In the aerodynamic performance optimization for aircraft, although both the Magnus effect and the Coanda effect have demonstrated significant potential increasing lift, reducing drag, and enabling flow control, the complex flow mechanisms arising from their coupled application remain insufficiently explored, which to some extent limits their engineering implementation. Major challenges in active flow control include structural vibrations and additional energy consumption induced by the Magnus effect, as well as uncertainties in flow separation and attachment behavior of the Coanda jet under varying conditions. To address these issues, the study proposes an innovative configuration that integrates a rotating trailing-edge cylinder with internal jet blowing to combine both effects within a single airfoil structure. Utilizing a unified numerical modeling approach, the research systematically investigates the influence of different jet momentum coefficients (Cµ ) and freestream Mach numbers (Ma) on the aerodynamic characteristics and coupled control performance of the airfoil. The results reveal that at moderate jet intensities (Cµ = 0.075), an optimal lift-to-drag ratio can be achieved under limited energy consumption, while higher Ma values, despite reducing aerodynamic efficiency, significantly suppress aerodynamic load oscillations, contributing to improved flight stability. By establishing an evaluation framework focusing on both aerodynamic performance and energy consumption, this study identifies two factors influencing the effectiveness of coupled control, thereby filling a gap in the research on Magnus–Coanda coupled control performance and providing a theoretical foundation for the engineering application of active flow control systems under multi-condition cases.

The membrane oxygenator serves as the core component of extracorporeal life support systems, and its gas exchange efficiency critically influences clinical outcomes. However, gas transfer is predominantly limited by the diffusion barrier within the blood-side boundary layer, where saturated red blood cells accumulate. Current research focuses mainly on static approaches such as optimizing fiber bundle configuration to promote passive blood mixing or modifying material properties, which are fixed after fabrication. In contrast, dynamic blood flow control remains an underexplored avenue for enhancing oxygenator performance. This study proposes an active pulsatile flow control method that disrupts the boundary layer barrier by optimizing periodic flow profiles, thereby directly improving gas exchange. A deep reinforcement learning framework integrating proximal policy optimization and long short-term memory networks was developed to autonomously search for optimal flow waveforms under constant flow conditions. A simplified stacked-plate membrane oxygenator was specially designed as the experimental platform to minimize flow path interference. Experimental results demonstrate that the optimized pulsatile profile increases the oxygen transfer rate by 20.64% without compromising hemocompatibility.

Stabilizing and shaping autonomous flows of active fluids is a fundamental challenge and a prerequisite for applications. We embed a light-responsive microtubule-based nematic in a proportional-integral control loop that adjusts the applied light intensity in response to real-time measurements of the spatially averaged flow speed. The self-regulating hardware-software-wetware system maintains a target flow speed against external or internal perturbations, including protein aging and aggregation, sample-to-sample variability, and temperature variation. Varying the controller’s gains reveals antagonistic roles between feedback and intrinsic processes, leading to nontrivial dynamics observed in fluctuation spectra. In particular, oscillations emerge from the interplay between the controller, motor binding kinetics, and active hydrodynamic relaxation. Accounting for the underlying binding timescale, our coarse-grained model and nematohydrodynamics simulations corroborate these observations. This work provides insight into the coupled dynamics of controlled active matter, laying the foundation for spatiotemporal patterning of active stress to generate and stabilize new dynamical configurations.

High-lift devices are essential aerodynamic features used to enhance aircraft performance during the low-speed regime, namely takeoff and landing, as well as in high-maneuverability flight regimes. In this paper, a comparative study of high-lift system design philosophies used in two classes of aircraft, commercial airliners and military fighters, is presented. Commercial aviation has an overriding interest in trailing-edge high-lift devices for fuel efficiency, safety, and economic maturity. Military fighter design has an overriding interest in leading-edge devices for enhanced aircraft maneuverability, controllability, and post-stall flight characteristics. The paper presents a systematic comparison of design philosophies used in high-lift system design in commercial transports and military fighters. Commercial aviation uses trailing-edge high lift devices on aircraft such as the Boeing and Airbus families for lift-to-drag ratio optimization, and to operate within acceptable margins of weight, size, and maintenance. Military fighter aircraft use trailing-edge and leading-edge devices, such as slats and Leading-Edge Vortex Controllers (LEVCONs), to achieve enhanced aircraft maneuverability, controllability, and post-stall flight characteristics. The LEVCON operation is presented, including the mechanism of vortex generation and delay of stall. The extent to which modern fighters integrate the leading-edge aerodynamic controls with digital flight control is discussed. A comparative analysis of airliner and fighter high lift system design philosophies is presented. Airliner high lift systems are designed to operate in a predictable, safe, and efficient regime of low-speed flight. Fighter high lift systems are designed to operate in a regime of extreme flight regimes, in particular high angles of attack. Finally, future trends in high lift system design are discussed including unmanned aerial vehicles (UAVs) and blended-wing-body configurations. A review of promising trends in adaptive wing geometries, smart materials, and active flow control actuators is presented, including the prospect of truly aerostructurally integrated intelligent high lift systems.

Abstract The application of active flow control (AFC) methods in an intercompressor duct (ICD) offers the possibility of further length reduction while suppressing separations. In particular, pulsed jet actuators (PJAs) are advantageous because the pulsation enhances mixing processes. However, the PJAs require fluid that has already been compressed by the downstream high-pressure compressor. Therefore, injecting this high-momentum fluid from a downstream component makes this approach very expensive. Consequently, a highly optimized design is required to achieve the maximum separation suppression while minimizing the external energy. However, the numerical optimization requires steady simulations to find an optimum design in manageable time scales. Therefore, this study helps in understanding if any aspects of unsteadiness are neglected by optimizing the PJA implementation with steady methods. Furthermore, the influence of the steady-state assumption in the optimization is quantified. The influence of the unsteadiness of the PJA is investigated by comparing steady and unsteady simulations. The unsteady simulations include unsteady Reynolds-averaged Navier–Stokes and delayed detached-eddy simulation. The numerical simulations are validated against experimental data obtained at the TU Berlin ICD test rig. After evaluating the different approaches, a conclusion is drawn on how unsteady flow control methods can be efficiently optimized. Consequently, the study shows that all the methods investigated have their advantages and disadvantages. Their use must be carefully selected according to the objective of the investigation.

Abstract This study numerically investigates passive and active flow control methods in a 2.5-stage, low-speed, highly loaded axial compressor with tandem stators. Two configurations are analyzed using unsteady Reynolds-averaged Navier–Stokes (URANS) simulations: a passive inter-stage recirculation channel and a novel combined approach incorporating a synthetic jet actuator (SJA). The recirculation channel connects the endwall regions downstream of the rotor trailing edge (suction) to the upstream stator (injection) via Coanda slots. The combined approach enhances the injected flow with SJA actuation above the injector, introducing additional momentum and periodic forcing while avoiding structural compromises to the blade. Transient simulations at the design point explore various peak actuation velocities, frequencies, and phases. Results show that the combined method achieves more significant reductions in total pressure losses in the tandem stator compared to the recirculation channel alone while maintaining comparable performance in the subsequent rotor and increasing static pressure rise. The energy consumption of the actuator is evaluated, and off-design conditions are analyzed, showing that unthrottled conditions benefit more from flow control due to stronger secondary flow effects in the tandem stator endwall regions. These findings highlight the potential of novel flow control techniques to stabilize endwall flow and improve performance, showing, for the first time, their impact in a multistage compressor setup featuring tandem stators and offering insights for future highly loaded compressor designs with greater aerodynamic challenges.

Abstract Energy harvesting from vortex-induced vibrations is a promising technology that relies on the vibrations of bluff bodies due to the vortex shedding phenomenon. Increasing the vibration amplitude at a given free stream kinetic energy is therefore equivalent to enhancing the efficiency of the harvesting device. In this study, we assess the potential of alternate slot blowing to amplify force fluctuations. Pressurized air is ejected alternately from the top and bottom parts of a cylinder. Through experimentation in a low-speed wind tunnel (Re = 8,000), we show that the magnitude of lift fluctuations can be enhanced by up to a factor of three compared to the unforced flow when the actuation is aligned with the natural vortex shedding frequency. Particle image velocimetry measurements indicate that this is caused by strong streamline bending, whereas at a higher forcing frequency, the vortex shedding is observed to be suppressed. This work elaborates on the physics of slot blowing for amplitude enhancement, and results suggest that a significant increase in the dynamic load acting on a cylinder can be achieved with carefully chosen active-flow control parameters, thereby promoting future energy harvesting applications.

Fluidic oscillators (FOs) are commonly used in active flow control (AFC) applications to delay the boundary layer separation from any bluff-body. These devices are also employed in combustion chambers to enhance mixing, or in heat transfer applications to promote the generation of a turbulent boundary layer and therefore enhance cooling. The frequency associated with the self-sustained oscillations generated by the FO depends on the Reynolds number and the internal dimensions of the oscillator. In fact, this work aims to clarify which are the most relevant FO internal dimensions capable of modifying the outlet flow frequency and which is the origin of the self-sustained oscillations. Two main internal modifications were considered. Initially, the feedback channel (FC) width is modified, but differently from previous research papers, then in the present study, each FC width is associated with a different mixing chamber (MC) inlet width, and this small modification in the inlet width is proved to have large implications in the FO outlet frequency. In fact, the influence of the MC inlet width is found to be more relevant than the modification in the FC width. The modification of the MC outlet inclination wall is also addressed in the present study. The MC pressure and the interaction between the main jet and the reverse mass flow jet are highly influenced by this particular modification. When analyzing the forces acting on the main jet as it enters the MC, it is observed that, regardless of the internal modification performed, the pressure forces play the most important role; therefore, we conclude that for the present FO configuration, the self-sustained oscillations are pressure driven.

Active Control of Bimodal Transonic Flow Over the Payload Region of a Launch Vehicle Model Using a Counterflow Jet

We train active neural-network flow controllers using a deep learning PDE augmentation method to optimize lift-to-drag ratios in turbulent airfoil flows at Reynolds number 5×104 and Mach number 0.4. Direct numerical simulation and large-eddy simulation are employed to model compressible, unconfined flow over two-dimensional (2D) and three-dimensional (3D) semi-infinite NACA 0012 airfoils at angles of attack α=5, 10, and 15 deg. Control actions, implemented through a blowing/suction jet at a fixed location and geometry on the upper surface, are adaptively determined by a neural network that maps local pressure measurements to optimal jet total pressure, enabling a sensor-informed control policy that responds spatially and temporally to unsteady flow conditions. The sensitivities of the flow to the neural network parameters are computed using the adjoint Navier–Stokes equations, which we construct using automatic differentiation applied to the flow solver. The trained flow controllers significantly improve the lift-to-drag ratios and reduce flow separation for both 2D and 3D airfoil flows, especially at α=5 and 10 deg. The 2D-trained models remain effective when applied out-of-sample to 3D flows, which demonstrates the robustness of the adjoint-trained control approach. The 3D-trained models capture the flow dynamics even more effectively, which leads to better energy efficiency and comparable performance for both adaptive (neural network) and offline (simplified, constant-pressure) controllers. These results underscore the effectiveness of this learning-based approach in improving aerodynamic performance.

Abstract Surface dielectric barrier discharge (SDBD) plasma actuators have demonstrated considerable promise in the domain of active flow control. To optimize their performance, it is essential to understand their discharge characteristics, volume force mechanisms, and energy efficiency. This study numerically investigates the dynamics of SDBD plasma actuators under different drive waveforms, including constant, linear ramp, and sinusoidal voltages. The results show that the polarity of the applied voltage significantly influences discharge modes and volume force generation mechanisms. Positive polarity induces self-sustaining streamers or diffuse glow, generating a downstream volume force. Conversely, at constant voltage, negative polarity is dominated by Trichel pulses, which produce an upstream volume force. When a negative ramp voltage is applied, the discharge transitions from Trichel pulses to a continuous, expanding negative corona/glow, with the volume force shifting from upstream to downstream. For a sinusoidal voltage, discharge triggering is predominantly associated with the rate of voltage change (dV/dt) and is influenced by surface charge accumulation. During a sinusoidal cycle, the discharge pattern undergoes dynamic evolution. It alternates between a positive polarity streamer, diffuse mode and a negative polarity Trichel, glow mode. Parametric studies show that, while the cycle-averaged volume force increases with voltage amplitude, the energy efficiency per unit volume force decreases. The optimal frequency, determined to be approximately 15 kHz, has been shown to maximize the average volume force. However, it has been observed that efficiency may decline when exceeding this threshold, due to the occurrence of inefficient streamer discharges at high dV/dt. The numerical results have been qualitatively validated against experimental optical measurements, thereby confirming the model’s effectiveness. This study provides a comprehensive understanding of SDBD plasma dynamics, volume force mechanisms, and energy efficiency, offering valuable guidance for the design and optimization of plasma actuators in aerodynamic applications.

Efficient active flow control strategy for confined square cylinder wake using deep learning-based surrogate model and reinforcement learning

Invariant control strategies for active flow control using graph neural networks

State-augmented deep reinforcement learning for active flow control around an elliptical cylinder

This study introduces a Deep Reinforcement Learning (DRL) framework for aerodynamic control of weakly compressible flow around an angled airfoil, aiming to optimize lift and drag through synthetic jet actuation. By combining pressure and velocity information from strategically placed sensors, the framework enhances the agent’s learning efficiency and control precision. Results demonstrate that integrating both variables improves total reward, reduces vortex shedding, stabilizes the wake, and minimizes lift fluctuations while lowering drag. The control policy, trained through 300 episodes using a Deep Q-Network (DQN) with five hidden layers of 128 neurons, achieves stable convergence and effective wake stabilization. Among the tested architectures, i.e. Traditional DQN, Double DQN, and Dueling DQN, the latter yields the most consistent learning behavior and highest performance by distinguishing state-value and advantage functions. Overall, the proposed DRL-based approach provides an efficient and robust strategy for active flow control in compressible aerodynamic applications, highlighting its potential for future engineering and aerospace systems.

This study proposes an active flow control strategy for an airfoil by integrating the immersed boundary–lattice Boltzmann method (IB-LBM) with the deep reinforcement learning (DRL) algorithm of Proximal Policy Optimization (PPO). The flow field is simulated using LBM, while the immersed boundary method is employed to accurately capture the interaction between the fluid and the moving airfoil. A PPO agent is trained to optimize the airfoil's motion in real time, with a reward function defined based on aerodynamic performance metrics, such as lift and drag coefficients. Numerical experiments are conducted under both steady and sinusoidal inflow conditions to assess the effectiveness and adaptability of the proposed control strategy. The results show that the PPO-controlled airfoil achieves substantial improvements in aerodynamic efficiency compared with uncontrolled cases, and the learned policy demonstrates robust transferability across different flow regimes. Overall, this work underscores the potential of coupling advanced computational fluid dynamics with DRL to tackle complex flow control problems and provides new insight for the intelligent optimization of wind energy systems.

Advancements and challenges of high-speed active flow control: Plasma actuators

In recent decades, renewable energy's share in global energy production has grown, with ambitious goals set for the green transition. Concentrating Solar Power (CSP) is crucial in this shift due to its energy storage and on-demand delivery capabilities, which prevent competition with intermittent sources like wind and photovoltaic (PV) systems. CSP enhances grid stability by providing energy during low production times and storing excess energy as heat. This stored heat, at high temperatures up to 550°C, can be used in industrial processes, including green fuel synthesis. The key components in CSP systems are the salt tanks, which are vulnerable to issues like corrosion, thermal shock, and thermal deformation, as seen in several projects worldwide. These issues are often due to temperature gradients in the tanks, which can cause buckling and fatigue rupture. The study focuses on strategies to minimize these risks, particularly through innovations in Vast's CSP v3.0 design. This includes a modular solar field arrangement to reduce temperature peaks and drops, active control of molten salt flow to match heat carrier fluid (HTF) temperatures, and a robust heat exchanger to buffer temperature changes. An innovative algorithm in the valve system at the molten salt tank inlets further enhances safety by directing hot salt to appropriate destinations, addressing the temperature differential issue that could reduce the equipment lifespan. This study, based on a numerical model of the entire plant and real weather data, tested various configurations to optimize the salt tanks' working conditions.

Heavy vehicles present high aerodynamic drag. This results in significant fuel consumption and, consequently, high emissions of harmful substances. This study examines the variation in aerodynamic drag in a European-type truck with different trailer configurations. Passive flow control by geometry modifications of the rear part of the trailer and active flow control using the Coanda effect were tested, with the aim of improving the aerodynamic efficiency of the vehicle. To achieve this, a modular structure of a 1:30 scaled truck was designed to enable different trailer configurations. Drag measurements were performed with a two-component external balance, and PIV tests were conducted to correlate the drag reduction with the aerodynamic changes behind the trailer. Passive control reduced drag by up to 5.7%, and active flow control reduced it by up to 12.6% compared to the unmodified base trailer. PIV flow visualization confirms that blowing effectively reduces the recirculation zone behind the trailer.

This paper presents results from active flow control experiments carried out on a single stage axial compressor. The flow under various forced conditions has been investigated using 2D 2C particle image velocimetry (PIV) on three radial planes along the blades’ span and two different operating points corresponding to the minimum mass flow at which the compressor naturally stalls, and to the lower stability limit reached with the control system activated. In particular, a control strategy using continuous blowing is compared with a pulsed one using the same injected mass flow. Comparison is performed with the base flow without control (when available), or with each other, based on the PIV results in the form of relative velocity maps or inlet/outlet flow characteristics.