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It is well known that the secondary flow, including vortexes, boundary layer, and three-dimensional separation, is detrimental to the efficiency and stability in the axial compressor. As a passive secondary flow control technique, the endwall fence is considered to overcome the adverse pressure gradient by blocking the crossflow. On this paper, a steady computational study is carried out in a high-speed compressor cascade. Two categories of fence configurations, i.e., embedded in the front and the back of flow passage, have been investigated. For each category, the fence position is selected at 7 locations ranging from 20% to 80% pitch length away from the blade pressure surface, the interval between each case is 10% pitch length. In the comparison between the datum and the fenced cascade, the case of 50% pitch length away from the blade suction surface in the category of front fences is most effective in the improvement of the aerodynamic performance. At the design point, this case decreases the loss coefficient and the blockage coefficient by 6.3% and 6.5%, respectively. Meanwhile, it increases the absolute value of the flow turning angle by 0.9%. From the perspective of the vortex structure, both optimum fences in the front and back category can suppress the passage vortex by inducing the counter-rotating fence vortex, of which scale has a relationship with the contact area between fence surface and the crossflow. Last but not least, the fenced cascade with an optimum performance both in loss mechanism and vortex structure has been investigated under varying inlet incidences. The comparison analysis of the baseline and optimum fence and demonstrates that there is a reduction of the loss exists at negative incidences while an augment occurs at positive incidences. In summary, the optimum case of endwall fence can effectively weaken the endwall loss and thereby enlarge the cascade operating range under negative incidences. INTRODUCTION The efficiency is probably the most crucial index for most turbomachines, which is influenced by some complex factors, such as profile loss, tip leakage loss, and endwall crossflow (Denton 1993). Over the past few decades, enormous efforts have been taken to reduce the endwall loss of different types of compressors. For modern high-speed compressors, both the higher transverse pressure gradient and the viscous effect may inevitably increase endwall loss, which carries the challenges to obtain further aerodynamic improvements (Gbadebo, Cumpsty, and Hynes 2005). Hence the endwall loss has a strong influence on overall cascade loss. The flow control technology, acting on a small scale, is used to bring the desired behaviour change into a larger flow (Gad-el-Hak 1996). It is proved that flow control is effective in the sources of endwall flow such as the boundary separation, skin-friction, low momentum, and wake mixing. The mainly two types of flow control, active and passive, are witnessing the interest of market and research (Hecklau et al. 2012). This kind of classification for flow control methods considers the energy involved and the control loop included. Active control such as boundary layer suction (Zhang et al. 2018), synthetic jet (Zander et al. 2011), and plasma actuation (Li et al. 2010), is widely researched depends on the recent advancement of computers and experiments. However, passive control is simpler to apply to an existing device and bring lower cost due to its simpler form. Passive flow control of endwall loss is currently employed via shaping: endwall fence/groove (Hage and Paschereit 2007), vortex generator (Diaa et al. 2015), endwall contouring (Chen et al. 2012), casing treatment, etc, which is beneficial to delay or provoke separation. As a structural bulge along streamwise on endwall surface, endwall fence is available to hinder the crossflow and

Control 0f Secondary Crossflow in a High-Speed Compressor Cascade by Endwall Fences with Varying Locations