Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D30: Wind Turbines: Atmospheric Forcing and Turbine Models |
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Chair: Tina Chow, University of California, Berkeley Room: 2016 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D30.00001: Scanning of wind turbine upwind conditions: numerical algorithm and first applications Marc Calaf, Gerard Cortina, Varun Sharma, Marc B. Parlange Wind turbines still obtain in-situ meteorological information by means of traditional wind vane and cup anemometers installed at the turbine's nacelle, right behind the blades. This has two important drawbacks: 1-turbine misalignment with the mean wind direction is common and energy losses are experienced; 2-the near-blade monitoring does not provide any time to readjust the profile of the wind turbine to incoming turbulence gusts. A solution is to install wind Lidar devices on the turbine's nacelle. This technique is currently under development as an alternative to traditional in-situ wind anemometry because it can measure the wind vector at substantial distances upwind. However, at what upwind distance should they interrogate the atmosphere? A new flexible wind turbine algorithm for large eddy simulations of wind farms that allows answering this question, will be presented. The new wind turbine algorithm timely corrects the turbines' yaw misalignment with the changing wind. The upwind scanning flexibility of the algorithm also allows to track the wind vector and turbulent kinetic energy as they approach the wind turbine's rotor blades. Results will illustrate the spatiotemporal evolution of the wind vector and the turbulent kinetic energy as the incoming flow approaches the wind turbine under different atmospheric stability conditions. Results will also show that the available atmospheric wind power is larger during daytime periods at the cost of an increased variance. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D30.00002: Influence of atmospheric stability on model wind turbine wake interface Amelia Taylor, Virgilio Gomez, Santiago Novoa, Suhas Pol, Carsten Westergaard, Luciano Castillo Differences in wind turbine wake deficit recovery for various atmospheric stability conditions (stratification) have been attributed to turbulence intensity levels at different conditions. It is shown that buoyancy differences at the wind turbine wake interface should be considered in addition to varying turbulence intensity to describe the net momentum transport across the wake interface. Mixing, induced by tip and hub vortices or wake swirl, induces these buoyancy differences. The above hypothesis was tested using field measurements of the wake interface for a 1.17 m model turbine installed at 6.25 m hub height. Atmospheric conditions were characterized using a 10 m meteorological tower upstream of the turbine, while a vertical rake of sonic anemometers clustered around the hub height on a downstream tower measured the wake. Data was collected over the course of seven months, during varying stability conditions, and with five different turbine configurations -- including a single turbine at three different positions, two turbines in a column, and three turbines in a column. Presented are results showing the behavior of the wake (particularly the wake interface), for unstable, stable, and neutral conditions. We observed that the swirl in the wake causes mixing of the inflow, leading to a constant density profile in the far wake that causes density jumps at the wake interfaces for stratified inflow. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D30.00003: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D30.00004: Turbulence structures in wind turbine wake: Effects of atmospheric stratification Kiran Bhaganagar Turbulence structure in the wake behind full-scale horizontal-axis WT under the influence of realistic atmospheric turbulent flow conditions has been investigated using actuator-line-model based large-eddy-simulations. Wind turbine simulations have revealed that, in addition to wind shear and ABL turbulence, height-varying wind angle and low-level jets are ABL metrics that influence the structure of turbine wake. Turbulent mixing layer forms downstream of the WT, the strength and size of which decreases with increasing stability. Height dependent wind angle and turbulence are the ABL metrics influencing the lateral wake expansion. Further, ABL metrics strongly impact the evolution of tip and root vortices formed behind the rotor. Two factors play an important role in wake meandering: tip vortex merging due to the mutual inductance form of instability and the corresponding instability of the turbulent mixing layer. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D30.00005: Influence of realistic atmospheric forcings on wind turbine wake interactions Mithu Debnath, Kiran Bhaganagar Atmospheric boundary layer structure is dictated by the stratification of the atmosphere; hence stratifications effects are critical in accurate representation of wind turbine wake physics. Large eddy simulation (LES) has been used to resolve atmospheric boundary layer turbulence and the wind turbine (WT) wake turbulence structures. The effect of atmospheric stratification on the evolution of tip and root vortices has been analyzed. For the first time, mutual induction mode of vortex instability leading to vortex merging in the wind turbine wake has been demonstrated under realistic ABL conditions. Vortex merging leads to enhanced Reynolds stresses and increased mixing. Finally, the effect of the turbulent mixing due to the shear layer on power production is analyzed [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D30.00006: Large eddy simulation of unsteady wind farm behavior using advanced actuator disk models Maud Moens, Matthieu Duponcheel, Gregoire Winckelmans, Philippe Chatelain The present project aims at improving the level of fidelity of unsteady wind farm scale simulations through an effort on the representation and the modeling of the rotors. The chosen tool for the simulations is a Fourth Order Finite Difference code, developed at Universite catholique de Louvain; this solver implements Large Eddy Simulation (LES) approaches. The wind turbines are modeled as advanced actuator disks : these disks are coupled with the Blade Element Momentum method (BEM method) and also take into account the turbine dynamics and controller. A special effort is made here to reproduce the specific wake behaviors. Wake decay and expansion are indeed initially governed by vortex instabilities. This is an information that cannot be obtained from the BEM calculations. We thus aim at achieving this by matching the large scales of the actuator disk flow to high fidelity wake simulations produced using a Vortex Particle-Mesh method. It is obtained by adding a controlled excitation at the disk. We apply this tool to the investigation of atmospheric turbulence effects on the power production and on the wake behavior at a wind farm level. A turbulent velocity field is then used as inflow boundary condition for the simulations. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D30.00007: Implementation of wind turbine parameterizations in a mesoscale-LES nested model framework Fotini Chow, Nikola Marjanovic, Jeffrey Mirocha Wind turbine performance depends on weather conditions, local topography, and wind turbine spacing, among other factors. Atmospheric simulations can be used to predict wind energy production at increasingly higher resolutions. Turbine models placed within such simulations can be used to investigate turbine operation and performance. This work describes the implementation of generalized actuator disk (GAD) and line (GAL) models into the Weather Research and Forecasting (WRF) mesoscale atmospheric model. WRF can be used in a grid nested configuration starting from the mesoscale ($\sim$10 km resolution) and ending with fine scale resolutions ($\sim$1-10 m) suitable for large-eddy simulations (LES). At LES scales it becomes possible to resolve both the thrust and torque forces generated on turbines and imparted to the atmosphere using GAD and GAL models. Both models include real-time yaw and pitch control to respond to changing flow conditions. Here, the GAD and GAL are tested for idealized and real model configurations and compared to data from a wind farm. Comparisons are also made that help determine the importance of turbine blade tilt away from the tower and the inclusion of tower and turbine hub drag effects. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D30.00008: A study of two subgrid-scale models and their effects on wake breakdown behind a wind turbine in uniform inflow Luis Martinez, Charles Meneveau Large Eddy Simulations (LES) of the flow past a single wind turbine with uniform inflow have been performed. A goal of the simulations is to compare two turbulence subgrid-scale models and their effects in predicting the initial breakdown, transition and evolution of the wake behind the turbine. Prior works have often observed negligible sensitivities to subgrid-scale models. The flow is modeled using an in-house LES with pseudo-spectral discretization in horizontal planes and centered finite differencing in the vertical direction. Turbines are represented using the actuator line model. We compare the standard constant-coefficient Smagorinsky subgrid-scale model with the Lagrangian Scale Dependent Dynamic model (LSDM). The LSDM model predicts faster transition to turbulence in the wake, whereas the standard Smagorinsky model predicts significantly delayed transition. The specified Smagorinsky coefficient is larger than the dynamic one on average, increasing diffusion thus delaying transition. A second goal is to compare the resulting near-blade properties such as local aerodynamic forces from the LES with Blade Element Momentum Theory. Results will also be compared with those of the SOWFA package, the wind energy CFD framework from NREL. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D30.00009: Large Eddy Simulation of wind turbines using the actuator line model and immersed boundary method Christian Santoni, Kenneth Carrasquillo-Sol\'Is, Stefano Leonardi Despite the growth of the energy extracted from wind turbines, the flow physics is still not fully understood even under ideal operational conditions. Large Eddy Simulations of the turbulent flow past a wind turbine in a channel have been performed. The numerical setup reproduces the experiment performed in a wind tunnel at the Norwegian University of Science and Technology (NUST). The code is based on a finite difference scheme with a fractional step and Runge-Kutta, which couples the actuator line model (ALM) and the Immersed Boundary Method (IBM). Two simulations were performed, one neglecting the tower and nacelle resulting in the rotating blades only, the other modeling both the rotating blades as well as the tower and nacelle with IBM. Results relative to the simulation with tower and nacelle have a very good agreement with experiments. Profiles of turbulent kinetic energy shows that the effect of the tower and nacelle is not confined to the hub region but extend to the entire rotor. In addition we placed the wind turbine over an undulated topography to understand how it affects the performances and wake of a wind turbine. Comparison with the results obtained for the smooth wall show an interaction between the rough wall and the wake. [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D30.00010: Comparison of Differences Between Model Wind Turbine Array and Porous Disk Array Boundary Layer Measurements Vasant Vuppuluri, Elizabeth Camp, Ra\'{u}l Bayo\'{a}n Cal Wind turbines are often represented in computational studies as actuator disks, also known as porous disks. A wind tunnel study is performed on a $4 \times 3$ model wind turbine array and equivalent porous disk array using Stereo Particle Image Velocimetry (SPIV) in order to compare the resulting wakes. Measurements are taken both upstream and downstream of the center turbine in the fourth row with SPIV planes both parallel and perpendicular to the rotor disk. The resulting flow fields are used to quantify the cumulative effects of the differences between the rotor and porous disk wakes. [Preview Abstract] |
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