Wind Turbines with Truncated Blades May Be a Possibility for Dense Wind Farms

• Main Authors: Shyuan Cheng, Yaqing Jin, Leonardo P. Chamorro
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Energies
• Subjects: turbine blades; truncated rotors; wind turbines; wind farms
• Online Access: https://www.mdpi.com/1996-1073/13/7/1810

We experimentally explored the impact of a wind turbine with truncated blades on the power output and wake recovery, and its effects within <inline-formula> <math display="inline"> <semantics> <mrow> <mn>2</mn> <mo>×</mo> <mn>3</mn> </mrow> </semantics> </math> </inline-formula> arrays of standard units. The blades of the truncated turbine covered a fraction of the outer region of the rotor span and replaced with a zero-lift structure around the hub, where aerodynamic torque is comparatively low. This way, the incoming flow around the hub may be used as a mixing enhancement mechanism and, consequently, to reduce the flow deficit in the wake. Particle image velocimetry was used to characterize the incoming flow and wake of various truncated turbines with a variety of blade length ratios <inline-formula> <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.6</mn> </mrow> </semantics> </math> </inline-formula>, 0.7, and 1, where <i>L</i> is the length of the working section of the blade of radius <i>R</i>. Power output was obtained at high frequency in each of the truncated turbines, and also at downwind units within <inline-formula> <math display="inline"> <semantics> <mrow> <mn>2</mn> <mo>×</mo> <mn>3</mn> </mrow> </semantics> </math> </inline-formula> arrays with streamwise spacing of <inline-formula> <math display="inline"> <semantics> <mrow> <mo>Δ</mo> <mi>x</mi> <mo>/</mo> <msub> <mi>d</mi> <mi>T</mi> </msub> <mo>=</mo> <mn>4</mn> <mo>,</mo> </mrow> </semantics> </math> </inline-formula> 5, and 6, with <inline-formula> <math display="inline"> <semantics> <msub> <mi>d</mi> <mi>T</mi> </msub> </semantics> </math> </inline-formula> being the turbine diameter. Results show that the enhanced flow around the axis of the rotor induced large-scale instability and mixing that led to substantial power enhancement of wind turbines placed 4<inline-formula> <math display="inline"> <semantics> <msub> <mi>d</mi> <mi>T</mi> </msub> </semantics> </math> </inline-formula> downwind of the <inline-formula> <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.6</mn> </mrow> </semantics> </math> </inline-formula> truncated units; this additional power is still relevant at 6<inline-formula> <math display="inline"> <semantics> <msub> <mi>d</mi> <mi>T</mi> </msub> </semantics> </math> </inline-formula>. Overall, the competing factors defined by the expected power reduction of truncated turbines due to the decrease in the effective blade length, the need for reduced components of the truncated units, and enhanced power output of downwind standard turbines suggest a techno-economic optimization study for potential implementation.