Evaluating techniques for redirecting turbine wakes using SOWFA

Theory Of Wing Sections Including A Summary Of Airfoil Data

A validation study using the NREL Phase VI wind turbine is presented. The aerodynamics simulations are performed using the finite element ALE‐VMS formulation augmented with weakly enforced essential boundary conditions. In all cases the rotor is assumed to be rigid and its rotation is prescribed. The rotor-only simulations are performed for a wide range of wind conditions and the computational results compare favorably with the experimental findings in all cases. The sliding-interface method is adopted for the simulation of the full wind turbine configuration. The full-wind-turbine simulations capture the blade‐tower interaction eect, and the results of these simulations are also in good agreement with the experimental data. Copyright c 2012 John Wiley & Sons, Ltd.

/pdf/finite-element-simulation-of-wind-turbine-aerodynamics-4juzex32s4.pdf

Finite element simulation of wind turbine aerodynamics: validation study using NREL Phase VI experiment

https://ris.utwente.nl/ws/files/30580604/1_s2.0_S0960148117308339_main.pdf

Comparison of wind farm large eddy simulations using actuator disk and actuator line models with wind tunnel experiments

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2014.0071

Simulation of wind turbine wakes using the actuator line technique

The major post-Cassini knowledge gap concerning Saturn’s icy moon Titan is in the composition of its diverse surface, and in particular how far its rich organics may have ascended up the ”ladder of life.” The NASA New Frontiers 4 solicitation sought mission concepts addressing Titan’s habitability and methane cycle. A team led by the Johns Hopkins University Applied Physics Laboratory (APL) proposed a revolutionary lander that uses rotors to land in Titan’s thick atmosphere and low gravity and can repeatedly transit to new sites, multiplying the mission’s science value from its capable instrument payload. Titan is an “ocean world” that is rich in both carbon and nitrogen.4,5 See Table 1 for data on Titan’s environment. FORMULATION OF THE DRAGONFLY CONCEPT The NASA community announcement in January 2016 identifying Titan as a possible target for the fourth New Frontiers mission opened new possibilities in Titan exploration (Box 1). Although the exploration of Titan’s seas had previously been considered, notably by the APL-led Titan Mare Explorer (TiME) Discovery concept,6,7 the timing mandated by the announcement of opportunity precluded such a mission. Specifically, with launch specified prior to the end of 2025, Titan arrival would be in the mid-2030s, during northern winter. This means the seas, near Titan’s north pole, are in darkness and direct-to-Earth (DTE) communication is impossible.8 Even with the higher budget threshold of New Frontiers 4 ($850 million plus launch and operations costs) compared with Discovery (~$450 million INTRODUCTION Saturn’s moon Titan is in many ways the most Earthlike body in the solar system.1–3 This strange world is larger than the planet Mercury and has a thick nitrogen atmosphere laden with organic smog, which partly hides its surface from view. Since cold Titan is far from the Sun, on Titan methane plays the active role that water plays on Earth, serving as a condensable greenhouse gas, forming clouds and rain, and pooling on the surface as lakes and seas. Titan’s carbon-rich surface is shaped not only by impact craters and by winds that sculpt drifts of aromatic organics into long linear dunes but also by methane rivers and possible eruptions of liquid water (“cryovolcanism”). While living things are ~70% water, and finding water has been a convenient initial focus for astrobiological investigations in the solar system, the chemical processes that conspire to lead to life rely on functions exerted by compounds of carbon, nitrogen, oxygen and hydrogen, with traces of sulfur and phosphorus (CHNOPS). In contrast to Europa (abundant in water, and perhaps sulfur), Dragonfly: A Rotorcraft Lander Concept for Scientific Exploration at Titan Johns Hopkins APL Technical Digest, Volume 34, Number 3 (2018), www.jhuapl.edu/techdigest 375 plus radioisotope power source and launch costs), it would be challenging indeed to provide a relay spacecraft and a sea probe. A lander with DTE communication would be possible at lower latitudes, however. The only detailed study of such a mission (see Box 2) was the 2007 Titan Explorer NASA Flagship Mission Study,9,10 led by the Johns Hopkins University Applied Physics Laboratory (APL). This study advocated the science that could be obtained from three platforms, an orbiter, a hot-air (Montgolfière) balloon, and a lander. The lander (designed before Titan’s seas had been discovered) was intended to be delivered to Titan’s Belet sand sea, a large—and thus easily targeted— dune field expected to be free of rock and gully hazards. After the lander’s parachute descent and landing on Pathfinder-like airbags (wherein if it landed on top of a dune, it would just roll down to the bottom), petals would unfold and science would begin, with cameras, a chemical analysis suite, a seismometer, and a meteorology package. Much of the science definition in the Titan Explorer Study was useful in formulating the Dragonfly proposal. A scientific limitation of a single lander, however, is that it explores only a single location. This limitation can be mitigated slightly at “grab-bag” landing sites where geological processes have gathered samples from a range of areas (in Mars Pathfinder’s case, a flood deposit of rocks; dune sands may similarly have material from a range of source locations). However, a lander with some kind of mobility, or augmented by some mobile element (e.g., a “fetch” rover), would help address the challenge of acquiring samples from sites more interesting than the landing point, a site that would be most likely selected for safety rather than for scientific interest. The concept of a rotorcraft lander on Titan tricklecharging a battery for brief atmospheric flights by using the power from a radioisotope power source had been proposed some 17 years ago.11,12 At that time, the vehicle was imagined to be a helicopter, a vehicle that is used on Earth for near-guaranteed access to a wide range of terrain, for personnel delivery, and for search and rescue. However, helicopters are mechanically complex (one

Dragonfly: A rotorcraft lander concept for scientific exploration at titan

Guidelines for Volume Force Distributions Within Actuator Line Modeling of Wind Turbines on Large-Eddy Simulation-Type Grids

Scaled ice accretion experiments on a rotating wind turbine blade

The objective of this work is a quantitative analysis of power loss of a representative 1.5-MW wind turbine subject to various icing conditions. Aerodynamic performance data are measured using a combination of ice accretion experiments and wind tunnel tests. Atmospheric icing conditions varying in static temperature, droplet diameter and liquid water content are generated in an icing facility to simulate a 45-min icing event on a DU 93-W-210 airfoil at flow conditions pertinent to 80% blade span on a 1.5-MW wind turbine. Iced airfoil shapes are molded for preservation and casted for subsequent wind tunnel testing. In general, ice shapes are similar in 2D profile, but vary in 3D surface roughness elements and in the ice impingement length. Both roughness heights and roughness impingement zones are measured. A 16% loss of airfoil lift at operational angle of attack is observed for freezing fog conditions. Airfoil drag increases by 190% at temperatures near 0° C, 145% near 10° C and 80% near 20° C. For a freezing drizzle icing condition, lift loss and drag rise are more severe at 25% and 220%, respectively. An analysis of the wind turbine aerodynamic loads in Region II leads to power losses ranging from 16% to 22% for freezing fog conditions and 26% for a freezing drizzle condition. Differences in power loss between icing conditions are correlated to variance in temperature, ice surface roughness and ice impingement length. Some potential control strategies are discussed for wind turbine operators attempting to minimize revenue loss in cold-climate regions. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of icing roughness on wind turbine power production

The current actuator line method (ALM) within an OpenFOAM computational fluid dynamics (CFD) solver was used to perform simulations of the NREL Phase VI rotor under rotating and parked conditions, two fixed-wing designs both with an elliptic spanwise loading, and the NREL 5-MW turbine. The objective of this work is to assess and improve the accuracy of the state-of-the-art ALM in predicting rotor blade loads, particularly by focusing on the method used to project the actuator forces onto the flow field as body forces. Results obtained for sectional normal and tangential force coefficients were compared to available experimental data and to the in-house performance code XTurb-PSU. It was observed that the ALM results agree well with measured data and results obtained from XTurb-PSU except in the root and tip regions if a three-dimensional Gaussian of width, e, constant along the blade span is used to project the actuator force onto the flow field. A new method is proposed where the Gaussian width, e, varies along the blade span following an elliptic distribution. A general criterion is derived that applies to any planform shape. It is found that the new criterion for e leads to improved prediction of blade tip loads for a variety of blade planforms and rotor conditions considered.

Sven Schmitz

Papers

Dragonfly: A rotorcraft lander concept for scientific exploration at titan

Guidelines for Volume Force Distributions Within Actuator Line Modeling of Wind Turbines on Large-Eddy Simulation-Type Grids

Scaled ice accretion experiments on a rotating wind turbine blade

Effect of icing roughness on wind turbine power production

Accuracy of State-of-the-Art Actuator-Line Modeling for Wind Turbine Wakes