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

The ingestion and flow in the disc 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 mid-passage gap (MPG) leakage flow. The SST k-ωmodel 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 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 non-uniformity of the mainstream pressure, alters the mainstream channel flow field, and intensifies the mainstream ingestion. When α = 90°,the radially leakage outflow generates momentum different from the mainstream, amplifying radial non-uniformity and intensifying mainstream ingress. Furthermore, the sealing efficiency increases with the cavity SFR in all MPG angle cases. The minimum cavity SFR of the α=90° case is the largest, with a 25% increase in minimum nondimensional sealing flow compared to the baseline case.