# Review of Passive Flow Control Methods for Compressor Linear Cascades
## 2 Chronological Evolution of Linear Cascade
From 1958 to 1963, research refined the understanding of flow patterns and loss mechanisms, focusing on wall effects and stall zones [32; 33]. In 1962, theoretical work predicted stall zones at blade corners, which experimental studies later validated by showing stall growth along blade roots and tips [34]. By 1963, investigations into secondary flow patterns in axial compressors promoted design improvements that reduced secondary flow losses [35]. Research through the 1970s further explored geometric effects on flow, revealing  
Figure 1: (**a**) First cascade testing apparatus, testing the NACA 65, 2-810 sections with stagger: 45\({}^{\circ}\) and solidity: 1 [22], (**b**) [PERSON]’s 5-inch cascade [24]. that aspect ratio had a significant impact. High aspect ratios increased deflection near stall, while low aspect ratios caused flow contraction at the centerline [36]. A 1978 study on wall boundary layers indicated that inviscid flow adjustments could dominate boundary layer behaviour through cascades, emphasizing the interplay between boundary layers and cascade aerodynamics [37]. Advancements in the 1980s and 1990s built on these foundational insights. A 1982 study introduced a method for computing secondary flows in cascades, incorporating Bernoulli surface rotation effects. While significant distortions were observed near endwalls, the impact on downstream flow was minimal [38]. In 1985, investigations using rotating pressure probes highlighted the complexity of vortex flows near rotor casing and end-wall-tip interactions. The studies revealed that flow unsteadiness distorted probe data, but dynamic calibration successfully corrected these inaccuracies [39]. Additional research during this period focused on the effects of increased blade loading, which often led to corner separation. In severe cases, this corner separation extended into full-span separation on the rotor. For second-stage stators, high blade loading caused significant growth in corner separation, with blockage reaching nearly 40% and extending to 70% of the blade span [40; 41]. These trends persisted into the 1990s, with researchers confirming that increased compressor loading amplified both the spread and intensity of corner separation. Studies from this era demonstrated how these effects could limit performance and highlighted the importance of advanced design techniques to mitigate separation [42; 43; 44]. The 1990s marked significant advancements in compressor blade design and cascade performance, with a strong focus on passive control methods. In 1993, hot-wire anemometry and pressure measurements revealed that narrow creenulations on blade edges enhanced wake mixing and reduced pressure losses more effectively than larger creenulations. This finding provided a practical approach to improving cascade efficiency and highlighted the potential of subtle blade-edge modifications [45]. Numerical studies from the same year demonstrated the benefits of grooved endwalls, which energized leakage flows and reduced blockage, offering a promising technique for stall suppression in compressor cascades [46]. Complementary research on tip leakage vortices showed intensified vorticity near the leading edge, which decayed downstream, further revealing the complex nature of leakage flow interactions [47]. In 1994, investigations into NACA 65-1810 blades with varying tip clearances revealed that larger clearances reduced the mixing efficiency of leakage flows, particularly when downstream mixing was incomplete [48]. These findings underscored the importance of optimizing blade and endwall geometries to mitigate losses and enhance overall performance. Later in the decade, a 1998 study using laser-Doppler velocimetry documented unsteady stalling phenomena in controlled-diffusion blades. This research identified regions of continuous and intermittent reverse flow, refining the understanding of blade surface interactions under challenging flow conditions [49].