Abstract
This paper presents the results of CFD simulations of reversing flow air turbines used as the power take- off system in Oscillating Water Column (OWC) Wave Energy Conversion (WEC) plant. One of the simpler tools to analyse such turbines is the blade element/actuator disc methodology. This requires the input of “interference factors” to model how the lift and drag characteristics of the cascade of blades on the turbine rotor are related to those of a single isolated aerofoil. In the first part of the paper, CFD modelling to obtain the lift and drag characteristics of various aerofoils arranged in linear cascades at different stagger angles is described. The CFD cascade lift and drag data are compared with reported experimental cascade aerodynamic data. The agreement within the range of usable stagger angles is excellent in the pre-stall range with some deviations shown in the post-stall. A comparison is also made between our 2D CFD interference factors and those previously reported by Weinig and others who used analytical, inviscid flow theory. It is found that the Weinig inviscid flow theory provides a reasonable prediction of the lift interference factor providing that both the angle of attack is relatively low and that the thickness of the blades is relatively small compared to the distance between blades. In the second part of the paper, three- dimensional simulations of a Wells air turbine rotor using CFD unstructured and structured grid designs are described. The results of the three-dimensional CFD simulations were then compared with those from our non-dimensional blade element model incorporating the linear cascade aerodynamic data described in the first part of the paper. The two sets of results are compared in terms of torque coefficient and pressure coefficient.