Accurate predictions on vertical axis wind turbine performance are important for the design process but also challenging because the flow is highly unsteady involving a strong variation of the angle of incidence. In the present work, a double-multiple-streamtube (DMS) approach is improved by analytical corrections. First, two-dimensional and three-dimensional computational fluid dynamics (CFD) simulations are performed for wind turbines at various tip speed ratios. The CFD results are used as a database to investigate the velocity field of the turbines and to derive reasonable physical basis for the modelling approach. Second, new analytical models are introduced to correct the angle of incidence seen by the airfoil section together with correction models for the streamtube expansion and dynamic stall effects. DMS simulations are then carried out and compared with experimental data for turbines with different rotor solidity and various operating ranges. The prediction accuracy is significantly improved by the new model not only for the power coefficient but also for the azimuthal variations of the blade loads. (C) 2019 Elsevier Ltd. All rights reserved.