Browsing by Author "Castillo, Luciano"
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- Assessing the Structural Impact of Low Level Jets over Wind TurbinesGutierrez, Walter; Araya, Guillermo; Kiliyanpilakkil, Praju; Basu, Sukanta; Ruiz-Columbie, Arquimedes; Tutkun, Murat; Castillo, Luciano (Virginia Tech, 2015-06)Low Level Jets (LLJs) are defined as regions of relatively strong winds in the lower part of the atmosphere. They are a common feature over the Great Plains in the United States. It has been reported that 75 % of LLJs in the Great Plains occur at night and with seasonal patterns, affecting significantly the wind energy production. Present results have corroborated some of the LLJ's known characteristics. LLJs develop due to the formation of stable stratification in the lower atmosphere. This paper is focused on the determination of the static/dynamic impact that real LLJs produced in West Texas have over wind turbines. High-frequency (50Hz) observational data from the 200-m tower data (Reese, Texas) have been input as inflow conditions into the NREL FAST code in order to evaluate the structural impacts of LLJ's on a typical wind turbine. Due to the higher levels of wind speed, the potential for power increase proportional to the cube of the velocity. It has been observed that during an LLJ event the level of turbulence intensities and TKE are significantly much lower than those during unstable conditions; as a result, cyclical aerodynamic loads on turbine blades are different. Low-frequency oscillations prevail in stable conditions with formation of LLJ, as opposed to high-frequency oscillations more prevalent in unstable conditions. The turbulent kinetic energy is lower in LLJ but the energy concentrates in particular frequencies that can stress the turbine. From the point of view of the wind turbine loads/stresses, we have detected frequencies that can be correlated with those from the incoming wind.
- Design of closed loop control for a wind turbine system coupled to a CV transmission systemNovoa, Santiago; Srivastava, Nilabh; Castillo, Luciano (Virginia Tech, 2015-06)Grid integration of renewable energy sources has proven to be a popular and challenging problem that has been extensively studied and continues to be a focus of interest. Most modern wind energy conversion systems utilize power electronics converters/inverters to maintain voltage phase, frequency and magnitude at the grid-dictated values. While power electronics is an expanding area of interest, currently available solutions report high failure rates and elevated monetary costs. In this paper we investigate the dynamic analysis of a gearless wind turbine coupled to an induction generator based on the dynamical understanding proposed by Ericson and Srivastava that describes both the steady state and the shifting behaviours of the V belt CVT. The Model uses the dynamics published by Carbone-Mangialardi to explain this relationship during creep mode shifting, and the dynamics by Shafai in Slip Mode shift, which provides thorough detail on the inertial interactions between the belt and the pulleys of CVT. Using Matlab/Simulink, we incorporate the CVT model into a wind turbine model coupled to an induction generator. The entire turbine/rotor - CVT/generator is coupled to the grid through the conventional grid- and rotor- side converters. By controlling the driver axial forces of the CVT we intend to be able to control low- and high- speed shaft speeds (i.e. perform speed control) to obtain maximum wind energy capture before the wind cut-out speed and provide an alternative to pitch control afterward. The intent is to understand how control inputs of the CVT affect power through the entire drivetrain to meet the objectives of: a) Maximal power extraction from the wind b) Better quality power for grid integration c) Tracking the grid demands without degrading the CVT performance The results for the overall integrated powertrain are presented and discussed in detail with the CVT and the induction generator operated in closed loop configuration. The simulations were all performed utilizing real wind data taken from a met tower in the South plains area, the data was sampled at 50 Hz.
- Wind Plant Aerodynamics - A Spectral Analysis for Energy EntrainmentCastillo, Luciano (2013-11-25)During the first portion of this seminar, extensive PIV data collected from a scaled down 3 blade, 3 x 5 turbine array is shown. In order to understand how large-scales motions play a role in providing mean kinetic energy (MKE) to the array, low dimensional tools based on a proper orthogonal decomposition (POD) are used to analyze the spatially developing velocity field inside the scaled array. From this analysis, modal decomposition of the Reynolds stresses and fluxes of the MKE are constructed. Thus, from these modal expansions it is established that low order modes have large contributions to Reynolds shear stress regardless of analysis domain. In addition, it will be shown that mean kinetic energy transport resulting from Reynolds shear stress typically serves to bring energy into the array while transport terms associated with Reynolds wall-normal stress typically removes energy from the array. Furthermore, it will be shown that the sum of the first 13 modes for the mean fluxes contributes 75% of the total Reynolds shear stress in the domain. The concept of coherent transfers of energy is employed here as means to uncover the scales responsible for the entrainment of mean kinetic energy into the array. The major contributions to the MKE entrainment are achieved by large-scale motions associated with sums of the Reynolds shear stress, (idiosyncratic) modes. Thus, the sum of the first 9 modes yield 54% of the total energy entrainment, with scales given by L ~ 13D associated with this sum. From these results, it is clear that scales of the order of the total wind farm size are those, which are critical in determining how much power can be extracted from the atmospheric boundary layer. In addition, during this seminar it will be shown that dispersive stresses are also important in the energy entrainment and dissipation in wind arrays with complex topography and where proximity between turbines exists. ABOUT THE SPEAKER Luciano Castillo is the Don-Kay-Clay Cash Distinguished Engineering Chair in Wind Energy and the Executive Director/ President of the National Wind Resource Center (NWRC) at Texas Tech University. After spending 12 years at Rensselaer Polytechnic Institute he joined the ME department at TTU in 2011. His research in turbulence using experimental techniques, direct numerical simulations and multi-scale asymptotic analysis has injected new ideas in turbulent boundary layers and improved our understanding of the effects of initial conditions on large scale turbulence, particularly on wind energy performance. Some of his awards include: the NASA Faculty Fellowship, the Martin Luther King Faculty Award, and the Robert T. Knapp Award on complex flows from the ASME among others. He published over 100 articles including a seminal paper on turbulent boundary layers and scaling laws.