Development and validation of an improved double-multiple streamtube model for predicting performance of H-type straight-bladed vertical axis wind turbines

H-type straight-bladed vertical axis wind turbines (H-type SB-VAWTs) are a promising concept for deep-sea floating wind power, yet traditional Double-Multiple Streamtube (DMS) models severely overestimate their aerodynamic performance. Existing improved DMS models for SB-VAWTs disagree on the relative contribution of the individual correction terms and generally lack sufficient consideration of the critical three-dimensional (3D) effects. A systematically corrected DMS model is therefore developed by integrating tip/aspect ratio and strut parasitic drag corrections, which act directly on 3D effects, with dynamic stall and flow curvature corrections for unsteady aerodynamic effects. Three-dimensional unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics simulations are conducted to resolve the 3D flow physics of a floating H-type SB-VAWT prototype, and comprehensive validation is performed across four VAWT cases with different configurations. The results reveal that 3D effects have a universal and decisive impact on H-type SB-VAWTs. The corrected DMS model not only remarkably reduces the prediction error of the power coefficient, but also accurately captures the blade azimuthal load variations. This study provides an efficient and high-precision numerical tool for aerodynamic prediction of H-type SB-VAWTs, supporting the design of offshore floating wind turbine systems.