Flow structure and performance analysis of Darrieus vertical axis turbines with swept blades: A critical case study on V-shaped blades

Blade geometric modification is one favorite way of enhancing the performance of vertical axis turbines. In this regard, V-shaped blades are a novel design featuring some leading-edge sweep angle. Currently, the relevant literature only focuses on finding the optimum parameters of the V-shaped blades and lacks a deep understanding of how they alter flow structure and whether they offer any performance improvement compared to other conventional types. To this aim, using three-dimensional numerical simulations, the flow structure and performance of two different V-shaped blade turbines, twisted and untwisted, are compared with straight and helical-blade turbines at tip speed ratios (TSRs) ranging from 0.69 to 1.5. Turbine torque average and fluctuation amplitude are chosen as the performance metrics. It is shown that the sweeping configuration of the V-shaped and helical types causes an inevitable spanwise flow, resulting in a performance loss, which makes neither type of V-shaped blade turbine advantageous at low TSRs.