Open Access Publications
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Open access publications by faculty, staff, postdocs, and graduate students in the Center for Research in Wind.
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Item New insights on wind turbine wakes from large-eddy simulation: Wake contraction, dual nature, and temperature effects(Wind Energy, 2023-05-17) Wu, Sicheng; Archer, Cristina L.; Mirocha, Jeffrey D.Large-eddy simulation (LES) has been adopted to study wind turbine wakes because it can capture fine-scale details of turbulent wind flows and interactions with wind turbines. Here, we use the LES version of the Weather Research and Forecasting (WRF) model with an actuator disk model to gain insights on several wake effects that have been traditionally difficult to measure. The first finding is that the wake has a “dual nature,” meaning that the wind speed deficit behaves differently from the added turbulent kinetic energy (TKE) and the two are not co-located in space. For example, the wind speed deficit peaks at hub height and reaches the ground within 8D (D is the rotor diameter), but added TKE peaks near the rotor tip and generally remains aloft. Second, temperature changes near the ground are driven by the added TKE in the rotor area and by atmospheric stability. The combination of these two factors determines the sign and intensity of the vertical heat flux divergence below the rotor, with convergence and warming associated with stable conditions and weak divergence and modest cooling with unstable conditions. Third, wakes do not expand indefinitely, as suggested by similarity theory applied to the wind speed deficit, but eventually stop expanding and actually contract, at different rates depending on atmospheric stability. The implication of these findings is that, in order to study wakes, it is not sufficient to focus on wind speed deficit alone, because TKE is also important and yet behaves differently from the wind speed deficit.Item Influence of Battery Energy, Charging Power, and Charging Locations upon EVs’ Ability to Meet Trip Needs(Energies, 2023-02-21) Kempton, Willett; Pearre, Nathaniel S.; Guensler, Randall; Elango, Vetri V.One year of high-resolution driving data from a sample of 333 instrumented gasoline passenger vehicles are used to create a trip inventory of U.S. vehicle travel requirements. A set of electric vehicles (EVs) is modeled, differing in battery size (kWh), recharging power (kW), and locations for charging when parked. Each modeled EV’s remaining energy is tracked while traversing the entire sample’s trip inventory in order to estimate how well each EV meets all U.S. driving requirements. The capital cost of refueling infrastructure is estimated per car, for gasoline and for each analyzed combination of charging station locations. We develop three metrics of the ability of different EV characteristics to meet trip requirements: the percentage of trips successfully met by each modeled EV, the number of days that the driver must “adapt” EV use to meet more demanding trip requirements, and the total driver time required for refueling. We also segment the market of trip patterns per car, finding that 25% to 37% of the vehicle population could meet all their drivers’ trip needs with a smaller-battery EV combined with community charging. This potential combination of EVs and charging would enable lower-price EVs and lower-cost recharging power, and would broaden EV availability to groups for whom today’s EVs and charging configurations are less accessible.Item Comparison of individual versus ensemble wind farm parameterizations inclusive of sub-grid wakes for the WRF model(Wind Energy, 2022-06-02) Ma, Yulong; Archer, Cristina; Vasel-Be-Hagh, AhmadWind turbine wakes can be predicted somewhat accurately with mesoscale numerical models, such as the Weather Research and Forecast (WRF) model, via a wind farm parameterization (WFP) that treats the effects of the wakes, which are sub-grid features, on power production and the environment. A few WFPs have been proposed in the literature, but none has been able to properly account for the individual wakes within a grid cell or the effects of overlapping wakes from multiple turbines. A solution to these two issues is a WFP that includes both a wake model, which is a simplified analytical model of the wind speed (or wind power) deficit caused by a wake, and a wake superposition model, which accounts for overlapping wakes. Several such WFPs are developed here for the WRF model—based on the Jensen, the Geometric, and the Gaussian wake models coupled with two wake superposition methods (based on a squared deficit and a squared velocity superposition)—and tested individually, as well as combined together in an ensemble (EWFP), at two modern offshore wind farms. Most WFPs perform satisfactorily alone, but the EWFP generally outperforms them at both farms. The issue of resolved versus sub-grid wakes is explored for single- and multi-cell cases and for directions of alignment and non-alignment between the wind direction and the turbine columns. Although different combinations of wake loss and wake superposition models might be preferred at other wind farms, the general findings and detailed performance statistics given here might provide useful guidance in their selection. Abbreviations: EWFP - ensemble wind farm parameterization GM - geometric model WFP - wind farm parameterization WRF - Weather Research and Forecast model XA - Xie and Archer (2015)Item Surface impacts of large offshore wind farms(Environmental Research Letters, 2022-05-25) Golbazi, Maryam; Archer, Cristina L.; Alessandrini, StefanoFuture offshore wind farms around the world will be built with wind turbines of size and capacity never seen before (with diameter and hub height exceeding 150 and 100 m, respectively, and rated power exceeding 10 MW). Their potential impacts at the surface have not yet been studied. Here we conduct high-resolution numerical simulations using a mesoscale model with a wind farm parameterization and compare scenarios with and without offshore wind farms equipped with these 'extreme-scale' wind turbines. Wind speed, turbulence, friction velocity, and sensible heat fluxes are slightly reduced at the surface, like with conventional wind turbines. But, while the warming found below the rotor in stable atmospheric conditions extends to the surface with conventional wind turbines, with extreme-scale ones it does not reach the surface, where instead minimal cooling is found. Overall, the surface meteorological impacts of large offshore wind farms equipped with extreme-scale turbines are statistically significant but negligible in magnitude.Item Marshaling ports required to meet US policy targets for offshore wind power(Energy Policy, 2022-02-16) Parkison, Sara B.; Kempton, WillettWe analyze infrastructure needed for offshore wind power targets set by U.S. state and federal policies—specifically, manufacturing, vessels, and offshore wind ports. By examining cost-competitive turbine and project sizes and infrastructure challenges, we identify marshaling ports as a key bottleneck. Through elicitation of requirements from supply chain, port, and vessel experts, we identify the necessary attributes for marshaling ports and calculate the area needed to meet policy targets. US marshaling ports are currently insufficient to meet either state or federal power targets. We calculate state commitments from state contracts and policies: in sum, 40 GW by 2040. Federal targets from the Biden Administration are 30 GW by 2030 and 110 GW by 2050. Either target yields more demand for marshaling area than is currently available or planned. The shortage of marshaling area supply has incorrectly been attributed to lack of suitable U.S. locations. Instead, we attribute it to developers having built ports to support early, smaller projects, and having located them to incentivize state power contracts rather than developing ports for long-term, large-scale, and economically-efficient use. Additional land suitable for marshaling ports exists, but it requires commitment from port authorities and port investors to develop it for this purpose.