  To bridge the gap between high and low fidelity numerical modeling tools for
vertical-axis (or cross-flow) turbines (VATs or CFTs), an actuator line model
(ALM) was developed and validated for both a high and a medium solidity
vertical-axis turbine at rotor diameter Reynolds numbers $Re_D \sim 10^6$. The
ALM is a combination of classical blade element theory and Navier--Stokes based
flow models, and in this study both $k$--$\epsilon$ Reynolds-averaged
Navier--Stokes (RANS) and Smagorinsky large eddy simulation (LES) turbulence
models were tested using the open-source OpenFOAM computational fluid dynamics
framework. The RANS models were able to be run on coarse grids while still
providing good convergence behavior in terms of the mean power coefficient, and
also approximately four orders of magnitude reduction in computational expense
compared with 3-D blade-resolved RANS simulations. Submodels for dynamic stall,
end effects, added mass, and flow curvature were implemented, resulting in
reasonable performance predictions for the high solidity rotor, more
discrepancies for the medium solidity rotor, and overprediction for both cases
at high tip speed ratio. The wake results showed that the ALM was able to
capture some of the important flow features that contribute to VAT's relatively
fast wake recovery---a large improvement over the conventional actuator disk
model. The mean flow field was better realized with the LES, which still
represented a computational savings of two orders of magnitude compared with
3-D blade-resolved RANS, though vortex breakdown and subsequent turbulence
generation appeared to be underpredicted, which necessitates further
investigation of optimal subgrid scale modeling.
