Turbine Simulation Research Articles

Numerical optimisation of the active lift turbines using OpenFoam's overset method

This work presents a preliminary study of the numerical optimization of "active lift turbine" using computational fluid dynamics (CFD). This active lift turbine is designed to improve efficiency of vertical axis energy recovery turbines (wind and tidal turbines). It uses a crank rod system to convert normal forces into momentum in order to improve the yield.
 After a validation work of CFD model in two dimensions, the numerical optimization of the tidal turbine system is carried out. In fact, due to the specific characteristics of the active lift turbine, the blades do not follow a circular trajectory (Fig. \ref{fig:combined}). The OpenFoam overset module is therefore chosen because it allows to control the motion of the blades easily \cite{Chalmers}. The Overset method allows a good performance evaluation and limits the risk of numerical divergence that could be caused by mesh deformation methods; Moreover it limits the computation time compared to remeshing methods. However, it is more expensive than a more traditional Arbitrary Mesh Interface method \cite{Openfoam}, which is not suitable for the active lift turbine simulations.
 The impact of several parameters on the performances is studied. The simulations are performed for a range of operating conditions including different inflow velocities, angles of attack and active flow turbine settings (like the amplitude of the radius variation, see Fig \ref{fig:combined}). The results are evaluated in terms of the turbine power output and efficiency.
 The results show the importance of numerical simulation for the development of new types of energy recovery systems. It allows a better understanding of the interactions between the turbine and the fluid, and of the operation of such systems.
 Further studies are required for the active lift turbine: conventional attempts at optimisation are not perfectly suited to this system. Improving the lift/drag ratio makes less sense when the normal forces should also be taken into account to improves the performances. Furthermore, other aspects of operation should be analysed: variation of the turbulence rate, implementation of boundary layer re-attachment systems...

Verification and validation of blade-resolved viscous-flow tidal turbine simulations

Tidal turbines are a renewable energy source on the rise. The exceptional predictability of tidal currents contributes to a high reliability of this technology, which represents a key advantage in the endeavor to become a major contributor to the energy mix. To foster the development and to support the design process of tidal turbines, reliable numerical modeling techniques are required. This paper presents verification and validation work performed within the framework of the Supergen ORE Tidal Turbine Benchmarking Study. Viscous-flow CFD code ReFRESCO is used to conduct blade-resolved simulations of the towing tank experiments. In a first approximation, a steady-state frozen-rotor approach is chosen. A transition model, γ-Reθ, is employed to predict the flow state transition on the turbine blades. In the process, the sensitivity to input turbulence quantities is highlighted. The numerical uncertainty is estimated based on mesh refinements. Finally, a conclusion is drawn to which accuracy the presented numerical models can predict the outcome of the experiments.

Fault tolerant control for DFIG wind turbine controlled by ADRC and optimized by genetic algorithm

This research work deals with the modelling, control and simulation of a wind turbine based on the doubly fed induction generator (DFIG) in the current sensor’s failure event. We present in the first time the model of the wind energy conversion system based on the DFIG and the control by active disturbances rejection control (ADRC) optimized by genetic algorithm. Particular focus is directed towards on a technique for detection, identification, isolation and reconfiguration of current sensor signals after failure. The combination of the two preceding techniques makes it possible to have a fault tolerant control to sensor faults which ensures continuity of service in all circumstances. The robustness of the proposed technique is tested under the MATLAB/Simulink environment.

Effects of turbulent inflow time scales on wind turbine wake behavior and recovery

Wind turbines experience a range of turbulent time and length scales related to the atmospheric boundary layer, wakes of upstream turbines, and wind farm effects. This work aims to investigate the impact of turbulent scales on wake behavior and recovery, in isolation from overall turbulence intensity, shear, or buoyancy. Large eddy simulations of a single turbine are conducted using idealized single time scale inflows and full spectra turbulent inflows, varying the predominant time scale in the equivalent Strouhal number range of St=0.04–0.5, while maintaining the same turbulence intensity and flow structures. Under idealized inflows, shorter inflow time scales result in a faster breakdown of tip vortices, while longer scales induce greater wake meandering. For full spectra turbulent inflows, shorter integral time scales result in a shorter near-wake region and enhanced wake recovery, while wake meandering occurs to a similar extent when adjusted for the near-wake breakdown location. A wake-generated turbulence region in the range of St=0.3–0.7 is identified in the streamwise velocity spectra, and inflows that contain more turbulent kinetic energy in this range show a faster redistribution from long inflow scales to smaller wake-generated turbulence and enhanced wake recovery. The improved wake recovery for the shortest integral time scale results in a 9% increase in mean rotor-averaged velocity and 35% increase in power at 12R downstream, compared to the longest integral time scale. Overall, it is shown that inflow turbulent scales have a significant impact on wake recovery, particularly through their impact on the near-wake breakdown.

Fast Frequency Control Strategy for Direct Drive Wind Turbines Considering the Suppression of Secondary Frequency Drop in the Power Grid

Inertia and damping in the power system are important parameters in frequency regulation and oscillation suppression. Inertia will reduce the rate and amplitude of frequency changes after active power sudden changes. Damping in the system can effectively suppress low-frequency oscillations after grid disturbances. As the penetration rate of wind turbines increases, it will significantly reduce the effective inertia in the power grid and reduce the friendliness of wind power grid connection. To provide better frequency support for the power grid in the event of large disturbances in the power system, this paper proposes a fast frequency control strategy for wind farms that considers the suppression of secondary frequency dips in the power grid. The strategy combines frequency droop control with grid frequency bias control and evaluates the kinetic energy reserve online based on wind power prediction and hourly speed, thus balancing the frequency regulation and suppression of secondary frequency dips in the power grid. A 2.5 MW direct drive wind turbine simulation model was built based on the PSCAD simulation platform, verifying the effectiveness of the proposed comprehensive control strategy.

Variable Blade Inertia in State-of-the-Art Wind Turbine Structural-Dynamics Models

This paper presents a comparison of two methods to represent variable blade inertia in two codes for aero-servo-elastic simulations of wind turbines: the nonlinear aeroelastic multi-body model HAWC2 and the nonlinear geometrically exact beam model BeamDyn for OpenFAST. The main goal is to enable these tools to simulate the dynamic behavior of a wind turbine with variable blade inertia. However, current state-of-the-art load simulation tools for wind turbines cannot simulate variable blade inertia, so the source code of these tools must be modified. The validity of the modified codes is proven based on a simple beam model. The validation shows very good agreement between the modified codes of HAWC2, BeamDyn and an analytical calculation. The add-on of variable blade inertias is applied to reduce the mechanical loads of a 5-megawatt reference wind turbine with an integrated hydraulic-pneumatic flywheel in its rotor blades.

Validation of Actuator Line Modeling and Large Eddy Simulations of Kite-Borne Tidal Stream Turbines against ADCP Observations

The representation of tidal energy in future renewable energy systems is growing. Most of the current tidal turbine designs are limited by the minimum current velocity required for efficient operation. The Deep Green (DG) is a kite-borne tidal power plant designed to sustain efficient operation in tidal current velocities as low as 1.2 ms−1. This could increase the geographical areas suitable for large-scale tidal power arrays. Numerical modeling of the Deep Green was carried out in a previous study using large eddy simulations and the actuator line method. This numerical model is compared with acoustic Doppler current profiler (ADCP) measurements taken in the wake of a DG operating in a tidal flow under similar conditions. To be comparable, and since the ADCP measures current velocities using averages of beam components, the numerical model data were resampled using a virtual ADCP in the domain. The sensitivity of the wake observations to ADCP parameters such as pulse length, bin length, and orientation of the beams is studied using this virtual ADCP. After resampling with this virtual ADCP, the numerical model showed good agreement with the observations. Overall, the LES/ALM model predicted the flow features well compared to the observations, although the turbulence levels were underpredicted for an undisturbed tidal flow and overestimated in the DG wake 70 m downstream. The velocity deficit in the DG wake was weaker in the observations compared to the LES. The ALM/LES modeling of kite-borne tidal stream turbines is suitable for further studies of array optimization and wake propagation, etc.

On the design and power output response of hydraulic wind turbines

Standard horizontal axis wind turbines typically use gearboxes for large-scale applications and direct coupling for small-scale designs to connect the rotor to the generator. However, gearboxes pose challenges due to their weight, cost, and exposure to dynamic loads and vibrations within the nacelle. A promising alternative is replacing mechanical transmission with a hydrostatic counterpart, offering advantages such as reduced nacelle mass, generator placement at the tower base, and elimination of the gearbox. It can potentially lead to cost savings of up to 20% in the levelized cost of electricity for offshore wind turbines. This study compares regulated hydrostatic transmission with unregulated transmission and damping components under different wind conditions, including atmospheric boundary layer and low-level jet inputs. Dynamic simulations of a horizontal axis wind turbine incorporating a hydrostatic transmission are conducted to evaluate its response to wind fluctuations caused by prevailing wind velocity profiles, atmospheric boundary layer, and low-level jet velocity profiles. Addressing torque fluctuations and power impact on power quality and mechanical components is crucial in wind turbine operation. The proposed hydrostatic transmission includes primary and secondary proportional controllers for adaptability to varying wind speeds, along with integrated accumulators in the high and low-pressure lines. The main findings indicate that the regulated hydrostatic transmission achieves an efficiency range of 69%–75% across various wind velocity profiles, surpassing the unregulated counterpart. It reduces torque fluctuation amplitude by 35% and improves efficiency by nearly 20% compared to the basic transmission. Torque and power fluctuations are also reduced by 35% and 40%. These improvements are attributed to the damping capabilities of the hydrostatic transmission and the actions of the proportional controller. Implementing the regulated hydrostatic transmission offers several technical and economic advantages, including relocating the generator to ground level and achieving continuous hydraulic variable transmissions without the need for a gearbox. The methodology is applicable to a range of wind turbine sizes.

Development of a wind turbine model and simulation platform using an acausal approach: Multiphysics modeling, validation, and control

AbstractThis article presents the development of the Control‐oriented, Reconfigurable, and Acausal Floating Turbine Simulator (CRAFTS). CRAFTS has a modular, hierarchical model architecture that enables rapid and accurate simulation of wind turbines. The architecture facilitates the incorporation of model variants, and its system reconfiguration features help simulate multiple design variants. CRAFTS also supports the integration of models developed on a causality‐free platform (e.g., Modelica®) with existing causal models. This article focuses on the validation of a land‐based wind turbine models against OpenFAST, an industry‐standard platform, for several test cases. Closed‐loop scenarios are also tested using the standard ROSCO controller and compared against OpenFAST. In addition, a nonlinear controller developed in our prior work is also evaluated. The test cases demonstrate the user‐friendly and computationally efficient capabilities of CRAFTS to facilitate control co‐design, assist in incorporating multiphysics models, be adaptable to design variants, and allow for rapid simulations to validate models and evaluate controllers.

A new coupling of a GPU‐resident large‐eddy simulation code with a multiphysics wind turbine simulation tool

AbstractThe development of new wind farm control strategies can benefit from combined analysis of flow dynamics in the farm and the behavior of individual turbines within one simulation environment. In this work, we present such an environment by developing a new coupling between the large‐eddy simulation (LES) code GRASP and the multiphysics wind turbine simulation tool OpenFAST via an actuator line model (ALM). In addition, the implementation of the recently proposed filtered actuator line model (FALM) within the coupling is described. The new ALM implementation is cross‐verified with results from four other commonly used research LES codes. The results for the blade loads and the near wake obtained with the new coupling are consistent with the other codes. Deviations are observed in the far wake. The results further indicate that the FALM is able to reduce the lift and power overprediction from which the traditional ALM suffers on coarse LES grids. This new simulation environment paves the way for future wind farm simulations under realistic weather conditions by leveraging GRASP's ability to impose data from large‐scale meteorological models as boundary conditions.

PERFORMANCE EVALUTATION OF HYDRO TURBINES BY CFD

The present work is aimed to carry out the Performance evaluation of typical medium head Francis Turbine model using Computational fluid Dynamics (CFD) Analysis. The analysis is conducted to check the hydrodynamic performance of the runner. For this purpose, Complete Francis turbine comprising spiral casing, stay vane, guide vane, runner and draft tube is modeled with the aid of CAD drawings. The model thus constituted resembles a numerical test rig for turbine performance evaluation. The next step involved is to generate a computational grid. The software used for this purpose is CFX-TURBOGRID. The solutions are obtained by proper specifications of the boundary conditions. Computational fluid Dynamics (CFD) simulation of turbine is carried out using TASC flow package and the results of analysis for 54 operating points with changing Guide vane opening, varying mass flow/turbine rpm, are compiled and optimum operating regime is identified. I have been performed the work of modeling, meshing and analysis inCorporate R & D, BHEL, Hyderabad. The results provided by the analysis are compared with experimental value. Peak efficiency for each guide vane opening is found out and highest efficiency around 94.00% is obtained. Keywords- Small hydro, Pelton turbine, CFD, ANSYS

Numerical Simulations of the NREL Phase VI Wind Turbine with Low-Amplitude Sinusoidal Pitch

Currently, most wind turbine performance analyses and simulations are performed assuming constant pitch and yaw angles during each rotation. Nevertheless, induced vibration or rotor imbalance can affect the pitch or yaw angle within each rotation. In this study, the effects of low-amplitude sinusoidal pitch angle oscillations of the blade on the performance of a wind turbine was investigated numerically by comparing it against the baseline (without pitch variations). Large eddy simulations were performed in which the motion of blades was handled by the curvilinear immersed boundary (CURVIB) method. The grid resolution was increased near the moving immersed boundaries using dynamic overset grids to resolve rotating blades. It was found that low-amplitude (up to 3 degrees) sinusoidal oscillations in the pitch angle negligibly affected the mean torque but increased its fluctuations and created distinct features in the wake of the turbine. In fact, the turbine’s mean torque at wind speed of 15 m/s decreases from 1245 N.m to 1223 N.m, while its fluctuation (standard deviation) increases from 2.85 N.m to 7.94 N.m, with a dynamic pitch of 0.5 degrees and frequency of 3.6 Hz.

Scale-resolving simulation of a low-pressure turbine on hybrid supercomputers

The increased computing power of modern hybrid supercomputers is expanding the applicability of scale-resolving simulations in scientific and industrial applications. This paper is devoted to such a supercomputer simulation technology for turbomachinery. A heterogeneous parallel algorithm is outlined and its parallel performance is demonstrated on various hybrid supercomputers by executing a single simulation on dozens of central and graphics processing units. The scale-resolving numerical simulation of the flow in a linear cascade of T106C high-lift low-pressure turbine blades is considered. The presence of a laminar–turbulent transition on the suction side of the blade, caused by the separation of the boundary layer, leads to a significant increase in the loss of kinetic energy. The effect of increasing losses with a decrease in the Reynolds number is captured. A strong dependence of the numerical results on the incoming turbulent flow conditions is observed. The effect of imposing synthetic turbulence at the inflow is studied, as well as the required mesh resolution to capture the laminar–turbulent transition well.

ANALISIS PENGARUH VARIASI DEBIT AIR TERHADAP KECEPATAN PUTARAN TURBIN CROSSFLOW PADA PEMBANGKIT LISTRIK TENAGA MIKROHIDRO

The Yeh Dikis River in Tabanan Regency Bali has a natural environment which is considered suitable to be used as a tourism destination. The factor that supports the Yeh Dikis River to become a tourism object is the river's potential to generate electricity. In this paper, a particular turbine for micro-hydro power plant is designed. The Yeh Dikis River has a water discharge of 0.381 m3/s with a head value of 8.2 meters, with a potential output power of 18.15 kW. The value of the water discharge and the output power are used to determine the type of turbine used. The computation and simulation showed that the crossflow turbine is suitable for the power plant. The analysis showed that a water discharge of 0.381 m3/s with a penstock diameter of 0.44 meters produces a specific rotational speed of 186 rpm; while a water discharge of 0.381 m3/s with a penstock diameter of 0.55 meters produces a turbine specification rotation speed of 160 rpm. This indicated that the effective head value affects the determination of the penstock diameter and the water velocity. The smaller diameter of the penstock produces, the higher the velocity of the water flow in the pipe. A low effective head will result in a low specific rotational speed. It was found that the optimum turbine power output for a water discharge of 0.381 m3/s with a penstock diameter of 0.44 meters is 18.15 kW. The work of the crossflow turbine is validated using a turbine simulator to determine the rotational speed of the turbine for a particular torque.

Hybrid physical and data driven modeling for dynamic operation characteristic simulation of wind turbine

Accurate simulation of wind turbines is the key to achieve efficient control of wind turbines and optimal scheduling of wind power systems. Most of the existing methods are physical simulation models, which have heavy computational burden, especially for large-scale wind turbines, and the simulation accuracy is poor under complex dynamic operating conditions. In response, this paper proposes a hybrid physical and data driven model for dynamic operation characteristic simulation of wind turbines. Firstly, a database of dynamic characteristics of wind turbine operation under various wind conditions is constructed, and then the sequence learning (Seq2Seq) model is used to mine the time series characteristics of wind turbine operation parameters. Combining with long short-term memory (LSTM) network, the mapping relationship between various operating parameter time series to establish. On this basis, an attention mechanism is added to the model to learn the dynamic response characteristics of rotor inertia to natural wind process. Through numerical example analysis, the method proposed in this paper can accurately excavate and learn the time sequence dynamic characteristics of wind turbine operating conditions and parameters under various wind conditions, thereby improving the simulation accuracy and calculation efficiency of wind turbine output power and load dynamic characteristics. Taking the actual wind turbine operation data as an example, the simulation accuracy of wind turbine output power reaches 99.8%. Compared with traditional methods, and the simulation accuracy of tower root load reaches 88.5%.

Wind Tunnel Experimental Study on the Efficiency of Vertical-Axis Wind Turbines via Analysis of Blade Pitch Angle Influence

This paper presents results of experimental investigations and numerical simulations of a vertical-axis H-type wind turbine, considering the influence of propeller blade pitch angle on turbine characteristics. An innovative airfoil profile based on a modified symmetric NACA0015 airfoil profile was used as the designed blade profile, which was tested in a wind tunnel over a range of Reynolds numbers from 50,000 to 300,000. The phenomenon of angle-of-attack variation and the resulting forces acting on the blades, particularly in the horizontal configuration and vertical axis of rotation, were discussed. Series of experiments were conducted on a 1:1 scale four-bladed turbine model in the wind tunnel to determine the characteristics, specifically the power coefficient distribution over the tip speed ratio for various Reynolds numbers and blade pitch angles. Subsequently, the turbine was modeled using Qblade software, and a series of calculations were performed under the same conditions. The numerical results were validated with the experimental data.

Maximum power point tracking control of wind turbines based on equivalent sinusoidal wind

The optimal parameter model method for maximum power point tracking (MPPT) control of wind turbines has good wind energy capture performance. However, there is a precondition that the quantitative relationship between optimal control parameters and turbulence characteristics is accurately described. The resolution of the existing turbulence frequency characterization indicators are insufficient. Therefore, a large number of sample data need to be obtained to clearly show the statistical relationship between them and the optimal control parameters, which is extremely time-consuming, and has a negative impact on the optimization results of control parameters. This paper equates the turbulent wind to the sinusoidal wind with the objective of the results of both acting on wind turbines are the same, so as to realize the extraction and index description of the dominant turbulent frequency components strongly related to the optimal control parameters. On this basis, a MPPT control method based on equivalent sinusoidal wind is proposed. This method greatly reduces the required sample size, and makes the setting of control parameters closer to the optimal value, which can further improve the efficiency of wind energy capture. Simulation analysis and experimental results based on wind turbine simulator verify the effectiveness of the proposed method.

Dynamic mode structure analysis of the near-wake region of a Savonius-type hydrokinetic turbine

Hydrokinetic turbine is a clean technology that can effectively use tidal energy, the Savonius-type runner is very suitable for natural flows, and has been widely used in tidal energy power stations. The dynamic structure of the flow field in the near-wake region downstream has strong impact on the dense layout of the turbine, but there has been no in-depth exploration till now. To explore the potential for beneficial interactions between turbines, this study conducted numerical simulations of Savonius-type turbine, combining fast Fourier transformation and Dynamic mode decomposition to conduct in-depth analysis of the velocity fluctuation frequency distribution and dynamic mode in near-wake region, and compared the advantages and disadvantages of the two methods. This research obtained the distribution of two main frequencies in the near-wake region and clarified their excitation sources. The frequencies of turbines are mixed in the far field, greatly affects the far-field flow state in the near-wake region. The DMD method has great advantages in flow field analysis, as it does not require prior knowledge of flow field compared to FFT method. The conclusions of this study provide new considerations for large-scale arrangement of turbine units, and provide a new method for the flow state analysis.

3D numerical simulation of the Darrieus vertical axis wind turbine with J-type and straight blades under various operating conditions including self-starting mode

A comprehensive three-dimensional numerical analysis is applied in this study to evaluate the competence of the J-type blades in the vertical axis wind turbines under wide range of operating conditions including various wind speeds, tip speed ratios and wind turbulence intensities. It is found that the vortices which are encapsulated in the concave part of the J-type blades escape from the tips of the blades and become stronger than those originated from the straight blades. Such strong wakes behind the J-type blades are responsible for larger negative effects on generating the torque at high tip speed ratios. Neither of the wind speed, nor the wind turbulence intensity have significant effects on performance of the J-type blade turbines. Of particular interest is to discover the behavior of the J-type blade under self-starting conditions which is a major shortcoming with Darrieus turbines. The results show that replacing the straight blades with the J-type blades causes the generated torque to increase by 26.9% and 37.6% at the wind speeds of 10 m/s and 5 m/s, respectively. Better performance of the J-type blades under self-starting conditions, makes them a promising candidate, especially at low wind speed regions such as urban areas.

Data-driven torque and pitch control of wind turbines via reinforcement learning

This paper addresses the torque and pitch control problems of wind turbines. The main contribution of this work is the development of an innovative reinforcement learning (RL)-based control method targeting wind turbine applications. Our RL-based control framework synergistically combines the advantages of deep neural networks (DNNs) and model predictive control (MPC) technologies. The proposed control strategy is data-driven, adapting to real-time changes in system dynamics and enhancing control performance and robustness. Additionally, the incorporation of an MPC structure within our design improves learning efficiency and reduces the high computational complexity typically found in deep RL algorithms. Specifically, a DNN is designed to approximate the wind turbine dynamics based on a continuously updated dataset composed of state and action measurements taken at specified sampling intervals. The real-time control policy is generated by integrating the online trained DNN into an MPC architecture. The proposed method iteratively updates the DNN and control policy in real-time to optimize performance. As a primary result of this work, the proposed method demonstrates superior robustness and control performance compared to commonly-employed MPC and other baseline wind turbine controllers in the presence of uncertainties and unexpected actuator faults. This effectiveness is showcased through simulations with a high-fidelity wind turbine simulator.