基于空气幕冷却的涡轮端壁改进冷却结构的高温数值验证

The cascade endwall is one of the regions with the most complex flow structure and heat transfer characteristics in the high-pressure turbine of an aero-engine. In order to improve overall cooling performance of a baseline turbine endwall with axially-arranged film cooling holes, this paper redesigned the film cooling scheme for critical heat transfer regions based on the flow structures and heat loads over the turbine endwall, by applying curtain cooling, fan-shaped film holes, and an iso-Mach number line row pattern for film holes, which enables the film coolant to overcome the influence of crossflows and secondary flows. As a result, the coolant adhesion and coverage area were significantly improved. In this study, conjugate heat transfer characteristics of the optimized cooling scheme for the endwall were verified using numerical simulations for an actual inlet condition for the high-pressure turbine of the aero-engine. The computational results revealed that, compared with the baseline cooling scheme, the optimized cooling scheme achieved a lower and more uniform metal temperature distribution for the same amount of coolant consumption under the inlet temperature of 2 150 K, effectively eliminating localized high-temperature hot spots observed in the baseline cooling scheme and increasing area-averaged overall cooling effectiveness on the endwall by 14.2% on average. The reduction of total pressure losses at the vane cascade exit by the optimized cooling scheme demonstrated that it improved the aerodynamic performance of the cascade. The distributions of coolant streamlines showed that curtain cooling provided better cooling performance for the endwall. When the blowing ratio of the curtain cooling reached at 1.85, it overcame the influence of the endwall-nearby vortices, so as to reach and cool the trailing-edge region, and to weaken the adverse influence of the secondary flows on film cooling in the pressure-side region. However, with the excessive blowing ratio of 2.12, the curtain coolant detached from the endwall surface and lost a portion of its cooling capability because of excessive jet momentum. It is thereby necessary to allocate the coolant usage among different cooling sources reasonably.