Phase-resolved aerodynamic work redistribution in vertical-axis wind turbines under geometric and pitch-angle perturbations

Abstract

Vertical-axis wind turbines (VAWTs) undergo periodic variations in relative velocity, angle of attack, and blade–wake interaction, making aerodynamic loading and energy transfer phase dependent. The cycle-averaged power coefficient CP cannot resolve how favorable work, aerodynamic work loss, and dominant work-producing phases are distributed with azimuthal angle θ. Here, a phase-resolved aerodynamic work framework is developed using a wind tunnel-validated three-dimensional unsteady computational fluid dynamics model of a straight-bladed H-type VAWT. Controlled variations in blade number, rotor geometry, and pitch-angle probe phase-resolved power and the partitioning of aerodynamic work into positive, loss, and net components; surface pressure, velocity fields, and vortical structures reveal the underlying flow physics. Rotor output is governed by the phase organization and mutual cancellation of blade loads over a revolution rather than by a single instantaneous load peak. At a tip-speed ratio λ = 1.5, the phase-resolved power coefficient CP(θ) exhibits a nonuniform multimodal distribution, with the dominant peak at θ ≈ 330° and CP,peak ≈ 0.615. Geometric and pitch-angle perturbations redistribute aerodynamic work through changes in local inflow, pressure loading, wake coupling, and vortex dynamics. Three modes emerge: positive-work modulation, positive–negative work rebalance, and phase reorganization, providing a unified physical interpretation of configuration-dependent VAWT energy conversion.