PITCH ANGLE & DECALAGE EFFECT IN BIPLANE BLADE DESIGN FOR WIND TURBINES

To reduce the environmental pollution and introduce new form of energy source, the popularity of harvesting energy from wind is increasing day by day. Wind turbines blades are growing longer, as increasing blade length is one of the best ways to produce more wind energy per turbine. However, longer blades require thicker root at the inboard section to counteract the bending load and this thicker root at the inboard section of the large wind turbine blades lower the blades aerodynamic efficiency. This loss of aerodynamic efficiency prevents these longer wind turbine blades from being fully effective as the cost to benefit ratio increases and less power is generated than the optimal value. Additionally, these long blades use a large amount of material. Longer blades require more support to remain structurally sound, which causes a large increase in mass. This material is hard to break down and decompose, causing them to take up a large amount of space in landfills when the blades are unserviceable or replaced because of damage and stress. To overcome this drawback and maximize the harvested energy from the wind, a novel "Biplane" shape wind turbine blade is proposed by the researchers which replaced the monoplane inboard section of the traditional wind turbine blades with the biplane inboard section. This new concept allows to design and manufacture longer wind turbine blade without any loose in aerodynamic efficiency and structural integrity. Biplane wind turbine blades have shown very interesting and promising characteristics in terms of both aerodynamics and structural performance. This new type of wind turbine blade can ensure more power, better aerodynamics efficiency, structural integrity along with lower manufacturing and transportation cost. Previous research conducted found the significant effect of gap and stagger in the aerodynamic performance of biplane blades. However, another very important parameter "pitch angle & decalage" that can improve the aerodynamic performance of biplane wind turbine blades remains unchecked. Keeping that in mind, the current research performed a detailed computational fluid dynamic (CFD) based analysis to find out the pitch angle & decalage effect in biplane wind turbine blade design. Our current research revealed that, apart from the contribution of gap and stagger, the effect of pitch angle & decalage can be significant. At a 6 degrees angle of attack, with both top and bottom blade aerofoil pitch angle setup at positive (+ve) 3 degrees which means decalage is 0 degrees, can improve the lift coefficient (C-l) and the lift to drag ratio (C-l/C-d) or aerodynamics efficiency raised around 48% higher while gap to chord ratio (g/c) and stagger to chord ratio (s/c) were kept 0.5 and 0.25 respectively obtained from the previous state of art.