

A plasma synthetic jet (PSJ) actuator array driven by a self-triggered Marx high-voltage generator can simultaneously actuate multichannel PSJ actuators to form jet arrays; however, the discharge frequency cannot be controlled by programmable electrical signals. To address this, programmable high-voltage pulses are used to trigger a Marx high-voltage generator and regulate the discharge frequency of the PSJ actuator array. The electrode gap range for achieving a programmable triggered discharge is determined, and typical discharge images and basic discharge characteristics are obtained. The effects of trigger frequency and voltage amplitude on the discharge frequency are studied. The high-speed Schlieren technique is used to obtain flow-field characteristics of five-channel PSJ actuators under a programmable triggered state. The programmable triggered Marx high-voltage generator can achieve programmable control of the discharge frequency with an approximate linear control range of 10–30 Hz and a nonlinear saturation range of 30–100 Hz. In the approximate linear control range, the discharge frequency increases almost linearly with trigger frequency under different trigger voltage amplitudes. One of the channels of the five-channel synthetic jet actuators achieves the highest jet height and speed of 70 m/s, while those of the others are similar but slightly lower. There is no significant decrease in the jet height or speed of the five-channel PSJ actuators with the increase in the trigger frequency, which is beneficial for flow-control applications.

Experimental investigation on periodic characteristics of high-frequency oblique slot plasma synthetic jet actuator

A plasma synthetic jet actuator with a high-frequency oblique slot was designed for supersonic flow control. The actuator's periodic operation characteristics were investigated using electrical parameter measurements and high-speed schlieren techniques. Experimental findings indicate that the actuator can stably operate within the frequency range of 0–2400 Hz. With increasing operating frequency, the breakdown voltage, maximum current, and discharge energy decrease, while the energy efficiency of the discharge increases. Moreover, the experiment revealed for the first time that an increase in the number of charged particles within the cavity leads to a decrease in breakdown voltage, and the concentration of charged particles reaches saturation at approximately 1200 Hz. High-speed schlieren observations indicate substantial inter-cycle influences in the periodic jet. At higher operating frequencies, the impact of inter-cycle flow field effects becomes more pronounced. The oblique slot plasma synthetic jet exhibits clear directionality in the distribution of shock waves and jet. The oblique slot jet also shows a significant wall attachment effect. These characteristics are beneficial for enhancing the flow control capability of the actuator. At 1200 Hz, the actuator achieves a discharge efficiency of 63% and a maximum jet front velocity of 309 m/s, showcasing its superior overall performance.

Flight test of flying wing aircraft controlled by dual synthetic jets at Ma0.2

To explore the application potential of zero-mass-flux dual synthetic jets in flight control of flying wing aircraft (FWA), dual synthetic jet actuators (DSJAs) are integrated into a FWA and flight tests without deflections of rudders are firstly carried out to verify the viability of DSJAs to manipulate three-axis attitudes at a cruising speed of 70 m/s. Two active flow control methods of circulation control and reverse jet control performed by DSJAs are utilized to execute the three-axis control. Novel flight control effectors based on DSJAs are designed and achieve the integration with the FWA. Flight tests show that three-axis flight control is realized by DSJAs distributed in different locations. The maximum roll, pitch and yaw angular velocities are 10.12°/s, 6.17°/s and 8.38°/s respectively. The work initially verifies rudderless flight control ability of DSJAs at a cruising speed of 70 m/s and the control ability will be improved by the further optimization of DSJAs.

LES Investigation of a Piston-driven Synthetic Jet Actuator with Multiple Orifices

A piston-driven synthetic jet actuator has the potential for application in flow control and fundamental studies of turbulence, although the high-speed flow generated by this actuator is less investigated than a low-speed synthetic jet. The interaction of high-speed jets issued from a piston-driven synthetic jet actuator with multiple orifices is investigated with large eddy simulation (LES). The maximum jet Mach number is related to the maximum pressure inside the actuator regardless of the number of orifices. Temporal variations of the jet Mach number are almost identical for different cycles, and the jet formation in each cycle occurs under the same conditions despite the unsteady nature of the jet interaction. The phase-averaged statistics are used to examine the interaction of the synthetic jets. The converging, merging, and combined regions known for the interaction of continuous jets appear for the interaction of the high-speed synthetic jets slightly before the end of the blowing phase. However, the converging region is not clearly observed at the beginning of the blowing phase because the jets tend to be parallel to each other. Therefore, the combined region forms at a late stage of the blowing phase. Before the jets are combined, velocity fluctuations in the blowing phase become large near the furthest locations where the jets reach. Once the jets merge by their interaction, large velocity fluctuations are observed at the downstream end of the merging region. The probability density functions of velocity fluctuations in the blowing phase tend to deviate from a Gaussian distribution along the centerline of the jets. This deviation is more significant for the two-orifice model than for the four-orifice model under the same actuation frequency.