Jens Sørensen

Jens Sørensen
Technical University of Denmark | DTU · Department of Wind Energy

Professor

About

290
Publications
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9,164
Citations

Publications

Publications (290)
Article
Full-text available
The actuator line method is a widely used technique to model wind turbines in computational fluid dynamics, as it significantly reduces the required computational expense in comparison to simulations using geometrically resolved blades. Actuator line coupled to an aeroelastic solver enables not only the study of detailed wake dynamics but also aero...
Article
The design of industrial wind turbine rotors is generally based on the blade-element/momentum (BEM) approach introduced by Glauert (1935). Essentially, the theory consists of combining a blade-element approach with axial momentum theory, and then introducing a tip correction to account for the finite number of rotor blades. This is required, as the...
Article
Full-text available
Wind farm Annual Energy Production (AEP) calculations are required to design energy efficient wind farm layouts. We investigate methods that can reduce the computational effort of AEP calculations using Reynolds-averaged Navier-Stokes simulations of an idealized atmospheric wind farm setup. In addition, we introduce a generalized wind turbine model...
Article
About a century ago, two different rotor models were proposed by Joukowsky (1912–1918) and Betz (1919). Both models were based on assumptions regarding the vortex structures of the wake and its induction on the rotor plane. However, due to complications of formulating the wake behavior into actual guidelines for the aerodynamic design of the rotor...
Article
Full-text available
Experiments were carried out in a water-filled elongated cup of a “kitchen scale,” where motion was created by a rotating disk with various micro- and nano-roughness in the top of the cup. The obtained results have shown that for some patterns of nanostructures, there is a noticeable growth of a vortex, generated by the disk, while other roughnesse...
Article
Full-text available
A numerical framework for determining the available wind power and associated costs related to the development of large-scale offshore wind farms is presented. The idea is to develop a fast and robust minimal prediction model, which with a limited number of easy accessible input variables can determine the annual energy output and associated costs...
Chapter
The aerodynamics of wind turbines concerns modeling and prediction of the aerodynamic forces on wind turbines. Wind turbine aerodynamics is the most central discipline for the design and construction of wind turbine blades. Here we give a status of the most important research areas within the aerodynamics of wind turbines, rotor wakes and wind farm...
Article
Full-text available
A total of 18 high-fidelity simulations of large wind farms have been performed by three different institutions using various inflow conditions and simulation setups. The setups differ in how the atmospheric turbulence, wind shear and wind turbine rotors are modeled, encompassing a wide range of commonly used modeling methods within the large eddy...
Article
Full-text available
Laminar-turbulent transition behavior of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high-frequency microphones mounted on a blade section are analyzed t...
Article
Full-text available
A new analytical model for representing body forces in numerical actuator disc models of wind turbines is compared to results from a BEM model. The model assumes the rotor disc being subject to a constant circulation, modified for tip and root effects. The advantage of the model is that it does not depend on any detailed knowledge concerning the ac...
Article
Full-text available
Abstract Our mathematical model of epithelial transport (Larsen et al. Acta Physiol. 195:171–186, 2009) is extended by equations for currents and conductance of apical SGLT2. With independent variables of the physiological parameter space, the model reproduces intracellular solute concentrations, ion and water fluxes, and electrophysiology of proxi...
Chapter
The chapter 'Stationary and Nonstationary Ion and Water Flux Interactions in Kidney Proximal Tubule: Mathematical Analysis of Isosmotic Transport by a Minimalistic Model' has now been made available open access under a CC BY 4.0 license.
Article
Utility-scale projects for hydrokinetic energy extraction from rivers, tidal or ocean currents could include tens to hundreds of turbines in densely‐packed hydro farms. The aim of the present paper is to obtain a better understanding of the power production and wakes generated by several devices modeling a straight array of horizontal-axis water tu...
Article
Full-text available
The motion of a helical vortex and the movement of the fluid particles along its axis are analyzed. The same form of the helical axis of the vortex and the trajectory of the particles sometimes leads to a false assumption of equality of these two different motions. The correct identification of both motions, however, is essential when considering t...
Article
Unsuitable wind farm layout design influences wind energy conversion efficiency as well as wind farm noise radiation. In the past, more attentions were paid on high energy efficiency wind farm design, but little progress was achieved on noise constrained wind farm optimization. The present work aims at developing a numerical optimization framework...
Preprint
Full-text available
Abstract. Laminar-turbulent transition behaviour of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high frequency microphones mounted on a blade section are...
Preprint
Full-text available
Abstract. A total of 18 high fidelity simulations of large wind farms have been performed by three different institutions using various inflow conditions and simulation setups. The setups differ in how the atmospheric turbulence, wind shear and wind turbine rotors are modelled, encompassing a wide range of commonly used modelling methods within the...
Article
Full-text available
The actuator line method (ALM) is today widely used to represent wind turbine loadings in computational fluid dynamics (CFD). As opposed to resolving the whole blade geometry, the methodology does not require geometry‐fitted meshes, which makes it fast to apply. In ALM, tabulated airfoil data are used to determine the local blade loadings, which su...
Article
The self-induced motion of a helical vortex - Volume 883 - Valery L. Okulov, Jens N. Sørensen
Article
Layout optimization of wind farms constitutes an important and challenging task in complex terrain. This is especially due to the complex interactions of the boundary layer flows in complex terrain and wind turbine wakes, which renders wake modelling in complex terrain difficult. This study tackles this challenge with a new engineering wake model,...
Article
Full-text available
In the present work, various data processing methods for laminar to turbulent transition detection on airfoils are assessed based on experimental data. For this purpose, NACA 63‐418 airfoil profile with surface microphones flush mounted both on the suction and the pressure side is used in the wind tunnel experiments. Reynolds numbers are changed in...
Article
An analytical model for representing body forces in numerical actuator disc models of wind turbines is developed and validated. The model is based on the assumption that the rotor disc is subject to a constant circulation modified for tip and root effects. The model comprises expressions for both the axial and the azimuthal force distributions, and...
Chapter
Full-text available
In the atmospheric boundary layer, the Coriolis force associated with the Earth’s rotation induces a spanwise wind shear in addition to the wall-normal one leading to a continuous change in wind direction with height. The spanwise wind shear in directionally sheared inflow has a significant impact on the formation and development of wind-turbine wa...
Conference Paper
Full-text available
The aim of the present paper is to obtain a better understanding of wakes generated by 2, 3 and 4 elements (disks and/or rotors) modeling an array of wind turbines in a wind farm. We here extend the results from our previous experimental model studies on the correlation between the behavior of the wake behind dual configurations of passive disks an...
Chapter
Full-text available
Our mathematical model of epithelial transport (Larsen et al. Acta Physiol. 195:171–186, 2009) is extended by equations for currents and conductance of apical SGLT2. With independent variables of the physiological parameter space, the model reproduces intracellular solute concentrations, ion and water fluxes, and electrophysiology of proximal convo...
Article
Full-text available
The present work investigates local flow structures and the downstream evolution of the core of helical tip vortices generated by a three-bladed rotor. Earlier experimental studies have shown that the core of a helical tip vortex exhibits a local helical symmetry with a simple relation between the axial and azimuthal velocities. In the present stud...
Article
Full-text available
The propagation of aerodynamic noise from multi-wind turbines is studied. An efficient hybrid method is developed to jointly predict the aerodynamic and aeroacoustics performances of wind turbines, such as blade loading, rotor power, rotor aerodynamic noise sources, and propagation of noise. This numerical method combined the simulations of wind tu...
Conference Paper
Full-text available
One of the main uncertainties in airfoil and rotor design is the determination of the position of transition on the blade as this can have considerable influence on the aerodynamic loads and in particular rotor power. Even for simulations on a rotor in uniform, steady inflow the determination of the position of transition is challenging. The atmosp...
Conference Paper
Full-text available
The present work examines the local structure and downstream evolution of both longitudinal vortexes behind the vortex generators and the helical tip vortices generated by the rotating 3-bladed rotor. Both wakes flow with the strong longitudinal or helical vortices have been studied by stereo PIV measurements in a wind tunnel or a water flume accor...
Conference Paper
Full-text available
The rain impact and ice accretion on different aerodynamic constructions represent a large problem to their safety and operation. Most current de-icing systems include either physical or chemical removal of ice, which is resource- and energy-intensive as well as environmentally polluting. A more desirable approach to prevent initial ice formation f...
Conference Paper
Full-text available
In the recent paper on the motion of helical vortices [VF2018] in J. Fluid Mech. 836, R1, doi:10.1017/jfm.2017.845 the model with both tangential and binormal velocities including in the helical motion was used in contrast to the classical approach when only the binormal component included. A large difference between both solutions was found. We d...
Article
Full-text available
The present work assesses the potential of a massive exploitation of offshore wind power in the North Sea by combining a meteorological model with a cost model that includes a bathymetric analysis of the water depth of the North Sea. The overall objective is to assess if the wind power in the North Sea can deliver the total consumption of electrici...
Article
Full-text available
In this study, an analytical wake model for predicting the mean velocity field downstream of a wind turbine under veering incoming wind is systematically derived and validated. The new model, which is an extended version of the one introduced by Bastankhah and Porté-Agel, is based upon the application of mass conservation and momentum theorem and c...
Article
A prescribed velocity‐vorticity boundary layer model for the vorticity transport equation is proposed, which corrects the unphysical upward deflection of the wake seen in a simpler prescribed velocity shear approach. A Lagrangian implementation of the boundary layer model has been investigated using our in‐house vortex solver MIRAS. The MIRAS code...
Article
Full-text available
In the present study, a computational fluid dynamic (CFD)-based blade optimization algorithm is introduced for designing single or multiple wind turbine rotors. It is shown that the CFD methods provide more detailed aerodynamics features during the design process. Because high computational cost limits the conventional CFD applications in particula...
Article
Full-text available
Flow characteristics of an S826 airfoil at different Reynolds numbers, ranging from 40,000–400,000 (based on airfoil chord length) and angles of attack from −10–25 degrees are thoroughly investigated in a low-speed wind tunnel. The airfoil’s lift and drag polars are first measured, and with a focus on pitching the airfoil in upstroke and downstroke...
Article
Full-text available
The mutual fluid-structure interaction between wind turbine(s) and the highly turbulent flow deep inside a large wind farm is investigated in order to elucidate on how to implement and perform dynamic wind farm control. The study employs a fully coupled LES and aeroelastic framework, which provide time resolved flow and turbine response governed by...
Article
Full-text available
The surface imperfections and the inflow turbulence in real operational conditions can cause significant deviations from the predicted wind turbine aerodynamic performance and energy yield. In this study, particular emphasis was placed on the effect of these parameters on the laminar-turbulent transition on wind turbine blades. For this purpose, th...
Conference Paper
Full-text available
The present work shows the results of a series of experimental investigations of the wake development behind a model rotor subject to upstream disturbances created either by another rotor or by a disk. The experiments are carried out in a water flume in order to control the flow and to carry out visualizations and to perform optical diagnostics. Th...
Article
Large-eddy simulation (LES) of a wind turbine under uniform inflow is performed using an actuator line model (ALM). Predictions from four LES research codes from the wind energy community are compared. The implementation of the ALM in all codes is similar and quantities along the blades are shown to match closely for all codes. The value of the Sma...
Article
The present review paper provides a comprehensive overview of the research activities on wind turbine aeroacoustics at DTU over the last 20 years, as well as it gives the state-of-the-art of noise prediction models for wind turbines under complex inflow conditions. Various noise generation models developed at DTU are described and analyzed, includi...
Article
Full-text available
A novel algorithm is developed to calculate the nonlinear optimal boundary perturbations in three-dimensional incompressible flow. An optimal step length in the optimisation loop is calculated without any additional calls to the Navier-Stokes equations. The algorithm is applied to compute the optimal inflow eddies for the flow around a wind turbine...
Article
To enhance the performance of horizontal axis wind turbines, it is proposed to place a cylindrical disc in front of the rotor in order to lead the incoming flow from the inner part to the outer part of the rotor blades. This is expected to increase the power output, as the kinetic energy is mainly captured at the outer part of the blades, where the...
Article
A hybrid filament-mesh vortex method is proposed and validated to predict the aerodynamic performance of wind turbine rotors and to simulate the resulting wake. Its novelty consists of using a hybrid method to accurately simulate the wake downstream of the wind turbine while reducing the computational time used by the method. The proposed method us...
Article
Full-text available
The aim of the current investigation is the rotor vibrations generated by the disturbances caused the different types of incoming wake-like flows. Those wakes arriving at the tested rotor were created by two ways: a passive wake generator (immobile disk) and an upstream rotating rotor as an active wake generator. The influence of both wakes on the...
Conference Paper
Full-text available
The present paper takes a broad view on our previous experimental studies of flows behind different single and dual configurations from passive disks or active rotors to establish new aspects of the wake development [1-4]. The aim of the present examination is to obtain a better understanding of the wake formations and interactions between wind tur...
Article
Full-text available
Ten simulations of large wind farms have been performed using a fully coupled LES and aero-elastic framework to form a database of full turbine operational conditions in terms of both production and loads. The performance is examined in terms of averaged power production and thrust, as well as 10min equivalent flapwise bending, yaw, and tilt moment...
Article
Large eddy simulations (LES) of wind farms have the capability to provide valuable and detailed information about the dynamics of wind turbine wakes. For this reason, their use within the wind energy research community is on the rise, spurring the development of new models and methods. This review surveys the most common schemes available to model...
Article
Full-text available
A number of large wind farms are modelled using large eddy simulations to elucidate the entrainment process. A reference simulation without turbines and three farm simulations with different degrees of imposed atmospheric turbulence are presented. The entrainment process is assessed using proper orthogonal decomposition, which is employed to detect...
Article
In the present work, an in-house UnSteady Double Wake Model (USDWM) is developed for simulating general flow problems behind bodies. The model is presented and used to simulate flows past a circular cylinder at subcritical, supercritical, and transcritical flows. The flow model is a two-dimensional panel method which uses the unsteady double wake t...
Article
In the current experiments, two identical wind turbine models were placed in uniform flow conditions in a water flume. The initial flow in the flume was subject to a very low turbulence level, limiting the influence of external disturbances on the development of the inherent wake instability. Both rotors are three-bladed and designed using blade el...
Article
Aerodynamic and structural dynamic performance analysis of modern wind turbines are routinely estimated in the wind energy field using computational tools known as aeroelastic codes. Most aeroelastic codes use the blade element momentum (BEM) technique to model the rotor aerodynamics and a modal, multi-body or the finite-element approach to model t...
Article
Full-text available
Obstacles like forests, ridges and hills can strongly affect the velocity profile in front of a wind turbine rotor. The present work aims at quantifying the influence of nearby located obstacles on the performance and wake characteristics of a downstream located wind turbine. Here the influence of an obstacle in the form of a cylindrical disk was i...
Conference Paper
Full-text available
There is an increasing interest in studying the development of far wakes behind two or more interacting wind turbines in order to determine the influence of wake interaction in relation to the design of wind farms. The focus of this experimental study is to understand and describe the resulting wake features for two rotors subjected to different op...
Conference Paper
Full-text available
Despite the advances in computing resources in the recent years, the majority of large wind-turbine rotor design problems still rely on aero-elastic codes that use blade element momentum (BEM) approaches to model the rotor aerodynamics. The present work describes an approach to wind-turbine rotor design by incorporating a higher-fidelity free-wake...
Chapter
Wind turbine aerodynamics is a central discipline for modelling and prediction of the aerodynamic forces on a wind turbine. From the aerodynamic analysis the performance and loads on the rotor blades, as well as other structures exposed to the wind, are determined. An aerodynamic model is normally integrated with models for wind conditions and stru...
Article
Full-text available
Numerous large eddy simulations are performed of large wind farms using the actuator line method, which has been fully coupled to the aero-elastic code, Flex5. The higher order moments of the flow field inside large wind farms is examined in order to determine a representative reference velocity. The statistical moments appear to collapse and hence...