Wind Turbulence Research Articles

Exploring Observational Heliophysics Across All Scales: Reflections and Insights From the 2023 NASA Heliophysics Summer School

AbstractThe field of heliophysics encompasses a diverse range of research areas and rich plasma environments, from the solar dynamo and solar wind turbulence, to the complex terrestrial thermosphere‐ionosphere‐magnetosphere (TIM) system, to investigations of both induced and intrinsic magnetospheres across the solar system. This perspective paper delves into the experiences and outcomes of a summer school held in person in Boulder, Colorado, USA, from 7–11 August, which offered a platform for interdisciplinary learning and collaboration. The event, supported by NASA's Living with a Star program and hosted by the University Corporation for Atmospheric Research and Cooperative Programs for the Advancement of Earth System Science, assembled a cohort of 26 graduate students and postdoctoral researchers from around the world, all engaged in heliophysics research. The summer school included a series of lectures, interactive activities, and a culminating capstone project. The participants' diverse backgrounds enriched discussions and encouraged novel approaches to traditional problems. The capstone projects spanned an array of topics, including investigating the origins of solar wind switchbacks, dissecting the sequence of events from solar eruptions and their corresponding terrestrial consequences, investigating the energy transfer from solar coronal mass ejections to Earth's magnetosphere, and advocating for the exploration of Coulomb collisions in understanding large‐scale global systems. Through this perspective, we shed light on the value of international and interdisciplinary collaboration in advancing heliophysics research. This perspective paper encapsulates the ethos of the summer school, serving as a testament to the continuing and collective pursuit of unraveling the mysteries of the heliosphere.

A new process-based and scale-aware desert dust emission scheme for global climate models – Part II: Evaluation in the Community Earth System Model version 2 (CESM2)

Abstract. Desert dust is an important atmospheric aerosol that affects the Earth's climate, biogeochemistry, and air quality. However, current Earth system models (ESMs) struggle to accurately capture the impact of dust on the Earth's climate and ecosystems, in part because these models lack several essential aeolian processes that couple dust with climate and land surface processes. In this study, we address this issue by implementing several new parameterizations of aeolian processes detailed in our companion paper in the Community Earth System Model version 2 (CESM2). These processes include (1) incorporating a simplified soil particle size representation to calculate the dust emission threshold friction velocity, (2) accounting for the drag partition effect of rocks and vegetation in reducing wind stress on erodible soils, (3) accounting for the intermittency of dust emissions due to unresolved turbulent wind fluctuations, and (4) correcting the spatial variability of simulated dust emissions from native to higher spatial resolutions on spatiotemporal dust variability. Our results show that the modified dust emission scheme significantly reduces the model bias against observations compared with the default scheme and improves the correlation against observations of multiple key dust variables such as dust aerosol optical depth (DAOD), surface particulate matter (PM) concentration, and deposition flux. Our scheme's dust also correlates strongly with various meteorological and land surface variables, implying higher sensitivity of dust to future climate change than other schemes' dust. These findings highlight the importance of including additional aeolian processes for improving the performance of ESM aerosol simulations and potentially enhancing model assessments of how dust impacts climate and ecosystem changes.

Influence of Excitation by Idling Rotor on Wind Turbine Ultimate Loads in Storm Conditions

Typical large scale pitch-controlled wind turbines idle their rotors during storm conditions. The design loads of wind turbines are calculated by aeroelastic simulations under various conditions. These include grid loss and failures, which can increase rotor speed and excite the first-mode of the tower bending. In this study, the influences of self-excitation by the idling rotor on the ultimate loads in storm conditions were investigated. Aeroelastic simulations were conducted for a three-bladed 5 MW upwind turbine as an example, under steady and extreme turbulent wind conditions according to the international design standard IEC61400-1 ed.4. As a result, we confirmed that yaw misalignment increases the idling rotor speed and 6P, second order harmonics of blade passing frequency, excites the first-mode tower bending, which can generate a large load on the tower. Pitch stick can increase the rotor speed but not as noticeably as yaw error. Although no clear provisions exist in wind turbine design standards or guidelines for the self-excited vibration during wind turbine idling, these results indicate that conditions must be set that consider self-excited vibration.

Monofractality in the Solar Wind at Electron Scales: Insights from Kinetic Alfvén Waves Turbulence.

The breakdown of scale invariance in turbulent flows, known as multifractal scaling, is considered a cornerstone of turbulence. In solar wind turbulence, a monofractal behavior can be observed at electron scales, in contrast to larger scales where multifractality always prevails. Why scale invariance appears at electron scales is a challenging theoretical puzzle with important implications for understanding solar wind heating and acceleration. We investigate this long-standing problem using direct numerical simulations of three-dimensional electron reduced magnetohydrodynamics. Both weak and strong kinetic Alfvén waves turbulence regimes are studied in the balanced case. After recovering the expected theoretical predictions for the magnetic spectra, a higher-order multiscale statistical analysis is performed. This study reveals a striking difference between the two regimes, with the emergence of monofractality only in weak turbulence, whereas strong turbulence is multifractal. This result, combined with recent studies, shows the relevance of collisionless weak KAW turbulence to describe the solar wind at electron scales.

Understanding wind turbine power converter reliability under realistic wind conditions

AbstractThe reliability of wind turbine power converters is crucial for analyzing wind energy project costs, and for estimating maintenance and downtime. The published literature in this field relies on evaluating the reliability effect of wind speed to estimate the converter lifetime. However, this paper demonstrates that wind turbulence intensity, which has not been widely considered in similar reliability analyses, shows a significant impact on converter lifetime. This paper uses 821 10‐min wind speed time series sampled at 1 Hz on the two most commonly deployed wind turbine converter topologies: the two‐level voltage source and the three‐level neutral point clamped. Electromechanical and thermal modelling, combined with statistical analysis shows that mean wind speed and turbulence intensity both impact the lifetime of both converter topologies. However, the paper estimates that the three‐level converter can operate 2.4 to 4.0 times longer than the two‐level converter depending on the operating wind speed and turbulence intensity.

Wind-Induced Response Analysis of the Transmission Tower-Line System Considering the Joint Effect

Wind load is one of the main control loads of transmission tower-line systems. Numerical simulation is the main method for studying the structural wind-induced response. The establishment of a refined transmission tower simulation model is the basis for accurately analyzing the dynamic response of a transmission tower-line system under a wind load. This paper first considered the mechanical properties of bolted joints under cyclic loading and established a transmission tower-line system model considering the joint effects. Then, the wind load was generated by the harmonic superposition method, and the wind dynamic time-history analysis of the tower-line system was conducted. The influence of the joint effect on the wind-induced response of the transmission tower-line system was studied, and the effects of turbulence intensity and wind attack angle on the bolted joint slip effect were discussed. The results showed that the joint effect significantly increased the displacement response of the transmission tower subjected to wind loads and affected the normal service performance of the tower-line system. When the turbulence intensity is 10%, the top displacement of the tower model considering the joint effect is approximately 2 times that of the ideal rigid frame model. After considering the joint effect, the additional [Formula: see text] effect caused by the increased displacement resulted in an increase in the stress of 75.6% members, and the maximum stress of the main member was located near the upper diaphragm of the tower leg. Therefore, considering the joint slip effect in angle steel transmission towers can improve the accuracy of the dynamic response analysis of transmission lines.

Development of a Load Model Validation Framework Applied to Synthetic Turbulent Wind Field Evaluation

The validation of aeroelastic load models used for load calculations on wind turbines substantially increases the confidence in the accuracy and correctness of these models. In this contribution, we introduce a framework for the validation of these models, integrating a normalized area metric as an objective, quantifiable validation metric that considers the entire statistical distribution of a model and a benchmark and additionally enables a comparison of model accuracy between sensors of different physical units. The framework is applied to test cases that evaluate varying synthetic turbulent wind fields. Two test cases with a focus on turbulence parameters and abnormal shear conditions based on comprehensive wind measurements at the Testfeld Bremerhaven are used to demonstrate the workflow with four different members using IEC-compliant and measurement-derived wind field parameters, respectively. Along with these measurements, an uncertainty model for synthetic wind fields is introduced to quantify propagated wind measurement uncertainties associated with the measured boundary conditions during a validation campaign. The framework is presented as a straightforward and concise methodology to not only find but also quantify mismatches of load models. Major mismatches are found for wind fields associated with larger uncertainties in the mean wind field due to a reduced spatial resolution of measurements.

Image based automatic wind velocity profiler for adaptive optics

Abstract Adaptive optics (AO) systems correct optical phase aberrations of the incoming light generated by the atmosphere. To do so simultaneous estimators of the atmospheric turbulence parameters are required. For the family of wide-field AO systems (WFAO), this information must be stratified in altitude. Among these vectorized estimations, wind profiling in altitude is needed for the reduction of temporal errors in AO loops or for the estimation of turbulence coherence time. This paper proposes a turbulence wind profiler called image processing based peak tracking algorithm (IPTA). IPTA is an image-processing based approach that automatically and reliably estimates wind velocity for several turbulent layers along the line of sight. The estimation of each wind layer is achieved by tracking peaks produced in cross-correlation maps from pairs of wavefront sensors (WFSs) slopes using the technique known as SLODAR (slope detection and ranging). Results for simulated and on-sky WFS datasets demonstrate that IPTA outperforms one of the state of the art wind profiler methods (the profiler covariance parametrization of wind velocity (CAW)) in terms of accuracy and speed. Results also show that, in terms of execution time, our method scales better when the number of WFS lenslets is increased. Being an open source and reliable tool, we believe IPTA can be a useful wind profiler for the adaptive optics community.

Assessment on natural ventilation and pollutant dispersion around sunken squares by transient simulation

Sunken square is a semi-open public space that has been gaining popularity in urban planning and designs. Its semi-open design is beneficial to ventilation of the connected underground spaces, but it is also subject to potential exposure to ground-level traffic pollutants. To evaluate the semi-open design’s influence on the balance between underground ventilation efficiency and the pollutant exposure, this study uses large eddy simulation (LES) to simulate turbulent wind flow characteristics and pollutant dispersion in a typical sunken square. The sunken square is connected to two indoor spaces with single-sided opening, and the design features of staircase and arcade are further tested for their influences on the wind flow field. The air change rate per hour (ACH, h−1) is adopted to quantify the ventilation efficiency of the two connected indoor spaces. Results show that the staircases amplify wind velocities for the indoor spaces but also bring higher pollutant concentrations inside together. Moreover, the design of the arcade at the opening prompts the vortex to shift towards the entrance, leading to a heightened concentration of pollutants. Meanwhile, the effective ACH is mostly contributed by the turbulent diffusion (ACHt), while the mean flow (ACHm) has much less effect on the ventilation of the indoor spaces. These findings of this study provide references for sunken square design.

Improving the Near-Surface Wind and Turbulence at the Edge of the Orographic Drag Gray Zone by Tuning the Roughness Length

Abstract In this paper, we present the implementation and evaluate the impact of the new roughness length configuration in the ALARO canonical model configuration of the ALADIN system at the edge of the orographic gravity wave drag gray zone. As an essential input for turbulence parameterization, the roughness length affects the near-surface turbulent fluxes and the screen-level interpolation of meteorological parameters. We utilize GMTED2010 and ECOCLIMAP-II databases to derive orographic and vegetation components of the effective roughness length and introduce tuning parameters enabling us to optimize predicted near-surface turbulent momentum fluxes and 10-m wind speed. Based on sensitivity tests, we (i) prove the necessity of tuning the roughness length fields, (ii) considerably reduce the RMSE of near-surface turbulent momentum fluxes (6%–7%) and 10-m wind speed for different groups of stations (3%–10%), and (iii) identify the tree height as the most influential input parameter in our computational domain. The RMSE decomposition indicates that the improvement of 10-m wind speed mostly comes from a decrease in the random error and bias of the mean. The variability is slightly underestimated, thus reducing the model accuracy for wind speeds above the 95th percentile but at an acceptable level. We explain that roughness length tuning also compensates for the missing roughness sublayer correction in our system. Finally, we show that, although the impact of the orographic gravity wave drag scheme at a horizontal mesh size of 1.8 km is generally small, it is still beneficial for capturing some finer features observed in atmospheric soundings. Significance Statement Aiming to improve the 10-m wind speed forecast without sacrificing the accuracy of turbulent momentum fluxes in the kilometric resolution numerical weather prediction model, we derived new roughness length fields from high-resolution physiography databases. Therein, we proved the importance of tuning the input orography and vegetation fields and, depending on the time of day and year, reduced the root-mean-square error of 10-m wind speed by 3%–10%. Further, we demonstrated that orographic gravity wave drag parameterization is still needed to predict finer details seen in wind profiles from atmospheric soundings. Finally, we discussed the related simplifications in our model and their implications and proposed steps toward a more consistent and complete treatment of the near-surface turbulence.

Influence mechanism and numerical reconstruction method of complex wind field acting on a large-MW floating wind turbine

The large-scale wind fields show a series of complex characteristics, including wind shear, turbulence intensity, and spatial coherence, which could significantly affect the coupled dynamic responses of floating wind turbines (FWTs). During numerical simulation, to obtain the coupled dynamic responses of large-scale FWTs more accurately, it is necessary to provide a more accurate simulation of the time scale and spatial scale characteristics of actual measured large-scale wind fields. This study investigated the influence mechanism and numerical reconstruction method of a complex wind field acting on a large-MW floating wind turbine. The influence mechanisms were concluded as follows: Wind shear was found to decrease the mean power generation and increase responses at 1P and 3P frequencies. Turbulent winds could significantly decrease the mean response and increase the low-frequency and 3P responses. The difference in spatial coherent structures between different wind fields was clarified by analyzing the proper orthogonal decomposition mode. As spatial coherence strengthened, the mean responses became smaller, the low-frequency responses became larger, and the 1P and 3P responses became smaller. On this basis, a numerical reconstruction method was proposed in this study to reconstruct large-scale numerical wind fields using wind speeds measured at finite spatial points in model tests or offshore measurements. This method accurately simulates the wind profile characteristics, turbulence intensity distribution along the vertical direction, and spatial coherence parameters of the wind field.

Direct Observation of Wave-Coherent Pressure Work in the Atmospheric Boundary Layer

Abstract Surface waves grow through a mechanism in which atmospheric pressure is offset in phase from the wavy surface. A pattern of low atmospheric pressure over upward wave orbital motions (leeward side) and high pressure over downward wave orbital motions (windward side) travels with the water wave, leading to a pumping of kinetic energy from the atmospheric boundary layer into the waves. This pressure pattern persists above the air–water interface, modifying the turbulent kinetic energy in the atmospheric wave-affected boundary layer. Here, we present field measurements of wave-coherent atmospheric pressure and velocity to elucidate the transfer of energy from the atmospheric turbulence budget into waves through wave-coherent atmospheric pressure work. Measurements show that the phase between wave-coherent pressure and velocity is shifted slightly above 90° when wind speed exceeds the wave phase speed, allowing for a downward energy flux via pressure work. Although previous studies have reported wave-coherent pressure, to the authors’ knowledge, these are the first reported field measurements of wave-coherent pressure work. Measured pressure work cospectra are consistent with an existing model for atmospheric pressure work. The implications for these measurements and their importance to the turbulent kinetic energy budget are discussed. Significance Statement Surface waves grow through a pattern of atmospheric pressure that travels with the water wave, acting as a pump against the water surface. The pressure pumping, sometimes called pressure work, or the piston pressure, results in a transfer of kinetic energy from the air to the water that makes waves grow larger. To conserve energy, it is thought that the pressure work on the surface must extract energy from the mean wind profile or wind turbulence that sets the shape of the wind speed with height. In this paper, we present direct measurements of pressure work in the atmosphere above surface waves. We show that the energy extracted by atmospheric pressure work fits existing models for how waves grow and a simple model for how waves reduce energy in the turbulent kinetic energy budget. To our knowledge, these are the first reported field measurements of wave-coherent pressure work.

Inverse problem for retrieving greenhouse gas fluxes at the non-uniform underlying surface from measurements of their concentrations at several levels

The study focuses on the formulation, analysis, and solution of the remote sensing inverse problem to retrieve surface carbon dioxide (CO2) fluxes from measurements of CO2 concentrations at different levels within the atmospheric boundary layer. A three-dimensional hydrodynamic model of turbulent greenhouse gas (GHG) transport was used as a forward model to link the surface GHG fluxes to the drone observations of GHG concentrations. The 3D model provides a GHG concentration distribution by solving the diffusion-advection equation using information on wind speed, its direction, and turbulent exchange coefficients. The surface GHG fluxes are considered as a boundary condition. The spatial distributions of wind speed and turbulence coefficient “for a moment in time” are computed from the relaxation problem for the averaged Navier-Stokes and continuity equations, using a 1.5 order closure scheme (E-ω model). The inverse problem is to retrieve a surface GHG flux by minimizing the difference between the measured and modelled concentrations at several levels. The algorithm was applied to estimate CO2 fluxes over a non-uniform forest canopy at the Roshny-Chu experimental site in the foothills of the Greater Caucasus (Chechen Republic). To test the forward numerical problem, data on surface topography, vegetation height and density, spatial distribution of photosynthetically active solar radiation, as well as data on plant photosynthesis and soil CO2 fluxes were used.

A New Thermal Management Strategy of IGBT in DFIG for Economic Benefit Maximization

Wind speed fluctuation generally shortens the lifetime of the insulated gate bipolar transistor (IGBT) module in the doubly fed induction generator (DFIG), which leads to frequent component replacement and cost increase of wind power generation. Conventional power control strategies consider solely the wind turbine output power maximization, and existing junction temperature thermal management strategies focus on IGBT lifetime extension, both of which are not effective under turbulent wind speed conditions and ignore the trade-off between the device reliability and output power for the overall DFIG economic benefit. To bridge the gap between the IGBT reliability and the output power under turbulent wind speed conditions, we propose a novel IGBT thermal management strategy for optimal economic benefit. Specifically, we first smooth the output power through a linear power control (LPC) method with conditions on the wind speed and turbine speed to reduce the IGBT low-frequency junction temperature fluctuation, which extends IGBT lifetime. We then propose a grid encirclement and suppression search (GESS) method that maximizes the economic benefit defined by LPC-smoothed output power and IGBT lifetime. Simulation shows that our proposed LPC-GESS strategy outperforms a competing strategy at economic benefit by a large margin, up to 15.3%. Our proposed strategy can potentially be used in wind power stations for fast and reliable economic benefit-oriented IGBT thermal management.

Heliospheric Diffusion of Stochastic Parker Spirals in Radially Evolving Solar Wind Turbulence

We present a stochastic field line mapping model where the interplanetary magnetic field lines are described by a density distribution function satisfying a Fokker–Planck equation that is solved numerically. Due to the spiral geometry of the nominal Parker field and to the evolving nature of solar wind turbulence, the heliospheric diffusion of the magnetic field lines is both heterogeneous and anisotropic, including a radial component. The longitudinal distributions of the magnetic field lines are shown to be close to circular Gaussian distributions, although they develop a noticeable skewness. The magnetic field lines emanating from the Sun are found to differ, on average, from the spirals predicted by Parker. Although the spirals remain close to Archimedean, they are here underwound, on average. Our model predicts a spiral angle that is smaller by ∼5° than the Parker spiral angle at Earth’s orbit for the same solar wind speed of V sw = 400 km s−1. It also predicts an angular position on the solar disk of the best magnetically connected footpoint to an observer at 1 au that is shifted westward by ∼10° with respect to the Parker’s field model. This significantly changes the angle of the most probable magnetic connection between possible sources on the Sun and observers in the inner heliosphere. The results have direct implications for the heliospheric transport of “scatter-free” electrons accelerated in the aftermath of solar eruptions.

Wind tunnel tests applied to wind energy management: comparison of measurements in closed-circuit and open-circuit wind tunnels

Power loss, damages overestimation and environmental impacts are the main problems related to wind energy and its planning and management. One of the tools used to analyse and manage this problem is the aerodynamic wind tunnel. In this work wind tunnel tests were performed in two different facilities, an open-circuit wind tunnel and a close-circuit wind tunnel, in order to study the suitability of these features to optimize wind farms layout and power quality and its dependence of the type of tests facility. Experimental results in this work are reported as wind speed and turbulence intensity vertical profiles and flow fields with a simulated ABL with and without the presence of a three-bladed wind turbine model. Results show that mean wind velocity is similar in both tunnels, but turbulence intensity is higher for the open-circuit wind tunnel.

A numerical study on load effects of low-rise buildings in a wind-blown sand environment

The transportation process of wind-blown sand, represented by sandstorms, occurs frequently in arid and semi-arid regions. The combined action of wind and sand impact load in a wind-sand environment poses a serious threat to the safety of construction, transportation and other engineering structures. However, most of the current structural designs only considers the effect of wind, and there is little detailed research on the surface load distribution of structures caused by sand impact, which leads to uncertainty in the safety assessment of engineering structures in wind-sand areas. In this paper, low-rise buildings which are easily damaged in strong wind-sand environments are taken as the research object. A numerical model of coupling turbulent wind field and particle motion was then established, and the reliability of the numerical simulation results was verified through wind tunnel experiments. Finally, the wind-sand movement around the low-rise building model and the load distribution characteristics on the building surface are simulated under different wind speed and sand concentration conditions. The results show that the edges and corners of engineering structures are subject to more severe particle erosion-abrasion. As the sand concentration increases in the flow field, the wind speed and the wind load acting on the structures weakens. Whereas the sand impact load increases with the increment of wind speed and sand concentration. The increased effect of sand particles on the total load can be considered by amplifying the wind load shape coefficient on the windward side. This study is helpful to understand the mechanism of sand wind-induced damage on low-rise buildings, and provides basic tools and a theoretical basis for the wind and wind-blown sand resistance design and performance optimization of engineering structures.

Wind and structural loads data measured on parabolic trough solar collectors at an operational power plant

Wind loading is a primary contributor to structural design costs of concentrating solar-thermal power collectors, such as heliostats and parabolic troughs. These structures must resist the mechanical forces generated by turbulent wind, while the reflector surfaces must maintain optimal optical performance. Studying wind-driven loads at a full-scale, operational concentrating solar-thermal power plant provides insights into the wind impact on the solar collector field beyond the capabilities of wind tunnel tests or state-of-the-art simulations. We conducted comprehensive field measurements of the atmospheric turbulent wind conditions and the resulting structural wind loads on parabolic troughs at the Nevada Solar One plant over a two-year period. The measurement setup included meteorological masts and structural load sensors on four trough rows. Additionally, a lidar scanned the horizontal plane above the trough field. In this study, we describe the high-resolution dataset characterizing the complex flow field and resulting structural loads. This first-of-its-kind dataset will enhance the understanding of wind loading on collector structures and will help in designing the next-generation solar collectors and photovoltaic trackers.

Yaw misalignment in powertrain degradation modeling for wind farm control in curtailed conditions

A framework characterizing the degradation of wind turbines for use in multiple-input damage-aware farm control is suggested. The focus is on the fatigue damage of the powertrain (drivetrain + generator) system, but the methodology may be extended to other components. A database of steady-state damage analyses for different operating conditions (average wind speeds, turbulence levels, power demands, and yaw misalignment angles) using aero-hydro-servo-elastic simulations is first generated. Then, a weighted damage index based on probabilistic long-term fatigue damage analysis of the powertrain system components is suggested and used to represent degradation at the farm level for control purposes. The focus is on curtailed conditions where the farm controller dispatches power commands to individual turbines in order to track a demanded power reference (rather than seeking to maximize power) at the farm level. As a secondary objective, the controller seeks to mitigate degradation through a smart combination of power commands and yaw offset angles, making use of the weighted degradation index. The potential of the proposed approach is demonstrated through a case study on the TotalControl Reference Wind Power Plant in a FLORIS-based simulation framework. The proposed farm controller is compared with the conventional one without damage mitigation feature and with damage mitigation but without yaw angle as the control input. It is found that combining yawing and downregulation effectively slows down degradation on the main bearing and powertrain as a whole.

Performance analysis of wind resource assessment programs in complex terrain.

In order to provide optimal sitting of wind turbines, a reliable estimate of the wind resource over a given area is required. This paper compared the performance of two models, WAsP and WindSim in predicting the power production of individual turbines. The prediction accuracy is determined as function of wind direction (terrain), turbine spacing and turbulence. Recommendations are made as to the reliability and suitability of these models for different situations