Experimental study on the rapid establishment of the transonic gap flow field

Abstract

In turbine engines, there is a clearance between the rotating blade and the stationary casing. The flow in the tip gap, which is mostly transonic, has a significant impact on the overall thrust and safety performance of the engine. This study aims at elucidating the mechanism of flow establishment in a simplified tip gap model. In this study, the basic structure and pressure distribution of the transient flow field in the gap region are first determined via schlieren techniques and pressure measurements, respectively. Based on these results, we develop a rapid modeling technique of the flow field and analyze the similarities between gap flows with different aspect ratios. As demonstrated by this study, the gap flow can be established within 0.65 s and the entire process comprises five stages. The increase in the downstream pressure and relative fluid viscosity in the gap are found to significantly influence the shock wave structures. Similarities are observed between flow fields in different gaps when the width-to-height ratio is small. With a large width-to-height ratio, the viscosity of the fluid dominates and the corresponding flow fields exhibit no similarity.