Special Issue "Active Flow Control Technologies for Energy and Propulsive Systems"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy".

Deadline for manuscript submissions: closed (31 October 2017).

Special Issue Editors

Prof. Dr. Antonio Ficarella
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Guest Editor
Dr. Maria Grazia De Giorgi
E-Mail Website
Guest Editor
Department of Engineering for Innovation, University of Salento, Via Per Arnesano, I-73100 Lecce, Italy
Interests: energy systems; propulsive systems; fluid machinery; applied fluid dynamics; combustion
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Special Issue Information

Dear Colleagues,

The topic of this Special Issue concerns the latest developments and investigations in the fields of flow control with a focus on the Energy and Propulsive Engineering applications.

Boundary layer separation entails great energy losses and limits the performance of most flow related devices. It imposes severe limitations not only on the design but it also affects the operation and performance of the devices. Therefore, the control of boundary layer separation or at least its alleviation is warranted.

Active flow control (AFC) is a fast-growing multi-disciplinary science and technology aimed at altering a natural flow state or development path into a more desired state.

These methods are used majorly to achieve transition delay, drag reduction, lift enhancement, turbulence management, separation postponement, noise suppression, etc. The potential benefits of flow control may include improved performance, affordability, fuel consumption economy, and environmental compliance.

The synergy of flow and noise control technologies is relevant to air vehicles, for example, in wake deficit reduction, reduced distortion at the engine inlet, laminar flow control, as laminar flow has less structural vibration induced noise.

In the aerospace field, the flow control has a significant impact on the aerodynamic design as well as on the propulsion systems (such as jet engines and rockets) of future aerospace vehicles. Regarding engine components, flow control in turbomachinery is needed to increase efficiency of thrust and power generation while reducing environmental footprints. Efficient combustor designs and stable compressor flows using flow control are needed for such purposes.

In recent years, attention has been also focused on the control and suppression of combustion instabilities by actively and continuously perturbing certain combustion parameters in order to interrupt the growth and persistence of resonant oscillations.

Implementing active flow control methods permits also to improve the performance of wind turbines.

Remarkable developments in control theory have considerably expanded the selection of available tools which may be applied to regulate physical systems. These techniques show great benefits for several applications in fluid mechanics, including the delay of flow transition, and thus of turbulence.

Manufacturing processes have been developed in recent years to create the micro-electro-mechanical systems that have been used as sensors for pressures, temperatures, mass flows, speeds measurements, and sound detection, and as actuators for the diagnosis and control of turbulent shear flows.

Active flow control research is characterized by a highly multi-disciplinary approach including theoretical, computational and experimental fluid dynamics, aerodynamics, physics, chemistry and propulsion.

Although many flow control technologies have been identified and researched at the basic level for many decades few have ever reached maturity and full-scale deployment on a commercial product.

Potential topics include, but are not limited to:

  • Accurate and efficient active and passive flow control devices for aeronautical applications

  • Sensor-actuator integrated systems, with a possible focus on MEMS devices

  • Smart structures combined with drag reduction techniques

  • Laminar flow and engine integration technologies

  • Synergy of active or passive flow and noise control technologies

  • Flow control in propulsive systems

  • Experimental characterization and reliable numerical simulation of flow field in the presence of actuators

  • Innovative air vehicle shapes and configurations (including morphing configurations) that have the potential to improve laminar flow and load controls 

Prof. Antonio Ficarella
Prof. Maria Grazia De Giorgi
Guest Editors

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Keywords

  • active flow control

  • fluidic jet

  • synthetic jet

  • MEMS devices

  • Wind turbine

  • Flow separation

  • noise control

Published Papers (9 papers)

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Editorial

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Editorial
Special Issue “Active Flow Control Technologies for Energy and Propulsive Systems”
Appl. Sci. 2020, 10(1), 221; https://doi.org/10.3390/app10010221 - 27 Dec 2019
Viewed by 451
Abstract
Active flow control (AFC) is a fast-growing, multi-disciplinary science and technology for energy and propulsive systems [...] Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)

Research

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Article
Mechanisms of Control Authority by Nanosecond Pulsed Dielectric Barrier Discharge Actuators on Flow Separation
Appl. Sci. 2019, 9(15), 2989; https://doi.org/10.3390/app9152989 - 25 Jul 2019
Cited by 2 | Viewed by 809
Abstract
The mechanisms that should be considered for separation flow control applications of nanosecond pulsed dielectric barrier discharge (DBD) actuators were investigated on a NACA 0015 profile for velocities of 10 m / s ( R e = 100,000 ) and 20 m / s ( R e = 200,000 ) in ambient wind tunnel conditions. Near and post-stall angles of attack were considered ( 16 and 24 ). The dominant frequencies existing in the flow were measured. Moderate voltage levels were applied (4 and 7 kV ) and the actuator was operated at these identified dominant frequencies and compared with known effective frequencies from literature. In all cases, influences by the actuator on the flow structures were observed and the operation of the actuator at the dominant flow frequencies of a stalled airfoil was shown to give control authority. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Heat Transfer and Friction Characteristics of Turbulent Flow through a Circular Tube with Ball Turbulators
Appl. Sci. 2018, 8(5), 776; https://doi.org/10.3390/app8050776 - 13 May 2018
Cited by 5 | Viewed by 1936
Abstract
One of the most commonly used methods of heat transfer enhancement is flow turbulization. This effect can be achieved, e.g., by placing special turbulizing elements into the channel. In this paper, the effects of ball turbulators (BTs) on the heat transfer and fluid [...] Read more.
One of the most commonly used methods of heat transfer enhancement is flow turbulization. This effect can be achieved, e.g., by placing special turbulizing elements into the channel. In this paper, the effects of ball turbulators (BTs) on the heat transfer and fluid friction characteristics in a circular tube are investigated through numerical simulation. The Reynolds number (Re) is in the range of 5000–35,000 under a condition of uniform heat-flux. BTs with different diameter ratios (e.g., 0.5, 0.75, and 1) and spacer lengths (40, 51.77, and 62.5 mm) are inserted in the circular tubes. The results show that the heat transfer rates in the tube equipped with BTs are around 1.26–2.01 times that of those in the plain tube. The BTs with a ball diameter ratio of one provide higher friction factors than 0.75 and 0.5 by about 34.6–46.2% and 51.1–63.4%, respectively. A smaller ball diameter ratio is more able to decrease the friction factor. The performance evaluation criterion (PEC) data indicate that the use of a smaller ball diameter ratio (BDR) and a smaller spacer length are preferred. The results also reveal that BTs with a larger diameter ratio and a smaller spacer length yield the highest heat transfer rate as well as the largest pressure loss. Compared with the plain tube, the fluid flow velocity near the tube wall is significantly improved when BTs are used at the same Reynolds number. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Computational Modelling of Rectangular Sub-Boundary Layer Vortex Generators
Appl. Sci. 2018, 8(1), 138; https://doi.org/10.3390/app8010138 - 19 Jan 2018
Cited by 20 | Viewed by 2116
Abstract
Vortex generators (VGs) are increasingly used in the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. Nevertheless, VGs may produce excess residual drag in some applications. The so-called sub-boundary layer VGs can provide an effective flow-separation control [...] Read more.
Vortex generators (VGs) are increasingly used in the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. Nevertheless, VGs may produce excess residual drag in some applications. The so-called sub-boundary layer VGs can provide an effective flow-separation control with lower drag than the conventional VGs. The main objective of this study is to investigate how well the simulations can reproduce the physics of the flow of the primary vortex generated by rectangular sub-boundary layer VGs mounted on a flat plate with a negligible pressure gradient with an angle of attack of the vane to the oncoming flow of β = 18°. Three devices with aspect ratio values of 2, 2.5 and 3 are qualitatively and quantitatively compared. To that end, computational simulations have been carried out using the RANS (Reynolds averaged Navier–Stokes) method and at Reynolds number Re = 2600 based on the boundary layer momentum thickness θ at the VG position. The computational results show good agreement with the experimental data provided by the Advanced Aerodynamic Tools of Large Rotors (AVATAR) European project for the development and validation of aerodynamic models. Finally, the results indicate that the highest VG seems to be more suitable for separation control applications. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Numerical Assessment of Virtual Control Surfaces for Load Alleviation on Compressor Blades
Appl. Sci. 2018, 8(1), 125; https://doi.org/10.3390/app8010125 - 17 Jan 2018
Cited by 5 | Viewed by 2482
Abstract
Virtual control surfaces for the optimization of steady and unsteady airloads on a compressor cascade are assessed numerically. The effects of mechanical surfaces are realized with plasma actuators, located both on the pressure and on the suction side of the blade trailing edge. [...] Read more.
Virtual control surfaces for the optimization of steady and unsteady airloads on a compressor cascade are assessed numerically. The effects of mechanical surfaces are realized with plasma actuators, located both on the pressure and on the suction side of the blade trailing edge. Suction side plasma actuation is thought to reproduce the effects of mechanical wing spoilers, whereas pressure side plasma actuation is meant to act as a mechanical Gurney flap. Indeed, actuators are operated to generate an induced velocity field that is opposite relative to the direction of the freestream velocity. As a consequence, controlled recirculating flow areas are generated, which modify the effective mean line shape, as well as the position of the Kutta condition application point—and in turn the developed airloads. Proper triggering of pressure/suction side actuation is found to be effective in altering the blade loading, with effects comparable to those of mechanical control surfaces. Traveling wave mode simulations show that significant reductions in the peaks of the blade pitching moment can be achieved on the whole spectrum of interblade phase angles. It is proved that virtual control surfaces can provide effective load alleviation on the cascade, with potential remarkable reduction of fatigue phenomena. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Numerical Characterisation of Active Drag and Lift Control for a Circular Cylinder in Cross-Flow
Appl. Sci. 2017, 7(11), 1166; https://doi.org/10.3390/app7111166 - 13 Nov 2017
Cited by 2 | Viewed by 2930
Abstract
Synthetic jet actuators have shown promise to control drag and lift for a bluff body in cross-flow. Using unsteady RANS CFD modelling, a significant modification of the drag coefficient for a circular cylinder in cross-flow at R e = 3900 is achieved by varying the actuation frequency. The variation in actuation frequency corresponds to a range in Stokes number of 2.4 < S t o < 6.4. The trends in drag coefficient modification largely agree with the findings of past publications, achieving a maximum drag reduction at S t o = 4.9 for a fixed jet Reynolds number of the synthetic jet of R e U ¯ o = 12. A decrease in the adverse pressure gradient near the jet orifice correlated with a momentum increase in the viscous sublayer and stronger vortical structures at the rear of the cylinder. In these same conditions, a decrease in turbulence intensity was observed in the far field wake, which is a relevant finding in the context of wind and tidal turbine arrays. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Model Based Open-Loop Wind Farm Control Using Active Power for Power Increase and Load Reduction
Appl. Sci. 2017, 7(10), 1068; https://doi.org/10.3390/app7101068 - 16 Oct 2017
Cited by 15 | Viewed by 2249
Abstract
A new wind farm control algorithm that adjusts the power output of the most upstream wind turbine in a wind farm for power increase and load reduction was developed in this study. The algorithm finds power commands to individual wind turbines to maximize [...] Read more.
A new wind farm control algorithm that adjusts the power output of the most upstream wind turbine in a wind farm for power increase and load reduction was developed in this study. The algorithm finds power commands to individual wind turbines to maximize the total power output from the wind farm when the power command from the transmission system operator is larger than the total available power from the wind farm. To validate this wind farm control algorithm, a relatively high fidelity wind farm simulation tool developed in the previous study was modified to include a wind farm controller which consists of a wind speed estimator, a power command calculator and a simplified wind farm model. In addition, the wind turbine controller in the simulation tool was modified to include a demanded power tracking algorithm. For a virtual wind farm with three 5 MW wind turbines aligned with the wind, simulations were performed with various ambient turbulent intensities, turbine spacing, and control frequencies. It was found from the dynamic simulation using turbulent winds that the proposed wind farm control algorithm can increase the power output and decrease the tower load of the most upstream wind turbine compared with the results with the conventional wind farm control. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Article
Control of Corner Separation with Plasma Actuation in a High-Speed Compressor Cascade
Appl. Sci. 2017, 7(5), 465; https://doi.org/10.3390/app7050465 - 29 Apr 2017
Cited by 15 | Viewed by 2457
Abstract
The performances of modern highly loaded compressors are limited by the corner separations. Plasma actuation is a typical active flow control methodology, which has been proven to be capable of controlling the corner separations in low-speed compressor cascades. The main purpose of this [...] Read more.
The performances of modern highly loaded compressors are limited by the corner separations. Plasma actuation is a typical active flow control methodology, which has been proven to be capable of controlling the corner separations in low-speed compressor cascades. The main purpose of this paper is to uncover the flow control law and the mechanism of high-speed compressor cascade corner separation control with plasma actuations. The control effects of the suction surface as well as the endwall plasma actuations in suppressing the high-speed compressor cascade flow separations are investigated with numerical methods. The main flow structures within the high-speed compressor cascade corner separation and the development of the corresponding flow loss are investigated firstly. Next, the performances of plasma actuations in suppressing the high-speed compressor cascade corner separation are studied. At last, the mechanisms behind the control effects of the suction surface and the endwall plasma actuations are discussed. Both the suction surface and the endwall plasma actuations can improve the high-speed compressor cascade static pressure rise coefficient, while reducing the corresponding total pressure loss and blockage coefficients. The suction surface plasma actuation can suppress not only the high-speed compressor cascade corner separation vortex but also the airfoil separation, so, compared to the endwall plasma actuation, the suction surface plasma actuation is more efficient in reducing the total pressure loss of the high-speed compressor cascade. However, through suppressing the development of the passage vortex, the endwall plasma actuation is more efficient in reducing the flow blockage and improving the static pressure rise of the high-speed compressor cascade. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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Review

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Review
Three Flow Features behind the Flow Control Authority of DBD Plasma Actuator: Result of High-Fidelity Simulations and the Related Experiments
Appl. Sci. 2018, 8(4), 546; https://doi.org/10.3390/app8040546 - 02 Apr 2018
Cited by 18 | Viewed by 2934
Abstract
Both computational and experimental studies are conducted for understanding of the flow separation control mechanism of a DBD (dielectric barrier discharge) plasma actuator. Low speed flows over an airfoil are considered. A DBD plasma actuator is attached near the leading edge of an [...] Read more.
Both computational and experimental studies are conducted for understanding of the flow separation control mechanism of a DBD (dielectric barrier discharge) plasma actuator. Low speed flows over an airfoil are considered. A DBD plasma actuator is attached near the leading edge of an airfoil and the mechanism of flow control of this small device is discussed. The DBD plasma actuator, especially in burst mode, is shown to be very effective for controlling flow separation at Reynolds number of 6.3 × 104, when applied to the flows at an angle of attack higher than the stall. The analysis reveals that the flow structure includes three remarkable features that provide good authority for flow separation control with the appropriate actuator parameters. With proper setting of the actuator parameters to enhance the effective flow features for the application, good flow control can be achieved. Based on the analysis, guidelines for the effective use of DBD plasma actuators are proposed. A DBD plasma actuator is also applied to the flows under cruise conditions. With the DBD plasma actuator attached, a simple airfoil turns out to show higher lift-to-drag ratio than a well-designed airfoil. Full article
(This article belongs to the Special Issue Active Flow Control Technologies for Energy and Propulsive Systems)
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