Aerodynamic Torque Research Articles

Comparative study between a discrete vortex method and an immersed boundary–lattice Boltzmann method in 2D flapping flight analysis

Numerical analysis of the flapping flight of insects has attracted great attention because of the expectation for insect-inspired micro air vehicles. A lot of numerical methods for the insect flight have been proposed, and they can be classified into two categories: inviscid flow solvers and viscous flow solvers. The discrete vortex method (DVM) has been regarded as a successful method in the first category, and the immersed boundary–lattice Boltzmann method (IB-LBM) has recently been developed as an efficient method in the second category. However, a detailed comparative study between these methods has not been sufficiently performed. In this study, we compare the DVM with the IB-LBM in two-dimensional flapping flight analysis. As a result, it is found that the aerodynamic forces obtained by the DVM are comparable to those by the IB-LBM, when the effect of separated vortices is not so accumulated, and when the forward speed of the model is smaller than the flapping speed. In addition, the DVM has a difficulty in estimating the aerodynamic torque. In terms of the computational time, the DVM is much faster than the IB-LBM. This result suggests that the DVM can be used for massive parametric studies or optimizations in flapping flight analysis, although there remain many issues in its accuracy.

Wind profile disturbance isolation and attenuation through an UIO–LPV approach in PMSG‐based wind turbines

Wind turbines operate under random and harsh operating conditions due to several environmental factors. The main source of disturbance is the wind profile due to wind shear and tower shadow influence on the aerodynamic torque driving the system. Disturbed aerodynamic torque induces unwanted operating conditions for all wind turbines subsystems. This study proposes a novel combined unknown input observer (UIO) and linear parameter varying (LPV) approach. In a first instance an UIO approach for disturbance isolation in the input aerodynamic torque as a simple, fast and accurate method. In addition, a comparison with an Extended Kalman filter approach for disturbance isolation is introduced. Then, when the isolation occurs, an LPV controller is used as an active controller for disturbance attenuation in the speed range of the wind turbine. The LPV controller injects a current signal into the generator opposing the disturbance signature introduced by the wind profile. The aim of the UIO-LPV strategy is limiting the amount of generated current and being able to extend the amount of disturbance attenuation. The strategy is applied to a permanent magnet synchronous generator (PMSG) based wind turbine with experimental tests and results by the means of a test rig.

Simulation-based insect-inspired flight systems.

Insects power and control their flight by flapping their wings. By controlling their aerodynamic forces and torques, they can generate precise and agile aerial manoeuvres. From an engineer's perspective, their closed-loop, flight control system depends on an overarching external mechanical 'frame' consisting of wings and thoracic shell, which is actuated by an internal system consisting of flight muscles and a complex nervous system. Insect flights are diverse but robust relying on the integration of different flexible structures including wings, exoskeletal elements, wing-hinges, musculoskeletal elements, and sensors. Computational modelling of biomechanics in insect-inspired flight systems can offer a powerful and feasible tool to unravel a passive and active mechanism (PAM) strategy, that is, how these flexible structures work interactively and complementarily to achieve a systematically efficient and robust flapping-wing dynamics and aerodynamics as well as flight control in various natural environments.

Mathematical Simulation of Satellite Motion with an Aerodynamic Attitude Control System Influenced by Active Damping Torques

The dynamics of a satellite moving in a central Newtonian force field in a circular orbit under the influence of aerodynamic and active damping torques depending on projections of the satellite’s angular velocity is studied. A method for determining all equilibrium positions (equilibrium orientations) of the satellite in the orbital coordinate system given the values of aerodynamic torque, damping coefficients, and the principal central moments of inertia is proposed. In the case when the axes of the coordinate system attached to the satellite coincide with the axes of the orbital coordinate system, necessary and sufficient conditions for the asymptotic stability of the corresponding zero equilibrium position are obtained using the Routh–Hurwitz criterion. The domains with satisfied asymptotic stability conditions for the zero equilibrium position are analyzed depending on various dimensionless parameters of the problem. The damping of spatial oscillations of the satellite is numerically studied for various values of aerodynamic torque and damping coefficients.

An elliptic foil rotating in uniform low-Reynolds-number flows

A computational study is conducted to systematically investigate the effect of rotating speed on vortex shedding characteristics and far-field wake patterns of an elliptic foil rotating in uniform cross flows at low Reynolds numbers. It is found that at low rotating speed, vortices shed at the advancing and retreating edges of the foil could form a strong vortex pair in the wake. At high rotating speed, adjacent vortices are closer to each other, thus may evolve into a single vortex. The far-field wake pattern also strongly depends on the rotating speed and demonstrates complex behaviors. It is observed that the wake can defect from downwards to upwards by increasing the rotating speed. The mean lift force increases monotonically with the rotating speed, while a significant drag reduction occurs at a small rotating speed, which is explained by the corresponding wake pattern. Furthermore, a rotating speed regime exists in which the mean aerodynamic torque is positive so that the rotation of the foil could be solely promoted by the flow, indicating a possibility of flow energy harvesting in this regime.

Variable Structure Control of a Small Ducted Wind Turbine in the Whole Wind Speed Range Using a Luenberger Observer

This paper proposes a new variable structure control scheme for a variable-speed, fixed-pitch ducted wind turbine, equipped with an annular, brushless permanent-magnet synchronous generator, considering a back-to-back power converter topology. The purpose of this control scheme is to maximise the aerodynamic power over the entire wind speed range, considering the mechanical safety limits of the ducted wind turbine. The ideal power characteristics are achieved with the design of control laws aimed at performing the maximum power point tracking control in the low wind speeds region, and the constant speed, power, and torque control in the high wind speed region. The designed control laws utilize a Luenberger observer for the estimation of the aerodynamic torque and a shallow neural network for wind speed estimation. The effectiveness of the proposed method was verified through tests in a laboratory setup. Moreover, a comparison with other solutions from the literature allowed us to better evaluate the performances achieved and to highlight the originality of the proposed control scheme.

Orientation of non spherical prolate dust particles moving vertically in the Earth’s atmosphere

Preferential particle orientation has been previously reported for desert dust and attributed on atmospheric electricity (Ulanowski et al., 2007). Depending on its strength, the total electric field within the dust layer can: (a) counteract the gravitational settling of large particles and (b) cause a preferential orientation of the non-spherical particles along the vertical direction (Fucks, 1958; Ulanowski et al., 2007). Both effects change the particle aerodynamics and impact radiative transfer. Here, we quantify the electrical and aerodynamic torques on the non-spherical prolate model that is frequently assumed for dust particles. The transport of these particles is assumed to only depend on the influence of electric and gravitational fields. We provide an analytical approximation for the calculation of the mean orientation angle of both charged and uncharged dust particles. We find that electric fields with strength greater than 60 kV/m are required for the alignment of particles up to 20 μm in diameter, with the electric field lines. If the particles are moving with the same speed and in the same direction with the wind, the aerodynamic torque is zero and particle orientation along the electric field requires 1–2 orders of magnitude lower electric field strengths.

Vibration Reduction Strategy for Offshore Wind Turbines

The operational environment of offshore wind turbines is much more complex than that of onshore wind turbines. Facing the persistent wind and wave forces, offshore wind turbines are prone to vibration problems, which are not conducive to their long-term operation. Under this background, first, how the wave affects the vibration characteristics of offshore wind turbines is analyzed. Based on the existing wave and wave load models, we analytically show that there exist fluctuating components related to the hydrodynamic frequency in the aerodynamic load and aerodynamic torque of offshore wind turbines. Simulation results based on a GH Bladed platform further validates the analysis. Second, in order to reduce the joint impacts of the wave, wind shear and tower shadow on the wind turbine, a variable pitch control method is proposed. The integrated tower top vibration acceleration signal is superimposed on the collective pitch reference signal, then the triple frequency (3P) fluctuating component of the wind turbine output power and the azimuth angle of each blade are converted into the pitch angle adjustment signal of each blade, which is superimposed on the collective pitch signal for individual pitch control. The simulation results show that the proposed pitch control strategy can effectively smooth the fluctuation of blade root flap-wise load caused by wind and wave, and significantly reduce the fluctuation of aerodynamic torque and output power of offshore wind turbines.

The paradox of the tight spiral pass in American football: A simple resolution

An American football is a rotationally symmetric object, which, when well-thrown, spins rapidly around its symmetry axis. In the absence of aerodynamic effects, the football would be a torque-free gyroscope and the symmetry/spin axis would remain pointing in a fixed direction in space as the football moved on its parabolic path. When a pass is well-thrown through the atmosphere, however, the symmetry axis remains—at least approximately—tangent to the path of motion. The rotation of the symmetry axis must be due to aerodynamic torque; yet, that torque, at first glance, would seem to have precisely the opposite effect. Here, we explain the action of aerodynamics on the ball's orientation at second glance.

Dynamic modification method for BEM of wind turbine considering the joint action of installation angle and structural pendulum motion

In this paper, the dynamic effects of wind turbine installation angle and wind turbine pendulum motion on the constant wind vector and the variation of the real wind vector acting on the blade are discussed respectively. The effects of these two conditions on the aerodynamic load and torque of wind turbine are analyzed. Based on this theory, the classical BEM is dynamically modified and the specific method of dynamic correction is proposed. The modified BEM is used to simulate the aerodynamic load and blade load distribution of wind turbines. By comparing and analyzing the previous methods, the correctness of this method is proved. A new aerodynamic load calculation method is proposed for the new energy industry, especially for the wind energy industry, which can assist engineers in the design, analysis, control and evaluation of wind turbines.

Wind energy conversion systems analysis of PMSG on offshore wind turbine using improved SMC and Extended State Observer

In this paper, an improved Sliding Mode Control(SMC) is proposed based on the Wind Energy Conversion System(WECS), which is with offshore wind turbine Permanent Magnet Synchronous Generator(PMSG) connected to the grid. Moreover, an aerodynamic torque observer is presented to improve the performance of Maximum Power Point Tracking(MPPT). Since the wind energy conversion system is a complicated nonlinear system, an enhanced reach law of sliding mode controller is designed to reduce the chattering issue. Compared to traditional control methods, the simulation results show that the control method proposed in this paper significantly improves the stability and robustness of PMSG-Based WECS in the area of MPPT.

Explicit Aerodynamic Model Characterization of a Multirotor Unmanned Aerial Vehicle in Quasi-Steady Flight

Abstract In the last years, the research on unmanned aerial systems (UASs) has shown a marked growth and the models to simulate UASs have been deeply studied. Although onboard controller algorithms have increased their complexity, most of them still rely on simplistic models. In essence, aerodynamic forces/torques are generally considered either insignificant compared to propulsion and inertial forces or acceptably modeled with constant aerodynamic coefficients estimated in a particular flight regime. However, the increase of power in the onboard computers allows to make controller algorithms more complex, and therefore, to increase the total performance of the UAS. In this regard, this work provides an explicit aerodynamic model for multirotor UAS that, unlike most of the current models, does not need iterations to be adjusted to the flight conditions at a higher computational cost. This explicit nature makes it an excellent choice for being implemented in onboard computers, thus covering a broad range of applications, from controller design to numerical analysis (e.g., the capture nonlinear phenomena like bifurcations). To obtain this accurate explicit mathematical aerodynamic model, a thorough analysis of a batch of simulations is carried out. In these simulations, the aerodynamic forces and torques are estimated using computer fluid dynamics (CFD), and the propulsive effects are taken into account via blade element momentum theory (BEMT). A study of its implementation for different regimes and platforms is also provided, as well as some potential applications of the solution, like robust control strategies or machine learning.

Is the Blade Element Momentum theory overestimating wind turbine loads? – An aeroelastic comparison between OpenFAST's AeroDyn and QBlade's Lifting-Line Free Vortex Wake method

Abstract. Load calculations play a key role in determining the design loads of different wind turbine components. To obtain the aerodynamic loads for these calculations, the industry relies heavily on the Blade Element Momentum (BEM) theory. BEM methods use several engineering correction models to capture the aerodynamic phenomena present in Design Load Cases (DLCs) with turbulent wind. Because of this, BEM methods can overestimate aerodynamic loads under challenging conditions when compared to higher-order aerodynamic methods – such as the Lifting-Line Free Vortex Wake (LLFVW) method – leading to unnecessarily high design loads and component costs. In this paper, we give a quantitative answer to the question of load overestimation of a particular BEM implementation by comparing the results of aeroelastic load calculations done with the BEM-based OpenFAST code and the QBlade code, which uses a particular implementation of the LLFVW method. We compare extreme and fatigue load predictions from both codes using sixty-six 10 min load simulations of the Danish Technical University (DTU) 10 MW Reference Wind Turbine according to the IEC 61400-1 power production DLC group. Results from both codes show differences in fatigue and extreme load estimations for the considered sensors of the turbine. LLFVW simulations predict 9 % lower lifetime damage equivalent loads (DELs) for the out-of-plane blade root and the tower base fore–aft bending moments compared to BEM simulations. The results also show that lifetime DELs for the yaw-bearing tilt and yaw moments are 3 % and 4 % lower when calculated with the LLFVW code. An ultimate state analysis shows that extreme loads of the blade root out-of-plane bending moment predicted by the LLFVW simulations are 3 % lower than the moments predicted by BEM simulations. For the maximum tower base fore–aft bending moment, the LLFVW simulations predict an increase of 2 %. Further analysis reveals that there are two main contributors to these load differences. The first is the different way both codes treat the effect of the nonuniform wind field on the local blade aerodynamics. The second is the higher average aerodynamic torque in the LLFVW simulations. It influences the transition between operating modes of the controller and changes the aeroelastic behavior of the turbine, thus affecting the loads.

Dynamical stresses in the high class wind turbine blades caused in nonhomogeneous nonstationary wind field. Part 1 Dynamical model

The wind turbines of a high class are with considerable sizes. For this reason, the consideration of the fluid field as a homogeneous when performing the aerodynamic analysis is not quite correct. In addition, due to the gusts and horizontal turbulence, the wind field is also nonstationary. All this causes dynamic, time-varying loads and fatigue. The determination of these loads is a major aim of this publication. The turbine blades are considered as Euler-Bernoulli beams under the impact of the aerodynamic thrust and torque forces as well as from this of the centrifugal force. The finite element method is applied to solve the partial differential equations describing the model under consideration. Two-node elements with four degrees of freedom for each node and a cubic, polynomial approximation of modal shapes were used. The deformations are relatively small in the separated finite elements and this makes it possible to apply the superposition principle.

CFD Simulation Analysis on Aerodynamic Parameters of Steel Tubular Transmission Tower Body

This paper utilizes the CFD simulation analysis method, calculates and analyzes the distribution characteristics of streaming around the typical steel tubular transmission tower body and the pressure field, researches the change law of wind load force (torque) coefficient along with each main shaft direction o tower body, and then compares it with corresponding wind tunnel test result, and verifies the adaptability of this CFD simulation result. The result shows that the pole member in the upwind direction on the steel tubular tower has obvious disturbance and shielding effect to wind speed distribution around the pole member of downwind direction. The wind direction has obvious influence on the aerodynamic (torque) parameters of tower body, especially the steel tubular - angle steel combined tower body. The above research result provides a certain theoretical support and value taking basis for the wind-resistant design of steel tubular transmission tower body.

Effect of the magnus force and torque on the projectile flight range

The paper considers the origin of the Magnus force and torque in the course of the projectile flight; analytical dependencies for their determination are given and justified. The mutual orientation of the Magnus force and angular torque vectors with respect to those of the drag and lift forces, as well as with respect to the stalling, polar quenching and equatorial damping torques acting on the projectile in flight is discussed. The effect of the Magnus force and torque on the firing characteristics of artillery systems is assessed. A mathematical model of the projectile flight is presented, as well as constraints that are imposed on it and that do not considerably affect the accuracy of the description of the spatial motion of the projectile. The mathematical model is implemented programmatically on the basis of a standard subroutine for numerical integration of differential equations written in the Maple software and contains the motion equations for the projectile mass center, the motion equations with respect to the projectile mass center and equations that allow one to determine the coordinates of the projectile fall points in the base reference system. To assess the effect of Magnus force and torque on the projectile flight range, the difference method is employed, which consists in solving the system of differential equations of the spatial motion of the projectile such that changing the magnitude of the Magnus force and torque (at the assumption of the constancy of the aerodynamic forces and torques), one obtains the variation in the projectile flight range. A protocol and a scheme for assessing the effect of deviation of the projectile range on the accuracy of determination of the Magnus force strength and torque, as well as the results of numerical simulation of the deviation of the flight range for the ОФ-462Ж projectile of the 122-mm howitzer Д-30 depending on the accuracy of determination of aerodynamic force coefficients and Magnus torque are presented. It is shown that the largest deviations in the projectile flight range are observed when shooting at large launching angles and full charge (projectile speed 690 m / s); the smallest corresponding values are observed for the fourth charge (projectile speed 276 m / s) at small launching angles.

Wind Turbines with Truncated Blades May Be a Possibility for Dense Wind Farms

We experimentally explored the impact of a wind turbine with truncated blades on the power output and wake recovery, and its effects within 2 × 3 arrays of standard units. The blades of the truncated turbine covered a fraction of the outer region of the rotor span and replaced with a zero-lift structure around the hub, where aerodynamic torque is comparatively low. This way, the incoming flow around the hub may be used as a mixing enhancement mechanism and, consequently, to reduce the flow deficit in the wake. Particle image velocimetry was used to characterize the incoming flow and wake of various truncated turbines with a variety of blade length ratios L / R = 0.6 , 0.7, and 1, where L is the length of the working section of the blade of radius R. Power output was obtained at high frequency in each of the truncated turbines, and also at downwind units within 2 × 3 arrays with streamwise spacing of Δ x / d T = 4 , 5, and 6, with d T being the turbine diameter. Results show that the enhanced flow around the axis of the rotor induced large-scale instability and mixing that led to substantial power enhancement of wind turbines placed 4 d T downwind of the L / R = 0.6 truncated units; this additional power is still relevant at 6 d T . Overall, the competing factors defined by the expected power reduction of truncated turbines due to the decrease in the effective blade length, the need for reduced components of the truncated units, and enhanced power output of downwind standard turbines suggest a techno-economic optimization study for potential implementation.

Stability improvement of large-scale power systems in the presence of wind farms by employing HVDC and STATCOM based on a non-linear controller

In this paper, a non-linear generalized predictive control (NGPC) has been used for the stability analysis in a hybrid power system consisting of series and parallel compensators in the presence of wind farms. In this system, STATCOM has been used as a parallel compensator for improving reactive power of the wind farm, and HVDC is employed to improve damping of transmission line connected to the power system. The proposed method is based on two internal and external control loops. The internal control loop is used to apply the switching signals suitable for the rotor-side converter in DFIG, HVDC’s converter, and the STATCOM inverter. In the external control loop, a disturbance observer has been employed to estimate the aerodynamic torque and to control the wind turbine’s speed. The aim of designing the observer is to evaluate the robustness of the controller under the changes of internal parameters of the system. The simulations have been implemented in the MATLAB software in different scenarios on a large-scale power system with 16 machines and 68 buses.

Simultaneous contact and aerodynamic force estimation (s-CAFE) for aerial robots

In this article, we consider the problem of multirotor flying robots physically interacting with the environment under influence of wind. The results are the first algorithms for simultaneous online estimation of contact and aerodynamic wrenches acting on the robot based on real-world data, without the need for dedicated sensors. For this purpose, we investigated two model-based techniques for discriminating between aerodynamic and interaction forces. The first technique is based on aerodynamic and contact torque models, and uses the external force to estimate wind speed. Contacts are then detected based on the residual between estimated external torque and expected (modeled) aerodynamic torque. Upon detecting contact, wind speed is assumed to change very slowly. From the estimated interaction wrench, we are also able to determine the contact location. This is embedded into a particle filter framework to further improve contact location estimation. The second algorithm uses the propeller aerodynamic power and angular speed as measured by the speed controllers to obtain an estimate of the airspeed. An aerodynamics model is then used to determine the aerodynamic wrench. Both methods rely on accurate aerodynamics models. Therefore, we evaluate data-driven and physics-based models as well as offline system identification for flying robots. For obtaining ground-truth data, we performed autonomous flights in a 3D wind tunnel. Using this data, aerodynamic model selection, parameter identification, and discrimination between aerodynamic and contact forces could be performed. Finally, the developed methods could serve as useful estimators for interaction control schemes with simultaneous compensation of wind disturbances.

Design and development of prototype carpal wrist cold gas propulsion system for attitude control applications

In recent years, the Philippine space program has launched several small-scale satellites, and lately has commissioned its own space program. Research on improving the subsystems of these satellites would be beneficial to future space programs in the Philippines. This paper will detail the process of designing, validating, fabricating, and testing a prototype Carpal Wrist Cold Gas Propulsion System (CW-CGPS). By making use of a carpal wrist’s (CW) hemispherical movement capabilities, the sixteen thrusters could theoretically be replaced by four mounted on opposite ends. Optimization of the propulsion system is based on finding the nozzle design with the most adequate values for thrust, Mach number, and specific impulse while the CW design is validated when it can be calibrated to move as the program dictates. This study uses multiple programs to simulate and verify the design. The conditions of the testing environment are established by resources from international space organizations. Assembly and feasibility are assessed based on the results of the research. It was found that the final optimized system had a model torque of 0.247 N-m, more than enough to overcome the maximum combined influence of the gravity gradient torque of 2.34E-06 N-m and aerodynamic torque of 1.57E-25 N-m. The design, development, and test campaign for the thruster system is presented.