Theoretical and Experimental Investigations of Performance and Loads on a Horizontal-axis Wind Turbine
Singh, Nand Kumar Ph.D, 2000
Supervisor(s): Sudhakar, K. and Sharma, G.K.
The thesis deals with three levels of prediction methodologies in increasing order of complexities and capabilities to predict mean and cyclic performance and loads of a horizontal-axis wind turbine. Model-1 considers the uniform, co-axial flow and is based on blade element combined with simplified vortex theory. It predicts the mean power performance and blade loadings. Model-2 takes into account rotor tilt, blade coning, wind shear and yaw and uses modified strip theory combining the blade element and momentum theory. Formulation in this model is based on various co-ordinate transformations and predicts mean as well as cyclic variation of power output and loads as a function of blade azimuth positions. Model-3 is an improvement over Model-2 in the sense that it considers the post-stall behavior of airfoil blades during operations at high winds, when all the sections of the blade operate in fully stalled region. Experimental investigations are carried out on an indigenously developed 200 k W BHEL wind turbine operating at Ramagiri windfarm in A.P, India. The instrumentation consists of a separate wind mast in front of the wind turbine with various sensors including anemometer, wind vane, temperature and pressure sensors installed on the mast, strain gages on the blade, power output, and other sensors to measure the blade azimuth positions and rotor axis positions. Totally 12 sensors have been monitored and the data were recorded in two groups, a) as 10 minutes average interval at sampling rate of 1 Hz to evaluate mean power curve and, b) data recorded continuously at higher sampling rate (100 Hz) and stored as 10 minutes time series on a multiple-head magnetic tape recorder for evaluation of cyclic variation of power output and loads. The data were subsequently downloaded using external pulse trigger through a PC-based data acquisition system exclusively developed for this purpose. All the 100 Hz acquired data has been extracted corresponding to the blade azimuth positions and analyzed using 3-D method of bins. Wind shear, yaw, power output at various yaw, cyclic variation of power output and blade root bending moments over one revolution of the blade have been obtained. Theoretical and experimental results have been compared and discussed. The conclusions and scope for further work have been presented in the thesis.