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The focus of this study is on the aerodynamic design of a 2000-W airborne wind turbine (AWT) situated 100 m above ground level. AWTs harness higher wind speeds at higher altitudes, making them more efficient than ground-based turbines in generating power. To achieve the desired performance, numerical methods, such as blade element momentum (BEM) and computational fluid dynamics (CFD) were employed for the aerodynamic design and analysis of the AWT system. The rotor cross-section of the three-blade rotor incorporates S223 and S822 airfoils, which are derived from the conventional NREL airfoils. The diffuser section of the AWT has an elliptical curve to accommodate the maximum volume of helium gas. Through simulations using both CFD and BEM, the performance of the bare rotor was assessed, as well as the diffuser-augmented wind turbine (DAWT) under design and off-design conditions. The results demonstrated that the DAWT is capable of meeting the desired power output in all scenarios. Moreover, the findings indicated that using the diffuser enhances the rotor output power coefficient by 18% and prevents significant power loss during off-design conditions. This highlights the effectiveness of the rotor-diffuser assembly in maximizing power generation and ensuring consistent performance of the AWT system. [ABSTRACT FROM AUTHOR]

Abstract Wind speed and direction variations across the rotor affect power production. As utility‐scale turbines extend higher into the atmospheric boundary layer (ABL) with larger rotor diameters and hub heights, they increasingly encounter more complex wind speed and direction variations. We assess three models for power production that account for wind speed and direction shear. Two are based on actuator disc representations, and the third is a blade element representation. We also evaluate the predictions from a standard power curve model that has no knowledge of wind shear. The predictions from each model, driven by wind profile measurements from a profiling LiDAR, are compared to concurrent power measurements from an adjacent utility‐scale wind turbine. In the field measurements of the utility‐scale turbine, discrete combinations of speed and direction shear induce changes in power production of −19% to +34% relative to the turbine power curve for a given hub height wind speed. Positive speed shear generally corresponds to over‐performance and increasing magnitudes of direction shear to greater under‐performance, relative to the power curve. Overall, the blade element model produces both higher correlation and lower error relative to the other models, but its quantitative accuracy depends on induction and controller sub‐models. To further assess the influence of complex, non‐monotonic wind profiles, we also drive the models with best‐fit power law wind speed profiles and linear wind direction profiles. These idealized inputs produce qualitative and quantitative differences in power predictions from each model, demonstrating that time‐varying, non‐monotonic wind shear affects wind power production.

Wind speed and direction variations across the rotor affect power production. As utility‐scale turbines extend higher into the atmospheric boundary layer (ABL) with larger rotor diameters and hub heights, they increasingly encounter more complex wind speed and direction variations. We assess three models for power production that account for wind speed and direction shear. Two are based on actuator disc representations, and the third is a blade element representation. We also evaluate the predictions from a standard power curve model that has no knowledge of wind shear. The predictions from each model, driven by wind profile measurements from a profiling LiDAR, are compared to concurrent power measurements from an adjacent utility‐scale wind turbine. In the field measurements of the utility‐scale turbine, discrete combinations of speed and direction shear induce changes in power production of −19% to +34% relative to the turbine power curve for a given hub height wind speed. Positive speed shear generally corresponds to over‐performance and increasing magnitudes of direction shear to greater under‐performance, relative to the power curve. Overall, the blade element model produces both higher correlation and lower error relative to the other models, but its quantitative accuracy depends on induction and controller sub‐models. To further assess the influence of complex, non‐monotonic wind profiles, we also drive the models with best‐fit power law wind speed profiles and linear wind direction profiles. These idealized inputs produce qualitative and quantitative differences in power predictions from each model, demonstrating that time‐varying, non‐monotonic wind shear affects wind power production. [ABSTRACT FROM AUTHOR]

A multi-objective optimum design of propellers is presented. Traditionally, the definition of propellers is done by choosing models that already exist on the market. However, with the advancement of technologies such as 3D printing and computer numerical control, the possibility for the designer to seek an optimized propeller for his design is increasingly feasible. In this scenario, this paper aims to propose a methodology that allows the designer to find alternative propeller designs. The methodology comprises the creation, refinement, and extension of an airfoil database available from the literature. The aerodynamic analysis uses the blade element theory and the optimization with evolutionary algorithms. Seven multi-objective constrained optimization problems were formulated, with two, three, and four conflicting objective functions concerning the propeller aerodynamic and geometric information, such as the thrust coefficient, the bending coefficient, the efficiency, and the volume of the propeller. Among them, for instance, two proposed formulations are: (i) maximizing the thrust and minimizing the bending coefficients simultaneously, (ii) maximizing the thrust coefficient, minimizing the bending coefficient, minimizing the volume of the propeller, and minimizing the efficiency simultaneously. The experiments analyzed the optimization of small propellers for two different engines, combustion and electric brushless. Five evolutionary algorithms were used to solve these problems, and solutions were extracted from the Pareto fronts using multi-criteria decision-making according to the decision-maker preferences. Finally, the complete data of the extracted solutions are provided, such as dimensions, angles, shapes, and performance characteristics. [ABSTRACT FROM AUTHOR]

In this study, models for the wake capture lift and drag force coefficients of a hovering flapping wing were presented using numerical fluid dynamics simulation to improve the blade element theory. The investigated wing is inspired by the fruit fly and has combined flapping and pitching movements. The effect of changing the wing acceleration time at the start (Δ τ A ) and end of the half cycle (Δ τ D ), as well as the Reynolds numbers in the range of 136–6800, on wake capture using the Taguchi orthogonal array test design, is investigated using the numerical fluid dynamics method, and the values of average lift and drag coefficients due to wake capture are obtained. These force coefficients were applied to linear and nonlinear regression methods to obtain the mathematical model, and a model for its changes was extracted. Finally, to obtain the instantaneous coefficients, the extracted models were placed in the normal distribution function, and the final instantaneous model was obtained. Examining the verification cases of the application of these wake capture relationships with the blade element theory, as well as the effects of translational force, rotational force and added mass force, revealed that this developed theory is capable of correctly predicting the wake capture force's initial peak. The force coefficient trend in the final quasi-steady model with wake capture is similar to the computational fluid dynamics (CFD) results, according to a qualitative examination of the lift and drag force coefficients in a half cycle. This demonstrates a significant result: this theory, which is divided into four parts: transnational, rotational, added mass and wake capture, adequately covers the general physics of these complex movements. [ABSTRACT FROM AUTHOR]

This work presents an actuator disk-like body force method designed for propeller modeling, which is based on a full coupling between computational fluid dynamics (CFD) and blade element theory (BET). An analysis is conducted on the model to identify best practices for source term distribution. It is found that the source term volume shape has no impact on propeller loads and flowfield and that the velocities used for the BET analysis at each radial section should be evaluated exactly where half the source terms have been distributed in the CFD domain. Four tip-loss corrections, including two from literature, are also analyzed and compared to lifting-line and Reynolds-averaged Navier-Stokes (RANS) blade-resolved computations. The best practices and the most effective tip-loss correction lead to a final model that is compared to lifting-line, RANS, and unsteady RANS computations for different pitch angles and incidence angles, on the ONERA HAD-1 three-bladed light propeller. The RANS/BET body force model predicts thrust within 3% for axial flow and 8% for cases with incidence. The same accuracy is obtained for wake prediction. [ABSTRACT FROM AUTHOR]

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Unmanned aerial vehicle (UAV) usage has witnessed a significant rise owing to its cost-effectiveness and versatile applications. However, the design techniques for UAV propellers, encompassing aerodynamic and structural analysis, have received limited attention from researchers. A well-designed propeller can effectively reduce battery consumption and enhance overall efficiency. This study focuses on mathematically designed propellers and compares them with advanced precision composite (APC) Slow Flyer propeller blades in terms of thrust coefficients, power coefficients, and efficiency. The investigation includes the utilization of tetrahedron meshing in simulations, employing the standard k-ω (k-omega) model. To evaluate the accuracy of the blade element theory (BET) in predicting thrust, the simulation data is compared with BET results. Furthermore, the study encompasses experimental testing to validate the simulation findings. The findings demonstrate that the mathematically modelled propeller outperforms the APC Slow Flyer propeller across all ranges of revolutions per minute (rpm). When comparing the results of both methods, BET exhibits an error difference of 10 % in higher rpm ranges, but this error diminishes as the rpm decreases. This study contributes a novel design technique for modelling propellers using mathematical formulas and provides a comprehensive comparison of their aerodynamic properties with existing propellers, utilizing both BET and computational fluid dynamics (CFD) methods, along with experimental validation. [ABSTRACT FROM AUTHOR]

Due to the complexity of tailoring the wing flexibility and selecting favorable kinematics, the design of flapping wings is a considerably challenging problem. Therefore, there is an urgent need to investigate methods that can be used to design wings with high energy efficiency. In this study, an optimization model was developed to improve energy efficiency by optimizing wing geometric and kinematic parameters. Then, surrogate optimization was used to solve the design optimization model. Finally, the optimal design parameters and the associated sensitivity were provided. The optimized flapping wing, inspired by hummingbirds, features large geometrical parameters, a moderate amplitude of the flapping angle, and low frequency. With the spanwise twisting deformation considered in the parameterization model, the optimization solver gave an optimized wing with a pitching amplitude of approximately 39 deg at the root and 76 deg at the tip. According to the sensitivity analysis, the length of the wing, flapping frequency, and flapping amplitude are the three critical parameters that determine both force generation and power consumption. The amplitude of the pitching motion at the wing root contributes to lowering power consumption. These results provide some guidance for the optimal design of flapping wings. [ABSTRACT FROM AUTHOR]

Modern horizontal-axis wind turbines produce maximum power at an optimal tip speed ratio, λopt, of around 7. This is also the approximate start of the high-thrust region, which extends to runaway at λR ≈ 2λopt where no power is produced and the thrust is maximized. The runaway thrust coefficient often exceeds unity. It is well known that the conventional axial momentum equation must be modified whenever the thrust coefficient approaches unity, but most past modifications have no sound physical basis. Our main revision is to include the “wake vorticity” term in the axial momentum balance. This term is related to blade element drag and acts to decouple the thrust from the induced axial velocity when it becomes large near the edge of the rotor as the runaway is approached. The wake vorticity term dominates the axial momentum equation in these conditions and leads to estimates of power and thrust that are consistent with the limited amount of high-quality experimental data in the high-thrust region.

Fixed-pitch coaxial, contrarotating rotors are often used in multirotor aircraft in applications ranging from payload delivery to urban air mobility. This paper examines minimizing net power at a given thrust for the coaxial pair using both an analytical approach based on blade element momentum theory and experimental results conducted in a hover test stand, as well as experimental results in hover for an X8 configuration multirotor. Appropriate distribution of thrust (realized via differential rotor speeds) to the upper and lower rotors results in approximately 5% savings in total power. Under this condition the thrust distribution is approximately 60% by the upper rotor and 40% by the lower rotor (which occurs when the lower rotor shaft speed is roughly 10% higher than the upper rotor shaft speed). Similar ratios were obtained in both the analytical solution and in experiment, at various total thrust levels. Hover flight tests of the X8 multirotor also showed approximately 5% reduction in hover power at this RPM setting. [ABSTRACT FROM AUTHOR]

The popular axial momentum theory relies on the steady, incompressible, axisymmetric, and inviscid flow through a so-called actuator disk. The most important result of this theory is the famous Betz-Joukowsky limit, stating that the maximum power coefficient achievable by an open disk is limited to 16/27. Generally, this value is obtained assuming a priori that the disk is radially uniformly-loaded and the flow is axially one-dimensional. This, however, does not prove that the uniform type is the optimal load, or else that it returns the maximum value of the extracted power. For this reason, this paper preliminary shows that 16/27 is the exact value of the maximum power coefficient of a uniformly loaded disk, even if the flow is not assumed as one-dimensional. Then, it proves, using a calculus of variation approach, that the radially uniform load is optimal. The proof refers to an approximate classical local form of the axial momentum equation. Finally, the paper points out that, since the proof of the Betz-Joukowsky limit relies on this simplifying assumption, the exact evaluation of the optimal radial distribution of the disk load, leading to the maximum value of the power coefficient, is still an open question. [ABSTRACT FROM AUTHOR]

Due to the complexity of tailoring the wing flexibility and selecting favorable kinematics, the design of flapping wings is a considerably challenging problem. Therefore, there is an urgent need to investigate methods that can be used to design wings with high energy efficiency. In this study, an optimization model was developed to improve energy efficiency by optimizing wing geometric and kinematic parameters. Then, surrogate optimization was used to solve the design optimization model. Finally, the optimal design parameters and the associated sensitivity were provided. The optimized flapping wing, inspired by hummingbirds, features large geometrical parameters, a moderate amplitude of the flapping angle, and low frequency. With the spanwise twisting deformation considered in the parameterization model, the optimization solver gave an optimized wing with a pitching amplitude of approximately 39 deg at the root and 76 deg at the tip. According to the sensitivity analysis, the length of the wing, flapping frequency, and flapping amplitude are the three critical parameters that determine both force generation and power consumption. The amplitude of the pitching motion at the wing root contributes to lowering power consumption. These results provide some guidance for the optimal design of flapping wings.

Condition-based maintenance programs for modern helicopters rely on algorithmic techniques to estimate the useful life remaining for life-limited components. Regime-recognition-based condition-based maintenance programs involve a regime recognition step and a damage estimation step in which damage is calculated based on the identified regimes. Recently, new probabilistic regime recognition algorithms have been developed that produce probability distributions over the regimes, rather than deterministic regime classifications. However, to date, there has been no method to convert regime distributions to damage estimates. This paper proposes a technique to compute a probability distribution over the fatigue damage for each life-limited component directly from the regime probability distributions. The method treats the incurred damage at a given time as a random variable and accumulates the total damage incurred as a sum of random variables. The damage distribution at each time is computed from the regime distribution and the regime damage rates. A primary advantage of the approach is that it captures uncertainty in the regime recognition process by treating damage as a random variable rather than a deterministic value. Simulation results illustrate the benefit of the probabilistic approach over a deterministic method, particularly for flights where there is significant uncertainty in the flown regimes. [ABSTRACT FROM AUTHOR]

The key problem in the development process of a tiltrotor is its mathematical modeling. Regarding that, this paper proposes a dividing modeling method which divides a tiltrotor into five parts (rotor, wing, fuselage, horizontal tail, and vertical fin) and to develop aerodynamic models for each of them. In that way, force and moment generated by each part are obtained. Then by blade element theory, we develop the rotor’s dynamic model and rotor flapping angle expression; by mature lifting line theory, the build dynamic models of the wings, fuselage, horizontal tail and vertical fin and the rotors’ dynamic interference on wings, as well as nacelle tilt’s variation against center of gravity and moment of inertia, are taken into account. In MATLAB/Simulink simulation environment, a non-linear tiltrotor simulation model is built, Trim command is applied to trim the tiltrotor, and the XV-15 tiltrotor is taken as an example to validate rationality of the model developed. In the end, the non-linear simulation model is linearized to obtain a state-space matrix, and thus the stability analysis of the tiltrotor is performed.

Placing a diffuser around a wind turbine can increase its power output, but not all mechanisms by which the diffuser alters the aerodynamics have been investigated thoroughly. Here, we concentrate on one such mechanism: the effect of the finite number of blades. In nearly all blade element analyses of wind turbines, finite blade effects are approximated by Prandtl's "tip loss factor" which goes to zero at the blade tip. We argue that this limiting behaviour cannot be correct for the axial velocity in the presence of a diffuser. We provide alternative "finite blade functions" which preserve the finite limit on the axial velocity, but do not alter the conventional limit of zero for the circumferential velocity. In maximizing the power output of a diffuser-augmented wind turbine, the change in the finite blade function for the axial velocity has a large impact on the power-producing region near the tip: it increases both the chord and the power output of an optimized blade. Further, the change appears to make diffuser-augmented turbine power output less sensitive to tip speed ratio than for a bare turbine. • A new model for the finite number of blades in diffuser-augmented wind turbines. • The blade loading is finite at the tip in contrast to bare turbines. • Finite blade functions to optimize chord and twist angle of shrouded blades. • Diffuser-augmented turbine power output seems to be less sensitive to tip speed ratio. • Good agreement is demonstrated with available experiments. [ABSTRACT FROM AUTHOR]

Windmills were developed to a high degree between their initial European use in the twelfth century and the twentieth century when mathematical analysis was first applied to optimise the design of their sails. It led immediately to the concept of twisted sails in which the weather angle decreased with radius. Various theories were tested experimentally by Smeaton, who found twisted sails to be better than common sails but less good than the Dutch sails then normally used. A century passed before Rankine applied Newton's laws of motion to derive their power and efficiency (power coefficient). Annular windmills were developed in both Britain and the United States where they were extensively tested by Perry, who found them as efficient as Smeaton's sails. In the twentieth century, Lanchester, Betz, and Joukowski independently derived an upper limit for windmill power coefficient and this, combined with aerodynamic theory and streamlined aerofoils led to the development of the modern wind turbine. [ABSTRACT FROM AUTHOR]

All rotating blades shed helical vortices which have a significant effect on the velocity over the blades and the forces acting on them. Nevertheless, knowledge of vortex behavior is not used in blade element theory (BET), the most common method to calculate the thrust produced by propellers and the power by wind turbines. Helical vortices of constant pitch and radius are also of fundamental interest as one of only three geometries that do not deform under their “self-induced” motion. This aspect of vortex theory is reviewed historically and the relationship with the forces acting on submerged bodies briefly reviewed. The development of helical vortex theory (HVT) in the 20th century is then described. It is shown that HVT allows BET to be used for a number of important problems that cannot be analyzed by current versions of the theory.

Despite many commercial applications make extensive use of Unmanned Aircraft Systems (UAS), there is still lack of published data about their performance under unconventional weather conditions. In the last years, multirotors and fixed wing vehicles, commonly referred to as drones, have been studied in wind environments so that stability and controllability have been improved. However, other important weather variables have impact on UAS performance and they should be properly investigated for a deeper understanding of such vehicles. The primary objective of our study is the preliminary characterization of a propeller in a climate-controlled chamber. Mechanical and electrical data have been measured while testing the propeller at low pressure and cold temperatures. Test results point out that thrust and electric power are strongly affected by air density. A comparison between the experimental data and the results of the Blade Element Theory is carried out to assess the theory capability to estimate thrust in unconventional environments. The overlap between experimental data and theory computation is appropriate despite geometrical uncertainties and corroborate the need of a reliable aerodynamic database. Propeller performance data under unconventional atmospheres will be leveraged to improve UAS design, propulsion system modelling as well as provide guidelines to certify operations in extreme environments. [ABSTRACT FROM AUTHOR]

The present investigation addresses two key issues in aerodynamic performance of a propeller–wing configuration, namely linear and nonlinear predictions with low-order numerical models. The developed aerodynamic model is targeted to be used in the preliminary aircraft design loop. First, the combination of selected propeller model, i.e. blade element theory with the wing model, i.e. lifting line theory and vortex lattice method is considered for linear aerodynamic model. Second, for the nonlinear prediction, a modified vortex lattice method is paired with the two-dimensional viscous effect of the airfoils to simplify and reduce the computational time. These models are implemented and validated with existing experimental data to predict the differences in lift and drag distribution. Overall, the predicted results show agreement with low percentage of error compared with the experimental data for various thrust coefficients and produced induced drag distribution that behaves as expected. [ABSTRACT FROM AUTHOR]

Drivetrain resistance of wind turbines is still challenging, since determining static and dynamic frictional torque is rather complex. Hence, the main motivation of this work is to experimentally investigate resisting torques of a drivetrain typically found in small wind turbines. Measurements are carried out using a bench setup comprising torque sensor, rpm encoder, generator and electrical motor. For further evaluation, an approach combining Newton's second law and blade element theory to assess the turbine behavior is employed, which is able to estimate the minimal wind velocity to start electrical generation, as well as the rated velocity of a small wind turbine. A theoretical expression for the friction torque is also demonstrated. An extension of SKF and Palmgren models are used to verify the friction torque on the bearings, which are often the main contributors to resistance in the turbine drivetrain. Assessments using a small wind turbine with 4 blades and 1.3 m diameter is performed to show the effect of the drivetrain resistance, in which its rotational speed changes according to the friction torque, yielding a more realistic response when the generator is loaded and unloaded. • Experimental investigation of resisting torques in small wind turbines. • Extensions of SKF and Palmgren models are used to determine bearing friction torque. • Semiempirical formulations present good accordance with experimental data. • The flow axial load on the wind rotor needs to be included in the dissipative torque. [ABSTRACT FROM AUTHOR]

The generation of electricity from free-flowing water is an important renewable energy source. In this paper, we introduce a new turbine concept based on a vertical axis turbine with two extraction planes and a rectangular harvest area suitable for rivers or ocean currents. Using numerical simulations, we show that the extension of the classic vertical axis turbine by linear sections can significantly improve efficiency, with gains of up to 12% in the case of the Reference Model 2 turbine, a benchmark prototype used for comparison. Based on the findings, a prototype is designed and built with a focus on optimizing the blade pitch using computational fluid dynamics simulations. The prototype is subsequently evaluated through performance measurements on a test boat. Our results show that the Linear Turbine has the potential to significantly improve the efficiency of kinetic energy converters for free-flowing water, with an efficiency of around 42% achieved in our small prototype. Key features of the turbine include its ability to generate electricity from rivers and ocean currents with minimal impact on the natural environment, its high potential efficiency, vertical construction, and linear working range. The design of the turbine is complex, but its potential applications include use in small-scale systems and as a environmental alternative to traditional hydroelectric dams. Further investigations are needed to focus on economic design and to validate improved designs with 3D fluid simulations. • New turbine concept with a vertical axis and two extraction planes. • High potential efficiency comparable or beyond traditional horizontal axis turbines. • Prototype design with tip speed ratio of 2 and 42% efficiency. • Design allows for easy extension and increased harvesting area. • Dynamic pitch adjustment for improved power generation. [ABSTRACT FROM AUTHOR]

Pakistan is facing energy crisis since last decade. This crisis can be effectively handled by utilizing alternative energy resources. Pakistan has a huge wind energy potential of about 50,000MW. The contribution of costal area of Sindh, Pakistan in the total wind energy potential is about 43000MW. The Jamshoro wind corridor has the highest wind potential of all coastal areas of Sindh. In this paper a wind blade design has been developed and optimized for Jamshoro wind corridor. The theoretical blade design include the airfoil selection, appropriate chord length selection and optimization of twist angle. The designed blade has been analyzed using Q-blade. Considering the Jamshorowind conditions, blade of around 43 meters have been designed and optimized theoretically. Then the theoretical design is also been checked and verified in Q-blade. Theoretical optimization includes using different combinations of NACA profiles and using exhaustive iterative method to get optimized twist angle. This ensures the design with maximum power output with respect to wind speed of Jamshoro. For low wind speeds, theoretical results and simulated results in Q-blade were almost same but for high wind speeds, results were significantly different due to limitation of iterations in theoretical design

In this study, the helicopter blade in forward-flight condition was investigated. The blade element theory (BET) was used throughout this analysis to investigate the angle of attack variations at the blade cross sections, lift distribution along the blade and effects of increasing helicopter speed. Prouty’s helicopter data was used to validate the analysis results. In this analysis, the helicopter blade was divided into 50 equally spaced elements and the azimuth ψ was set at 7.2° for each movement of the blade. The helicopter speed of 80 m/s was considered. The analysis revealed that the computation results were in good agreement with Prouty’s diagram. Furthermore, it was also evident that in the case of a helicopter in forward-flight condition, the blade at retreating side was generally at low angle of attack and experienced low lift, in contrast to the blade at advancing side. The increment of the helicopter speed affected the lift distribution along the blade. The reverse flow area was widened two times from that given by the original Prouty’s diagram. In addition, it was proven that each helicopter has its own speed limit called velocity never exceed (VNE). It was also shown that BET is important in conducting the analysis to modify the helicopter blade design for the aerodynamic characteristics’ improvement as well as stability and general performance enhancement for the helicopter.

The propulsion system of a multi-rotor UAV plays a fundamental role in the aircraft flight characteristics. In fact, it generally represents the major contributor to the aerodynamic forces acting on the vehicle. While several approaches for modeling rotor thrust and drag forces exist, the problem of identifying the parameters for these models is still challenging. In this paper we propose a systematic method for identifying a limited number of parameters which guarantee accurate thrust and drag prediction according to Blade Element Theory (BET). Simple experimental tests employing a popular rotor system and a custom-made quadrotor are used both in the identification phase and for the final validation. The discussion of the results illustrates the accuracy of the method, while highlighting the modeling limit of BET. A refinement using Blade Element Momentum Theory is proposed and validated with the support of experimental data. [ABSTRACT FROM AUTHOR]

An embedded Reynolds-Averaged Navier-Stokes blade element actuator disk model is used to investigate the hydrodynamic design of tidal turbines and their performance in a closely spaced cross-stream fence. Turbines designed for confined flows are found to require a larger blade solidity ratio than current turbine design practices imply in order to maximise power. Generally, maximum power can be increased by operating turbines in more confined flows than they were designed for, although this also requires the turbines to operate at a higher rotational speed, which may increase the likelihood of cavitation inception. In-array turbine performance differs from that predicted from single turbine analyses, with cross-fence variation in power and thrust developing between the inboard and outboard turbines. As turbine thrust increases the cross-fence variation increases, as the interference effects between adjacent turbines strengthen as turbine thrust increases, but it is observed that cross-stream variation can be mitigated through strategies such as pitch-to-feather power control. It was found that overall fence performance was maximised by using turbines designed for moderately constrained (blocked) flows, with greater blockage than that based solely on fence geometry, but lower blockage than that based solely on the turbine and local flow passage geometry to balance the multi-scale flow phenomena around tidal fences.

Aiming at the global efficiency of solar chimney power plant (SCPP), we design a wind turbine generation device to elevate its electricity generating efficiency. Based on wind power utilization theory, a new method is proposed to design a type of wind turbine blade for SCPP. The lift and resistance coefficients on different Reynolds numbers of NACA4418 airfoil, which is suitable for experimental solar electricity generation system, are determined by Profili-V2.0 airfoil design software, a program written in Matlab to calculate chord length of the airfoil. The optimization is conducted by class-shape-transformation (CST) parameterization method and Xfoil software. An airfoil design program is designed on the basis of blade element theory and attack angle with the highest lift coefficient to iteratively determine the inflow angle and setting angle. Prandtl’s tip-loss factor is applied to correct the setting angle, after the airfoil data are input into AutoCAD to build an airfoil model which is then imported into Solidworks to draw blades. A new way is put forward to design wind turbine blades in SCPP. [ABSTRACT FROM AUTHOR]

Highlights • The methodology for systematic design of novel hybrid UAV systems is discussed. • The design approach is established using the example of a novel variable pitch quadrotor biplane UAV for payload delivery. • Modified BEMT is used for rotor design and lifting line theory is used for wing design. • Rotor RPM used for hover mode is reduced by approximately 38% to optimize the performance of proprotors during forward flight. • A proof-of-concept vehicle is fabricated and its stable hovering flight is demonstrated by implementation of a PID controller. Abstract This paper discusses the conceptual design and proof-of-concept flight demonstration of a novel variable pitch quadrotor biplane Unmanned Aerial Vehicle concept for payload delivery. The proposed design combines vertical take-off and landing (VTOL), precise hover capabilities of a quadrotor helicopter and high range, endurance and high forward cruise speed characteristics of a fixed wing aircraft. The proposed methodology is described by taking an example of a VTOL Unmanned Aerial Vehicle (UAV) for a mission requirement of carrying and delivering 6 kg payload to a destination at 16 km from the point of origin. First, the design of proprotors is carried out using a physics based modified Blade Element Momentum Theory (BEMT) analysis, which is validated using experimental data generated for the purpose. Proprotors have conflicting requirement for optimal hover and forward flight performance and a compromise solution has to be chosen. Next, the biplane wings are designed using simple lifting line theory. The airframe design is followed by power plant selection and transmission design. Finally, weight estimation is carried out to complete the design process. The proprotor design with 24° preset angle and − 24 ∘ twist is found to be suitable for the current mission profile, based on 70% weightage to forward flight and 30% weightage to hovering flight conditions. A reduction in operating RPM of the proprotors from 3200 during hover to 2000 during forward flight results in 27% increase in proprotor efficiency. The VTOL UAV design proposed in this paper is also predicted to consume 64% less power in airplane mode compared to the quadrotor mode, thereby establishing the benefit of this hybrid concept. A proof-of-concept scaled prototype is fabricated using commercial-off-the-shelf parts and a Proportional Integral Derivative (PID) controller is developed and implemented on open source PixHawk autopilot board to enable stable hovering flight and attitude tracking during hover flight tests. [ABSTRACT FROM AUTHOR]

Most small wind turbines do not have pitch adjustment of the blades. This makes starting at low wind speed a serious challenge which is magnified by the drivetrain resistance caused by bearing friction, generator cogging torque and so on. Typically the resistive torque is much less than the rated generator torque so drivetrain resistance is safely ignored once power production commences but must be considered when the rotor torque is low. This occurs during starting and when the turbine approaches the runaway condition of no output load. Equations are derived here for the drivetrain resistance of a small turbine as part of an analysis of starting and runaway which is compared to wind tunnel measurements. This paper focuses on the resistance due to the bearings in the drivetrain, especially on the transition from high static to significantly lower dynamic resistance as high static resistance increases the wind speed at which a turbine starts. The measurements were made using a three-bladed turbine with no other loads so they include both starting performance and runaway. The results demonstrate a static resistive torque about seven times the dynamic one, giving a theoretical starting wind speed of 4.20 m/s which is 6% higher than the measured value. Good agreement is found between the analysis and measurements of rotor angular velocity over the whole operating range from starting to runaway, highlighting the importance of this work for estimating the minimum wind speed for the starting of small wind turbines. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments are performed to investigate the aerodynamic characteristics of a quadrotor helicopter in a uniform flow. At first, the thrust and drag coefficients of a single rotor under low-Reynolds number conditions are measured to deduce the basic design parameters of the rotor. Second, the aerodynamic interference between two rotors in a tandem configuration is investigated. It is experimentally found that the thrust coefficient of the rear rotor is a maximum of 11% lower than that of the front rotor during forward flight. Moreover, it is found that the interference effect of the front rotor on the rear rotor can be predicted qualitatively using a theoretical formula on the basis of the Biot-Savart Law. Finally, it is shown that the theoretical predictions of the thrust coefficient and drag coefficient agree well with the experimental results of a quadrotor helicopter model within limited ranges of the inflow ratio and advance ratio. [ABSTRACT FROM AUTHOR]