NUMERICAL STUDY ON AERO-HYDRODYNAMICS WITH INTER- TURBINE SPACING VARIATION FOR TWO FLOATING OFFSHORE WIND TURBINES Yang Huang Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Decheng Wan * Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China * Corresponding author: dcwan@sjtu.edu.cn ABSTRACT To investigate the influence of the inter-turbine spacing on the performance of the floating offshore wind turbine (FOWT) in the floating wind farm, coupled aero-hydrodynamic simulations of two spar-type FOWT models with inter-turbine spacing variation under shear wind and regular wave conditions are performed in the present work. An unsteady actuator line model (UALM) is embedded into in-house code naoe-FOAM-SJTU to establish a fully coupled CFD analysis tool for numerical simulations of FOWTs. From the simulation results, the unsteady aerodynamic power and thrust are obtained, and the hydrodynamic responses including the six- degree-of-freedom motions and mooring tensions are available. Detailed flow visualizations of wake velocity profiles and vortex structures are also illustrated. The coupled performance of floating offshore wind turbines with inter-turbine spacing variation are analyzed, and the influences of inter-turbine spacing on aero-hydrodynamic characteristics of coupled wind- wave flow field are discussed. It is found that the power output of downstream wind turbine increases with inter-turbine spacing. Coupled aero-hydrodynamic characteristics of flow filed are significantly affected by inter-turbine spacing. INTRODUCTION The inter-turbine spacing is a key factor of wind farm layout design parameters, and it has significant effects on the initial investment cost, annual energy production and maintenance cost of the wind farm. Small inter-turbine spacing results in reduced aerodynamic power output, increased fatigue loads and reduced cable laying cost, while large inter-turbine spacing leads to contradictory results. The determination of inter-turbine spacing should consider the influence of wake effect, turbulence effect, fatigue load and annual energy production on the wind turbines during the service lifetime. A series of researches have been conducted to investigate the influence of inter-turbine spacing on the onshore wind farms. Choi et al. [1, 2] studied the effects of inter-turbine spacing on aerodynamic power output, axial wind speed, pressure drop and wake characteristics of a 6 MW wind farm consisting of three sets of 2MW wind turbines in tandem layout. CFD simulations for a wind farm consisting of two sets of 2MW wind turbines were also performed. The effects of separation distance between turbines on aerodynamic power output and wake interactions were discussed. Ai et al. [3] investigated the influence of inter-turbine spacing changing from three to nine times of rotor diameter on aerodynamics for two in-line NREL-5MW wind turbines. The strong wake interactions were observed clearly. However, there are limited literatures focusing on the layout design of floating wind farms. Complicated environment loads and coupling effects between the wind turbine and floating platform make the predictions of aero-hydrodynamic performance of FOWTs quite difficult. Some researchers studied the coupled aero-hydrodynamic performance of the FOWT with computational fluid dynamics (CFD) method. Li et al. [4] investigated the influence of different wind fields on the power generation and aerodynamic performance of FOWTs. The influence of wind shear and inflow turbulence on the Proceedings of the ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering OMAE2019 June 9-14, 2019, Glasgow, Scotland, UK OMAE2019-95520 1 Copyright © 2019 ASME Attendee Read-Only Copy