Highlights• CFD used for novel vertical axis wind turbine design.• A new parameterisation scheme developed • Design of Experiments and Nelder-Mead simplex optimisation used.• New blade design developed -currently being tested. AbstractThe approach and results of a parametric aerodynamic optimisation study is presented to develop the blade design for a novel implementation of a vertical axis wind turbine. It was applied to optimise the two-dimensional cross-sectional geometry of the blades comprising the turbine. Unsteady viscous computational fluid dynamic simulations were used to evaluate blade performance. To compare geometries, the non-dimensional Coefficient of Power was used as a fitness function. Moving meshes were used to study the transient nature of the physical process. A new parameterisation approach using circular arcs has been developed for the blade cross sections. The optimisation process was conducted in two stages: firstly a Design of Experiments based response surface fitting was used to explore the parametric design space followed by the use of a NelderMead simplex gradient-based optimisation procedure. The outcome of the optimisation study is a new blade design that is currently being tested in full-scale concept trials by a partnering wind energy company.