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Flying-wing unmanned aerial vehicles can use active flow control technology to replace traditional control surfaces, avoiding radar echoes generated by control surface deflection, and can achieve better stealth performance. This article proposes a joint optimization method for high aspect ratio flying-wing unmanned aerial vehicles loaded with circulation controllers, which considers both aerodynamic and stealth performance. A joint optimization framework based on surrogate model is established for the two-dimensional airfoil containing circulation control (CC) mechanism, and the Pareto frontier solution set is obtained through optimization solution. The aerodynamic and stealth performance of the two-dimensional airfoil corresponding to three points in the Pareto front is evaluated, and the numerical results confirm the feasibility of the joint optimization method proposed in this paper. [ABSTRACT FROM AUTHOR]

This paper numerically simulates synthetic jet (SJ) for circulation control on a NACA0015 airfoil, and analyzes the control mechanism of suction stroke and blowing stroke through the calculated flow field results. The Reynolds number (Re) based on the airfoil chord length (c) and the oncoming flow velocity (U∞) was 250000. The SJ slots are respectively arranged at the upper trailing edge (TE) and the lower TE of the airfoil. The results show that applying the SJ control at the upper TE and the lower TE has a significant effect on lift enhancement, whose control effect is related to momentum coefficient (Cμ) and reduced frequency (F+). Both the suction stroke and blowing stroke of SJ contribute to lift enhancement. When the upper trailing-edge jet is applied, the control effect on lift enhancement is slightly weakened with the increase of the reduced frequency. Conversely, the control effect of the lower trailing-edge jet increases as the reduced frequency increases. Whether the SJ is arranged on the upper TE or the lower TE, the control effect increases as the momentum coefficient increases. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The enhancement in the jet pressure ratio and jet velocity contributes to expanding the control efficiency and control boundary of circulation control airfoil under high subsonic incoming flow. However, because of an excessive jet pressure ratio, the jet separates prematurely on the Coanda surface, resulting in control failure. In a bid to improve the adhesion capability of the jet under a high pressure ratio, a circulation control airfoil with a converging nozzle and back-facing step structure at the trailing edge was numerically simulated based on the Reynolds averaged Navier−Stokes equation (RANS), and a study was conducted on the complex flow structure of the under-expansion jet on the Coanda surface and the impact of design parameters such as jet pressure ratio, ellipticity, and nozzle height on the jet separation. The results show that the back-facing step provides an expansion space for the under-expansion jet and changes the shock-boundary layer interaction form. As the jet pressure ratio and nozzle height increase, the size of the shock cell increases, the strength of the intercepting shocks on both sides increases, and Mach reflection occurs, resulting in jet stratification and in a decline in the adhesion capability of the jet. The combination design of proper ellipticity and the back-facing step contributes to forming a closed low-pressure vortex area behind the step and promote jet attachment. Reducing the nozzle height can improve the adhesion capability of the jet under a high pressure ratio. [ABSTRACT FROM AUTHOR]

The interaction of airflow and sea waves seriously affects the flight stability and cruising safety of ground effect vehicles. The influence of different sea states and different angles of attack were analyzed numerically on the aerodynamic characteristics of the airfoil under ground effect of wavy wall. The influence of the constant blowing and periodic blowing methods was further studied on the aerodynamic force of the airfoil under ground effect. The simulation results show that the lift coefficient of the airfoil changes periodically with the wave under the wavy ground wall. The amplitude of the lift coefficient fluctuation is larger with the increasing of wave height and angle of attack, or the decreasing of wavelength. Applying the circulation control method for periodic blowing in the same period as the relative motion of the waves can effectively weaken the fluctuation of the airfoil lift coefficient under wavy sea conditions and improve the flight stability and safety of ground effect vehicles.

The internally blown flap is of efficient lift enhancement ability,but stall angle of attack drops significantly at a higher jet momentum.In order to improve the stall characteristics,the stall characteristics of the internally blown flap with the droop leading edge is studied.The numerical simulation of flow fields of a subsonic airfoil with droop leading edge combined with seamless flaps under the effect of circulation control are conducted.The influence rules of the blowing momentum coefficient on the stall characteristics are studied.The effects of leading edge rigid deflection,camber and thickness changes on the improvement of stall characteristics are studied.The effects of doop leading edge with different flap angle are also studied.The results show that,with the increase of the blowing momentum coefficient,the stall angle of attack is firstly droped rapidly and then slightly increased.The pressure gradient on the upper surface of the airfoil is reduced by the leading edge droop devices,the trend of the momentum thickness of the foil boundary layer increasing with the angle of attack is delayed,and the stall angle of attack is increased effectively.By gradually changing the curvature of the leading edge surface,the target that the leading edge droop design has the best effect on the improvement of stall characteristics is realized.

Abstract The blade pitch of a Vertical Axis Wind Turbine can have a profound impact on the aerodynamic loading experienced by the turbine. This in turn impacts the structural loads and the performance of the machine. In order to characterize the effects of changing pitch, studies are conducted with fixed pitch offsets from a neutral pitch position in the open jet wind tunnel of TU Delft. Measurements with strain gages bonded to the turbine struts are used to estimate the normal loading of the blades. The measured behavior gives insights into the sensitivity of the turbine loading to the blade pitch angle. Aerodynamic phenomena associated with VAWTs are evident in the data including dynamic stall and blade vortex interaction. Shifting of turbine blade pitch is shown to alter the azimuthally varying normal loading, causing changes in magnitude and direction of rotor thrust. Frequency responses of the turbine and platform mounting structure are presented for rotating and fixed reference frames, respectfully. The effects of stall due to high pitch offsets is shown to excite higher per rev frequencies in both the rotor normal measurements and platform accelerations. The data sets are made available for validation of numerical models.

Featured Application: Gust load control, aircraft weight reduction, aircraft drag reduction. Effective control of aerodynamic loads, such as maneuvering load and gust load, allows for reduced structural weight and therefore greater aerodynamic efficiency. After a basic introduction in the types of gusts and the current gust load control strategies for aircraft, we outline the conventional gust load alleviation techniques using trailing-edge flaps and spoilers. As these devices also function as high-lift devices or inflight speed brakes, they are often too heavy for high-frequency activations such as control surfaces. Non-conventional active control devices via fluidic actuators have attracted some attention recently from researchers to explore more effective gust load alleviation techniques against traditional flaps for future aircraft design. Research progress of flow control using fluidic actuators, including surface jet blowing and circulation control (CC) for gust load alleviation, is reviewed in detail here. Their load control capabilities in terms of lift force modulations are outlined and compared. Also reviewed are the flow control performances of these fluidic actuators under gust conditions. Experiments and numerical efforts indicated that both CC and surface jet blowing demonstrate fast response characteristics, capable for timely adaptive gust load controls. [ABSTRACT FROM AUTHOR]

To improve the low aerodynamic efficiency and reduce the high energy consumption of a single-stage circulation control wing, a multistage circulation control wing was designed. By combining force measurement and particle image velocimetry (PIV), the aerodynamic and flow-field characteristics of an aerofoil were investigated with respect to the increase in the number of blowing slots, changes in the blowing coefficient, and different blowing ratios for three slots. The force measurement results revealed that the maximum lift-to-drag ratio resulting from simultaneous blowing into the three slots increased by 95.3% compared with that in the absence of circulation control. With an increase in the blowing coefficient, two stages were observed: separation control and supercirculation control. In the separation control stage, the lift and drag coefficients significantly increased and decreased, respectively. In the supercirculation control stage, the lift coefficient gradually increased with the blowing coefficient, whereas the drag coefficient remained unchanged. When the blowing ratio (blowing flow ratio of three slots) in the three slots was 3:1:2, the maximum lift-to-drag ratio of the wing could reach 143.48%. The effects of different slot positions on the aerodynamic control were found to vary. The effects of Slot.1 and Slot.3 in terms of the drag reduction and lift, respectively, were evident, and the influence of Slot.2 on blowing between these two slots played a role in jet relay. The PIV results revealed that multistage blowing circulation increased the curvature of the trailing-edge streamline, thus increasing the equivalent aerofoil camber and improving the wing lift. At a high angle of attack, this circulation demonstrated a flow separation control effect. [ABSTRACT FROM AUTHOR]

Over the last decade, many flight tests of the conventional/canard/flying-wing layout UAVs (unmanned aerial vehicle) have proven that the trailing-edge circulation control (CC) is an effective method to generate a significant rolling moment for the rolling control. However, the Coanda jet's three-dimensional effects, especially the Coanda jet direction, on the design of UCAVs (unmanned combat air vehicle) have not been revealed and discussed clearly yet. In order to solve this problem, the effects of the Coanda jet direction on the swept wing's aerodynamics and flow physics are investigated in detail in this paper. An in-house CFD(computational fluid dynamics) solver HyperFLOW with the Spalart–Allmaras for Rotation and Curvature turbulence model and the velocity inlet boundary has been validated by 2-D and 3-D CC cases and is used in this work. The research reveals that compared with the Coanda jet in the freestream direction (FJ jet), the Coanda jet perpendicular to the trailing edge (PJ jet) has a more significant impact on the aerodynamic loads and flow structures for swept wings, including increasing lift, drag, and nose-down moment, enhancing the wingtip vortex and weakening the thickness vortex. In contrast, the FJ jet performs better in improving the lift-to-drag ratio of swept wings. On a typical UCAV, the generalizability of the conclusion about the Coanda jet direction effects on the aerodynamic characteristics is verified. The current research gets an insight into the three-dimensional effects of the trailing-edge CC and provides solid support for implementing the CC technology into practical aircraft concepts. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the flow fields and aerodynamic loading of a two bladed H‐type vertical axis wind turbine with active variable pitch for load and circulation control. Particle Image Velocimetry is used to capture flow fields at six azimuthal positions of the blades during operation, three upwind and three downwind. Flow phenomena such as dynamic stall and tower shadow are captured in the flow fields. The phase‐averaged velocity fields and their time and spatial derivatives are used to calculate the normal and tangential loading at each position for each pitching configuration using the Noca formulation of the flux equations. The results show the effect of load shifting from the upwind to downwind region of the actuator using pitch and the effects of dynamic stall on the blades. The results also provide an unique database for model validation.

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The enhancement in the jet pressure ratio and jet velocity contributes to expanding the control efficiency and control boundary of circulation control airfoil under high subsonic incoming flow. However, because of an excessive jet pressure ratio, the jet separates prematurely on the Coanda surface, resulting in control failure. In a bid to improve the adhesion capability of the jet under a high pressure ratio, a circulation control airfoil with a converging nozzle and back-facing step structure at the trailing edge was numerically simulated based on the Reynolds averaged Navier−Stokes equation (RANS), and a study was conducted on the complex flow structure of the under-expansion jet on the Coanda surface and the impact of design parameters such as jet pressure ratio, ellipticity, and nozzle height on the jet separation. The results show that the back-facing step provides an expansion space for the under-expansion jet and changes the shock-boundary layer interaction form. As the jet pressure ratio and nozzle height increase, the size of the shock cell increases, the strength of the intercepting shocks on both sides increases, and Mach reflection occurs, resulting in jet stratification and in a decline in the adhesion capability of the jet. The combination design of proper ellipticity and the back-facing step contributes to forming a closed low-pressure vortex area behind the step and promote jet attachment. Reducing the nozzle height can improve the adhesion capability of the jet under a high pressure ratio.

The blade pitch of a Vertical Axis Wind Turbine can have a profound impact on the aerodynamic loading experienced by the turbine. This in turn impacts the structural loads and the performance of the machine. In order to characterize the effects of changing pitch, studies are conducted with fixed pitch offsets from a neutral pitch position in the open jet wind tunnel of TU Delft. Measurements with strain gages bonded to the turbine struts are used to estimate the normal loading of the blades. The measured behavior gives insights into the sensitivity of the turbine loading to the blade pitch angle. Aerodynamic phenomena associated with VAWTs are evident in the data including dynamic stall and blade vortex interaction. Shifting of turbine blade pitch is shown to alter the azimuthally varying normal loading, causing changes in magnitude and direction of rotor thrust. Frequency responses of the turbine and platform mounting structure are presented for rotating and fixed reference frames, respectfully. The effects of stall due to high pitch offsets is shown to excite higher per rev frequencies in both the rotor normal measurements and platform accelerations. The data sets are made available for validation of numerical models. [ABSTRACT FROM AUTHOR]

• Maritime wing sail propulsion was enhanced using the circulation control technique. • Circulation-controlled airfoil performance was simulated by a calibrated GEKO model. • Energy-saving potential was evaluated via the Energy Efficiency Design Index (EEDI). Amidst mandatory policies aimed at energy savings and emission reductions in the shipping industry, wind-assisted ship propulsion technology has gained prominence for its immediate practicality in promoting environmental sustainability. Wing-sails possess favorable aerodynamic characteristics and adjustable capabilities, yet their efficiency is impeded by flow separation at high angles of attack. This study addressed the challenge of mitigating delayed separation and enhancing lift at large angles of attack for wing-sails through technical solutions involving trailing-edge circulation control and leading-edge boundary layer control. Three-dimensional steady-state flow fields of conventional and circulation-controlled wing-sails were accurately modeled using a Generalized k - ω (GEKO) model across angles of attack ranging from 0° to 30°. Under moderate jet strength conditions with a velocity ratio of 5, the stall angle of attack of the circulation-controlled wing-sail was delayed by approximately 6°. Furthermore, compared to a conventional wing-sail, the circulation-controlled variant exhibited a 111 % increase in maximum lift coefficient and a 120 % rise in maximum resultant force coefficient. The energy-saving and emission reduction benefits of implementing this innovative technology were quantified using the Energy Efficiency Design Index (EEDI) on a real very large crude carrier (VLCC). The circulation-controlled wing-sail demonstrated a 10.38 % reduction in EEDI under optimal operating conditions with medium jet strength, compared to an unassisted vessel. Moreover, this reduction was enhanced by 77.55 % compared to incorporating a conventional wing-sail. These discoveries signify an advancement in wind-assisted ship propulsion technology on an innovative frontier, promising greater energy utilization and reduced fuel consumption, thereby facilitating the achievement of stringent green ship standards. [ABSTRACT FROM AUTHOR]

This paper presents the flow fields and aerodynamic loading of a two bladed H‐type vertical axis wind turbine with active variable pitch for load and circulation control. Particle Image Velocimetry is used to capture flow fields at six azimuthal positions of the blades during operation, three upwind and three downwind. Flow phenomena such as dynamic stall and tower shadow are captured in the flow fields. The phase‐averaged velocity fields and their time and spatial derivatives are used to calculate the normal and tangential loading at each position for each pitching configuration using the Noca formulation of the flux equations. The results show the effect of load shifting from the upwind to downwind region of the actuator using pitch and the effects of dynamic stall on the blades. The results also provide an unique database for model validation. [ABSTRACT FROM AUTHOR]

The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering. This is most commonly achieved by mechanical flapping or pulsed plasma actuation. On larger UAVs, with Reynolds numbers greater than 105, externally driven and autonomous fluidic systems continue to dominate. These include traditional circulation control techniques, autonomous synthetic jets, and discrete sweeping jets. Plasma actuators have also shown increased technological maturity. Energy efficiency is a major challenge, whether it be batteries and power electronics on nano and micro air vehicles or acceptably low compressor bleed on larger UAVs. Further challenges involve the development of aerodynamic models based on experiments or numerical simulations, as well as flight dynamics models. [ABSTRACT FROM AUTHOR]

For lessening the weight and volume of flow control system, enlarging the circulation control applying area of angle of attack (AOA), and achieving nice controlling characteristics, a novel lift enhancement method based on dual synthetic jet actuators (DSJAs) and synthetic jet actuator (SJA), and an adaptive proportional integral and differential (PID) algorithm based on radial basis function neural network are introduced. DSJAs are uniformly located along the chord to suppress the separation and trailing-edge SJA is applied to achieve the high circulation. Velocities of actuators are modulated to realize the real speed profile and on–off controlling laws of DSJAs are designed. Numerical simulations show that DSJAs and SJA could suppress the separation completely and move leading-edge stagnation point and trailing-edge separation point downstream even at AOA of 19°, hence achieve the highest lift and nose-down moment augmentation ( Δ Cl max = 0.92, Δ Cm max = 0.02534), and Δ L / D can reach 11.39 at AOA of 18°. Stalling is delayed to more than 19°. Linear lift area and pitch-break angle are both increased to 16°. Δ Cl / C μ can reach 76.7, indicating the greatest control efficiency. The results of adaptive PID control, whose controlling effects are proved better than PID, indicate that lift could track the objective with the rise time of 0.0325 s and finally keep steady, suggesting the nice stability and rapidness. [ABSTRACT FROM AUTHOR]

Effective control of aerodynamic loads, such as maneuvering load and gust load, allows for reduced structural weight and therefore greater aerodynamic efficiency. After a basic introduction in the types of gusts and the current gust load control strategies for aircraft, we outline the conventional gust load alleviation techniques using trailing-edge flaps and spoilers. As these devices also function as high-lift devices or inflight speed brakes, they are often too heavy for high-frequency activations such as control surfaces. Non-conventional active control devices via fluidic actuators have attracted some attention recently from researchers to explore more effective gust load alleviation techniques against traditional flaps for future aircraft design. Research progress of flow control using fluidic actuators, including surface jet blowing and circulation control (CC) for gust load alleviation, is reviewed in detail here. Their load control capabilities in terms of lift force modulations are outlined and compared. Also reviewed are the flow control performances of these fluidic actuators under gust conditions. Experiments and numerical efforts indicated that both CC and surface jet blowing demonstrate fast response characteristics, capable for timely adaptive gust load controls.

To improve the low aerodynamic efficiency and reduce the high energy consumption of a single-stage circulation control wing, a multistage circulation control wing was designed. By combining force measurement and particle image velocimetry (PIV), the aerodynamic and flow-field characteristics of an aerofoil were investigated with respect to the increase in the number of blowing slots, changes in the blowing coefficient, and different blowing ratios for three slots. The force measurement results revealed that the maximum lift-to-drag ratio resulting from simultaneous blowing into the three slots increased by 95.3% compared with that in the absence of circulation control. With an increase in the blowing coefficient, two stages were observed: separation control and supercirculation control. In the separation control stage, the lift and drag coefficients significantly increased and decreased, respectively. In the supercirculation control stage, the lift coefficient gradually increased with the blowing coefficient, whereas the drag coefficient remained unchanged. When the blowing ratio (blowing flow ratio of three slots) in the three slots was 3:1:2, the maximum lift-to-drag ratio of the wing could reach 143.48%. The effects of different slot positions on the aerodynamic control were found to vary. The effects of Slot.1 and Slot.3 in terms of the drag reduction and lift, respectively, were evident, and the influence of Slot.2 on blowing between these two slots played a role in jet relay. The PIV results revealed that multistage blowing circulation increased the curvature of the trailing-edge streamline, thus increasing the equivalent aerofoil camber and improving the wing lift. At a high angle of attack, this circulation demonstrated a flow separation control effect.

The geometric effects of Coanda trailing edges on the aerodynamic performance of an airfoil are numerically evaluated for a range of different freestream Mach numbers and momentum coefficients. A Circulation control (CC) airfoil with a circular trailing edge (ACTE) proves to have better control effectiveness at low subsonic freestream speeds (Mach = 0.1). A CC airfoil having an elliptic trailing edge (AETE) outperforms the ACTE at high subsonic flow conditions. The occurrence of C μ -stall for the AETE is greatly postponed, and meanwhile the maximum net lift coefficient increment achieved for the AETE (Δ C L = 0.51) is slightly higher than that of the ACTE (Δ C L = 0.50) at Mach 0.6. Compared to the ACTE, the AETE is found to have better control consistency at different operating velocities and better control stability when the Coanda jet is supersonic. Through careful consideration of the aerodynamic performance and the control effects, the most appropriate axial ratio for an AETE ellipse is within the interval from 1.5 to 2. Finally, the flow field instability phenomenon and the jet detachment induced by the supersonic Coanda jet are investigated. A self-sustained shock-wave instability phenomenon without jet detachment is first observed in this paper. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The lift of an aircraft can be effectively enhanced by circulation control (CC) technology at subsonic speeds, but the efficiency at transonic speeds is greatly decreased. The underlying mechanism of this phenomenon is not fully understood. In this study, Reynolds averaged Navier—Stokes simulation with k−ω shear stress transport model was utilized to investigate the mechanism of lift enhancement by CC in transonic flow. For validation, the numerical CC results were compared with the NASA experimental data obtained for transonic CC airfoil. Thereafter, the RAE2822 airfoil was modified with a Coanda surface. The lift enhancement effects of CC via steady blowing with different momentum coefficients were tested at Ma=0.3 and 0.8 at α=3∘, and various fluid mechanics phenomena were investigated. The results indicate that the flow structure of the CC jet is insensitive to the incoming flow conditions because of the similarity to the local static pressure field around the trailing edge of the airfoil. Owing to the appearance of shockwaves on the airfoil surface in the transonic regime, the performance of the CC jet is restricted to the trailing edge of the airfoil. Transonic CC achieved a slight improvement in aerodynamic performance owing to a favorable shift in the shockwave pattern and accelerated flow in the separation region on the airfoil surfaces. Revealing the mechanism of lift enhancement of CC in the transonic regime can facilitate the rational design of new fluidic actuators with high activity and expand the potential applications of CC technology.

The coflow jet (CFJ) technology, as a new type of integrated flow control technology, has shown potentials in lift enhancement and drag reduction, stall characteristics improvement. The history of the CFJ technology and the research situations at home and abroad is reviewed. The mechanism of CFJ technology’s abilities in lift enhancement and drag reduction is discussed, the theoretical values are also investigated. The research status and typical applications are analyzed. The key issues of this technology in aircraft design, such as aircraft integrated design method, design and analysis technology, component layout strategy and flight control system, are summarized.

Abstract The circulation control around the Darrieus turbine blades is considered as a significant practical solution so as to improve the machine's performance. This paper describes a kinematics-based method, through which the pitching motion of the blades varies in such a way that the flow is controlled around them as well as across the rotor. For this purpose, the potential flow approach is used to derive the blade pitching laws being compatible with the unsteady Kutta-Joukowski condition at the trailing edge of the blade. By means of this, a constant circulation around the blade is ensured. Preliminary CFD investigations have evidenced the operating conditions at which the constant-circulation framework may be applied to turbulent flows in order to control the vortex shedding and avoid blade-vortex interactions. Nonetheless, a strict application of this concept prevents the turbine from harvesting the energy. As an alternative strategy, the application of a locally variable-circulation is proposed in order to enhance the power output without compromising on flow control. Three major accomplishments of the variable-circulation-based blade pitching proposition are the following: a. flow control around the turbine blades with definite patterns of vortical structures, b. consistent increase in the turbine's coefficient of power, and c. widened operating range of the turbine. Highlights • Kinematics-based blade pitching laws for a hydrokinetic turbine are developed. • Power characteristics deteriorate with a constant circulation around the blades. • Piecewise circulation laws optimise the power output without compromising on flow control. • Definite patterns of vortical structures allow to install the turbines in arrays. [ABSTRACT FROM AUTHOR]

Abstract Large eddy simulation of a NACA0015 circulation control airfoil using synthetic jets is conducted. A chord Reynolds number of 1.10 × 105, the excitation frequency of 175 Hz, the momentum coefficients of 0.0044 to 0.0688, and the angles of attack of 0°, 6°, and 12° are employed in this study. The numerical results presented in this paper show good agreement with the experimental results. Fluctuations in the lift and drag coefficients on the non-actuated airfoil are found to be governed by the vortex shedding frequency. Provided that the momentum coefficient is sufficiently high, the lift and drag coefficients tend to fluctuate at the synthetic jet frequency. The mean lift coefficient linearly increases with the momentum coefficient at a low momentum coefficient range and its incremental rate begins to decline at a high momentum coefficient range. Increasing the angle of attack of the airfoil is observed to slightly reduce the slope of the lift increment. [ABSTRACT FROM AUTHOR]

This paper describes a comprehensive methodology to reduce the power penalties of an Air Supply Unit (ASU) used in Circulation Control Unmanned Aerial Vehicles (UC2AVs). Circulation Control (CC), which is an active flow control technique that can be used on fixed-wing aircraft to achieve lift augmentation, requires the use of an efficient CC system on-board. The experimental testbed for a CC system and the development and integration of both a PID and Fuzzy Logic (FL) control scheme are presented in this paper. Ground test experimental results indicate that power penalties can be minimized throughout the flight envelope. The results indicate that the behavior of both controllers exhibits a correlation to the simulation data above 67%. Additionally, both controllers present similar energy usage characteristics, when applied throughout a simulated flight envelope. Results also show that PI control displays a faster rise time and less overshoot than FL control in most cases, but also a longer settling time. Overall the PI controller displays better regulation of the dynamics of the CC system’s behavior. The use of the active CC regulation systems described in this study provides opportunities for application to commercial UAV technology, providing important advances in this rapidly growing field. [ABSTRACT FROM AUTHOR]

The existing experimental methods and numerical models were difficult to get accurate aerodynamic characteristics of the anti-torque system of a NOTAR under rotor wake. To solve this problem, a new three-dimensional aerodynamic model with momentum source based on finite volume method was proposed in this paper. By means of time domain equalization and spatial interpolation, the complicated dynamic meshes on blade were replaced by the nonblade fixed rotor domain with momentum source. And the model was calculated by steady, compressible and three-dimensional Reynolds averaged N-S equation. In this paper, a typical NOTAR was took for research, the aerodynamic characteristics including flow field and variation regularity of lateral force with momentum coefficient of anti-torque system during hover condition was obtained by applying the above computational model, and the accuracy of which was verified by corresponding experimental data. In addition, the model was also used to analyze the key factors that influence working condition of the tail boom, including length of tail boom, area of nozzle and fan pressurization. And the curves of variation regularity were given. The model and work in this paper could provide reference for further research and design on anti-torque system for NOTAR. [ABSTRACT FROM AUTHOR]

A new partial circulation control (PCC) method is implemented on the blunt trailing edge DU97-Flatback airfoil, and compared with the traditional full circulation control (FCC) based on numerical analysis. When the Coanda jet is deactivated, PCC has an attractive advantage over FCC, since the design of PCC doesn't degrade aerodynamic characteristics of the baseline flatback section, in contrast to FCC, which is important in practical use in case of failure of the circulation control system. When the Coanda jet is activated, PCC also outperforms FCC in several respects. PCC can produce much higher lift coefficients than FCC over the entire range of angles of attack as well as the entire range of jet momentum coefficients under investigation, but with slightly higher drag coefficients. The flow field of PCC is less complex than that of FCC, indicating less energy dissipation in the main flow and hence less power expenditure for the Coanda jet. The aerodynamic figure of merit (AFM) and control efficiency for circulation control are defined, and results show that PCC has much higher AFM and control efficiency than FCC. It is demonstrated that PCC outperforms FCC in terms of effectiveness, efficiency and reliability for flow control in the blunt trailing edge wind turbine application. [ABSTRACT FROM AUTHOR]