Book Description

There has been a substantial growth in the total installed wind energy capacity worldwide, especially in China and the United States. Icing difficulties have been encountered depending on the location of the wind farms. Wind turbines are adapting rotor ice protection approaches used in rotorcraft applications to reduce aerodynamic performance degradation related to ice formation. Electro-thermal heating is one of the main technologies used to protect rotors from ice accretion and it is one of the main technologies being considered to protect wind turbines. In this research, an anti-icing configuration using electro-thermal heating was explored to find optimum power density requirements to keep the rotor blade free of ice at all times. The objective of these experiments were to identify the feasibility of the power requirements from the stake holders and determine an initial power density for the de-icing approach. The electro-thermal heater system located on the spinning wind turbine representative blade sections were powered through a slip-ring. The wind turbine sections were scale models of the 80% span region of a generic 1.5 MW wind turbine blade. The icing cloud impact velocity was matched with a 1.5 MW wind turbine at full production. Three icing conditions were selected for this research: Light, Medium and Severe. Light icing conditions were created using clouds at -8C with a 0.2 g/m3 liquid water content (LWC) and water droplets of 20 m median volumetric diameter (MVD). Medium icing condition clouds had a LWC of 0.4 g/m3 and 20 m MVD, also at -8C. Severe icing conditions had an LWC of 0.9 g/m3 and 35 m MVD at -8C. Experimental anti-icing results were compared with LEWICE, a NASA developed analytical heat transfer software. The average output temperature discrepancy between the suction and pressure sides of the airfoil were 39.5% and 11.1%, respectively. The correlation coefficient of the pressure-side output temperature and power density showed a positive correlation of 0.9516. The anti-icing configuration with the allocated power requirements was deemed unfeasible. This thesis then discusses the design process required to develop a de-icing ice protection system (ice is allowed to accrete to then be removed) for wind turbines and a design procedure was developed. Initially, ice accretion thickness gradients along the span of the rotor blade for light, medium and severe icing conditions were collected. Ice accretion rates along the span of the representative full-scale turbine blade in the severe icing condition ranged from 1.125 mm/min to 1.85 mm/min. Given the maximum power available for the de-icing system (100 kW), heating zones were determined along the span and the chord of the blade. The maximum available power density for each span-wise heater section was 0.385 W/cm2. The heating sequence started at the tip of the blade, to allow de-bonded ice to shed off along the span of the rotor blade due to centrifugal forces. Given the continuity of the accreted ice, heating a zone could de-bond the ice over that specific zone, but the ice formation could not detach from the blade as it would be cohesively connected to the ice over its adjacent inboard zone. The research determined the critical minimum ice thickness required to shed the accreted ice mass with a given amount of power availability by not only melting the ice interface over the zone, but also creating sufficient tensile forces to break the cohesive ice forces between two adjacent heating zones. The quantified minimum ice thickness to overcome ice cohesive forces were obtained for all identified icing conditions. The minimum ice thicknesses required for effective shedding at 26.7%, 44.4% and 62.2% of the span were 7.2mm, 5mm and 4mm, respectively. The digitized ice areas of these thicknesses were used to calculate the centrifugal force at each heater section. The experiment data was critical in the design of a time sequence controller that allows consecutive de-icing of heating zones along the span of the wind turbine blade with the allocated power.