Beyond Axial Deceleration: A Volume-Based Model for Renewable Energy Conversion in Incompressible Flows

This paper introduces a novel theoretical framework for energy conversion in natural flow systems, primarily focusing on ocean currents while extending its applicability to rivers and artificial channels. The proposed model is based on the concept of volumetric coupling between a conversion device and the surrounding incompressible flow. In contrast to classical approaches, which rely on axial deceleration and wake expansion, this method considers the interaction with an extended upstream volume of fluid whose inertia and continuity support energy extraction through controlled momentum deflection. This dynamic interaction is embedded within the Energy Restoration by Geophysical Fields (ERGF) model, which interprets these flows as open systems sustained by persistent physical mechanisms such as gravity, planetary rotation and thermohaline gradients in oceans, or topographic level differences in rivers and canals. Within this theoretical framework, the study analyses a resonant ideal turbine configuration designed to operate in continuous coupling with the flow, extracting mechanical power with minimal disturbance to large-scale hydrodynamics. Although experimental validation is ongoing, the paper outlines standardised testing methodologies (IEC, ITTC) that will underpin future performance assessments. The theoretical contributions presented herein aim to support the development of highly efficient and low-impact renewable energy systems based on volumetric interaction and continuous energy replenishment principles.