Identifying the theoretical performance limit for Vertical Axis Wind Turbines

The classical Betz limit establishes a maximum efficiency of 59.3% for Horizontal Axis wind Turbines (HAWTs) under ideal flow conditions. This limit is extended to Vertical-Axis Wind Turbines (VAWTs), despite their fundamentally different energy extraction mechanisms. This study proposes a revised limit of 64% for VAWTs, derived from conservation laws and analogous to other performance limits such as the Betz Limit and Carnot Heat Pump correlation. To incorporate the assumptions for both the derivations, a porous jump based CFD environment will be used to test the formulation, wherein a thin resistive flow region within the control volume represents the turbine and introduces an energy extraction factor, without introducing non ideal flow characteristics, to understand energy extraction ceilings. Preliminary results suggest that the traditional Betz reference frame under-represents the full potential performance of VAWTs and overlooks the dominant physical constraints unique to crossflow configurations. The ideal axial induction factors also differ between HAWTs and VAWTs , giving rise to the discrepancy in the limits. The revised limit offers a framework to better understand the underlying drivers of efficiency and to inform future turbine optimization. Future work will include power spectral analysis, incorporating prevalent flow and flow interaction characteristics in both turbines, followed by experimental validation to assess model fidelity and extract design-relevant insights.