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Numerical simulation for optimization of hybrid Darrieus-Savonius wind turbine

Vertical axis wind-turbines (VAWT) can be divided in Darrieus and Savonius designs. The advantage of the Darrieus design is higher energy conversion efficiency. The advantage of the Savonius design is the self-starting ability and lower tip-speed ration (TSR). By combining both designs (Figure 1a) into a hybrid design might offer a combination of the mentioned advantages of both designs [1-2]. This research considers the possibility of numerical simulation and optimization of the hybrid VAWT design. An initial optimization using only the maximum power coefficient as a criterion has shown that the optimized design does not have the desirable self-starting ability (Figure 2). Thereby the both aspects of the design should be considered (Figure 1b). In the simplest optimization, only two shape variables can be used by only scaling a fixed-shape Darrieus and Savonius components. In more complex optimization, the number of variables can rise to 10-20 [3]. The prerequisite to any optimization is the selection of appropriate numerical simulation parameters. The number of required timesteps for the convergence of 2D CFD simulation for a Darrieus design alone was shown to be about 105 which about 103 core-hours [4]. This means that only a relatively small number of simulations can be conducted in a realistic time- scales thereby reducing the possible number of variables in optimization. This research discusses the possibilities of reduction of simulation time by adaptive time-step control. The reduction of the optimization time is considered by adaptively increasing the CFD fidelity for potentially good design.

Vertical axis wind-turbine ; Hybrid Darrieus-Savonius ; CFD ; Optimization

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