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Hardware-in-the-loop wind-tunnel testing of wake interactions between two floating wind turbines

Alessandro Fontanella, Kristjan Milic, Alan Facchinetti, Sara Muggiasca, Marco Belloli

TL;DR

This paper addresses the two-way coupling between wake development and platform motion in floating wind farms by introducing a hardware-in-the-loop wind-tunnel framework that couples two scaled rotors with a real-time aero-hydro-servo-elastic model. The methodology uses a 1:150 geometric scale and 1:2.5 velocity scale to reproduce inflow and aerodynamic loads while computing hydrodynamic effects numerically, enabling fully coupled wake–motion experiments. Key findings show that a downstream turbine in the upstream wake experiences reduced mean thrust and damped platform motion in mean terms, yet exhibits enhanced low-frequency motion due to wake turbulence; PSD analysis confirms elevated low-frequency energy in the wake that excites platform resonances. The approach provides a controlled, repeatable experimental basis for validating floating wind-farm models and control strategies, offering insight into wake-induced excitation mechanisms relevant to fatigue and layout optimization, while acknowledging scaling limitations for absolute load magnitudes.

Abstract

Wake interactions in floating wind farms are inherently coupled to platform motion, yet most experimental studies to date neglect this two-way coupling by prescribing platform movements. This work presents a hardware-in-the-loop (HIL) wind-tunnel methodology to investigate wake interactions between two floating wind turbines with fully coupled aerodynamic loading and platform dynamics. The approach integrates physical wind-tunnel testing of two scaled rotors with a real-time numerical model that accounts for platform motion, mooring restoring forces, and hydrodynamic loads. Experiments conducted under low-turbulence inflow conditions show that a downstream turbine operating in the wake of an upstream turbine experiences reduced mean thrust and platform deflections due to the decreased inflow velocity, alongside enhanced low-frequency platform motions driven by increased turbulent energy in the wake. The proposed HIL framework provides a controlled experimental basis for studying wake-induced excitation mechanisms and supports the validation of floating wind farm models and control strategies.

Hardware-in-the-loop wind-tunnel testing of wake interactions between two floating wind turbines

TL;DR

This paper addresses the two-way coupling between wake development and platform motion in floating wind farms by introducing a hardware-in-the-loop wind-tunnel framework that couples two scaled rotors with a real-time aero-hydro-servo-elastic model. The methodology uses a 1:150 geometric scale and 1:2.5 velocity scale to reproduce inflow and aerodynamic loads while computing hydrodynamic effects numerically, enabling fully coupled wake–motion experiments. Key findings show that a downstream turbine in the upstream wake experiences reduced mean thrust and damped platform motion in mean terms, yet exhibits enhanced low-frequency motion due to wake turbulence; PSD analysis confirms elevated low-frequency energy in the wake that excites platform resonances. The approach provides a controlled, repeatable experimental basis for validating floating wind-farm models and control strategies, offering insight into wake-induced excitation mechanisms relevant to fatigue and layout optimization, while acknowledging scaling limitations for absolute load magnitudes.

Abstract

Wake interactions in floating wind farms are inherently coupled to platform motion, yet most experimental studies to date neglect this two-way coupling by prescribing platform movements. This work presents a hardware-in-the-loop (HIL) wind-tunnel methodology to investigate wake interactions between two floating wind turbines with fully coupled aerodynamic loading and platform dynamics. The approach integrates physical wind-tunnel testing of two scaled rotors with a real-time numerical model that accounts for platform motion, mooring restoring forces, and hydrodynamic loads. Experiments conducted under low-turbulence inflow conditions show that a downstream turbine operating in the wake of an upstream turbine experiences reduced mean thrust and platform deflections due to the decreased inflow velocity, alongside enhanced low-frequency platform motions driven by increased turbulent energy in the wake. The proposed HIL framework provides a controlled experimental basis for studying wake-induced excitation mechanisms and supports the validation of floating wind farm models and control strategies.
Paper Structure (11 sections, 4 equations, 6 figures, 1 table)

This paper contains 11 sections, 4 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Methodology
  3. Wind farm scaling and implications for the HIL approach
  4. Aerodynamic representativeness for wake--motion coupling
  5. Experimental setup and HIL system architecture
  6. Real-time HIL control and dynamic modeling
  7. Aerodynamic load reconstruction and force feedback
  8. Results
  9. Verification tests with no wind
  10. Steady wind test
  11. Conclusions

Figures (6)

  • Figure 1: (a) Experimental setup of the floating wind farm in the wind tunnel. (b) Schematic representation of the hardware-in-the-loop system used to emulate the dynamic behavior of the floating wind farm.
  • Figure 2: Block diagram of the hardware-in-the-loop control framework.
  • Figure 3: Platform surge and pitch motions of the two wind turbines from free-decay tests conducted in still air, without wind-turbine force feedback ("open loop") and with force feedback ("closed loop").
  • Figure 4: Inflow conditions along a horizontal line at hub height, shown for the free-stream region and two locations between WT1 and WT2. (a) Mean wind speed normalized by the free-stream value. (b) Turbulence intensity.
  • Figure 5: Platform surge and pitch motions of the two wind turbines with wind.
  • ...and 1 more figures