IMPROVING EFFICIENCY AND RANGE OF AXIAL COMPRESSOR SYSTEMS AT LOW REYNOLDS NUMBER USING MICRO DESIGN FEATURES

Abstract

The need for compressors with higher efficiency or a wider working range has inspired numerous techniques to improve the performance of compressor blades. However, current mechanisms still offer limited efficient improvements without structural complexity and high operational cost. Surface textures are amongst the most appealing approaches, as they provide considerable advancement in blade performance with easy implementation. This thesis presents an investigation on the improvement of compressor blade performance using herringbone riblets in a linear cascade. The novel herringbone riblets were designed based on both micro and macro structure of the secondary feather on pigeon wing. Advanced laser processing technique was used to manufacture the herringbone riblets on foils, which were then applied on blade suction surface. The total pressure loss coefficients and flow turning angles at the cascade exit in the cases with and without herringbone riblets were measured using a five-hole probe at a range of low Reynolds number and three angles of attack. The results show that over a critical Reynolds number, herringbone riblets produce a serrated structure in the wake zone and offer a significant loss reduction percentage and increase in flow turning angle. Before the critical Reynolds number, the herringbone riblets are only capable of improving the uniformity of the wake flow and do not improve average loss coefficient and flow turning angle. A higher Re brings about a stronger serrated structure, while returning a slightly lower loss reduction percentage. At off design angles of attack, the herringbone riblets are still capable of reducing the loss and increasing the flow turning angle over the critical Re, with a higher improvement at higher angles of attack. Both deeper and wider riblets extend loss reduction effect towards lower Reynolds number, this is, however, at the expense of a lower loss reduction percentage at higher Reynolds number. A similar alteration of critical Reynolds number towards lower value is achieved by the upstream shift of herringbone riblets. However, this results in a slight deterioration in loss coefficient at higher Reynolds number. Likewise, the herringbone riblets with half wavelength yield a larger deterioration in loss coefficient, although the critical Reynolds number is not changed. The experiments at higher turbulence intensity show that loss reduction effect is extended toward lower Reynolds number without degradation in the blade performance at higher Reynolds number, which proves the robust effectiveness of herringbone riblets at different turbulence intensities. The accomplishment of using herringbone riblets for separation control on compressor blade has not only paved the way for their potential applications in compression system, but also provides a new perspective on the role of bird feathers in the improvement of flight efficiency.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lin Li (Supervisor) & Shan Zhong (Supervisor)