Airborne Wind Turbine Research Articles

Design and Performance Evaluation of a Mid-Range Airborne Wind Turbine

Design and Performance Evaluation of a Mid-Range Airborne Wind Turbine

Laboratory-Scale Airborne Wind Energy Conversion Emulator Using OPAL-RT Real-Time Simulator

Airborne wind energy systems (AWES) are more efficient than traditional wind turbines because they can capture higher wind speeds at higher altitudes using connected kite generators. Securing a real wind turbine or a site with favorable wind conditions is not always an assured opportunity for conducting research. Hence, the Research and Development of the Laboratory Scale Airborne Wind Energy Conversion System (LAWECS) require a better understanding of airborne wind turbine dynamics and emulation. Therefore, an airborne wind turbine emulation system was designed, implemented, simulated, and experimentally tested with ground data for the real time simulation. The speed and torque of a permanent magnet synchronous motor (PMSM) connected to a kite are regulated to maximize wind energy harvesting. A field-oriented control technique is then used to control the PMSM’s torque, while a three-phase power inverter is utilized to drive the PMSM with PI controllers in a closed loop. The proposed framework was tested, and the emulated airborne wind energy conversion system results were proven experimentally for different wind speeds and generator loads. Further, the LAWECS emulator simulated a 2 kW, 20 kW, and 60 kW designed with a projected kite area of 5, 25, and 70 square meters, respectively. This system was simulated using the Matlab/Simulink software and tested with the experimental data. Furthermore, the evaluation of the proposed framework is validated using a real-time hardware-in-the-loop environment, which uses the FPGA-based OPAL-RT Simulator.

Recent technology and challenges of wind energy generation: A review

Energy is an integral part of economic growth and social development. Renewable energy sources are naturally occurring, which can help in reducing the dependency on non-renewable resources. The increasing effects of climate change have led to the utilization of renewable energy resources for power generation, among which wind is one of the significant sources of power generation. It provides a reliable, sustainable, and environmentally friendly alternative contributing to national energy security in the current age of decreasing global reserves of non-renewable resources across the globe. This paper reviews the wind energy technologies used, mainly focusing on the types of turbines used and their future scope. Further, the paper briefly discusses certain future wind generation technologies, namely airborne, offshore, smart rotors, multi-rotors, and other small wind turbine technologies. It also briefly discusses ways to improve the efficiency of different turbine generation technologies, majorly non-conventional ideas of wind turbine technologies based on cross axis wind turbine (CAWT), vertical axis wind turbine (VAWT), magnetic-based wind turbine. Overall, the summarization of wind energy here consists of four aspects: (1) wind turbine structure, (2) wind power generation technologies, (3) wind energy assessment methodologies, (4) limitation of developed technologies and future scope of wind energy development.

Power conversion performance of airborne wind turbine under unsteady loads

The study presents the systematic analysis of power conversion performance of the airborne wind turbine (AWT) using time-resolved air loads. The power harvesting behavior of the rotating blades in shell configuration is numerically investigated to analyze the influence of wind shear, yawed and tilted inflows at design operating conditions. An inherently unsteady scheme of the sliding mesh is incorporated to capture the complex flow field across the 3-bladed rotor. The fully-resolved computations closely match the expected results derived from the empirical calculations. The conversion performance supplements the turbine's power curve as a means of determining the distribution of aerodynamic forces, performance coefficients, vortex structure and shell thrust loadings. The time-marching response of the AWT gradually attains steady flow characteristics after two rotation periods when the wind shear profile is fully aligned with the rotor's axis of rotation. This yields a beneficial gain of 64% more power output with the rotor in shell configuration than those of the bare configuration. Meanwhile, cyclic fluctuations (±21%) significantly undermine the continuous production of power in the case of skewed flow conditions. Moreover, the flow misalignment causes a localized shifting of effective forces on the rotor plane due to the intricate impact of the shell structure.

Performance assessment of a balloon assisted micro airborne wind turbine system

Abstract This study intends to examine the performance of a balloon-assisted micro airborne wind turbine in a low wind speed location. The influence of the balloon separation gap on the airborne wind energy system (AWES) performance is also explored. A micro-AWES with a diameter of 3 m and a power output of 1 kW was fabricated and tested at 50, 100, 150, 200, and 250 m. Further, the optimum separation spacing of 13 m was maintained between the balloon and the ducted turbine to reduce balloon turbulence on the turbine. The airborne wind turbine achieved a maximum power output of 250 W at 250 m height while the average wind speed remained 6 m/s. The maximum power coefficient obtained was 0.25 while annual energy production (AEP) remained 1200 kWh. The low power coefficient is credited to the turbulence and drifting in the airborne system and the drag caused by the airborne structure. While a cost-effective commercial model of micro AWES is still being developed, the present work attempts to harvest wind energy at high elevations in low wind speed areas.

Design and performance analysis of an airborne wind turbine for high-altitude energy harvesting

The airborne wind turbine (AWT) offers the opportunity to be installed in challenging heights. For this purpose, the present study focuses on the aerodynamic design of an airborne rotor lifted to high altitude from the viewpoint of airborne technology. The rotor blade is modeled by imposing the elevated wind dataset while the outer shape is comprised of multi-profiles of thick airfoils. Numerical approaches of the BEM and RANS-CFD are employed for insight into performance analysis. The extracted results of the CFD data agreed well with the empirical computations. The induced effect of the diffuser on the rotor is demonstrated through an auxiliary shell structure. A range of 3D simulations varying the airloads are conducted to investigate the on-design and off-design behavior of the rotor. The power coefficient (Cp), effective forces and mass amplification are computed and discussed in terms of performance indicators. The design analysis reveals the significance of the chosen design specification to an operational height of 400 m. The noticeable finding confirms that the optimal Cp of the resulting rotor always occurs at rated conditions and equally valid for both configurations. Additionally, a power gain of 21.3% is obtained from the rotor equipped with the diffuser geometry.

Review on Unconventional Wind Energy

Fossil fuel is the major source of energy and is a fast depleting resource. The phenomenal increase in fossil fuel consumption has adversely affected carbon footprint impacting our environment. With strict environmental regulations in place, the focus towards renewable sources of energy is gaining momentum supported by recent advancement in technologies in wind, hydro and solar. Wind turbines were the first forms of clean energy has seen a major increase in power production. The site restrictions, have limited the wind turbine from being used to its maximum potential. In recent years, the concept of some unconventional methods is being proposed. In this review, the various types of wind turbines are emphasized with their recent advances and depicting the challenges faced in various aspects. The reviews contain details mainly about 4 types of wind turbines i.e. floating offshore wind turbine, airborne wind turbine, highway wind turbine systems and locomotive mounted wind turbine.

Aerodynamic performance optimization of an airfoil-based airborne wind turbine using genetic algorithm

The present manuscript proposes an aerodynamically optimized airfoil-based-shell for performance enhancement of the buoyant airborne turbine system. An integrated code, based on a genetic algorithm, is developed to parametrize the asymmetric airfoil NACA-9415, analyse its aerodynamics and optimize the lift of the airfoil. The 3D steady-state analysis is performed on the optimized shell geometry with NREL-IV rotor using Reynolds Averaged Navier-Stokes (RANS) equation along with k−ωSST turbulence model. The performance of the airborne wind turbine with the optimized shell configuration is assessed in terms of aerodynamic coefficients including shell thrust coefficient, shell back pressure coefficient, turbine power coefficient and power augmentation ratio. The comparison of wind turbine performance with optimized and original NACA-9415 shell configuration demonstrates that shell optimization results in a maximum power coefficient of 1.25 and power augmentation ratio of 2.1 compared to the Betz limit.

Unsteady aerodynamic performance analysis of an airborne wind turbine under load varying conditions at high altitude

The blade air loads of the Airborne Wind Turbine (AWT) may be significantly influenced by the unsteady flow-field at high altitude. Under these susceptible situations, the rotor needs in-depth considerations with respect to transient aspects. The present study focuses on the unsteady aerodynamic performance of stand-alone rotor under the influence of wind shear, yawed, and tilted configurations. The Computational Fluid Dynamics (CFD) transient simulations based on the sliding mesh approach are carried out for analyzing the unsteady behavior of the rotor by lifting the rotor assembly at an airborne altitude from the ground. All simulations are conducted at optimal operating conditions of wind speed and tip speed ratio. In-house Unsteady Blade Element Momentum (UBEM) code using the wind shear, dynamic stall, dynamic wake, and yaw /tilt model are applied to acquire an empirical assessment in terms of rotor torque, thrust, and power coefficient. Finally, the CFD simulated results are compared against the performance curves generated by the UBEM model and acceptable agreement is found within 4.1% deviation at peak operational conditions. The results further reveal that the time-varying aerodynamic loads on the rotor blade gradually achieve steady behavior after three rotation periods. Meanwhile, unique similarities are found in yawed and tilted inflow cases and a 10.7% loss in power coefficient is observed due to rotor yawed inflows. Additionally, in the absence of tower shadows, the strong flow interactions around the rotor blade impose a positive impact on power output. Despite the complexity of unsteady flow phenomena, this present study would be helpful to design a more proficient airborne rotor under the varying load conditions.

Airborne Wind Turbine to Produce More Power from High Altitude Winds

This examination identifies a structure for the higher height Airborne Wind Turbines. Winds at high height are quicker than winds close to the world's surface and contain multiple occasions the power giving an amazing undiscovered vitality asset. Also, high height winds are accessible all the more reliably contrasted with close surface breezes. Henceforth, Airborne Wind Turbines produce a progressively unsurprising and uniform power yield bringing about twofold the vitality generation when contrasted with a traditional turbines. The higher elevation Airborne Wind turbines would at first fly at a tallness multiple times higher than ordinary breeze turbines by vertical take-off. The lift required for the Airborne Wind Turbine's vertical take-off is provided by engine generators associated with the turbines, at long last the all-out frameworks conveyed by helium expand. The breezes at high elevation moving through the turbines turn the generators at rapid. The power created by the turbines is transmitted to the ground by means of the strengthened composite tie that stays the Airborne Wind Turbine to the ground.

Scalability and compatibility analyses of airborne wind technology for maritime transport

Wind energy is a source freely available in the oceans. New developments in the wind industry are towards high altitude wind turbines, known as Airborne Wind Energy Systems. The airborne wind technology is rapidly developing with several different design concepts, e.g. Skysail, Makani, KiteMill. There are mainly two types of airborne wind technology: propulsion-supporting and electricity-generating. Electricity generating airborne technology is mainly used for land-based buildings and fixed offshore structures and with small-scale airborne turbines. Thus, the applications of this technology in the maritime industry are limited to ship propulsion-support only and no scalable airborne wind turbine is used on board of a vessel. Therefore, the objective of this study is to explore the application of electricity-generating airborne turbines on the board of a ship. The exploration is mainly to determine how scalable these turbines shall be to satisfy a ship’s electricity needs and how compatible the design of these turbines can be with the ships design. . Therefore, a scalability analysis based on crosswind kite power model is applied to determine the technical requirements to scale up the existing airborne turbine to meet the electricity demand of a ship. Moreover, a compatibility analysis is applied to determine the technical interfaces and constrains between the airborne turbine configuration and the ship architecture. In this case, a commercial electricity-generating airborne turbine and a commercial floating storage unit are considered as part of the case study. The developed scalability model indicates that the traction force is the most critical design parameter to scale up a wind turbine. On the other hand, the developed compatibility model shows that there is a notorious complexity in merging airborne and ship technology due to their contexts. Consequently, this research appears to be relevant for both, the airborne technology industry and the maritime industry toward more innovative and cost-effective applications.

Performance of buoyant shell horizontal axis wind turbine under fluctuating yaw angles

The paper presents the effect of fluctuating yaw angle and wind speed on the performance of a horizontal axis airborne wind turbine of three different shell shapes for the high altitude operational conditions. For this purpose, a numerical analysis has been performed by considering the ranges of yaw angle and wind speed of 0°−20° and 10m/s−25m/s, respectively. The turbine shell shapes are based on the three aerofoil profiles of NACA-5415, NACA-9415 and NACA-5425 to investigates the influence of the aerofoil camber and thickness. The turbine has been modelled using a NREL Phase IV rotor with the fixed rotor radius of 2m for all shell configurations. A 3-D numerical analysis has been conducted by implementing k−ω SST turbulence model to solve the Reynolds-averaged Navier-Stokes equations. Numerical results demonstrated that the increment in both the tip speed ratio and yaw angle augmented the rotor thrust coefficient. At the high yaw angles, the buoyant shell is prone to encounter instability due to unbalancing of the aerodynamic forces subjected to the shell body. Among all the studied shell configurations, the NACA-9415 aerofoil based shell displayed the relatively higher turbine power coefficient as well as the stable operation.

Aerodynamic analysis of an airborne wind turbine with three different aerofoil-based buoyant shells using steady RANS simulations

The manuscript investigates aerodynamic performance of an airborne wind turbine with varying shell configurations in an effort to elaborate the influence of shell aerodynamics on the performance of the buoyant airborne wind turbine for operating conditions at an altitude of 400 m above the sea level. A systematic study has been conducted on the three airborne duct shapes based on the NACA-5415, NACA-9415 and NACA-5425 cambered aerofoils by considering NREL Phase IV rotor and constant airborne shell throat diameter of 4.02 m. Three dimensional steady state simulations have been performed by employing k-ω SST turbulence model for a range of wind speeds10–25 m/s at zero angle of attack (the angle between wind direction and turbine rotational axis). The performance of the studied turbines have been analysed in terms of rotor thrust coefficient, duct thrust coefficient, turbine power coefficient, swallowed mass flow rate and pressure distribution along the shell. Results demonstrate that among all the considered shell configurations, the NACA-9415 shell based turbine demonstrated highest power coefficient. Increment in the both, aerofoil camber (5–9% of chord length) and thickness (15–25% of the chord length) resulted in 2.05 and 1.45 times higher turbine power coefficient respectively in comparison to the reference aerofoil (NACA-5415) shell based turbine.

Aeroelastic Analysis of a Large Airborne Wind Turbine

This paper presents an extension of the simulation code ASWING to aeroelastic analysis of an airborne wind turbine. The device considered in this study consists of a tethered rigid wing with onboard-mounted wind turbines designed for wind energy harvesting in crosswind flight operation. The electrically conducting tether is deployed from a ground station and represented as a linear elastic spring with stiffness, mass, and frontal area emulating the properties of the real tether. The tether splits into several bridle lines to distribute the load transfer from the wing and to some degree also constrain its roll motion. The comparatively short bridle lines are considered to be inelastic with insignificant mass and aerodynamic drag contributions. The simulation model is validated by wind tunnel tests of a simplified scale model of the bridled wing. The comparison of computed and measured dynamic aeroelastic response shows that the tether force and the geometry of the bridle line system can strongly influence the flutter speed of the wing. In a final step, the simulation model is used to analyze the divergence, control reversal and effectiveness, and flutter behavior of a next-generation large-scale airborne wind turbine. The results confirm the significant influence of the geometry of the bridle line system on static and dynamic aeroelastic phenomena. It is concluded that classical methods used for suppression of aeroelastic instabilities can be applied to bridled wings only if this influence is taken into account.

Effect of rotor axial position on the aerodynamic performance of an airborne wind turbine system in shell configuration

Wind energy has been one of the most widespread types of intermittent renewable energy harvesting source. Airborne wind turbine (AWT) stands out among other available techniques for harvesting wind energy because of its ability to operate at multiple times higher altitudes. This paper presents the aerodynamic performance of an AWT system at an altitude of 400m with NREL Phase IV rotor position variation within the buoyant shell. The unsteady numerical simulations have been carried out at rotor axial positions of 0.25L, 0.3L, 0.35L, 0.4L and 0.45L (L is the shell length) from the inlet, in order to investigate rotor torque variation in one complete rotor revolution. Additionally, steady-state simulations of the AWT system have been performed at various wind speeds (7m/s–20m/s) and yaw angles (0°–15°), to investigate the optimum aerodynamic performance of buoyant shell and rotor. Results demonstrate that by placing the rotor at the shell inlet (0.25L) with step placed at the shell outlet, maximum torque enhancement of 25.3% can be attained at wind speed of 15m/s. Buoyant shell exhibits equilibrium at 0° yaw angle due to symmetric pressure distributions on the shell body. Whereas for yaw angle >0°, instability instigated by non-uniform pressure distributions results in the oscillation of shell. However restoring torque damps out these vibrations and provides assistance in re-establishing equilibrium position.

Impact of altitude and power rating on power-to-weight and power-to-cost ratios of the high altitude wind power generating system

This paper presents a static comprehensive optimization study and analysis of the high altitude wind power (HAWP) generating system based on the medium voltage AC (MV-AC) transmission. The analytical expressions for weight and cost of the transmission line, the mechanical structures (turbine + frame), the generator, and the blimp/aerostat are derived as functions of output power rating and altitude. The optimal voltages for the MV-AC transmission of the HAWP for various power ratings and altitudes are evaluated using the derived equations. The optimal transmission voltage, thus obtained is used to estimate the weight of the tether wire (transmission line) and the generator. The weight of the mechanical frame, the air-borne wind turbine (AWT), and the light gas (Hydrogen/Helium) filled blimp are also estimated for different power ratings and altitudes. The material costs of each major component of the HAWP generating system are obtained from the manufacturers' datasheets and used to compute the overall material cost. From the estimated weight and cost, the overall power-to-weight (P/W) and power-to-cost (P/C) ratios of the HAWP generating system are evaluated. Finally, the optimal operating altitude for a specific power rating that exhibits the best P/W and reasonably good P/C ratios can be selected for the development and installation of the HAWP generating system.

Consideration for Vertical Axis Wind Turbine Assuming to Use for Airborne Wind Turbine

Consideration for Vertical Axis Wind Turbine Assuming to Use for Airborne Wind Turbine

Aerodynamic performance analysis of an airborne wind turbine system with NREL Phase IV rotor

Wind energy becomes more powerful and consistent with an increase in altitude, therefore, harvesting the wind energy at high altitude results in a naturally restocked source of energy which is cheaper and far more efficient than the conventional wind power system. Airborne wind turbine (AWT), one of the many techniques being employed for this purpose, stands out due to its uninterrupted scheme of energy production. This paper presents the aerodynamic performance of AWT system with NREL Phase IV rotor at an altitude of 400m. Unsteady simulation of the airborne system has been carried out and variations in the rotor’s torque for a complete revolution are reported and discussed. In order to compare the performance of the shell mounted configuration of Phase IV rotor with its standard test configuration, steady state simulations of the rotor are also conducted under various wind conditions for both configurations. Finally, for stable design of the buoyant airborne system, aerodynamic forces on the shell body are computed and reported.

Comprehensive Conceptualization, Design, and Experimental Verification of a Weight-Optimized All-SiC 2 kV/700 V DAB for an Airborne Wind Turbine

This paper details the design, implementation, and experimental verification of a minimum weight input series output parallel structured dual active bridge (DAB) converter for an airborne wind turbine system. The main power components of the DAB converter, particularly the bridge circuits, the actively cooled high-frequency transformer and inductor, and the cooling system, which largely contribute to the total system weight, are designed and realized based on multiobjective considerations, i.e., with respect to weight and efficiency. Furthermore, the design includes all necessary considerations to realize a fully functional prototype, i.e., it also considers the auxiliary supply, the control for a stable operation of the system, which also comprises an input filter, over the specified operating range, and the start-up and shut down procedures. These considerations show the complex interactions of the various system parts and reveal that a comprehensive conceptualization is necessary to arrive at a reliable minimum weight design. Experimental results validate the proposed design procedure for a realized lightweight DAB hardware prototype with a rated power of $ \mathrm {6.25~\,kW}$ . The prototype weighs $ \mathrm {1.46~\,kg}$ , i.e., features a power-to-weight ratio of $ \mathrm {4.28~\,kW{/}\,kg}$ ( $ \mathrm {1.94~\,kW{/}\,lb}$ ), and achieves a maximum full-load efficiency of 97.5%.

Airborne wind turbine shell behavior prediction under various wind conditions using strongly coupled fluid structure interaction formulation

High altitude wind harvesting has been acknowledged as one of the green and efficient future prospects for renewable energy. Different techniques have been adopted over the time to exploit the source effectively. Airborne Wind Turbine System is one of those techniques that are however still in its initial stages. In the present study, the behavior of the airborne wind turbine shell is predicted numerically under various wind conditions. A partitioned strongly coupled fluid–structure interaction formulation was employed to anticipate the behavior of the turbine shell at different wind speeds and varying angles of attack. Two commercial solvers for fluid and structural domains were engaged as black box solvers. Fixed point iteration with dynamic under relaxation was employed to couple the solvers. Dynamic and kinematic constraints were satisfied at each time step to ensure strong coupling of the solvers. This study would be helpful to better understand the behavior of airborne wind turbine shell under different conditions of the wind for a stable and proficient design.