Adjoint based optimisation for efficient VAWT blade aerodynamics using CFD

The objective of this work is to demonstrate the viability of applying Adjoint methods to aerodynamic optimisation of VAWTs. Adjoint methods are very powerful optimisation techniques which have been implemented effectively in other fields, yet there is an absence of such work within VAWT literature.

A ‘semi-transient’ optimisation process is proposed, using Adjoint optimisation data from single instances in time to improve VAWT performance. This is challenging due to the unsteady nature of VAWT aerodynamics. A pitching aerofoil model approximates the VAWT flow field, drastically reducing computational cost. Details are given on the necessary CFD model(s), Adjoint solver settings, and optimisation philosophy.

The optimisation process was applied to a typical VAWT in the commercial CFD software ANSYS Fluent. A high tip-speed-ratio case is chosen to minimise unsteady flow affects. The results show novel blade geometries which improve the VAWT average power coefficient when compared to the original NACA0018 blade.

Such a method is novel in the field of VAWTs, and the use of Adjoint methods with low cost CFD models provides an efficient optimisation methodology that can be readily adopted by the VAWT design community. This work sets the foundation for a new and very promising avenue for VAWT research.