An improved BEM-type model for Vertical-Axis Wind Turbines by incorporation of base-suction effects

We present a modified double-multiple streamtube (DMST) model for vertical-axis wind turbines (VAWT). This approach builds on blade element momentum theory (BEMT) and accounts for the azimuthal dependence of blade aerodynamics by discretizing the flow into a set of adjacent streamtubes, each featuring two actuator disks in tandem. BEMT equations are solved twice in each streamtube, once at the upstream and once at the downstream turbine half cycle, respectively. The Rankine-Froude actuator disk theory, which traditionally constitutes the momentum aspect of BEMT is replaced by a recently developed model for the drag of two-dimensional flat plate of arbitrary porosity. This model takes into account the effect of base suction in the wake and yields realistic wake velocities. This is critical for DMST models as wake velocities from upstream actuators are used as input to downstream streamtubes. Global performance predictions are compared to the unique Princeton HRTF wind tunnel measurements conducted at full dynamic similarity with respect to full-scale turbines operating at high Re-numbers  ($0.5\times10^6<Re_D<5\times10^6$), with varying tip-speed ratios ($0.75<TSR<2.5$) and solidities ($0.45<St<1.12$). The proposed model performs significantly better than conventional DMST models.