Large-Eddy Simulation of Tidal Currents in Portsmouth Harbor: Implications for Turbine Array Design

Tidal energy systems are inherently site-specific, with their potential strongly influenced by local topography and bathymetry. Field-scale simulations, supported by high-resolution digital mapping of narrow tidal channels, are critical for capturing turbulent flow dynamics and optimizing reliable energy extraction. This study presents large-eddy simulations (LES) of a 6 km stretch of the Portsmouth Harbor to support the deployment of tidal turbine arrays under both ebb and flood conditions. The digital elevation model of the Piscataqua River was reconstructed using a combination of remote sensing data and field measurements. The study aims to (1) identify technically viable sites for tidal energy deployment and (2) optimize turbine placement within the selected area. To represent a range of realistic tidal inflows, four inlet boundary conditions were considered: (1) a synthetic log-law velocity profile applied to both tidal phases, (2) turbulent inflow from a straight-channel precursor simulation, (3) flood-tide turbulence from a 500 m upstream river segment, and (4) ocean-driven conditions derived from the Regional Ocean Modeling System (ROMS). Simulation results were used to assess local hydrodynamics and inform turbine array design. Findings indicate that turbulent structures during ebb tide are the dominant factor influencing both energy output and layout optimization, with a 5-meter rotor diameter emerging as the most effective configuration for the site.