The Role of Dynamic Stall in Aerofoil Shape Optimisation for Curvilinear Blade Kinematics

TL;DR

This paper explores how aerofoil shape optimization can improve blade performance in vertical-axis turbines by controlling dynamic stall effects, with validation through simulations and experiments, highlighting the importance of stall severity for optimization success.

Contribution

It introduces a physics-based condition for effective aerofoil optimization in dynamic stall environments, emphasizing the role of rotor solidity and stall severity in blade performance enhancement.

Findings

Optimization improves aerodynamic loading by suppressing vortex separation under light stall.

Effectiveness of optimization depends on dynamic stall severity and rotor solidity.

Aerofoil shape modification is effective mainly in high-solidity, moderated stall regimes.

Abstract

This study investigates the influence of aerofoil shape optimisation on blade aerodynamic performance under curvilinear and unsteady kinematics characteristic of vertical-axis turbines and cycloidal propellers. Using a cyclorotor in hover as a representative configuration, aerofoil optimisation was performed using two-dimensional unsteady Reynolds-averaged Navier-Stokes simulations coupled with Kriging. The optimised design was subsequently validated experimentally through force measurements and flow-field characterisation using particle image velocimetry. Performance was enhanced through the suppression of leading-edge vortex separation during the primary thrust peak. This finding also reveals a governing constraint: the effectiveness of aerofoil optimisation depends on dynamic stall severity. Under light dynamic stall, geometric modification promotes vortex attachment and improves aerodynamic loading. Under deep dynamic stall, flow separation dominates the blade aerodynamics, and aerofoil shape modification cannot suppress leading-edge vortex shedding. The stall severity is regulated by rotor solidity through its influence on the induced throughflow-to-blade-speed ratio and the resulting effective incidence. Aerofoil optimisation is therefore viable primarily in high-solidity configurations that operate within a moderated stall regime. These findings establish a physics-based condition for aerofoil optimisation in curvilinear dynamic stall environments.