Aerodynamic Performance Of Rotor Research Articles

Airfoils optimization based on deep reinforcement learning to improve the aerodynamic performance of rotors

Airfoil optimization is the key to improving the aerodynamic performance of a rotor. However, conventional optimization approaches cannot modify the airfoil shape intelligently in the way that an aircraft designer would. Because the optimization process is largely uninterpretable and ungeneralizable, the optimization knowledge and experience cannot be extracted and applied to similar optimization tasks. To address these issues, we propose an optimization framework for rotor airfoils based on deep reinforcement learning (DRL). Our DRL-based framework is capable of learning an interpretable and generalizable optimization strategy for alleviating the dynamic stall of a rotor airfoil. First, to enhance the efficiency of airfoil dynamic stall optimization, a deep neural network is trained to predict the dynamic stall hysteresis loops of rotor airfoils as a surrogate model. The asynchronous advantage actor–critic reinforcement learning algorithm is employed to train and learn the optimization strategy for alleviating the dynamic stall of the rotor airfoil. Next, the OA212 rotor airfoil is optimized using the well-trained optimization strategy. The results show that the dynamic stall characteristics of the airfoil are improved after optimization. The lift coefficients of the optimized airfoil are significantly enhanced, and the drag and moment coefficients peaks are reduced by 46.3% and 73.8%, respectively, compared with the baseline airfoil. Then, 20 airfoils are optimized using the well-trained optimization strategy to evaluate the generalizability of the dynamic stall optimization strategy. The results demonstrate that the optimization strategy learned by DRL for the rotor airfoil optimization is generalizable. Finally, the numerical simulation results comparing a rotor with baseline airfoils to one with optimized airfoils demonstrate that the aerodynamic performance of the optimized rotor is superior to that of the baseline rotor.

Aerodynamic and structural multidisciplinary optimization design method of fan rotors based on blade curvature constraints

The optimization design of the actual fan/compressor rotors is a multidisciplinary problem. The aerodynamics and strength multidisciplinary optimization design of the fan/compressor rotors can improve the aerodynamic performance of rotors as much as possible under the condition of satisfying the structural strength requirements. However, the conventional multidisciplinary optimization of aerodynamics and structures will significantly increase the amount of computation cost and time period. Thus, it is difficult for conventional multidisciplinary optimization methods to be used in real-world engineering practices. In order to reduce the computational burden and time cost of the multidisciplinary optimization design, this paper firstly proposes a multidisciplinary optimization design method for rotors based on blade curvature constraints. In the optimization, the self-organizing map (SOM) method is applied to analyze and extract the constraint value of the blade curvature. And the blade curvature constraint value is used as a penalty function instead of the time-consuming high-fidelity FEM, which greatly reduces the computational cost and runtime of the multidisciplinary optimization. Besides, the Free-form deformation (FFD) method is adopted to realize the flexible deformation of the three-dimensional blade with the smallest number of design variables and polynomial chaos Kriging is used as a surrogate model for aerodynamic performance prediction in the optimization process. The method verification and mechanism analysis are carried out by studying a fan rotor. Data mining of FEM samples shows that, in the optimization design space, the maximum spanwise curvature of the blade is monotonically related to the maximum stress of the blade. And the maximum streamwise curvature, maximum spanwise slope, maximum streamwise slope, and maximum thickness of the blade have no related relationship with the maximum stress of the blade. Compared with the conventional multidisciplinary optimization design method based on the surrogate models of high-fidelity computational fluid dynamics (CFD) and finite element method (FEM), the time cost of the multidisciplinary optimization design method based on curvature constraints is reduced by 10 times, and the time cost of the multidisciplinary optimization is significantly reduced. The results show that, in terms of structural performance, the maximum stress of the aerodynamic optimization method without blade curvature constraints is 426 MPa, which exceeds the yield limit of aluminum alloy material (420 MPa), and the maximum stress of the multidisciplinary optimization design with blade curvature constraints proposed in this paper is 344 MPa. In terms of aerodynamic performance, the isentropic efficiency of the aerodynamic optimization method without blade curvature constraints and the method proposed in this paper are increased by 2.1% and 1.8%, respectively. Therefore, the proposed method reduces the maximum stress of the blade by 19.5% with little influence on the aerodynamic performance.

Improvement of wind turbine aerodynamic performance by vanquishing stall with active multi air jet blowing

The effects of jet blowing on blade suction side of NREL phase VI horizontal axis wind turbine (HAWT) for alleviation of degraded flow due to boundary layer separation were investigated. A 3D innovative multi-jet blade is simulated using FLUENT 18.2 software applying SST k-ω turbulence model. The spanwise blade portions for jets are outer, middle and inner. Furthermore, twelve jets with 0.04 local chord width have deployed in four chordwise locations of x/c = 0.1, x/c = 0.3, x/c = 0.5 and x/c = 0.7. The torque is sensitive to some dimensionless parameters such as Tip Speed Ratio (TSR) and jet velocity ratio (VR). At the best condition, torque increases about two times with respect to baseline blade. The jet velocity ratios are 1.2, 2.0, 2.4, 2.8, and 3.2.Applying changes in jet parameters, the flow pattern and quality improved. Also, the aerodynamic torque synergy of combinations of two, three and four jets were compared with that of a single jet and the direct relationship between the number of activated jets and the increase in torque was proved. The results showed that jets in blade outer part, have more effects in aerodynamic performance of rotor than the other blade portions. T1 jet produced the highest increase in torque.

Effect of Growth in Turbine Size on Rotor Aerodynamic Performance of Modern Commercial Large-Scale Wind Turbines

In this study, the impact of growth in turbine size on aerodynamic rotor performance of modern commercial large-scale wind turbines was investigated. For this examination, three different commercial large-scale wind turbines of models VESTAS V80-2MW, V90-3MW, and V126-3.3MW operating on three existing onshore wind farms were selected. In order to determine the effects of turbine size growth on aerodynamic rotor performance, turbine power output P, turbine power coefficient, Cp, turbine rotational speed, Ω, thrust force, T, tip speed ratio, λ, and flow angle, ϕ, values obtained from these turbines were compared at the same magnitude of free-stream wind speeds, U∞. The results reveal that decreasing specific power decreases the rated output wind speed of the wind turbines; hence, the reduction in the rated output of wind speed contributes to the tendency of higher power capacity. Moreover, it was determined that the enlargement in the turbine size has a profound influence on the parameters that affect the performance of the turbine such as rotational speed, Ω, thrust force, T, tip-speed ratio, λ, and flow angle, ϕ. For instance, higher thrust loads and tip-speed ratios were acquired for the turbines having a larger rotor diameter which results in better aerodynamic efficiency of the turbine.

Investigation on aerodynamic characteristics of bionic membrane nano rotor

In this paper, the bionic membrane structure is introduced to improve the aerodynamic performance of nano rotor at the low Reynolds number. The aerodynamic characteristics of nano rotor made of hyperelastic material as membrane blades are studied. Firstly, based on the hyperelastic constitutive model, a finite element model of the rotor is established and compared with the results of the modal test to verify the accuracy of the model. Then the computational fluid dynamics model of membrane nano rotor is established which combined with the finite element model. The aerodynamic characteristics of the membrane rotor under hovering conditions are studied using fluid–structure interaction method. It is found that the calculation results matched well with the experiment results. The design of the structural parameters such as the membrane proportion, shape, and position of the membrane rotor is optimized. The influence of each parameter on the aerodynamic performance of the rotor is obtained. Under certain structural conditions, the performance can be effectively improved, which provides a new idea for the design of the nano rotor.

Aerodynamic Rotor Performance of a 3300-kW Modern Commercial Large-Scale Wind Turbine Installed in a Wind Farm

Abstract Wind turbine technology in the world has been developed by continuously improving turbine performance, design, and efficiency. Over the last 40 years, the rated capacity and dimension of the commercial wind turbines have increased dramatically, so the energy cost has declined significantly, and the industry has moved from an idealistic position to an acknowledged component of the power generation industry. For this reason, a thorough examination of the aerodynamic rotor performance of a modern large-scale wind turbine working on existing onshore wind farms is critically important to monitor and control the turbine performance and also for forecasting turbine power. This study focuses on the aerodynamic rotor performance of a 3300-kW modern commercial large-scale wind turbine operating on an existing onshore wind farm based on the measurement data. First, frequency distributions of wind speeds and directions were obtained using measurements over one year. Then, wind turbine parameters such as free-stream wind speed (U∞), far wake wind speed (UW), axial flow induction factor (a), wind turbine power coefficient (CP), tangential flow induction factor (a′), thrust force coefficient (CT), thrust force (T), tip-speed ratio (λ), and flow angle (ϕ) were calculated using the measured rotor disc wind speed (UD), atmospheric air temperature (Tatm), turbine rotational speed (Ω), and turbine power output (P) parameters. According to the results obtained, the maximum P, CP, CT, T, and Ω were calculated as approximately 3.3 MW, 0.45, 0.6, 330 kN, and 12.9 rpm, respectively, while the optimum λ, ϕ, U∞, and Ω for the maximum CP were determined as 7.5–8.5, 6–6.3°, 5–10 m/s, and 6–10 rpm, respectively. These calculated results can contribute to assessing the economic and technical feasibility of modern commercial large-scale wind turbines and supporting future developments in wind energy and turbine technology.

Aerodynamic performance of a small-scale tilt rotor: Numerical simulation and experiment in steady state

The present work studies the aerodynamic performance of a small-scale rotor in tilting transition states through wind tunnel tests and numerical simulations. Firstly, the test platform for the rotor aerodynamics is built up, and the Computational Fluid Dynamics (CFD) model of flow field around the rotors is established based on the multiple reference frame method. Secondly, the effects of flow velocity, tilt angle and advance ratio on the aerodynamic performance of the rotor are investigated using both the numerical simulation and the wind tunnel test. It is found that for the Model 8038 rotor with maximum effeciency of 0.567 at advance ratio of 0.43, the rotor thrust coefficient increases with the increase of the Reynolds number. At Reynolds number of 410 thousand to 820 thousand, the thrust coefficient increases slightly with the increase of the rotating speed. The results also show that the thrust coefficient decreases with the increase of the advance ratio. With high-speed airflow and relatively low-speed rotation, “windmill” phenomenon is found in the experiment. The tilting of the rotor from level flight to hovering increases the thrust coefficient. Highly dependency of the tilt angle on the thrust coefficients at given advance ratios is found in the wind tunnel tests.

Strongly-coupled aeroelastic free-vortex wake framework for floating offshore wind turbine rotors. Part 2: Application

This two-part paper presents the integration of the free-vortex wake method (FVM) with an aeroelastic framework suitable to model the rotor-wake interactions engendered by floating offshore wind turbine (FOWT) rotors in operation. Part 1 of this paper introduces the numerical development and validation of an aeroelastic framework. Due to a lack of experimental aeroelastic benchmarks for FOWTs, a series of validation studies are conducted against the rotor aerodynamic and structural performance of the National Renewable Energy Laboratory (NREL) 5-MW reference wind turbine. Part 2 of this paper focuses on the modeling and simulating different aeroelastic operational conditions of FOWTs. Numerical results of the current framework capture consistently the aerodynamic rotor performance, such as power, thrust, and torque of wave-induced pitching FOWTs. In addition, the presented aeroelastic framework yields additional information about the power, thrust, and torque fluctuations due to the out-of-phase blade passing frequency and corresponding blade deflections. The fidelity of the presented framework demonstrates, for the first time, an FVM-based aeroelastic method capable of carrying out investigations on rotor-wake interactions and relevant aeroelastic phenomena of FOWTs.

Strongly-coupled aeroelastic free-vortex wake framework for floating offshore wind turbine rotors. Part 1: Numerical framework

This two-part paper presents the integration of the free-vortex wake method (FVM) into an aeroelastic framework suitable to model the rotor-wake interactions engendered by floating offshore wind turbine (FOWT) rotors in operation. Part 1 of this paper introduces the numerical development and validation of an aeroelastic framework. Because no experimental aeroelastic benchmarks exist for FOWTs, a series of validation studies are conducted against the rotor aerodynamic and structural performance of the National Renewable Energy Laboratory (NREL) 5-MW reference wind turbine. Part 2 of this paper focuses on the modeling of different aeroelastic operational conditions of FOWTs. Numerical results of the current framework captures consistently the aerodynamic rotor performance, such as power, thrust, and torque of wave-induced pitching FOWTs. In addition, the presented aeroelastic framework captures additional information about the power, thrust, and torque fluctuations due to the out-of-phase blade passing frequency and corresponding blade deflections. The fidelity of the presented framework showcases, for the first time, an FVM-based aeroelastic method capable of carrying out investigations on rotor-wake interactions and relevant aeroelastic phenomena of FOWTs.

Fluid-structure coupled computations of the NREL 5 MW wind turbine by means of CFD

Abstract This paper presents a fluid-structure coupled simulation tool for high-fidelity simulations of wind turbine rotors. Coupling the open source Computational Fluid Dynamics (CFD) code OpenFOAM and the inhouse structural solver BeamFOAM, the developed tool allows the analysis of flexible wind turbines blades by means of CFD without a significant increase in computational costs. To demonstrate the capabilities of the coupled solver, the aero-elastic response of the NREL 5 MW reference wind turbine is computed for various conditions and specific results are compared to findings of other authors. The solver framework is then used to investigate the effect of blade deformations on aerodynamic key parameters such as power, thrust and sectional forces. It is shown, that the structural deformations have a clear influence on the aerodynamic rotor performance. Especially for the case of yawed inflow, significant implications can be observed in terms of loads and local induction factors. Compared to the fluid-structure coupled framework, the rigid CFD solver underpredicts the forces acting on the blades for most of the cases. Consequently, the presented results are expected to contribute to improve the correction models used in aerodynamic models of lower fidelity like those based on the Blade Element Momentum theory.

The Effect of Mounting Vortex Generators on the DTU 10MW Reference Wind Turbine Blade

The aim of the current work is to analyze possible advantages of mounting Vortex Generators (VG's) on a wind turbine blade. Specifically, the project aims at investigating at which radial sections of the DTU 10 MW Reference Wind Turbine blade it is most beneficial to mount the VG's in order to increase the Annual Energy Production (AEP) under realistic conditions. The present analysis was carried out in several steps: (1) The clean two dimensional airfoil characteristics were first modified to emulate the effect of all possible combinations of VG's (1% high at suction side x/c=0.2-0.25) and two Leading Edge Roughness (LER) values along the whole blade span. (2) The combinations from Step 1, including the clean case were subsequently modified to take into account three dimensional effects. (3) BEM computations were carried out to determine the aerodynamic rotor performance using each of the datasets from Step 2 along the whole blade span for all wind speeds in the turbine control scheme. (4) Employing the assumption of radial independence between sections of the blades, and using the results of the BEM computations described in Step 3, it is possible to determine for each radial position independently whether it is beneficial to install VG's in the smooth and LER cases, respectively. The results indicated that surface roughness that corresponds to degradation of the power curve may to some extent be mitigated by installation of VG's. The present results also indicated that the optimal VG configuration in terms of maximizing AEP depends on the degree of severity of the LER. This is because, depending on the condition of blade surface, installation of VG's on an incorrect blade span or installation of VG's too far out on the blade may cause loss in AEP. The results also indicated that the worse condition of the blade surface, the more gain may be obtained from the installation of VG's.

Numerical analysis of aerodynamic performance of rotors with leading edge slats

Numerical analysis of aerodynamic performance of rotors with leading edge slats

Numerical analysis of aerodynamic performance of rotors with leading edge slats

A three dimensional compressible Navier-Stokes analysis capable of computing flows around wings and rotors with partial-span flaps or slats is described. This analysis is cast in a moving body-fitted coordinate system permitting arbitrary motion of the solid surfaces to be directly modeled. This methodology is validated through several single and multi-element rotor and wing configurations. The analysis is subsequently applied to two helicopter rotors. The effects of leading edge slats on the aerodynamic performance of these rotors in hover is studied. It is demonstrated that leading edge slats can significantly improve the hover performance at high pitch settings, with an increase in thrust and a reduction in torque. At low pitch settings, the slats were found to be detrimental to the rotor performance. Many practical issues such as surface imperfections, proper sealing of the slat during retraction, control loads and other implementation aspects should be carefully evaluated in the event of a practical design of a slat. However, in the present study only the aerodynamic effects of slats are addressed and no practical issues are considered.