Drag and Noise Reduction of Flatback Airfoil by Span-wise Wavy Trailing Edge

Abstract

The flatback airfoil is a promising idea for future large wind turbine blade structure design; however, it causes notable drag increase and low frequency tonal noise due to the presence of span-wise coherent standing flow and Karman vortex shedding at the trailing edge. Current dissertation proposes a span-wise wavy trailing edge design as a solution to flatback airfoil drag and noise, and provides relevant CFD results. Proposed span-wise wavy trailing edge prevents the span-wise coherent standing flow and vortex shedding, and results in a decrease of the tonal noise and pressure drag of the airfoil. Delayed Detached Eddy Simulation is employed in HPC environments. In-house developed N-S solvers, OVERTURNS (CPU-based) and GPURANS3D (GPGPU) are used for the computation.

A design parametric study for the span-wise wavy trailing edge is conducted in the first half of the dissertation. Aerodynamic and aeroacoustic performance of a particular flatback airfoil (FB3500-1750, tTE is 17.5% of a chord length) and various span-wise wavy trailing edge modifications are investigated, regarding the influence of the major wave design parameters. A total of 16 design variations of the wavy trailing edge are investigated. For a Reynolds number 666,000 and Mach number 0.3, the best trailing edge wave design is a combination of the less portion - more than 0.25c length - shallow wave depth; the best design reduces 60% (maximum) of the flatback airfoil with only 7% lift loss, and results in about 150% (maximum) of lift/drag ratio increase. Measured tonal noise is also reduced by about 20-25dB(SPL) with the best performance design.

In the second half of the dissertation, the isolated rotor simulation is performed for a straight-flat trailing edge wind turbine blade and its wavy trailing edge modification. In the simulation, the Blunt-Wavy trailing edge (a combination of trailing edge augmentation and wavy modification) is proposed and applied at the inboard of baseline blade (SNL100-03FB). Applying the best performance wavy design, overall turbine power generation is increased by 2.62% and tonal noise is decreased by 5-15dB.