Effect of Blade Slot Positioning Close to Blade Root on the Performance of Highly Loaded Helium Compressor

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Abstract
The helium compressor has the inherent characteristics of a lower single-stage pressure ratio and a higher number of stages than an air compressor. The highly loaded design method effectively addressed the compressibility issue of the helium compressor. However, the compressor designed with this technique has narrow passages, short blades, and a large bending angle, making the end-wall secondary flow more intense than a conventional compressor. In this paper, numerical simulation and experimental validation has been conducted to identify the effectiveness of the axial slot close to the blade root in improving end-wall secondary flow in a high-load helium compressor cascade, and to provide data and experimental support for the engineering application of high-load helium compressors. The analytical results show that slotting can utilize the self-pressure difference to generate gap leakage vortices, and the axial momentum generated by the leakage vortices blows away the vortices formed due to the separation of corner area. The airflow flows close to the suction surface of the blade and breaks away at the trailing edge of the blade, merges with the main flow and forms a new vortex. As the height of the channel increases, the blowing away of the vortices in the corner region becomes more pronounced and the cascade improvement performance is better. The test results show that the total pressure loss coefficient at the design operating point is reduced by 6.167% when a slot height of 8.53 mm is positioned at 65% Ca (axial chord length). The improvement effect becomes 16.469% better at a 4° attack angle.

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