[Paper Review] Maximizing wind farm power output with the helix approach -- experimental validation and wake analysis using tomographic PIV

Daan van der Hoek, Bert Van den Abbeele+2 more|arXiv (Cornell University)|Jun 22, 2023

Wind Energy Research and Development4 citations

TL;DR

This paper validates the helix approach—a novel wind farm control method using dynamic individual pitch control to induce a helical velocity profile in turbine wakes—through wind tunnel experiments with tomographic PIV. The method enhances wake recovery by accelerating blade tip vortex breakdown, increasing combined power output by up to 15% in a two-turbine setup.

ABSTRACT

Wind farm control can play a key role in reducing the negative impact of wakes on wind turbine power production. The helix approach is a recent innovation in the field of wind farm control, which employs individual blade pitch control to induce a helical velocity profile in a wind turbine wake. This forced meandering of the wake has turned out to be very effective for the recovery of the wake, increasing the power output of downstream turbines by a significant amount. This paper presents a wind tunnel study with two scaled wind turbine models, of which the upstream turbine is operated with the helix approach. We used tomographic particle image velocimetry to study the dynamic behavior of the wake under influence of the helix excitation. The measured flow fields confirm the wake recovery capabilities of the helix approach compared to normal operation. Additional emphasis is put on the effect of the helix approach on the breakdown of blade tip vortices, a process that plays an important role in re-energizing the wake. Measurements indicate that the breakdown of tip vortices, and the resulting destabilization of the wake is enhanced significantly with the helix approach. Finally, turbine measurements show that the helix approach was able to increase the combined power for this particular two turbine setup by as much as 15%.

Motivation & Objective

• To experimentally validate the helix approach for wind farm power maximization using scaled wind tunnel models.
• To analyze the dynamic wake behavior under helix excitation using tomographic PIV.
• To investigate the impact of the helix approach on blade tip vortex breakdown and wake re-energization.
• To quantify the power output improvement in a two-turbine wind farm configuration under helix control.

Proposed method

• Scaled wind tunnel experiments were conducted with two wind turbine models, one upstream turbine operated with the helix approach.
• Tomographic particle image velocimetry (tomo-PIV) was used to measure three-dimensional, time-resolved flow fields in the wake.
• The helix approach was implemented via dynamic individual pitch control (DIPC), inducing periodic yaw and tilt moments with a phase difference to create a helical thrust pattern.
• Wake characteristics were compared between normal operation and helix operation to assess recovery and mixing.
• Vortex breakdown dynamics were analyzed by tracking vorticity evolution and pairing behavior of blade tip vortices.
• Power output was measured for both upstream and downstream turbines to quantify overall system gain.

Experimental results

Research questions

• RQ1 How does the helix approach affect wake recovery and velocity deficit dissipation in a two-turbine wind farm setup?
• RQ2 What is the impact of the helix approach on the breakdown and pairing of blade tip vortices in the wake?
• RQ3 To what extent does the helix approach enhance turbulent mixing and entrainment in the wake?
• RQ4 What is the measurable increase in combined power output when using the helix approach compared to conventional control?

Key findings

• The helix approach significantly enhanced wake recovery, reducing the velocity deficit downstream of the upstream turbine.
• Tomographic PIV measurements confirmed that the helix approach accelerates the breakdown of blade tip vortices, increasing turbulent mixing.
• The helical wake structure induced by DIPC led to stronger entrainment of high-momentum flow into the wake, re-energizing it more effectively.
• The breakdown of tip vortices was observed to be more rapid and intense under helix control, contributing to faster wake recovery.
• The combined power output of the two-turbine setup increased by up to 15% under the helix approach compared to normal operation.
• The experimental results confirm the effectiveness of the helix approach in enhancing wake mixing and power maximization, consistent with prior large eddy simulation findings.