Design and Optimization of Leading-Edge Tubercles for a Transonic Axial Compressor

In nature, the front of the flippers of humpback whales are structured with protuberances, so-called tubercles, giving them excellent manoeuvrability. Inspired by this, tubercles can be implemented on the leading edge of compressor blades as a form of passive flow control, improving performance and possibly stall margin. In the present work, the effect of leading-edge tubercles in a single-stage transonic compressor is investigated numerically. The base compressor operates at a mass flow rate of up to 0.83 kg/s and is capable of reaching pressure ratios of up to 1.8 and isentropic efficiencies of up to 87% while the flow is accelerated to relative inlet Mach numbers of up to 1.5. The tubercles are initially implemented on the leading edges of the rotor blades and stator vanes via a sinusoidal function and hence as a function of amplitude and wavelength. A genetic algorithm is then used to optimize the compressor aerodynamic performance by means of steady-state CFD at design-point conditions of a mass flow rate of 0.8 kg/s and a speed of 77,000 rpm. By computing and comparing the performance maps of the reference and the optimized compressor, off-optimization point performance can be assessed. An in-depth analysis of the flow field allows the identification of the underlying effects behind the performance improvement for the tubercle-shaped topology: the creation of counter rotating vortices, laminar separation bubbles and the reduction in tip leakage vortex size at suction side-incidence.