Sandrine Aubrun

• Doctor of Philosophy
• Professor at École Centrale de Nantes

When comparing Large Eddy Simulations with wind tunnel experiments, choosing the appropriate boundary conditions is crucial to ensure an accurate representation of wind flow. This becomes particularly challenging for Atmospheric Boundary Layer (ABL) wind tunnels, which frequently incorporate calibrated obstacles to replicate the appropriate model-s...

Wind power is expected to make the biggest contribution to renewable energy deployment targets for 2030 and beyond. Installed wind power capacity in the European Union is around 236 GW (end 2021); with 207 GW of onshore wind and 28 GW of offshore wind, it covers 15% of electricity demand (8% in France). The most promising scenarios aim to achieve a...

The complex dynamics introduced by floating platforms present new challenges in the study of wind turbine wakes, and numerous questions remain unresolved due to the early stage of this technology and limited operational experience. Previous studies showed that harmonic motions with realistic amplitude and frequency and under a modelled atmospheric...

The development of floating offshore wind turbines poses new challenges since the floating platform introduces complex dynamics in the wind turbine wake. These wake dynamics are intricately tied to the advection velocity, referring to the velocity of the downstream propagation of the air flow, and used in the context of wind farm modelling. The pre...

The growing interest in floating offshore wind turbines (FOWTs) is rooted in the potential source of increased offshore energy production. As the technology is still in a pre-industrial state, several questions remain to be addressed where little field data are available. This study uses physical modelling at a reduced scale to investigate the sign...

L’éolien est l’énergie qui devrait apporter la plus grande contribution aux objectifs de déploiement d’énergie renouvelable pour 2030 et au-delà. La capacité éolienne installée dans I’Union européenne est d’environ 236 GW (fin 2021) ; avec 207 GW d’éolien terrestre et 28 GW d’éolien en mer, elle couvre 15 % de la demande d’électricité (8 % en Franc...

The growing interest in floating offshore wind turbines (FOWTs) is rooted in the potential source for increased offshore energy production. As the technology is still in a pre-industrial state, several questions remain to be addressed where little field data is available. This study uses physical modelling at a reduced scale to investigate the sign...

We performed large eddy simulations to study micro-scale wind–wave interactions under undisturbed freestream conditions. We identified that standard approaches lead to wave-related disturbances at the top boundary. Therefore, we developed a numerical strategy to maintain an undisturbed wind speed at the top, while considering arbitrary waves at the...

Intra-array wake meandering increases fatigue loading in downstream turbines and decreases farm total power output. In the case of floating offshore wind turbines (FOWTs), the motions of the floating substructure could have a non-neglectable contribution to wake meandering dynamics. This research experientially analyses the influence of imposed mot...

L'intérêt de plus en plus important pour les technologies d'éoliennes en mer telles que les éoliennes flot-tantes nécessite une plus grande compréhension de leur sillage, ce qui permet une meilleure optimisation des nouveaux parcs. De fait, plusieurs algorithmes de suivi de sillage permettant d'estimer le centre du sillage ont été développés avec u...

To achieve more accurate weather and climate forecasting, and propose efficient engineering solutions for exploiting offshore renewable energies, it is imperative to accurately describe the atmospheric turbulent flow in the offshore environment. The ocean’s dynamics raise specific challenges for the aforementioned applications, as they significantl...

A scanning LiDAR is employed to study micro-scale wind–wave interactions, at 18 m above the ocean. The analyses provide an original, space-time modal perspective, of wind–wave interaction mechanisms.

With the development of floating wind farms, the understanding of the far wake becomes of utmost importance because it cannot only be based on the experience acquired on fixed offshore turbine as the range of motion of the floater due to met-ocean conditions is in the same order of magnitude compared to the energetic turbulent scales of the atmosph...

This study is a follow up on a previous one carried out within the frame of the French project SMARTEOLE, during which, a ground-based scanning LiDAR measurement campaign was conducted in the onshore wind farm of Sole du Moulin Vieux. That previous study focused on the wakes of two wind turbines that experienced different degrees of interaction dep...

Floating LIDAR systems (FLS) are a cost-effective way of surveying the wind energy potential of an offshore area. However, as turbulence intensity estimates are strongly affected by wave-induced buoy motion, it is essential to correct them. In this study, we quantify the turbulence intensity measurement error of a WindCube v2® mounted on a 12-ton a...

As wind turbines are usually clustered in wind farms, knowledge of the evolution of the wind turbine wakes is important because downstream turbines will be exposed to them, causing higher loads and maintenance times. For that reason, wind turbine wakes have been studied intensively and different engineering wake models were derived. However, none o...

This article investigates the far wake response of a yawing upstream wind turbine and its impact on the global load variation in a downstream wind turbine. In order to represent misalignment and realignment scenarios, the upstream wind turbine was subjected to positive and negative yaw maneuvers. Yaw maneuvers could be used to voluntarily misalign...

This paper investigates the effect of yawing a wind turbine on its wake deviation dynamics and on the global load variation of a downstream wind turbine during a positive and negative yaw manoeuvre, representing a misalignment/realignment scenario. Yaw manoeuvres could be used to voluntarily misalign wind turbines when wake steering control is targ...

This work focuses on the analysis of the wake dynamics during yaw manoeuvres. Farm control is becoming always more crucial and voluntary misalignment is one valuable strategy employed to optimize the overall production. Indeed, the appropriate misalignment of a wind turbine can improve the rate of production and the lifetime of the downstream one,...

The wind energy farming in the offshore environment is characterized by ever-increasing structures and costs, for which reducing structural damage and maximizing production become an imperative. Such challenge is faced by site planning, intelligent design and active control systems that ultimately require a fine Atmospheric Boundary Layer (ABL) des...

Wind farm control is a current hot topic that deals with the capacity to improve the overall wind power production of a farm by controlling individual wind turbines in order to mitigate their wake effects. The dynamic properties of these different strategies need to be taken into account in order to improve wind farm control models. In this work a...

Floating offshore wind turbines (FOWTs) are a potential source for increased offshore energy production. As the technology is still in a pre-industrial state several questions remain to be addressed where little field data is available. This study uses physical modelling at a reduced scale to investigate the unsteady behaviour and the development o...

In a century where the green energy is a vital challenge, research about wind turbine is taking its place to give an alternative solution to polluting and fossil energies. Various scales of studies are possible for wind turbine production and lifetime optimization, such as the farm, the wind turbine or the blade. In this study we focused on the all...

Wind energy has been growing remarkably fast worldwide in recent years, the challenge for the wind industry is to increase productivity and optimize the installation of wind farms in increasingly complex sites, such as off-shore sites and forest sites where there is a high variation topographic. Wind energy production is growing in complex sites a...

Nine research teams organized a round-robin measurement campaign of the wake of two porous discs in a homogeneous and “low-turbulent" flow. Mean streamwise velocity and turbulence intensity profiles at four diameters downstream of the discs were measured and compared through such metrics as the maximum velocity deficit, the maximum turbulence inten...

The present study shows preliminary results of the SOFTWIND project that aims at developing an innovative experimental test bench dedicated to floating wind turbine wave tank testing. The following methodology is based on a “software in the loop” approach that combines numerical modeling with physical modeling. The originality of the experimental a...

The present investigation deals with Dielectric Barrier Discharge (DBD) induced jets flowing over curved surfaces and studied in the framework of a circulation control application, carried out by acting near the rounded trailing-edge of an airfoil. These jets are characterized experimentally via Particle Image Velocimetry (PIV) in quiescent air con...

The present study focuses on the wakes of two wind turbines that, depending on the wind direction, experienced different degrees of interactions, by processing field wake observations made from a 7-month ground based scanning LiDAR measurement campaign. This duration ensures an acceptable statistical convergence of the ensemble-averaged flow fields...

Within the frame of the French project ANR SMARTEOLE, a 7-month measurement campaign had been set-up in the north of France to study the wake behaviour of 2 wind turbines, with a set-up using scanning LiDAR scenarii that captured the wakes of 2 wind turbines for different degrees of interactions. An extensive statistical study of the wakes behaviou...

This study focuses on the experimental implementation of a fluidic lift control strategy on wind turbine blades with the objective of reducing the aerodynamic load fluctuations experienced by the rotors. Blades are equipped with a row of blowing jets located in the vicinity of the rounded trailing-edge of the airfoil. Two configurations are perform...

This work focuses on the dynamic analysis of a modelled wind turbine wake during yaw manoeuvres. Indeed, in the context of wind farm control, misalignment of wind turbines is envisaged as a solution to reduce wind turbine wake interactions, by skewing the wake trajectory. To optimize the control strategies, the aerodynamic response of the wake to t...

To reduce the levelized cost of energy, the energy production, robustness and lifespan of horizontal axis wind turbines (HAWTs) have to be improved to ensure optimal energy production and operational availability during periods longer than 15–20 years. HAWTs are subject to unsteady wind loads that generate combinations of unsteady mechanical loads...

In several papers, the importance of the atmospheric flow in the wake development of wind turbines (WT) has been pointed out, making it clear that it is necessary to have long-term on-field observations for an appropriate description of the wake development, its structure and dynamics. This work presents a statistical approach to wake meandering, y...

A feasibility study for implementing circulation control method to improve aerodynamic load alleviation on wind turbine blade airfoils was performed. The experiments investigated the ability of surface elongated-DBD actuators attempting to control the streamline separation point at a rounded trailing edge, leading to the modification of the velocit...

Within the frame of the French project ANR SMARTEOLE, a 6-month measurement campaign has been set-up in the north of France to study the wake behaviour of two wind turbines, with an original set-up using: one ground based scanning LIght Detection And Ranging system (LIDAR), 2 nacelle-mounted LIDARs and a nacelle-embedded 2-axis inclinometer. The pr...

On behalf of the European Academy of Wind Energy (EAWE¹) and WindEurope (formerly the European Wind Energy Association, EWEA, until April 2016), we have the pleasure of presenting the Scientific Proceedings of the WindEurope Summit 2016. WindEurope Summit 2016 took place in Hamburg from 27-29 September 2016 and was one of the largest and most impor...

Forest areas are of increasing interest for the wind energy industry. However, they induce complex flows with strong shear and high turbulence levels. Stably stratified atmospheric conditions, typical during nighttime and especially in winter, add to the challenge of accurately estimating wind resources. Such conditions typically imply strong wind...

In order to reduce the aerodynamic load fluctuations on wind turbine blades by innovative control solutions, strategies of active circulation control acting at the blade airfoil trailing edge are studied, allowing lift increase and decrease. This study presents a comparison of results obtained by performing surface plasma and continuous fluidic jet...

This experimental study focuses on the implementation via plasma actuators of a circulation control strategy on a wind turbine aerofoil with a rounded trailing-edge with the objective of reducing the aerodynamic load fluctuations on blades. Three sets of multi-DBD (Dielectric Barrier Discharge) actuators with different positions around the trailing...

Accumulation of gas inside a valley exposed to crosswind is experimented in this paper to extrapolate it to a case of a forest fire approaching a thalweg. Experimentations were done inside a wind tunnel using a 1/400 forest model configured as a valley with two different internal angles. The forest was modelled by mesh cylinders so that a parallel...

In the wind-energy sector, wind-power forecasting, turbine siting, and turbine-design selection are all highly dependent on a precise evaluation of atmospheric wind conditions. On-site measurements provide reliable data; however, in complex terrain and at the scale of a wind farm, local measurements may be insufficient for a detailed site descripti...

During a forest fire, a possible scenario to explain sudden and dangerous eruptions is the ignition of volatile organic compounds (VOC) gas pockets. The latter could be created by the topography such as canyons or valleys but the wind-induced shear layer over a flat forest can also be responsible for concentrated gas pockets ejections. In the prese...

Pulsed jets vortex generators are used to control a flow separation along a 25 • ramp with sharp edge. The actua-tor optimization is done following the results of previous studies. Before to perform closed loop control, the present study deals with open loop control. In this case, the interactions of the actuation with the separated flow is observe...

The present study deals with the real-time estimation of the wind turbine wake meandering and the determination of the best indicators to measure in order to build a real-time wake meandering model. Results are obtained through experiments performed in an atmospheric boundary layer wind tunnel, where a specific set-up enables to measure simultaneou...

This work studies effects of large-scale turbulent structures on wake meandering using Large Eddy Simulations (LES) over an actuator disk. Other potential source of wake meandering such as the instablility mechanisms associated with tip vortices are not treated in this study. A crucial element of the efficient, pragmatic and successful simulations...

Coherent structures dominate the shear flow in and above the vegetation canopy, affecting the transport of passive scalars. Their detailed understanding is therefore of great interest for a number of environmental studies such as organic gas exchange, pollution dispersion, or forest fire propagation. In the present study, a forest embedded in an at...

The present work proposes an experimental methodology to characterize the unsteady properties of a wind turbine wake, called meandering, and particularly its ability to follow the large-scale motions induced by large turbulent eddies contained in the approach flow. The measurements were made in an atmospheric boundary layer wind tunnel. The wind tu...

A model wind turbine has been designed at the University of Hamburg within the scope of the FP7 fundend project WAUDIT. The purpose of the experiment described in this paper is to characterize the performances of two rotors by means of measuring the thrust coefficient Ct. Ct is a similarity parameter for the wake and is thought to be the most effec...

Wind turbine wakes are known to be affected by the large atmospheric turbulent scales, which can cause trajectory variations within a wide frequency band. This phenomenon, called meandering, is suspected to be a cause of premature wear on turbines located inside wind farms. This work proposes a method to generate and apply synthetic turbulent veloc...

Turbulent boundary layer separation induced by a salient ramp and a smooth-edge one are characterized. Upstream from the separation point, the momentum thickness Reynolds number Reθ≈3500Reθ≈3500. Pressure distribution and gradient pressure distribution are analyzed on the overall model. Upstream from the ramp, boundary layer is characterized using...

A series of numerical simulations of the flow over a forest stand have been conducted using two different turbulence closure models along with various levels of canopy morphology data. Simulations have been validated against Stereoscopic Particle Image Velocimetry measurements from a wind tunnel study using one hundred architectural model trees, th...

The turbulent dispersion process responsible of the VOCs transport within and above the canopy is still under study. This issue is of great interest since VOCs contribute to the global chemical reactions encountered into the troposphere. At the forest scale, VOCs are expected to travel within and above the forest, interacting with each other or wit...

Experimental results on the wake properties of a non-rotating simplified wind turbine model, based on the actuator disc concept, and a rotating model, a three-blade wind turbine, are presented. Tests were performed in two different test sections, one providing a nominally decaying isotropic turbulent inflow (turbulence intensity of 4% at rotor disc...

This study presents the results of an experimental analysis of the unsteady features of the flow around the rear part of an Ahmed body with rear slant angle of 25°. This analysis focuses on the 3D separated and reattaching zone that develops on the rear slanted surface and provides new information, improving the understanding of the flow unsteadine...

Wake modelling plays a central role in wind farm planning through the evaluation of losses, the prediction of the energy yield, and the estimation of turbine loads. These models must be reasonably accurate - to minimise financial risk - and yet economical so that many configurations can be tested within reasonable time. While many such models have...

Wind turbine long term power production prediction and maintenance planning has shown to be inaccurate. One reason is that unsteady wind turbine wake interaction in wind turbine fields is not taken into account in classical models used by the industry. The far wake of a wind turbine located in an atmospheric boundary layer flow is characterized by...

This work considers separated flow past ground vehicles. It consists in analyzing the effect of canceling the separation on the rear slant of an Ahmed body (inclined at 25°) on the different structures developing in the wake. In order to better understand the flow features when canceling separation by means of flow control for drag reduction, two m...

Experimental results on the unsteady behaviour of the wake of a modelled wind turbine in an atmospheric boundary layer (ABL) wind tunnel are presented. Tests were performed by modelling in the wind tunnel an ABL above a neutral moderately rough terrain at a geometric scale of 1:400, and a wind turbine with the help of the actuator disk concept. In...

The present paper aims to summarise the activities from the Laboratory PRISME of the University of Orléans in the context of wind resource assessment with the '3%-vision' suggested by the European Wind Energy Technology Platform, and particularly of the wind turbine wake properties. Based on experimental investigations in an atmospheric boundary la...

In order to determine the physics driving the wind turbine wake meandering process [4], a previous study has been performed in an atmospheric boundary layer wind tunnel focusing on the unsteady behaviour of a modelled wind turbine wake (i.e. physical modelling based on the actuator disc concept). It was proven that the presence of turbulent scales...

In order to study the wind turbine wake and its eventual interactions with neighbouring wind turbines, several numerical and physical modelling approaches are used. Some model the wind turbine with the simplest model, that is the actuator disc concept, adding a drag source (i.e. pressure loss) within the surface swept by the blades (numerical [2],...

The present paper presents a study of the wake meandering phenomenon with the help of physical modelling in atmospheric boundary layer (ABL) wind tunnel. The wind turbine is modelled at a geometric scale of 1:400 with a static porous disk (actuator disk concept). The main objective of the present work was to supply quantitative information on the m...

In complex terrains, the assessment of the local wind resource is a main research area. In very sloppy terrain, classical linear models fail in the prediction of the wind and numerical models are under development. In this context, physical modelling in wind tunnel is a possible complementary tool. Indeed, wind tunnel testing is able to provide acc...

This paper proposes to compare turbulence length scales measured with three different experimental systems commonly used in aerodynamic measurements, namely hot wire anemometer, Laser Doppler Velocimetry and Particle Image Velocimetry, using turn-key systems from Dantec and TSI, and for three different turbulent flows: a homogeneous and isotropic t...

A model of a generic vehicle shape, the Ahmed body with a 25° slant, is equipped with an array of blowing steady microjets 6mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing or suppre...

This paper presents the results of an experimental investigation of the separated flow over the 25 deg. inclined rear slanted surface of an Ahmed body. Experiments performed using hot wire anemometry and PIV concentrate on the symmetry plane of the geometry. Results show an average separated flow as well as a low Strouhal number spectral activity....

This paper presents the experimental results and analytical arguments concerning simplified geometries of the rear window and windscreen of automotive vehicles in order to contribute to a better understanding of the swirling structure formation and vortex bursting processes. Static pressure distributions and skin friction line visualizations on bot...

A model of a generic vehicle shape, the Ahmed body with a slant angle of 25°, is equipped with an array of blowing steady microjets 6mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing...

This study presents results of an experimental analysis of the unsteady features of the flow around the rear part of an Ahmed body with a rear slant angle of 25°. This analysis focuses on the half elliptic separation bubble that developps on the rear slanted surface and brings new information, improving the understanding of the flow unsteadiness. F...

This study is about the meandering phenomenon of a wind turbine wake. The atmospheric boundary layer is reproduced in a wind tunnel as well as wind turbines using porous discs. Hot wire anemometry is used to carry out time investigations through the study of space-time correlations. Particle Image Velocimetry is also used to observe the spatial dev...

The purpose of the present work is to study the various specific time scales of the turbulent separating flow around a square cylinder, in order to determine the Reynolds number effect on the separating shear layer, where occurs a transition to turbulence. Unsteady analysis based on large eddy simulation (LES) at intermediate Reynolds numbers and l...

This paper combines a wind tunnel and a numerical study about the wind turbines wakes. Results in homogeneous flows are presented before comparisons in a moderately rough atmospheric boundary layer (z0 = 0.06m, α = 0.17, turbulence intensity at hub height = 14%). Wind turbines were modelled in a wind tunnel as porous discs made of metallic mesh at...

Fluctuation of the separation point on an airfoil under high turbulence level is investigated using pressure measurements and flow visualisations. The characteristics of the unsteady loads induced by Karman vortex shedding are studied. This is related with a local approach based on the study of the oscillation zone. A method based on the pressure s...

The impact of biogenic trace gases on tropospheric chemistry, air quality, and the formation of secondary products affecting our climate on a regional and global scale are far from being understood. A considerable lack of knowledge exists concerning a typical forest stand as a net source of reactive trace compounds into the troposphere. The concept...

A new concept to model a finite forest area in a boundary layer wind tunnel is proposed. A specific arrangement of rings made from metallic mesh is used in order to reproduce the effect of trees on the atmospheric boundary layer. The comparison between field data and wind tunnel data of wind profiles through the canopy is satisfying and that justif...

Two complementary methods, field experiments and physical modelling in a wind tunnel, have been used to investigate the dispersion of tracer-gas released from the ventilation system of a pig barn, under near-neutral stability conditions. In both cases, concentration fluctuations were measured and the deduced statistical results were compared. The c...

This study takes part to the project "Emission and CHemical transformation of biogenic volatile Organic compounds: investigations in and above a mixed forest stand" (ECHO) funded by the German atmospheric research program AFO 2000. The contribution of Hamburg University is a better understanding of the transport of biogenic emissions in the atmosph...

This study takes part to the project ``Emission and CHemical transformation of biogenic volatile Organic compounds: investigations in and above a mixed forest stand'' (ECHO) funded by the German atmospheric research program AFO 2000. The contribution of Hamburg University is a better understanding of the transport of biogenic emissions in the atmos...

In order to complement a previous collaborative testing of eddy structure identification methods in free turbulent shear flows, a study about the influence of the transverse location of these large-scale vortical structures on their signatures for the same referenced data base is carried out. Using vorticity-based conditional sampling, events which...

INTRODUCTION The increasing urbanisation process and requests for quality of life from residents force the competent authorities to take care of inconveniences caused by neighbouring odour sources. These sources consist of gas released from industrial or agricultural activities. The smell of these gases may be a nuisance to inhabited areas. Odour d...

The effect of the source location and the direction of the propagation on the laminar-turbulent transition on swept-wing three-dimensional boundary layers are investigated experimentally. Also the crossflow case is handled in detail. The source for the acoustic excitation is placed in four different locations: in front of the wing, on top of the te...

The effect of sound on laminar-turbulent transition process is studied for 3D boundary layers governed by streamwise or crossflow instabilities. We quantify the upstream shift of the transition location versus frequency range of acoustic excitation and versus sound level in both cases. Then, the comparison between linear stability theory results an...

Les écoulements turbulents décollés, présents dans les applications industrielles, ont des comportements fortement instationnaires caractérisés par la présence de structures tourbillonnaires cohérentes dans la couche cisaillée incurvée créée par le décollement. Par la présence de la recirculation et de la zone de recollement, les structures cohéren...

The coherent structures in a turbulent flow behind a backward-facing step are analysed experimentally by the vorticity-based conditional method, and numerically by the semi-deterministic modelling. The conditional method is applied to hot wires rake measurements in a sub-sonic wind tunnel. The semi-deterministic modelling is based on a simplified a...

The coherent structures in a turbulent flow behind a backward-facing step are analysed experimentally by the vorticity-based conditional method, and numerically by the semi-deterministic modelling. The conditional method is applied to hot wires rake measurements in a sub-sonic wind tunnel. The semi-deterministic modelling is based on a simplifed ap...

The study of unsteady phenomena in separated flows is of current interest owing to existence of strong instabilities developing large scale vortical structures in the separated zone (aero-acoustic strain in materials, perturbation in combustion chambers). The physical nature of these structures is not well known yet and, up to now, although some nu...

This contribution is about wind turbines modelling in a wind tunnel, taking into account the atmospheric boundary layer. Wind turbines are modelled using the concept of porous disc which can replicate the wind velocity deficit and the shear- produced turbulence in the flow going through the turbine. It is especially focussed on the influence of the...

This paper presents the modifications that have been performed in the Lucien Malavard wind tunnel to enable to physical modelling of atmospheric boundary layers. The first modelled ABL is characteristic of a rough-type terrain. Its properties are shown.

L'objet de l'étude présente est de déterminer et d'analyser les différentes échelles de temps caractéristiques de l'écoulement turbulent décollé au dessus d'un cylindre à section carrée, et d'en étudier la dépendance au nombre de Reynolds. Le nombre de Reynolds de l'écoulement varie dans la gamme Re=50 à Re=200,000. La mise en oeuvre d'outils de Si...