Nobuhito Oka

Simultaneous optimization of rotor blade and wind-lens for aerodynamic design of wind-lens turbine

An optimum aerodynamic design method for the new type of wind turbine called “wind-lens turbine” has been developed. The wind-lens turbine has a diffuser with brim called “wind-lens”, by which the wind concentration on the turbine rotor and the significant enhancement of the turbine output can be achieved. In order to design efficient wind-lens turbines, an aerodynamic design method for the simultaneous optimization of rotor blade and wind-lens has been developed. The present optimum design method is based on a genetic algorithm (GA) and a quasi-three-dimensional design of turbine rotor. In the GA procedure, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used as evaluation and selection model. The Real-coded Ensemble Crossover (REX) is used as crossover model. The quasi-three-dimensional design consists of two parts: meridional viscous flow calculation and two-dimensional blade element design. In the meridional viscous flow calculation, an axisymmetric viscous flow is numerically analyzed on a meridional plane to determine the wind flow rate through the wind-lens and the spanwise distribution of the rotor inlet flow. In the two-dimensional rotor blade element design, the turbine rotor blade profile is determined by a one-dimensional through flow modeling for the wind-lens turbine and a two-dimensional blade element theory based on the momentum theorem of the ducted turbine. Total performances and three-dimensional flow fields of the optimized wind-lens turbines have been investigated by Reynolds averaged Navier-Stokes (RANS) simulations, in order to verify the present design method. The RANS simulations and the flow visualization have been applied to conventional and optimum design cases of the wind-lens turbine, in order to elucidate the relation between their aerodynamic performances and the flow fields around them. The numerical results show that separation vortices behind the wind-lens brim play a major role in the wind concentration and the diffuser performance of the wind-lens. As a result, it is found that the aerodynamic performance of wind-lens turbine is significantly affected by the interrelationship between the internal and external flow fields around the wind-lens.Copyright

Aerodynamic design for wind-lens turbine using optimization technique

An optimum aerodynamic design method has been developed for the new type of wind turbine called “wind-lens turbine”. The wind-lens turbine has a diffuser with brim called “wind-lens”, by which the wind concentration on the turbine rotor and the significant enhancement of the turbine output can be achieved. The present design method is based on a genetic algorithm (GA) and a quasi-three-dimensional design of turbine rotor. The quasi-three-dimensional design consists of two parts: meridional viscous flow calculation and two-dimensional blade element design. In the meridional viscous flow calculation, an axisymmetric viscous flow is numerically analyzed on a meridional plane to determine the wind flow rate through the wind-lens and the spanwise distribution of the rotor inlet flow. In the two-dimensional rotor blade element design, the turbine rotor blade profile is determined by a one-dimensional through flow modeling for the wind-lens turbine and a two-dimensional blade element theory based on the momentum theorem of the ducted turbine. In the present optimization method, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used as evaluation and selection model. The Real-coded Ensemble Crossover (REX) is used as crossover model. The present aerodynamic design method has been applied to the coupled design of turbine rotor and wind-lens. Total performances and flow fields of the wind-lens turbines designed have been investigated by Reynolds averaged Navier-Stokes simulations, in order to verify the present design method.Copyright

Aerodynamic Performances and Flow Fields of Pareto Optimal Solutions in an Aerodynamic Design of a Wind-Lens Turbine

The new type of shrouded wind turbine called “wind-lens turbine” has been developed. The wind-lens turbine has a brimmed diffuser called “wind-lens”, by which the wind concentration on the turbine blade and the significant enhancement of the turbine output can be achieved. A simultaneous optimization method for the aerodynamic design of rotor blade and wind-lens has been developed. The present optimal design method is based on a genetic algorithm (GA) which enables multi objective aerodynamic optimization. In the present study, aerodynamic performances and flow fields of the Pareto optimal solutions of wind-lens turbines designed by the present optimal design method have been investigated by wind-tunnel tests and three-dimensional Reynolds averaged Navier-Stokes (RANS) analyses. Output power coefficients obtained from the wind-tunnel tests in the optimal wind-lens turbine exceeded the Betz limit, which is the performance limitation for bare wind turbines. The numerical results and the experimental results show that the suppression of flow separations in the diffuser is important to achieve significant improvement in aerodynamic performances. As a result, it is found that the aerodynamic performance of wind-lens turbine is significantly affected by the interrelationship between the internal and external flow fields around the wind-lens.Copyright

Suppression of Secondary Flows in an Axial Flow Turbine Rotor With a Novel Blade Design Concept

This paper presents a novel blade design concept about control of the secondary flow in axial turbines to improve the internal efficiency. A rotor blade for the high and intermediate pressure stage of a steam turbine was designed by one-dimensional inverse method incorporated with throughflow calculation.In the throughflow calculation, the axisymmetric Navier-Stokes equations are solved, assuming that the meridional flow is axisymmetric and viscous. To take into account the blade loading, a blade force is introduced as a body force to the governing equations. The blade force contains the inviscid blade effect only, namely, the pressure difference across a blade. The blade force acts in the direction perpendicular to a three-dimensional blade camber surface, which is constructed from camber lines stacked in blade height direction, so that the flow convects along the surface. The camber line is calculated by one-dimensional inverse method, based on a given blade loading distribution and the meridional velocity distribution from the throughflow calculation. The present throughflow calculation method was validated for a direct problem, using blade geometry of existing turbine rotor. The blade force with the camber surface in the present method was able to express the secondary flow inside the turbine by modifying the camber surface appropriately. As a result, the calculation result showed good agreement with the experimental result.The turbine rotor blade was redesigned with the present method, modifying the chord-wise blade loading distribution so as to suppress the development of the secondary flow. The way of modifying the chord-wise blade loading distribution is based on a new idea, which can be actualized by the present design method. It was confirmed that the secondary flow was successfully suppressed as intended in the designed rotor.Copyright