Passive-adaptive composite structures for unsteady fluid loading. A. Gallagher, S.W. Boyd and S.R.Turnock Fluid Structure Interactions Research Group; Faculty of Engineering and the Environment Fluid Structure Interactions Research Group Acknowledgement: This project is supported by the Engineering and Physical Sciences Research Council FSI Away Day 2012 Figure 1: In-service bending of wind turbine blades. (Green Energy Ohio: Background Traditional methodologies for the development of lifting surfaces for all applications (such as wings, wind turbine blades and yacht appendages) have sought to build structures with sufficient stiffness to maintain a single optimised shape which is a compromise over a range of operating conditions. A more efficient solution may be the use of tuned deformation in these structures to achieve the dual goals of reducing weight by reducing the stiffness requirement and also increasing the operational efficiency by allowing a tuned deformation response. Gust alleviation can significantly reduce the stiffness and strength requirements of the supporting structure. Additionally, the structure stores potential energy when deformed, and by incorporation of the release of this energy in the design blade operation, on passing of the gust may contribute the power output of the turbine. Wind/tidal turbine efficiency The power that a wind or tidal turbine can extract from a flow is limited by the performance of the blade design. The performance of the blade is modified by varying chord length and twist over the length of the blade, with the goal of optimising the lift to drag ratio for a given flow velocity. However, fluctuations in the flow velocity force the blades to operate outside of this optimal lift/drag regime, reducing the efficiency of the turbine. Figure 2: Some structural options for wind turbine blade construction. (Gurit Manual: Wind Turbine Blade Structural Engineering) Aims To optimise the efficiency of a composite lifting structure subject to unsteady fluid loading by tailoring the structure to give a tuned deformation response. Objectives Understand current foil construction techniques. Scale the loading regime to the achievable test size. Evaluate the quasi-static response of a simple foil under point and fluid loading. Design and construct a passive-adaptive composite foil and characterise its performance. Investigate the dynamic characteristics of a passive-adaptive composite foil under unsteady loading. Current structural configurations: Load bearing structures of current wind turbine blades vary widely. Some lend themselves to an adaptive design more than others, such as the box spar construction shown here: Experimental approach A phased approach is being taken to build the experimental capability : Current Work In this initial phase of the project a simple NACA 00 # series foil will be designed, constructed and built to verify the instrumentation capabilities for measurement and characterisation of an adaptive composite foil, using Digital Image Correlation and Particle Image Velocimetry in the wind tunnel. This will set the design parameters to allow the construction of a passive- adaptive composite foil in Phase 2. Figure 3: Flowchart of experimental and theoretical stages Figure 4: Phase 1 Experimental Plan