Yu Nishio

<p>A new airfoil for straight-bladed vertical axis wind turbines is designed by a genetic algorithm and two-dimensional vortex method aimed at improving both the starting performance and efficiency at a cruising condition, which is the tip-speed ratio of λ = 2.0. The new airfoil has a negative camber and its aerodynamic performance is remarkably improved at the second and the third quadrants in the rotating plane, compared with the conventional NACA0018 airfoil.</p>

<p>Boundary layer receptivity to a sheet-type disturbance is experimentally investigated using an airfoil-shaped disturbance generator, which is installed upstream of an elliptical leading edge of a flat plate. The velocity fluctuation taken into the boundary layer first decays and then grows algebraically downstream. Stationary streaky structures, in which high- and low-speed regions are aligned in the spanwise direction, are found inside the boundary layer. The observation of the velocity waveform suggests that parts of hairpin vortices exist frequently observed between the high- and low-speed regions in the streaky structures.</p>

<p>Splashing behavior of a thin liquid film on a rotating disk is simulated by an incompressible SPH method to evaluate the effect of the grooves at the disk edge of a liquid atomizer. When the number of grooves is larger than the averaged number of ligaments in the clean disk condition, the same number of ligaments as the grooves are generated at the disk edge. Under the condition, the generated droplets tend to have similar sizes.</p>

<p>Behavior of a fluttering flag in a uniform flow is simulated by a three-dimensional incompressible SPH method under impermeable and permeable conditions. A permeable flag model is newly proposed on the basis of a spring-mass model. By comparing the oscillating motions of impermeable and permeable flags, it is found that amplitude of oscillation of the permeable flag is smaller than the impermeable flag. Besides, only the region near the free end oscillates under the permeable condition.</p>

<p>New airfoils for straight wing vertical axis wind turbine are designed using a genetic algorithm and two-dimensional vortex method aimed at improving the starting performance or the efficiency at a given rotational speed. Compared to a basic airfoil of NACA0018, these characteristics are improved in the optimized airfoils. It is also found that the change in the location of the aerodynamic center contributes to the increase of torque.</p>

<p>Three-dimensional simulation using an incompressible SPH method is carried out to investigate the scattering behavior of a liquid film flow spreading from the edge of a rotating disk. Computational domain is limited to a fan-shaped region near the edge of the disk using a periodic boundary condition in order to reduce the computational cost while keeping the spatial resolution as high as possible. The numerical results qualitatively agree with the experimental results though the number of ligaments is 1/2 to 1/3 of the experimental values. It is also found that droplets of nearly uniform diameters can be obtained by properly placing radial grooves at the edge.</p>

<p>Wind tunnel experiment is carried out to measure the unsteady torque generated by each blade of a straight-bladed vertical axis wind turbine using strain gauges. The results show that the measurement system measures correct torques when the wind turbine is not rotating. However, there is still a room for improvement when the wind turbine is rotating.</p>