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active flow control for Drag Reduction Through Multi-agent Reinforcement Learning on a Turbulent Cylinder at ReD=3900

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flow TURBULENCE AND COMBUSTION 2025年 1-25页

作者： Suarez, Pol Alcantara-avila, Francisco Miro, Arnau Rabault, Jean Font, Bernat Lehmkuhl, Oriol Vinuesa, Ricardo KTH Royal Inst Technol FLOW Engn Mech S-10044 Stockholm Sweden Barcelona Supercomp Ctr BSC CNS Barcelona 08034 Spain Delft Univ Technol Fac Mech Engn NL-2600 AA Delft Netherlands

This study presents novel drag reduction active-flow-control (AFC) strategies for a three-dimensional cylinder immersed in a flow at a Reynolds number based on freestream velocity and cylinder diameter of ReD=3900. The cylinder in this subcritical flow regime has been extensively studied in the literature and is considered a classic case of turbulent flow arising from a bluff body. The strategies presented are explored through the use of deep reinforcement learning. The cylinder is equipped with 10 independent zero-net-mass-flux jet pairs, distributed on the top and bottom surfaces, which define the AFC setup. The method is based on the coupling between a computational-fluid-dynamics solver and a multi-agent reinforcement-learning (MARL) framework using the proximal-policy-optimization algorithm. This work introduces a multi-stage training approach to expand the exploration space and enhance drag reduction stabilization. By accelerating training through the exploitation of local invariants with MARL, a drag reduction of approximately 9% is achieved. The cooperative closed-loop strategy developed by the agents is sophisticated, as it utilizes a wide bandwidth of mass-flow-rate frequencies, which classical control methods are unable to match. Notably, the mass cost efficiency is demonstrated to be two orders of magnitude lower than that of classical control methods reported in the literature. These developments represent a significant advancement in active flow control in turbulent regimes, critical for industrial applications.

关键词： Fluid mechanics Drag reduction Deep learning active flow control Multi-agent reinforcement learning

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Deep reinforcement learning for active flow control in bluff bodies: A state-of-the-art review

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OCEAN ENGINEERING 2025年 327卷

作者： Moslem, Foad Jebelli, Mohammad Masdari, Mehran Askari, Rasoul Ebrahimi, Abbas Univ Tehran Tehran Iran Sharif Univ Technol Tehran Iran City St Georges Univ London London England Univ Tehran Coll Interdisciplinary Sci & Technol Tehran Iran

active flow control (AFC) of bluff bodies is a critical concept in a variety of engineering applications, ranging from structural safety to clean energy harvesting. The current study reviews the application of deep reinforcement learning (DRL) in AFC of bluff bodies with a focus on key studies between 2017 and 2024. DRL has improved AFC capabilities by enabling real-time optimization and adaptive control. The review showed a focus on a single circular cylinder, generally simulated two-dimensionally at a low Reynolds number of 100, using CFD tools like OpenFOAM and FEniCS. Synthetic jets are favored actuators and Proximal Policy Optimization (PPO), is the most widely used DRL algorithm. Despite significant advances, key challenges still remain in the field. Scalability to higher Reynolds numbers and turbulent flows, high computational cost, and sensor optimization issues are the main challenges, which have been the focus of significant efforts to address. The review identifies inconsistent reporting of hyperparameters and varied training procedures, which may hinder reproducibility of works for further steps. Future research should address these gaps to extend the applicability of DRL in practical AFC systems. A comprehensive framework is also proposed to connect initial simulation results with real-world applications.

关键词： active flow control Machine learning Deep reinforcement learning Bluff body

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Comprehensive characterization of a pneumatic active flow control system using in-situ hot wire calibration

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flow MEASUREMENT AND INSTRUMENTATION 2025年 102卷

作者： Cetin, Cenk Yavuz, Mehmet Metin Turkish Aerosp Ind Inc TR-06890 Ankara Turkiye Middle East Tech Univ Mech Engn Dept TR-06800 Ankara Turkiye

Pneumatic active flow control systems have great potential to control the aerodynamic phenomena including, separation, circulation, and turbulence. To quantify the effectiveness of such flow control schemes, thorough characterization of developed systems is critical in addition to estimating aerodynamic and stability favor. In the present work, experimental characterization of an in-house active blowing system capable of steady and periodic excitations, based on fast switching solenoid valves, is presented via in-situ calibration scheme. Measurements are performed using a constant temperature anemometry system, and characterization is presented for a sample 45o swept delta wing aerodynamic surface. The performance of the developed system is comprehensively investigated for a square wave form excitation with control parameters including an excitation frequency range of 1-32 Hz, duty cycle values of 25 and 50 %, and supply line regulator settings corresponding to supply rate range of 34 m/s <= Ublow,ref <= 60 m/s. The results indicate that the response of the flow control system to control signals is influenced by both the signal parameters and the aerodynamic surface design. Full characterization of such systems using in-situ approaches provides valuable calibration schemes for the mentioned parameters, which is crucial for assessing aerodynamic effectiveness and developing closed-loop flow control systems.

关键词： Experimental aerodynamics Non-slender delta wing active flow control Steady blowing Unsteady blowing In situ calibration

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Large-scale horizontal axis wind turbine aerodynamic efficiency optimization using active flow control and synthetic jets

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ENERGY 2025年 319卷

作者： Nabhani, Ahmad Tousi, Navid M. Coma, Marti Bugeda, Gabriel Bergada, Josep M. Univ Politecn Cataluna Dept Fluid Mech Jordi Girona 31 Barcelona 08034 Spain Univ Politecn Cataluna Dept Phys Jordi Girona 31 Barcelona 08034 Spain Multibody Works SLU Fac Philol Sant Tomas 17 B-1St Cugat valles Cugat Del valles 08172 Barcelona Spain Univ Politecn Cataluna Dept Civil & Environm Engn Jordi Girona 31 Barcelona 08034 Spain Int Ctr Numer Methods Engn CIMNE Edif C1 Campus Nord UPC C-Gran CapitaS-N Barcelona 08034 Spain

Efficiency increase is seen as one of the main goals of any energy-converting device. In this direction, the present study aims to demonstrate that large-scale wind turbines can still be improved in order to generate larger amounts of energy. The research presented in this manuscript consists of two main blocks. Initially, it analyzes via Computational Fluid Dynamics (CFD) the boundary layer dynamics on a set of pre-determined airfoils cut along the DTU-10MW reference blade by using the 2D URANS k - !SST turbulence model. The aim of this initial stage is to identify the boundary layer separation point, its associated frequency, and peak-to-peak amplitude for each airfoil cut along the blade, evaluating as well their respective aerodynamic characteristics. The second main goal of the present research consists of implementing the active flow control (AFC) technology and, when employing synthetic jets, to reattach the boundary layer in all airfoils where it is separated. To accomplish this second goal efficiently, the five parameters associated with the AFC implementation performed on each airfoil will be obtained through respective genetic algorithm optimizations. An energy assessment is finally undertaken at each airfoil to validate the respective energy gain obtained. When comparing the net power gain, before and after AFC implementation, generated by each of the airfoils evaluated, net power gains between 23 and 36 kW are obtained in all airfoils analyzed, clarifying that the proposed technology is capable of improving the performance of the wind turbines, very likely at any operating condition.

关键词： Wind turbines Power enhancement active flow control Synthetic jets Optimization Aerodynamic efficiency

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Suppression of flow separation of a high-lift wing with active flow control

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AEROSPACE SCIENCE AND TECHNOLOGY 2025年 159卷

作者： Sun, Qiangqiang Bahri, Faycal Jabbal, Mark Stryczniewicz, Wit Jefferson-Loveday, Richard Stefes, Bruno Buescher, Alexander Univ Nottingham Fac Engn Nottingham NG7 2RD England Lukasiewicz Res Network Inst Aviat Aerodynam Dept Al Krakowska 110-114 PL-02256 Warsaw Poland Kings Coll London Fac Nat Math & Engn Sci London WC2R 2LS England Airbus Operat GmbH Airbus Allee 1 D-28199 Bremen Germany

flow separation caused by the integration of a leading edge slat cut-out to accommodate an ultra-high bypass ratio engine reduces the maximum lift coefficient. In this study, an active flow control approach including 88 pulsed jet nozzles near the leading edge is used to control flow separation over a multi-element high-lift aerofoil. A hybrid large-eddy simulation (LES) and stress-blended eddy simulation (SBES) method is deployed to analyze flow physics and wind tunnel tests are also performed for the flow with/without control. The results show that severe flow separation is observed for the clean case by visualizing the streamlines on the airfoil's surface via numerical and experimental methods. Compared with the clean case, the stall angle is delayed by around 4 degrees, and the maximum lift coefficient is increased by more than 15% after deploying the active flow control. Meanwhile, when the active flow control is imposed, a lift enhancement region caused by the vortex shedding downstream of the jet nozzles is formed adjacent to the leading edge, and its scale becomes larger along the spanwise direction.

关键词： Lift enhancement flow separation Multi-element wing active flow control Pulsed jet flow control

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active flow control Technology Based on Simple Droop Devices and a Co-flow Jet for Lift Enhancement

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AEROSPACE 2025年第3期12卷 198-198页

作者： Jiao, Jin Chen, Cheng Wang, Bo Ying, Pei Wei, Qiong Nie, Shengyang Xihang Univ Sch Aircraft Xian 710077 Peoples R China China Aerodynam Res & Dev Ctr Aerosp Technol Inst Mianyang 621000 Peoples R China Chinese Acad Sci Inst Engn Thermophys Beijing 100190 Peoples R China Xian Univ Technol Sch Civil Engn & Architecture Xian 710048 Peoples R China

The missions of modern aircraft require multiple abilities, such as highly efficient taking-off and landing, fast arrival, and long-endurance hovering. It is difficult to achieve all technical objectives using traditional aircraft design technology. The active flow control technology using the concept of a co-flow jet (CFJ) is a flow control method without a mass source that does not require air from the engine. It has strong flow control ability in low-speed flow, can greatly improve the stall angle of the aircraft, and can obtain large lift enhancement. At transonic conditions, it can lead to a larger lift-drag ratio with a small expense. CFJ technology has great application potential for aircraft due to its flexible control strategy and remarkable control effect. In this paper, the concept of a combination of CFJ and variable camber technology is proposed which realizes the change of airfoil camber to meet different task requirements with the movable droop head. By using the built-in ducted fan, air is blown and sucked in the jet channel so as to realize CFJ flow control. In a state of high-speed flight, complete geometric restoration is achieved by closing the channel and retracting the droop head. In this paper, the design and aerodynamic analysis of a CFJ device with variable camber based on a supercritical airfoil with small camber and a small leading-edge radius are carried out using the computational fluid dynamics (CFD) method. Comparative studies are conducted for different schemes on the taking off and landing performances, and discussions are had on core technical parameters such as power consumption. The results indicate that by utilizing the CFJ technology with more than 10 degrees of droop device, the maximum lift coefficient of a supercritical airfoil with a small camber and leading-edge radius, which is suitable for transonic flight, can be increased to a value larger than 4.0.

关键词： variable camber co-flow jet active flow control lift-drag ratio maximum lift coefficient power consumption

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Advancements in the physical simulation of near-surface extreme wind phenomena using hybrid active-passive flow control in a large boundary layer wind tunnel

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2025年 259卷

作者： Pinyochotiwong, Y. Catarelli, R. A. Chen, T. A. Phillips, B. M. Masters, F. J. Bridge, J. A. Gurley, K. R. Univ Florida Engn Sch Sustainable Infra & Env Gainesville FL 32611 USA

This paper presents advancements in the reduced-scale physical simulation of near-surface synoptic and non- synoptic extreme wind phenomena in a long-fetch boundary layer wind tunnel (BLWT). This research was carried out at the University of Florida's BLWT, which is one of the National Science Foundation's (NSF) Natural Hazards Engineering Research Infrastructure (NHERI) Experimental Facilities (EF). flow fields in the UF BLWT are created by three computer-controlled flow-conditioning stages: vaneaxial fans (VAF), automated roughness elements collectively called the Terraformer (TF), and a multi-fan array called the flow Field Modulator (FFM). The VAF and TF together can generate traditional BLWT log law atmospheric surface layer (ASL) wind velocity profiles. The FFM provides additional mean flow shaping, active turbulence modulation, and the ability to create nonstationary flow fields toward simulating non-synoptic events. A novel governing convergence algorithm (GCA) was developed to provide seamless closed-loop control of the three flow-conditioning stages toward achieving target profiles in the downwind test section. Three case studies covering a broad range of target flow conditions are demonstrated. The first case is a stationary non-monotonic mean target profile, illustrating the mean flow shaping capabilities of the GCA. The second case is a nonstationary non-monotonic transitioning flow, illustrating how the FFM can be used to transition between two GCA-converged targets. The third case is a stationary ASL flow profile where the GCA is used to converge longitudinal mean, turbulence intensity, and integral length scale profiles simultaneously. The results demonstrate that a multi-stage flow control approach with closed-loop convergence can achieve user-specified complex and transient flow conditions. The resultant flow capabilities expand the traditional limits of flow simulation, bringing the breadth of behaviors in real wind events and our controlled study

关键词： Boundary layer wind tunnel Physical simulation active flow control Multi-fan Turbulence modulation Downburst Gust front Velocity profile

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Mitigation of flow separation in a highly bent intake duct with active and passive flow control

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AERONAUTICAL JOURNAL 2025年第1335期129卷 1381-1398页

作者： Max, P. Stoessel, M. Kozulovic, D. Krummenauer, M. Univ Bundeswehr Munich Inst Jet Prop Dept Aerosp Engn Munich Germany Bundeswehr Tech Ctr Aircraft & Aeronaut Equipment Manching Germany

Typically, the fuselage of a modern military aircraft is designed in such a way that the propulsion system is integrated into it. The main reasons are reduction of installation space and minimisation of radar signature. Those requirements can be achieved by using highly bent engine intakes, which are occluding a direct line of sight to the compressor system. Depending on their design, secondary flows and flow separation can be expected due to the strong curvature of the intake system. In this study, a serpentine intake in front of the Larzac 04 test engine is investigated experimentally and its performance compared with and without flow stabilising measures. In detail, a configuration with vortex generators was compared experimentally with a configuration of active flow control by injected air. In order to analyse and compare the efficiency of both systems, the dimensionless total pressure coefficient, the distortion coefficient (DC60) and detailed surface pressure distributions as well as the aerodynamic interface plane are evaluated. In addition, different throttle lines were recorded for surge line evaluation of the low pressure compressor of the Larzac engine and compared for each flow-stabilising measure investigated. It was found that the application of injecting air showed a larger improvement in surge margin and reduction in distortion coefficients compared to the passive flow control.

关键词： highly bent engine intakes active flow control passive flow control

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Effect of active/passive flow control based on synthetic jet of stator blades on a single stage axial compressor

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY 2025年

作者： Wang, Guang Chen, Xiangyi Chu, Wuli Guilin Univ Aerosp Technol Sch Aeronaut & Astronaut 2 Jinji Rd Guilin 541004 Guangxi Peoples R China Northwestern Polytech Univ Sch Power & Energy Xian Peoples R China

To investigate the effect of synthetic jet on the stator blade's suction surface on the axial compressor's performance and stability, a high-speed subsonic single-stage axial compressor is numerically simulated in this paper. The results show that there is an optimal excitation position. Under this position's excitation, the compressor's peak efficiency is improved, and the comprehensive stability margin is also slightly improved. The analysis of internal flow field shows that the improvement of compressor efficiency is mainly due to the reduction of stator blockage, which reduces the stator's channel loss and outlet loss. At the same time, the reduction of stator channel blockage also optimizes the inter-stage matching of the compressor, which is of positive significance for the improvement of rotor channel flow. To further improve the stability margin of the compressor, a coupling flow control method combining the rotor casing treatment with the synthetic jet on the stator suction surface is proposed. The results show that compared with the simple casing treatment, the flow stability margin of the single axial compressor is expanded from 4.38% to 5.46%, and the peak efficiency is improved from -0.93% to only -0.3%.

关键词： Axial compressor active flow control synthetic jet performance improvement numerical simulation

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active flow control over a NACA23012 Airfoil using Hybrid Jet

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DEFENCE SCIENCE JOURNAL 2021年第6期71卷 721-729页

作者： Singh, Deepak Kumar Jain, Anuj Paul, Akshoy Ranjan Indian Inst Technol Delhi Dept Appl Mech New Delhi 110016 India Motilal Nehru Natl Inst Technol Allahabad Dept Appl Mech Prayagraj 211004 India

A time-dependent numerical simulation is performed to examine the flow separation control with the action of a hybrid jet (the combination of synthetic and continuous jets) over a NACA23012 airfoil. The unsteady Reynolds averaged Navier-Stokes (URANS) simulation is performed with Spalart-Allmaras (SA) turbulence model to simulate the flow field around the airfoil to analyse the effect of the hybrid jet. A combined jet is placed at the point of flow separation on the upper surface of the airfoil which is located at the 12% of the chord length from the leading edge of the airfoil for a given flow configuration. flow simulations are performed at a chord-based Reynolds number of 2.19 x 106 for the hybrid jet oscillating frequency of 0.159 at a blowing ratio of 3.0. The contribution of the continuous jet in the hybrid jet is evident by the flow control. Variation in the continuous jet velocity is studied, which improved the aerodynamic characteristics of the airfoil. The maximum improvement in lift to drag ratio is observed from 11.19 to 22.14 at an angle of attack of 22 degree. The stall angle also shows an enhancement from 18 degree to 20 degree.

关键词： active flow control Airfoil Synthetic jet Continuous jet Hybrid jet

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