Numerical modelling of vertical axis turbines using the actuator surface model

Abstract

This paper presents the development and validation of a lightweight fluid solver based on the Navier–Stokes equations coupled to a special blade element method (BEM) for vertical axis turbines. This method is called Actuator Surface Model (ASM) and leads to a medium fidelity tool designed to bridge the gap between expensive blade resolving computational fluid dynamics (CFD) calculations and simple, often inaccurate momentum models such as the double-multiple streamtube (DMST) model. Since the simulation runs on coarse meshes, it is possible to use an explicit solver with a reasonable time step to significantly reduce the computing time to almost real-time speed. The fluid model is validated for the classical lid-driven cavity flow problem, while the coupled ASM code is compared with three different experimental measurements from the literature. For a more accurate description of blade specific phenomena, several higher order corrections were implemented, such as dynamic stall, parasitic drag and finite aspect ratio. The model is able to calculate the performance of all tested turbines reasonably well and can predict the maximum efficiency up to a few percent. Therefore it is an excellent alternative for a fast and precise initial design of vertical axis turbines compared to traditional BEM methods.