Nacelle wind speed transfer function (NTF) is usually used for power prediction and operational control of a horizontal axis wind turbine. Nacelle wind speed exhibits high instability as it is influenced by both incoming flow and near wake of a wind turbine rotor. Enhanced understanding of the nacelle wind speed characteristics is critical for improving the accuracy of NTF. This paper presents Reynolds-averaged Navier–Stokes (RANS) simulation results obtained for a multi-megawatt wind turbine under both stable and dynamic incoming flows. The dynamic inlet wind speed varies in the form of simplified sinusoidal and superposed sinusoidal functions. The simulation results are analyzed in time and frequency domains. For a stable inlet flow, the variation of nacelle wind speed is mainly influenced by the blade rotation. The influence of wake flow shows high frequency characteristics. The results with stable inlet flow show that the reduction of the nacelle wind speed with respect to the inlet wind speed is overestimated for low wind speed condition, and underestimated for high wind speed condition. Under time-varing inflow conditions, for the time scale and fluctuation amplitude subject to the International Electrotechnical Commission (IEC) standard, the nacelle wind speed is mainly influenced by the dynamic inflow. The variation of inflow can be recovered by choosing a suitable low pass filter. The work in this paper demonstrates the potential for building accurate NTF based on Computational Fluid Dynamics (CFD) simulations and signal analysis.
A series of numerical simulations were conducted to study the influences of separated over-fire air (SOFA) distribution, yawing and tilting angles on the flue gas temperature deviation of a 660MW tangentially coal-fired boiler. The turbulent flow, combustion, pollutants and emission characteristics were investigated. The numerical model developed in the study was first validated with field test, which showed good consistence between the numerical and experimental results. Further study indicated that with the increase of SOFA rate, the coal burnout rate, temperature uniformity coefficient and temperature deviation on the temperature detection line (TDL) declined, and the NOx emission dropped. Increase the SOFA yawing angle in reverse tangential direction leads to reduction of high temperature region in the center of lower furnace exit section and in the left of upper furnace exit section, which is positive in reducing gas temperature deviation. Tilting SOFA nozzle upward leads to upward movement of high temperature region in the upper furnace burnout region, increases in gas temperature of upper and lower furnace exits, decreases in temperature distribution uniformity coefficient of furnace exit section and a slight decrease in coal burnout rate, which is negative for reducing gas temperature deviation. (CSPE)
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