Browsing by Subject "wind turbine"
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Item Effect of Surface Roughness on Wind Turbine Performance(2014-06-25) Ehrmann, Robert SchaeferWind farm operators observe production deficits as machines age. Quantifying deterioration on individual components is difficult, but one potential explanation is accumulation of blade surface roughness. Historically, wind turbine airfoils were designed for lift to be insensitive to roughness by simulating roughness with trip strips. However, roughness was still shown to negatively affect performance. Furthermore, experiments illustrated distributed roughness is not properly simulated by trip strips. To understand how real-world roughness affects performance, field measurements of turbine-blade roughness were made and simulated on a NACA 63_(3)-418 airfoil in a wind tunnel. Insect roughness and paint chips were characterized and recreated as distributed roughness and a forward-facing step. Distributed roughness was tested in three heights and five density configurations. The model chord Reynolds number was varied between 0:8 to 4:8 ? 10^(6). Measurements of lift, drag, pitching moment, and boundary-layer transition were completed. Results indicate minimal effect from paint-chip roughness. As distributed roughness height and density increase, lift-curve slope, maximum lift, and lift-to-drag ratio decrease. As Reynolds number increases, bypass transition occurs earlier. The critical roughness Reynolds number varies between 178 to 318, within the historical range. Little sensitivity to pressure gradient is observed. At a chord Reynolds number of 3:2?10^(6), the maximum lift-to-drag ratio decreases 40% for 140 ?m roughness, corresponding to a 2.3% loss in annual energy production. Simulated performance loss compares well to measured performance loss on an in-service wind turbine.Item Impact of Tsunamis on Near Shore Wind Power Units(2011-02-22) Parambath, AshwinWith the number of wind power units (WPUs) on the rise worldwide, it is inevitable that some of these would be exposed to natural disasters like tsunamis and it will become a necessity to consider their effects in the design process of WPUs. This study initially attempts to quantify the forces acting on an existing WPU due to a tsunami bore impact. Surge and bore heights of 2m, 5m and 10m are used to compute the forces using the commercially available full 3D Navier Stokes equation solver FLOW3D. The applicability of FLOW3D to solve these types of problems is examined by comparing results obtained from the numerical simulations to those determined by small scale laboratory experiments. The simulated tsunami forces on the WPU are input into a simplified numerical structural model of the WPU to determine its dynamic response. The tsunami force is also used to obtain base excitation which when applied on the WPU would be equivalent dynamically to the tsunami forces acting on it. This base excitation is useful to obtain the response of the WPU experimentally, the setup for which is available at University of California, San Diego's (UCSD) Large High Performance Outdoor Shake Table (LHPOST). The facility allows full scale experimental setup capable of subjecting a 65kW Nordtank wind turbine to random base excitations. A stress analysis of turbine tower cross section is performed in order to assess the structural integrity of the WPU. It has been determined that the WPU is unsafe for bore/surge heights above 5 m. It has also been postulated that the structural responses could be considerable in case of the taller multi megawatt wind power units of present day.