Numerical Investigation on Influence of Midpassage Gap Leakage on Ingestion and Flow Characteristics in the Downstream Wheelspace of the 1.5-Stage Turbine

Abstract The ingestion and flow in the disk cavity significantly affect the performance and the operating safety of turbines. This paper focuses on the 1.5-stage turbine downstream wheelspace and conducts a numerical simulation to reveal the mainstream ingestion and flow characteristics in the downstream wheelspace with the effect of the midpassage gap (MPG) leakage flow. The SST k–ω model was employed for analytical computations, with results rigorously validated against experimental data to ensure accuracy and reliability. Then, the cavity sealing efficiency was calculated for different injection angles (a) under different cavity sealing air flow rates (SFR). In addition, the transient pressure frequency characteristics are obtained with the fast Fourier transform (FFT). The effect of MPG leakage mass flow rates and injection angles on the unsteady vortex in the main passage and the low-pressure regions in the rim clearance is captured via FFT. The results show that the MPG leakage flow increases the circumferential and radial nonuniformity of the mainstream pressure, alters the mainstream channel flow field, and intensifies the mainstream ingestion. When a = 90 deg, the radially leakage outflow generates momentum different from the mainstream, amplifying radial nonuniformity and intensifying mainstream ingress. Furthermore, the sealing efficiency increases with the cavity SFR in all MPG angle cases. The minimum cavity SFR of the a = 90 deg case is the largest, with a 25% increase in minimum nondimensional sealing flow compared to the baseline case. This study provides critical insights into the complex interactions between MPG leakage flow and mainstream ingestion in turbine wheelspace, contributing to a deeper understanding of flow mechanisms in turbine systems.