Jens Nørkær Sørensen

Wind turbine wake aerodynamics

Abstract The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions, thereby excluding wind shear, wind speed and rotor setting changes and yawed conditions. The emphasis is put on measurements in controlled conditions. For the far wake, the survey focusses on both single turbines and wind farm effects, and the experimental and numerical work are reviewed; the main interest is to study how the far wake decays downstream, in order to estimate the effect produced in downstream turbines. The article is further restricted to horizontal axis wind turbines and excludes all other types of turbines.

In Vivo Visualization of Amyloid Deposits in the Heart with 11C-PIB and PET

Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-11C]2-(4′-methylamino-phenyl)-6-hydroxybenzothiazole (11C-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of 11C-PIB PET in systemic amyloidosis affecting the heart. Methods: Patients (n = 10) diagnosed with systemic amyloidosis—including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type—and healthy volunteers (n = 5) were investigated with PET/CT using 11C-PIB to study cardiac amyloid deposits and with 11C-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention. Results: Myocardial 11C-PIB uptake was visually evident in all patients 15–25 min after injection and was not seen in any volunteer. A significant difference in 11C-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with 11C-PIB. No correlation between 11C-PIB retention index and myocardial blood flow as measured with 11C-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient. Conclusion: 11C-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.

Analysis of wake states by a full-field actuator disc model

Various wake status have been analysed by a numerical method that combines the actuator disc principle with the Navier–Stokes equations. Results are compared with one-dimensional momentum theory and experiments. The computations are in excellent agreement with one-dimensional momentum theory for rotors working in the windmill brake state as well as in the propeller and hover states. The computations demonstrate that the turbulent wake and vortex ring states are unstable regimes for a rotor with constant loading and that these states, after a complicated transient phase, settle to a steady state. Copyright

Unsteady actuator disc model for horizontal axis wind turbines

A non-linear and unsteady actuator disc model for horizontal axis wind turbines is presented. The model consists of a finite-difference solution of the axisymmetric Euler equations in a vorticity-streamfunction formulation. We here show some results, steady as well as unsteady, for an actuator disc with a prescribed elliptic load distribution and for the 20 m radius Nibe turbine. Generally, the results are found to be in good agreement with measurements.

Actuator Line Simulation of Wake of Wind Turbine Operating in Turbulent Inflow

The wake of a wind turbine operating in an atmospheric turbulent inflow without mean shear is simulated using a numerical method, which combines large eddy simulations with an actuator line technique. A turbulent inflow with the same spectral characteristics as the atmosphere is produced by introducing time varying body forces in a plane upstream the rotor. The results of the simulation are compared to those obtained on a wind turbine in uniform inflow at the same mean wind speed and from this comparison a number of features of the influence of inflow turbulence on wake dynamics are deduced. Furthermore, the results are used to verify the validity of some of the basic assumptions employed in simpler engineering models and to study their bounds of application. The large amount of data from the wake simulation can easily be used in simple engineering methods to model a wind turbine operating in the wake of an upstream turbine

Stability of helical tip vortices in a rotor far wake

As a means of analysing the stability of the wake behind a multi-bladed rotor the stability of a multiplicity of helical vortices embedded in an assigned flow field is addressed. In the model the tip vortices in the far wake are approximated by infinitely long helical vortices with constant pitch and radius. The work is a further development of a model developed in Okulov ( J. Fluid Mech. , vol. 521, p. 319) in which the linear stability of N equally azimuthally spaced helical vortices was considered. In the present work the analysis is extended to include an assigned vorticity field due to root vortices and the hub of the rotor. Thus the tip vortices are assumed to be embedded in an axisymmetric helical vortex field formed from the circulation of the inner part of the rotor blades and the hub. As examples of inner vortex fields we consider three generic axial columnar helical vortices, corresponding to Rankine, Gaussian and Scully vortices, at radial extents ranging from the core radius of a tip vortex to several rotor radii. The analysis shows that the stability of tip vortices largely depends on the radial extent of the hub vorticity as well as on the type of vorticity distribution. As part of the analysis it is shown that a model in which the vortex system is replaced by N tip vortices of strength Γ and a root vortex of strength − N /Γ is unconditionally unstable.

First-in-Human Molecular Imaging of HER2 Expression in Breast Cancer Metastases Using the 111In-ABY-025 Affibody Molecule

The expression status of human epidermal growth factor receptor type 2 (HER2) predicts the response of HER2-targeted therapy in breast cancer. ABY-025 is a small reengineered Affibody molecule targeting a unique epitope of the HER2 receptor, not occupied by current therapeutic agents. This study evaluated the distribution, safety, dosimetry, and efficacy of 111In-ABY-025 for determining the HER2 status in metastatic breast cancer. Methods: Seven patients with metastatic breast cancer and HER2-positive (n = 5) or -negative (n = 2) primary tumors received an intravenous injection of approximately 100 μg (∼140 MBq) of 111In-ABY-025. Planar γ-camera imaging was performed after 30 min, followed by SPECT/CT after 4, 24, and 48 h. Blood levels of radioactivity, antibodies, shed serum HER2, and toxicity markers were evaluated. Lesional HER2 status was verified by biopsies. The metastases were located by 18F-FDG PET/CT 5 d before 111In-ABY-025 imaging. Results: Injection of 111In-ABY-025 yielded a mean effective dose of 0.15 mSv/MBq and was safe, well tolerated, and without drug-related adverse events. Fast blood clearance allowed high-contrast HER2 images within 4–24 h. No anti–ABY-025 antibodies were observed. When metastatic uptake at 24 h was normalized to uptake at 4 h, the ratio increased in HER2-positive metastases and decreased in negative ones (P < 0.05), with no overlap and confirmation by biopsies. In 1 patient, with HER2-positive primary tumor, 111In-ABY-025 imaging correctly suggested a HER2-negative status of the metastases. The highest normal-tissue uptake was in the kidneys, followed by the liver and spleen. Conclusion: 111In-ABY-025 appears safe for use in humans and is a promising noninvasive tool for discriminating HER2 status in metastatic breast cancer, regardless of ongoing HER2-targeted antibody treatment.

Numerical Computations of Wind Turbine Wakes

Numerical simulations of the Navier-Stokes equations are performed to achieve a better understanding of the behaviour of wakes generated by wind turbines. The simulations are performed by combining ...

A model for unsteady rotor aerodynamics

Abstract An aerodynamic model for the simulation of unsteady flow past rotors of wind turbines is presented. The model consists of solving the unsteady, axisymmetric Euler or Navier-Stokes equations by a finite-difference method subject to volume forces determined from tabulated airfoil data. Results are compared to the blade-element momentum theory and experiments for the cases of a rotor with a prescribed constant normal load and steady as well as unsteady flows past the 2 MW Tjaereborg wind turbine. The model is found to be in better agreement with measurements than the momentum theory and in particular excellent agreement is obtained with dynamic in-flow phenomena from measured pitching transients.

Evaluation of Proper Orthogonal Decomposition--Based Decomposition Techniques Applied to Parameter-Dependent Nonturbulent Flows

The proper orthogonal decomposition (POD) method as a systematic technique to analyze parameter-dependent problems may be inappropriate as a practical tool for generating low-dimensional models. We propose a weighted POD (w-POD) as an alternative to give higher priority to low-energetic or important modes by simply weighting. A predefined POD (p-POD) is suggested, where modes are selected not only on the basis of energy but also on some a priori knowledge of the system. The techniques are tested on a flow problem undergoing steady or unsteady transition but may in general be applied to nonlinear systems of discretized PDEs closed by additional linear algebraic equations. Various residual functions to measure the quality of the reduced models are introduced. They provide lower limits of residual energy to ensure an adequate physical representation for a given modeling. It is shown that modes extracted locally may generally not contain information regarding the global dynamics, and the dynamics may not be correctly predicted over a longer range of model parameters. It is demonstrated that by weighting and predefining base vectors it is possible to improve the POD techniques capability to generate low-dimensional models.