Numerical Wind Research Articles

Experimental and Computational Fluid Dynamics: decades of turbulent EFD/CFD complementarity

An overview of the parallel evolution of computations and experiments in fluid dynamics in the context of turbulent flows is given, viewed from an experimental side. It is evident that experiments can no longer be seen as only validations for computations and that forecasting for “numerical wind tunnels” is not yet valid. The growing evidence of organized motions in turbulent flows pushes in parallel both experiments and numerical approaches to develop new measurement technologies and numerical methods. Many tools and concepts are shared both by experiments and computations. These approaches appear to be quite complementary and both communities will gain from the mutual fertilization.

INVESTIGATION OF THE PERFORMANCE CHANGES OF THE SAVONIUS WIND TURBINE ROTORS WITH THE SAME FRONT VIEW AREA OF LOOK BY CHANGE OF THE ASPECT RATIO

In this study, Savonius type wind turbine rotors with the same front view area were produced with 3D printers by changing their aspect ratios, and then both experimental and numerical analyzes were carried out according to them attaching end plate and without end plate situations. The wind tunnel in the university was used in the experimental analysis. For numerical analysis, rotors and wind tunnels modeled in CAD program were analyzed in Ansys Fluent program. The analyzes made are for imaging purposes only, and the results in the experimental analyzes are accepted as correct. The reduction of aspect ratios in the uncapped analyzes decreased the overall efficiency, but the opposite effect was observed when the analyzes were repeated with the end plate. In addition, while negative pressure was observed in the rotors made without cover (bare case) in the digital images, this situation was not seen in the analyzes made with the end plate.

Calibrated consistent flow generator for tall building aerodynamics using large eddy simulation

Ensuring proper matching of the target wind characteristics of the inflow is vital for the accuracy of both experimental and numerical wind studies. In the current study, a calibrated turbulent inflow generation technique was developed to accurately simulate the inflow boundary condition for large eddy simulation (LES) of the lower region of the atmospheric boundary layer (ABL) based on a newly developed technique, namely consistent discrete random flow generator (CDRFG). The proposed technique, namely Calibrated-CDRFG (C-CDRFG), targets specific incoming turbulence at distances downstream to account for dissipation of the turbulent kinetic energy. The proposed technique generates accurate turbulent velocities with proper turbulence intensity, spectra, coherency, and correlation at the target distance downstream for a range of terrain conditions. The technique was validated by evaluating the wind-induced loads and responses for the Commonwealth Advisory Aeronautical Research Council (CAARC) and comparing that to the existing wind tunnel (WT) wind-induced response for the angle of attack (AOA) ranging between 0° and 90°. It was found that the resulting wind-induced response from the C-CDRFG technique resulted in an average matching of 91% of the wind tunnel results. The proposed technique is believed to be computationally efficient, flexible, and easy to be sustainable for parallel computing environments and thus provides significant value for Large Eddy Simulation (LES) wind engineering applications.

Research on Wind Load Characteristics on the Surface of a Towering Precast Television Tower with a Grid Structure Based on Large Eddy Simulation

Local wind pressures on tiny rods of complex grid structures are difficult to obtain through wind tunnel tests due to their small sizes after scaling down, resulting in a lack of data support in wind load calculations for similar structures. However, local wind pressures on tiny rods can be obtained through numerical wind tunnel simulation using full-sized models. In order to investigate the wind pressure distribution of a grid structure and the influence of grid structures on the wind load of core tubes, three different television tower models are established based on an engineering example for large eddy simulations. A turbulence inlet generator (NSRFG) is adopted in the simulations while reproducing a portion of the wind tunnel test section including the mean and fluctuating pressures for validation. The results indicate that the mean wind pressures on the intersection of rods in the windward zone of the grid structure are higher than those on adjacent rods. Distinct reductions in the mean and fluctuating wind pressure of the grid structure are found in different zones. Moreover, resultant wind load forces and bending moments in the X and Y direction of the grid structure generally exceed 70% of the total wind loads. Based on simulation results, extreme net wind pressures of the grid structure and shape coefficients of enclosed regular octagonal cross-section buildings with the grid structure are provided for reference.

Numerical Simulation and Wind Tunnel Test on the Wind-Induced Response of Three Typical Types of Greenhouse Main Structures

Investigating the wind-induced vibration response of the greenhouse structure, and the wind pressure distribution on its surface takes on a critical significance when the main structure is under large wind loads. A computational fluid dynamics-based study was conducted, and wind tunnel tests were performed to study the wind pressure distribution on the surface of the greenhouse structure. First, three types of greenhouses, including Venlo, Round-arch, and Saw-tooth type greenhouses, were selected as the design models for the study. In addition, the double-span, four-room structure model was built to explore the wind pressure distribution and the extreme wind pressure coefficient on the greenhouse surface for 13 (0°–180°, every 15°) directions of the wind direction to obtain the wind load characteristics in the greenhouse surface under different conditions. The results of the wind tunnel tests were consistent with those of the simulations, with the maximum wind pressure in the X-direction occurring at 30°-wind and the maximum wind pressure in the Y-direction at 75°-wind. The maximum negative wind pressure acting locally on the roof of the greenhouse was twice the maximum positive pressure acting on the windward side of the greenhouse. Accordingly, it is necessary to strengthen the structure in regions sensitive to wind direction with significant response to wind.

Machine learning forecasts of Scandinavian numerical weather prediction wind model residuals with control theory for wind energy

The quality of wind data from the numerical weather prediction significantly influences the accuracy of wind power forecasting systems for wind parks. Therefore, an in-depth investigation of these wind data themselves is essential to improve wind power generation efficiency and maintain grid reliability. This paper proposes a novel framework based on machine learning for concurrently analyzing and forecasting predictive errors, called residuals, of wind speed and direction from a numerical weather prediction model versus measurements over a while. The performance of the framework is testified by a wind farm inside the Arctic. It is demonstrated that the residuals still contain significant meteorological information and can be effectively predicted with machine learning and the linear autoregression works well for multi-timesteps predictions of overall, East–West,​ and North–South wind speeds residuals by comparing the four forecast learning algorithms’ performance. The predictions may be applied to correct the NWP wind model, making quality feedback improvements for inputs for wind power forecasting systems.

Time-variant post-processing method for long-term numerical wind speed forecasts based on multi-region recurrent graph network

Weather Research and Forecasting (WRF) is widely used for long-term wind speed prediction. To reduce the inherent systematic error of the WRF, a graph-based wind speed prediction model is proposed by post-processing the WRF. The proposed model contains four stages. In stage 1, the WRF model is applied to generate raw wind speed prediction results. In stage 2, Planar Maximally Filtered Graph (PMFG) is used to construct an informative graph of the wind field. In stage 3, Deep Autoencoder-like Nonnegative Matrix Factorization (DANMF) and Subgraph Alignment and Region Organization (SARO) are utilized to divide the graph into several regions. In stage 4, Multi-region Recurrent Graph Network (MRGN) model is proposed to build multiple regional models, aggregate them via time-variant ensemble weights, and generate improved long-term wind speed prediction results. The wind speed prediction results on 25 real meteorological monitoring nodes show that: (1) the proposed model outperforms WRF and 3 state-of-the-art models with a 95% confidence level; (2) the proposed model tends to produce better performance in strongly dynamic wind speed; (3) the proposed model has enough computational efficiency for practice. In conclusion, the proposed model is effective to improve WRF performance and has application potential.

Validation of the Aeolus Level-2B wind product over Northern Canada and the Arctic

Abstract. In August 2018, the European Space Agency (ESA) launched the Aeolus satellite, whose Atmospheric LAser Doppler INstrument (ALADIN) is the first space-borne Doppler wind lidar to regularly measure vertical profiles of horizontal line-of-sight (HLOS) winds with global sampling. This mission is intended to assess improvement to numerical weather prediction provided by wind observations in regions poorly constrained by atmospheric mass, such as the tropics, but also, potentially, in polar regions such as the Arctic where direct wind observations are especially sparse. There remain gaps in the evaluation of the Aeolus products over the Arctic region, which is the focus of this contribution. Here, an assessment of the Aeolus Level-2B (L2B) wind product is carried out, progressing from specific locations in the Canadian North to the pan-Arctic. In particular, Aeolus data are compared to a limited sample of coincident ground-based Ka-band radar measurements at Iqaluit, Nunavut, to a larger set of coincident radiosonde measurements over the Canadian North, to Environment and Climate Change Canada (ECCC)'s short-range forecast, and to the reanalysis product, ERA5, from the European Centre for Medium-Range Weather Forecasts (ECMWF). Periods covered include the early phase of the first laser flight model (flight model A – FM-A; September to October 2018), the early phase of the second laser flight model (flight model B – FM-B; August to September 2019), and the middle phase of FM-B (December 2019 to January 2020). The adjusted r-squared between Aeolus and other local datasets is around 0.9 except for lower values for the comparison to the Ka-band radar, reflecting limited sampling opportunities with the radar data. This consistency is degraded by about 10 % for the Rayleigh winds in the summer due to solar background noise and other possible errors. Over the pan-Arctic, consistency, with correlation greater than 0.8, is found in the Mie channel from the planetary boundary layer to the lower stratosphere (near surface to 16 km a.g.l.) and in the Rayleigh channel from the troposphere to the stratosphere (2 to 25 km a.g.l.). In all three periods, Aeolus standard deviations are found to be 5 % to 40 % greater than those from ECCC-B and ERA5. We found that the L2B estimated error product for Aeolus is coherent with the differences between Aeolus and the other datasets and can be used as a guide for expected consistency. Our work shows that the high quality of the Aeolus dataset that has been demonstrated globally applies to the sparsely sampled Arctic region. It also demonstrates the lack of available independent wind measurements in the Canadian North, lending urgency to the need to augment the observing capacity in this region to ensure suitable calibration and validation of future space-borne Doppler wind lidar (DWL) missions.

A comprehensive statistical analysis for residuals of wind speed and direction from numerical weather prediction for wind energy

Wind data are vital for the research in renewable energy research. Their quality from numerical weather prediction significantly influences the wind energy models. This paper utilizes a comprehensive statistical analysis for analyzing predictive errors, named residuals of wind speed and direction modeled by numerical weather prediction models. The analysis, taken an Arctic wind site as an example, effectively integrates statistical inference, probabilistic modeling, and hypothesis tests. It is proven that the residuals still contain important meteorological information. The introduced statistical analysis may be used to replenish residuals and explore complex intrinsic properties of numerical weather wind models and contributions to wind energy modeling.

Study on Nonlinear Aerodynamic Characteristics of a Semi-Closed Box Bridge Deck Based on Coupled Amplitude Variation

This paper explores the nonlinear characteristics of the self-excited aerodynamic forces of a semi-closed box deck section to perfect the theory of aeroelastic response analysis. A numerical wind tunnel model was established based on the computational fluid dynamics (CFD) method. The heaving-pitching coupled motion is realized by loading user-defined function (UDF) and dynamic grid technology. The self-excited aerodynamic forces varying with amplitude are identified and analyzed, and the reliability of the aerodynamic results obtained by numerical simulation is verified in the wind tunnel test. In the heaving-pitching coupled motion, the results show that the nonlinear characteristics of aerodynamic forces, especially the aerodynamic moment, are mainly affected by the pitching motion. The phenomenon of high-order harmonic energy transfer is observed with the increase in pitching amplitude, and the main component of high-order harmonic can be determined by the pitching amplitude. The contribution of heaving motion to aerodynamic forces nonlinear components is small, but its influence on nonlinear characteristics is complex. Small amplitude heaving motion plays a positive damping role in heaving-pitching coupled motion, and its scope and effect of positive damping action are affected by pitching motion. The extreme value heaving amplitude of positive damping action is observed in the aerodynamic lift.

A Meandering-Capturing Wake Model Coupled to Rotor-Based Flow-Sensing for Operational Wind Farm Flow Prediction

The development of new wake models is currently one of the key approaches envisioned to further improve the levelized cost of energy of wind power. While the wind energy literature abounds with operational wake models capable of predicting in fast-time the behavior of a wind turbine wake based on the measurements available (e.g., SCADA), only few account for dynamic wake effects. The present work capitalizes on the success gathered by the Dynamic Wake Meandering formulation and introduces a new operational dynamic wake modeling framework aimed at capturing the wake dynamic signature at a low computational cost while relying only on information gathered at the wind turbine location. In order to do so, the framework brings together flow sensing and Lagrangian flow modeling into a unified framework. The features of the inflow are first inferred from the turbine loads and operating settings: a Kalman filter coupled to a Blade Element Momentum theory solver is used to determine the rotor-normal flow velocity while a Multi-Layer Perceptron trained on high-fidelity numerical data estimates of the transverse wind velocity component. The information recovered is in turn fed to a Lagrangian flow model as a source condition and is propagated in a physics-informed fashion across the domain. The ensuing framework is presented and then deployed within a numerical wind farm where its performances are assessed. The computational affordability of the proposed model is first confirmed: 7 × 10−4 wall-clock seconds per simulation second are required to simulate a small 12 turbines wind farm. Large Eddy Simulations of wind farm using advanced actuator disks are then used as a baseline and a strong focus is laid on the study of the wake meandering features. Comparison against the Large Eddy Simulation baseline reveals that the proposed model achieves good estimates of the flow state in both low and high Turbulence Intensity configurations. The model distinctly provides additional insight into the wake physics when compared to the traditional steady state approach: the wake recovery is consistently accounted for and the wake meandering signature is captured as far as 12D downstream with a correlation score ranging from 0.50 to 0.85.

Fully-passive tethered flapping airfoil to harvest high-altitude wind energy

Airborne Wind Energy (AWE) system is an emerging technology aiming at harvesting high-altitude wind energy, which cannot be exploited by tower-mounted wind turbines. In the state-of-the-art AWE system, airborne actuators and ground-based drivers are necessary to control the posture and movements of the airborne component because it generates power through a complicated reciprocating motion. However, the control units required in the traditional AWE system inevitably introduce additional weight and decrease the system reliability, posing a challenge to designing a light airborne component with full automation. To address this issue, we developed a highly compact AWE system without any mechanical driver or control module. By adopting a biomimetic flapping airfoil, the new AWE system avoids the unnecessary power consumption of traditional design and yields consistent power output via a fully-passive flapping motion. Through a systematic optimization of structural parameters in a numerical wind tunnel, the fully-passive AWE system demonstrated efficient energy harvesting with a power coefficient of 0.825 and an efficiency of 18.9%. This advanced technology cannot only solve the fundamental issues that have persisted in the AWE system, but also offer a low-cost approach to enhance high-altitude wind power generation.

Wind Action Effects on Heliostat – CFD and FEM Study

Heliostats account for 45% of the total cost of a solar power tower, so optimizing their structural is critical to overall plant viability. Static wind charging of heliostats, as well as forces and moments applied by steady wind in any weather, has a high impact on the heliostat components design. For the reason that wind tunnel testing is expensive and the profile of flow field is difficult to obtain, numerical wind tunnel was used to study the wind load of the heliostat by Computational Fluid Dynamics (CFD) method and a (FEM) method. A 3D simulation has been performed for the Algerian climate, to evaluate this effect at different configurations of the heliostat. This paper provides details about the mesh generation method applied to complex projects under different working conditions. The effects of wind direction, azimuth and elevation angles on the wind pressure distribution are summarized. The coefficients of drag, lift and moment under diverse operating conditions were calculated. The CFD models of the wind around the heliostat are validated to the theoretical and experimental data.

Investigations of Exterior Wind Flow and Aerodynamic Coefficient around Y-Plan Shape Tall Building

In recent years, the construction of skyscrapers is emerging in many countries and the study on the behaviour of wind around the building receives an additional interest among structural engineers and architects. Mostly, tall skyscrapers are planned in the shape of ‘Y’ in order to have a maximum exterior view and to support the central core of the structure. In the current scenario, it is important to study the actual wind load for irregular plan shape building. This paper presents the numerical wind flow simulation around ‘Y’ plan shape tall building using ANSYS Fluent software and validation is done using wind tunnel testing. The building model and wind velocity are scaled to the ratio 1:300 and 1:5 respectively. A wind velocity of 10 m/s is applied both for wind tunnel testing and for the numerical simulation. Error analysis is carried out in order to check the accuracy of the results obtained between wind tunnel and CFD. From the test results the mean Cp is investigated for various faces of the building for the wind angle 0˚, 45˚ and 90˚ from both using CFD and wind tunnel. The investigation of drag and lift coefficient is made on Y-plan shape building and it is observed that the maximum drag occurs at 45˚ wind angle, because of the less projected area when compared with the other wind angles 0˚ and 90˚ respectively. Further, this paper continues with the physics of wind flow behaviour around Y-plan shape building and flow character such as vortex formation, streamlines and identification of wake region for different wind angles.

Experimental and numerical study on heatwave effect over an airfoil for unmanned aerial vehicle applications

PurposeThe heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency. The purpose of this study is to investigate the effects of heatwave upon the low Reynolds number airfoil aerodynamic performance.Design/methodology/approachIn this research, the heatwave effects on micro-aerial vehicles’ wing operation are also demonstrated both numerically and experimentally, at the Chord-based Reynolds number Rec = 2 × 105, and under the influence of various environmental temperatures, i.e. 27ºC (room temperature), 40ºC and 50ºC for various flying conditions. A numerical investigation of the low Reynolds number flows with the thermal effect around the unmanned aerial vehicle is presented using the k–ɛ turbulent model. Besides that, the low Reynolds number-based wind tunnel experimental setup is developed to determine the effects of a heatwave over an airfoil. Then, the numerical simulations and wind tunnel experiments are conducted.FindingsThe numerical and wind tunnel’s experimental investigations have been performed on a 2D airfoil under a heatwave environment, i.e. 27ºC, 40ºC and 50ºC for different flight conditions. The numerical and experimental results revealed that the heatwave effect and aerodynamic performance are validated with experimental results. The lift and drag coefficients for both numerical and experimental results show very good correlation at Reynolds number 2 × 105.Practical implicationsThe consequences of the increasing temperatures to varying degrees will also be experienced by all commercial aircraft. That is why some great findings are presented here, which are highly relevant for the current and future airline operations. However, sooner than later, the aviation industry should also begin to consider the rising effects of temperature on aircraft operations to develop the loss-reducing adaptable plans.Originality/valueFrom the numerical and wind tunnel experimental results, the recorded maximum lift coefficients are observed to be 2.42, 2.39 and 2.36 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, numerically. Similarly, the recorded maximum lift coefficients are observed to be 2.410, 2.382 and 2.354 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, experimentally. The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency.

Numerical Simulation of Orbit Controlled Hot-gas Lateral Jet of the triangular plate with rudder

Hypersonic interception weapons have high requirements for the efficiency and accuracy of the control system. As an effective control approach, the thermochemical non-equilibrium effect of jet flow must be considered in order to accurately predict the aerodynamic characteristic. At present, relevant researches are mostly focused on the low-flow rate hot jet, while numerical simulation and wind tunnel test studies on high-flow rate hot jet are rare. In this paper, the interaction flow field of the rail-controlled jet at the altitude of 60Km and 70Km has been simulated by solving the three-dimensional viscous fluid governing equations. The influence of the thermalchemical non-equilibrium effect of the jet interaction on the flow field characteristics and aerodynamic characteristics of the aircraft was analyzed. The primary results show that: (1) The flow fields of the cold-gas jet, frozen-gas jet and hot-gas jet have significant differences under the high-flow rate jet condition, which is mainly reflected the size and the pressure value of the separation region before the nozzle. The separation region length of the cold-gas jet is approximately twice that of the hot-gas jet and the length of the frozen-gas jet is between them; (2)Jet interaction will increase the surface pressure of the aircraft and reduce the skin-friction. When Ma=25, the aerodynamic interaction of hot jet is only about 30% of that of cold jet; (3) Jet interaction on aerodynamic characteristics increases with altitudes. With the increase of Mach number, the difference between the predicted results of hot jet and cold jet is enlarged because of the enhancement of the thermochemical non-equilibrium effect.

Comparing and validating intra-farm and farm-to-farm wakes across different mesoscale and high-resolution wake models

Abstract. Numerical wind resource modelling across scales from the mesoscale to the turbine scale is of increasing interest due to the expansion of offshore wind energy. Offshore wind farm wakes can last several tens of kilometres downstream and thus affect the wind resources of a large area. So far, scale-specific models have been developed but it remains unclear how well the different model types can represent intra-farm wakes, farm-to-farm wakes as well as the wake recovery behind a farm. Thus, in the present analysis the simulation of a set of wind farm models of different complexity, fidelity, scale and computational costs are compared among each other and with SCADA data. In particular, two mesoscale wind farm parameterizations implemented in the mesoscale Weather Research and Forecasting model (WRF), the Explicit Wake Parameterization (EWP) and the Wind Farm Parameterization (FIT), two different high-resolution RANS simulations using PyWakeEllipSys equipped with an actuator disk model, and three rapid engineering wake models from the PyWake suite are selected. The models are applied to the Nysted and Rødsand II wind farms, which are located in the Fehmarn Belt in the Baltic Sea. Based on the performed simulations, we can conclude that both WRF + FIT (BIAS = 0.52 m s−1) and WRF + EWP (BIAS = 0.73 m s−1) compare well with wind farm affected mast measurements. Compared with the RANS simulations, baseline intra-farm variability, i.e. the wind speed deficit in between turbines, can be captured reasonably well with WRF + FIT using a resolution of 2 km, a typical resolution of mesoscale models for wind energy applications, while WRF + EWP underestimates wind speed deficits. However, both parameterizations can be used to estimate median wind resource reduction caused by an upstream farm. All considered engineering wake models from the PyWake suite simulate peak intra-farm wakes comparable to the high fidelity RANS simulations. However, they considerably underestimate the farm wake effect of an upstream farm although with different magnitudes. Overall, the higher computational costs of PyWakeEllipSys and WRF compared with those of PyWake pay off in terms of accuracy for situations when farm-to-farm wakes are important.

Wind Field Characteristics of Complex Terrain Based on Experimental and Numerical Investigation

With the intensification of energy consumption, how to make rational and efficient use of wind energy has been studied all over the world. The construction of facilities to obtain wind energy requires an accurate assessment of the wind characteristics of the local terrain. In order to study the wind characteristics on an island in Southeast China, a 1:1300 terrain model is established, and the characteristics of mean wind and fluctuating wind are studied by numerical simulation and wind tunnel test. The results show that wind speed is affected by the incoming wind direction and local terrain. Wind speed on windward slopes and flat areas with no obstructions is higher, and wind speed on leeward slopes and valleys is lower. Then, the wind attack angle of each measuring point is mainly in the range of −10°~10°, which is much higher than that in flat areas. The positive and negative wind attack angles are controlled by the incoming wind direction, and the size is closely related to the local terrain. As for pulsation characteristics, the disturbance of the inflow determines the turbulence intensity. The incoming wind direction mainly affects the turbulence intensity on the hillside, while the turbulence intensity in the valley and flat area is controlled by the local terrain. In addition, the fluctuating wind speed power spectra on the island is more consistent with the von Karman spectrum, which is quite different from the Kaimal spectrum. The bandwidth on hillsides and valleys will not change with the change in inflow, but for flat areas, the bandwidth is greatly affected by the inflow direction.

Study on the influence of baffles on the aerodynamic coefficients of long-span flexible bridge section

In the study of wind resistance performance of Bridges, the study of aerodynamic coefficients directly affects the accuracy of wind resistance performance of bridges. In this paper, the aerodynamic coefficients of main girder section of single-tower single-side suspension curve suspension cable footpath bridge are studied by numerical simulation and wind tunnel test. In order to improve the wind resistance performance of the bridge, the aerodynamic performance of the bridge section was improved by optimizing the bridge section and adding baffles, and the aerodynamic coefficient was obtained by wind tunnel test. The first section in your paper

Assessment of a heterogeneous computing CFD code in wind farm simulations

The use of heterogeneous architectures, based on CPU-GPU processors, has led to a significant increase in the performance of parallel computing applications. In recent years, this approach has been implemented in various computational fluid dynamics (CFD) codes to take advantage of the compute capability of the GPU graphics cards. The objective of this work is to assess the performance of a general purpose CFD open-source code in wind energy applications, running in a heterogeneous architecture. To this aim, a numerical wind turbine model was migrated from a CPU-based Fortran program to the CFD code. Several timing tests were performed on a local computing station, while running simulations of well-documented wind tunnel experiments. The results obtained show a significant reduction in computational time and resource required, indicating a great potential of the GPU-accelerated CFD code to be used in large wind farms simulations or in real-time applications.