Abstract

In this paper, we investigated the effects of herringbone riblets, a type of bio-inspired micro-scale surface patterns, on the pressure losses and flow turning angles in a linear cascade over a range of low Reynolds numbers from 0.50×105 to 1.50×105 and at three different angles of attack. Our experiments showed that despite the micro-scale size of herringbone riblets they produced a significant reduction in pressure loss coefficient and a substantial increase in flow turning angle except at the low end of Reynolds numbers tested. In comparison to the baseline case without riblets, the highest reduction in mean pressure loss achieved was 36.4% which was accompanied by an increase of average turning angle of 4.1°. It was observed that the loss reduction is associated with a reduction in the maximum pressure loss at lower angles of attack and a narrower wake zone at higher angles of attack as a result of suppression of flow separation on the blade suction surface. It was also noted that such a significant improvement in performance was accompanied by the appearance of a serrated wake structure in the contours of pressure loss coefficient. The improvement in blade performance was attributed to the secondary flow motion produced by herringbone riblets which energises the boundary layer. Overall, this work has produced convincing experimental evidence that herringbone riblets can be used as passive flow control devices for reducing flow separation in compressors at low Reynolds numbers.

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