Experimental investigation of flow periodicity in variable geometry turbine adjustable guide vane sector cascades

The variable geometry turbine (VGT) adjustable guide vane (AGV) is a key component in next-generation variable cycle engines, with its flow control capability and aerodynamic performance playing a crucial role in the turbine and overall engine performance. The AGV controls flow capacity by rotating the blade angle, which inevitably results in tip clearances at both ends of the blades. In this study, the rationality of the tip clearance setting on both sides of the AGV sector cascade in the experiment is systematically studied, and the influence of the tip clearance effect on the periodicity parameters of the flow field is revealed by experimental means. Under the three typical angular displacement conditions of −10°, 0°, and +10°, the five-hole probe flow field measurement, pressure and aerodynamic torque measurement techniques were comprehensively used to quantitatively characterize the influence of tip clearance on the periodic distribution of six parameters such as flow periodicity, flow angle, total pressure loss coefficient, and aerodynamic torque. The results show that after eliminating the tip clearance on both sides of the cascade, the periodicity deviation of the total pressure loss coefficient at the isentropic Mach number of 0.8 decreases by 0.59%, and the periodicity deviation of the flow angle decreases by 0.76%. Comparing the six periodicity analysis results, the periodicity deviation after the elimination of the tip clearance is smaller than that of the tip clearance setting. Eliminating the tip clearances on both sides can effectively enhance the channel flow periodicity. This finding provides a scientific basis for setting the boundary conditions of the VGT AGV vane sector cascade.