Actuators

Research

19 pages, 8948 KiB

Open AccessArticle

Dual Synthetic Jet Actuator and Its Applications—Part IV: Analysis of Heat Dissipation and Entropy Generation of Liquid Cooling with Dual Synthetic Jet Actuator

by Ying Kang, Zhenbing Luo, Xiong Deng, Yinxin Zhu and Zhixun Xia

Actuators 2022, 11(12), 382; https://doi.org/10.3390/act11120382 - 19 Dec 2022

Viewed by 1649

Abstract

Increasing heat flux restricts the development of the miniaturization of electronic devices. There is an urgent need for a heat dissipation method that will efficiently cool the chip. This paper presents a novel liquid cooling device based on dual synthetic jets actuator (DSJA) [...] Read more.

Increasing heat flux restricts the development of the miniaturization of electronic devices. There is an urgent need for a heat dissipation method that will efficiently cool the chip. This paper presents a novel liquid cooling device based on dual synthetic jets actuator (DSJA) technology. The characteristics of the temperature and velocity field of the device are numerically studied by a three-dimensional coupled heat transfer model. The entropy generation rate caused by heat transfer and fluid friction was studied to analyze the effective work loss and irreversibility of the heat transfer process. When the DSJA is turned on, the temperature of the heat source with a heat flux of 200 W/cm² is 73.07

^{\circ}

C, and the maximum velocity is 24.32 m/s. Compared with the condition when the the DSJA is closed, the temperature decreases by 25.15

^{\circ}

C, and the velocity increases by nearly 20 m/s. At this time, the total inlet flow is 1.26 L/min. The larger frictional entropy generation is mainly distributed near the inlet and outlet of the channel and the jet orifice. The higher the velocity is, the more obvious the frictional entropy generation is. Due to the large temperature gradient, there is a large thermal entropy generation rate at the fluid–solid interface. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

14 pages, 7574 KiB

Open AccessArticle

Dual Synthetic Jets Actuator and Its Applications—Part III: Impingement Flow Field and Cooling Characteristics of Vectoring Dual Synthetic Jets

by Xiong Deng, Zhaofeng Dong, Qiang Liu, Can Peng, Wei He and Zhenbing Luo

Actuators 2022, 11(12), 376; https://doi.org/10.3390/act11120376 - 15 Dec 2022

Cited by 1 | Viewed by 1562

Abstract

In order to understand the impingement flow field and cooling characteristics of vectoring dual synthetic jets (DSJ), an experimental investigation was performed to analyze the parameter effects. With the variation of the slot location, the vectoring angle of DSJ can be adjusted from [...] Read more.

In order to understand the impingement flow field and cooling characteristics of vectoring dual synthetic jets (DSJ), an experimental investigation was performed to analyze the parameter effects. With the variation of the slot location, the vectoring angle of DSJ can be adjusted from 34.5° toward the left to 29.5° toward the right. The vectoring function can greatly extend the length of impingement region. There are three local peaks both for the local cooling performance (Nu) and the whole cooling performance (Nu_avg). Although the peak Nu at a certain location of the slider is higher than that at the center, the corresponding Nu_avg is lower. As for different driving frequencies, the vectoring angle reaches its minimum of 9.7° at 350 Hz, but the Nu is obviously improved. There is one local peak of Nu_avg values at 350 Hz rather than three local peaks at 250 Hz and 450 Hz. The slot locations where the Nu_avg of 250 Hz and 450 Hz reach maximum are different. With the increase in driving voltage from ±100 V to ±200 V, the vectoring angle drops from 46.9° to 22.2°, but both Nu and Nu_avg are improved. The maximum Nu_avg of each driving voltage occurs at the center location of the slider. The choking effect and the cross flow have dominated the vectoring angle and the cooling performance of impingement DSJ. Vectoring DSJ will give impetus to the thermal management of large-area electric devices in spaced-constrained cooling and removing dynamic hotspots. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

24 pages, 11165 KiB

Open AccessArticle

Deep Reinforcement Learning for Flow Control Exploits Different Physics for Increasing Reynolds Number Regimes

by Pau Varela, Pol Suárez, Francisco Alcántara-Ávila, Arnau Miró, Jean Rabault, Bernat Font, Luis Miguel García-Cuevas, Oriol Lehmkuhl and Ricardo Vinuesa

Actuators 2022, 11(12), 359; https://doi.org/10.3390/act11120359 - 2 Dec 2022

Cited by 14 | Viewed by 3795

Abstract

The increase in emissions associated with aviation requires deeper research into novel sensing and flow-control strategies to obtain improved aerodynamic performances. In this context, data-driven methods are suitable for exploring new approaches to control the flow and develop more efficient strategies. Deep artificial [...] Read more.

The increase in emissions associated with aviation requires deeper research into novel sensing and flow-control strategies to obtain improved aerodynamic performances. In this context, data-driven methods are suitable for exploring new approaches to control the flow and develop more efficient strategies. Deep artificial neural networks (ANNs) used together with reinforcement learning, i.e., deep reinforcement learning (DRL), are receiving more attention due to their capabilities of controlling complex problems in multiple areas. In particular, these techniques have been recently used to solve problems related to flow control. In this work, an ANN trained through a DRL agent, coupled with the numerical solver Alya, is used to perform active flow control. The Tensorforce library was used to apply DRL to the simulated flow. Two-dimensional simulations of the flow around a cylinder were conducted and an active control based on two jets located on the walls of the cylinder was considered. By gathering information from the flow surrounding the cylinder, the ANN agent is able to learn through proximal policy optimization (PPO) effective control strategies for the jets, leading to a significant drag reduction. Furthermore, the agent needs to account for the coupled effects of the friction- and pressure-drag components, as well as the interaction between the two boundary layers on both sides of the cylinder and the wake. In the present work, a Reynolds number range beyond those previously considered was studied and compared with results obtained using classical flow-control methods. Significantly different forms of nature in the control strategies were identified by the DRL as the Reynolds number

R e

increased. On the one hand, for

R e \leq 1000

, the classical control strategy based on an opposition control relative to the wake oscillation was obtained. On the other hand, for

R e = 2000

, the new strategy consisted of energization of the boundary layers and the separation area, which modulated the flow separation and reduced the drag in a fashion similar to that of the drag crisis, through a high-frequency actuation. A cross-application of agents was performed for a flow at

R e = 2000

, obtaining similar results in terms of the drag reduction with the agents trained at

R e = 1000

and 2000. The fact that two different strategies yielded the same performance made us question whether this Reynolds number regime (

R e = 2000

) belongs to a transition towards a nature-different flow, which would only admits a high-frequency actuation strategy to obtain the drag reduction. At the same time, this finding allows for the application of ANNs trained at lower Reynolds numbers, but are comparable in nature, saving computational resources. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

16 pages, 6998 KiB

Open AccessArticle

Characteristics of a Fluidic Oscillator with Low Frequency and Low Speed and Its Application to Stall Margin Improvement

by Zhuoqi Liu, Tianyu Pan, Shiqi Wang and Zhaoqi Yan

Actuators 2022, 11(12), 341; https://doi.org/10.3390/act11120341 - 22 Nov 2022

Viewed by 1673

Abstract

Active flow control methods are commonly used in expanding the operating range of compressors. Indeed, unsteady active control methods are the main focus of researchers due to their effectiveness. For constructing an unsteady active control system, reliable actuators are significant. To compare with [...] Read more.

Active flow control methods are commonly used in expanding the operating range of compressors. Indeed, unsteady active control methods are the main focus of researchers due to their effectiveness. For constructing an unsteady active control system, reliable actuators are significant. To compare with conventional actuators such as synthetic jet actuators and rotating valves, fluidic oscillators have structurally robust characteristics and can generate self-excited and self-sustained oscillating jets, which leads to its higher applicability in compressors under severe working conditions. Thus, to explore the feasibility of unsteady active control systems by the usage of fluidic oscillators, a low-frequency and low-speed oscillator is first designed and experimentally studied for improving the stability of a low-speed axial flow compressor. During the experiments, a special casing is designed to install 15 uniformly distributed oscillators in the tip region of compressor. Based on the unsteady micro injections of the rotor tip with rotor rotation frequency, the results indicate that the frequency/period of oscillators are flexible, in which the values are decoupled with the variation of inlet pressure. When the inlet-to-outlet pressure ratio of the oscillator is in the range of 1.1~2.0, the maximum velocity ranges from 30 m/s to 80 m/s. Moreover, the mass flow rate of the single oscillator only varies from 0.017‰ to 0.059‰ from the designed compressor mass flow rate. For the improvement of the compressor stall margin, the value is 3.45% when the total mass flow of oscillators is 0.08% of the designed compressor mass flow. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

21 pages, 8448 KiB

Open AccessArticle

Evolution and Near-Wall Effect of the Vortex Structures Induced by In-Line Twin Synthetic Jets in a Crossflow

by Hongxin Wang, Degang Xu, Linwen Li, Kaiwen Zhou, Xin Wen and Hui Tang

Actuators 2022, 11(8), 234; https://doi.org/10.3390/act11080234 - 16 Aug 2022

Viewed by 1422

Abstract

This paper aims to further the understanding of the mixing process of in-line twin synthetic jets (SJs) and their impact in the near-wall region in a flat-plate laminar boundary layer. A numerical study has been carried out, in which colored fluid particles and [...] Read more.

This paper aims to further the understanding of the mixing process of in-line twin synthetic jets (SJs) and their impact in the near-wall region in a flat-plate laminar boundary layer. A numerical study has been carried out, in which colored fluid particles and the Q criterion are used to track the SJ-induced vortex structures at the early stage of the evolution. Interacting vortex structures at four selected phase differences are presented and analyzed. It is found that the fluid injected at the early stage of the blowing stroke mainly contributes to the formation of the hairpin legs, the fluid injected near the maximum blowing mainly contributes to the formation of the hairpin head, and the fluid injected at the late stage of the blowing stroke contributes very little to the formation of the hairpin vortex. It is also confirmed that, irrespective of the phase difference, the hairpin vortex issued from the upstream actuator is more capable of maintaining its coherence than its counterpart issued from the downstream actuator. The influence of the interacting vortex structures on the boundary layer is also studied through investigating excess wall shear stress. In all cases, a pair of streaks of high wall shear stress can be observed with similar size. Among them, the streaks have the strongest wall shear stress, with the largest gap at phase difference 0 when partially interacting vortex structures are produced. The findings can provide valuable guiding information for the applications of synthetic jets in heat transfer, mixing control, and flow control in a crossflow. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

12 pages, 3018 KiB

Open AccessArticle

Dual Synthetic Jets Actuator and Its Applications—Part II: Novel Fluidic Thrust-Vectoring Method Based on Dual Synthetic Jets Actuator

by Jie-Fu Liu, Zhen-Bing Luo, Xiong Deng, Zhi-Jie Zhao, Shi-Qing Li, Qiang Liu and Yin-Xin Zhu

Actuators 2022, 11(8), 209; https://doi.org/10.3390/act11080209 - 29 Jul 2022

Cited by 7 | Viewed by 1956

Abstract

A novel fluidic thrust-vectoring (FTV) control method based on dual synthetic jets actuator (DSJA) is proposed and evaluated. Numerical simulations are governed by the compressible Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations. According to the results, DSJA is capable of deflecting a primary jet with [...] Read more.

A novel fluidic thrust-vectoring (FTV) control method based on dual synthetic jets actuator (DSJA) is proposed and evaluated. Numerical simulations are governed by the compressible Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations. According to the results, DSJA is capable of deflecting a primary jet with a velocity of 100 m/s and a height of 50 mm by approximately 18 degrees with a momentum coefficient of 1.96%. It produces comparatively linear control characteristics in almost all deflection angles evaluated (0~23 degrees). The low pressure generated by DSJA, the ejecting enhanced by DSJA, and the co-flow effect produced by the accelerated secondary jet all play roles in the deflection of the primary jet. Since the primary jet is strong enough, the potential of DSJA to provide thrust vector control is revealed. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

14 pages, 16899 KiB

Open AccessArticle

Dual Synthetic Jets Actuator and Its Applications—Part I: PIV Measurements and Comparison to Synthetic Jet Actuator

by Zhenbing Luo, Zhijie Zhao, Xiong Deng, Lin Wang and Zhixun Xia

Actuators 2022, 11(8), 205; https://doi.org/10.3390/act11080205 - 22 Jul 2022

Cited by 9 | Viewed by 1875

Abstract

In order to understand the differences between dual synthetic jets (DSJs) and synthetic jets (SJs), particle image velocimetry (PIV) technology is used to capture the basic flow field characteristics of a dual synthetic jet actuator (DSJA) and a synthetic jet actuator (SJA), and [...] Read more.

In order to understand the differences between dual synthetic jets (DSJs) and synthetic jets (SJs), particle image velocimetry (PIV) technology is used to capture the basic flow field characteristics of a dual synthetic jet actuator (DSJA) and a synthetic jet actuator (SJA), and then a careful comparison between them is implemented. The results indicate that a cycle of the DSJ is divided into two stages. In the near-field downstream, a pair of synthetic jets entrain fluid around them and interact with each other, making the flow field complex, and the time-periodic diaphragm dominates them. There is an unfavorable phenomenon of “self-support” between the two jets. In the far-field downstream, the two jets merge into a single, more stable SJ with a higher velocity and a double characteristic frequency. The DSJs have also shown good vectoring characteristics, with the vectoring deflection angle (VDA) changing from about −46° to 46°. The above results demonstrate that the DSJA may replace the traditional SJA in all kinds of applications and extend the applying area of the SJ to more active flow control systems, which cannot be qualified by traditional SJA. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

16 pages, 4896 KiB

Open AccessArticle

Influence of Synthetic Jets on Multiscale Features in Wall-Bounded Turbulence

by Biaohui Li, Jinhao Zhang and Nan Jiang

Actuators 2022, 11(7), 199; https://doi.org/10.3390/act11070199 - 18 Jul 2022

Cited by 1 | Viewed by 1259

Abstract

This experimental research focuses on the impacts of submerged synthetic jets on a fully-developed turbulent boundary layer (TBL) under a drag reduction working case. Two-dimensional velocity vectors in the flow field are captured with the aid of a particle image velocimetry (PIV) system. [...] Read more.

This experimental research focuses on the impacts of submerged synthetic jets on a fully-developed turbulent boundary layer (TBL) under a drag reduction working case. Two-dimensional velocity vectors in the flow field are captured with the aid of a particle image velocimetry (PIV) system. Proper orthogonal decomposition (POD) analyses provide evidence that synthetic jets notably attenuate the induction effect of prograde vortex on the low-speed fluid in large-scale fluctuation velocity field, thereby weakening the bursting process of near-wall turbulent events. Furthermore, the introduced perturbance redistributes the turbulent kinetic energy (TKE) and concentrates the TKE onto small-scale coherent structures. Modal time coefficients in various orders of POD are divided into components of multiple frequency bands by virtue of complementary ensemble empirical mode decomposition (CEEMD). It is found that the turbulence signals are shifted from low-frequency to high-frequency bands thanks to synthetic jets, thus revealing the relationship between scales and frequency bands. One further method of scale decomposition is proposed, that is, the large-scale fluctuating flow field will be obtained after removing the high-frequency noise data with the help of continuous mean square error (CMSE) criterion. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

15 pages, 2780 KiB

Open AccessArticle

Transonic Buffet Active Control with Local Smart Skin

by Kai Ren, Chuanqiang Gao, Fangqi Zhou and Weiwei Zhang

Actuators 2022, 11(6), 155; https://doi.org/10.3390/act11060155 - 10 Jun 2022

Cited by 2 | Viewed by 1848

Abstract

Transonic flight has high economic benefits, but the appearance of transonic buffet limits the flight envelope. The shock control bump currently used for transonic buffet suppression tends to degrade the aerodynamic performance of the non-buffeting state. In this study, a smart skin system [...] Read more.

Transonic flight has high economic benefits, but the appearance of transonic buffet limits the flight envelope. The shock control bump currently used for transonic buffet suppression tends to degrade the aerodynamic performance of the non-buffeting state. In this study, a smart skin system is used to eliminate the fluctuating load of transonic buffet by measuring the airfoil lift coefficient as the feedback signal and adjusting the local skin height using data-driven, model-free adaptive control. Since the actuator height is dynamically adjusted only after the occurrence of transonic buffet, the smart skin can completely suppress the fluctuating load and does not affect the aerodynamic performance in the non-buffeting state. The suppression effect of the proposed smart skin on transonic buffet is verified by numerical simulation of the flow. The simulation results show that due to the introduction of closed-loop control, the fluctuating load of transonic buffet can be effectively suppressed for different positions and maximum heights of the actuator. Even when the flow state changes, the robust smart skin system can also achieve the control goal. Therefore, smart skins combining flexible materials and control technologies have the potential to effectively improve the aerodynamic performance of aircraft. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

20 pages, 6287 KiB

Open AccessArticle

Experimental and Numerical Study on Incident Shock Wave/Boundary Layer Interaction Control

by Chuanbiao Zhang, Yanhao Luo, Hua Liang, Shanguang Guo and Hesen Yang

Actuators 2022, 11(6), 148; https://doi.org/10.3390/act11060148 - 2 Jun 2022

Cited by 1 | Viewed by 1871

Abstract

This study was designed to explore the control effect of pulsed arc discharge plasma actuation on the incident shock wave/boundary layer interaction (ISWBLI). Research was conducted on an ISWBLI flow field with 10 kHz single-channel pulsed arc discharge plasma actuation and pulsed arc [...] Read more.

This study was designed to explore the control effect of pulsed arc discharge plasma actuation on the incident shock wave/boundary layer interaction (ISWBLI). Research was conducted on an ISWBLI flow field with 10 kHz single-channel pulsed arc discharge plasma actuation and pulsed arc discharge plasma actuation array applied at Mach 2.0 experimentally and numerically. In the investigation, high-speed schlieren flow field visualization technology was adopted, focusing on the change in shock wave intensity caused by plasma actuation. Combined with the detached eddy simulation (DES) method, the numerical simulation focused on the regulating effect of plasma actuation on the separation zone. The key research results showed that, in terms of the spatial flow field, the simulation results were consistent with the experimental results. The single-channel actuation could only just achieve the control effect on the ISWBLI, while array actuation effectively weakened the shock wave intensity. Furthermore, the ISWBLI separation zone in the base flow field was crescent shaped. Its length at the middle of the flat plate was longer than that at the two sides. It was identified that, after applying single-channel actuation, the start of separation slightly moved forward. Similarly, after the application of array actuation, the start point of separation at the middle section in a spanwise direction moved forward by about 19 mm. The length of the separation zone increased by 30 mm but reduced at the two sides. Its influence, spanwise, was also significantly diminished. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

14 pages, 3168 KiB

Open AccessArticle

Experimental Study of Dynamical Airfoil and Aerodynamic Prediction

by Zheyu Shi, Kaiwen Zhou, Chen Qin and Xin Wen

Actuators 2022, 11(2), 46; https://doi.org/10.3390/act11020046 - 2 Feb 2022

Viewed by 2210

Abstract

Dynamic stall is a critical limiting factor for airfoil aerodynamics and a challenging problem for active flow control. In this experimental study, dynamic stall was measured by high-frequency surface pressure tapes and pressure-sensitive paint (PSP). The influence of the oscillation frequency was examined. [...] Read more.

Dynamic stall is a critical limiting factor for airfoil aerodynamics and a challenging problem for active flow control. In this experimental study, dynamic stall was measured by high-frequency surface pressure tapes and pressure-sensitive paint (PSP). The influence of the oscillation frequency was examined. Dynamic mode decomposition (DMD) with time-delay embedding was proposed to predict the pressure field on the oscillating airfoil based on scattered pressure measurements. DMD with time-delay embedding was able to reconstruct and predict the dynamic stall based on scattered measurements with much higher accuracy than standard DMD. The reconstruction accuracy of this method increased with the number of delay steps, but this also prolonged the computation time. In summary, using the Koopman operator obtained by DMD with time-delay embedding, the future dynamic pressure on an oscillating airfoil can be accurately predicted. This method provides powerful support for active flow control of dynamic stall. Full article

(This article belongs to the Special Issue Active Flow Control: Recent Advances in Fundamentals and Applications)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Active Flow Control: Recent Advances in Fundamentals and Applications

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (11 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI