Experimental Investigation of Nonperiodic Endwall Film Cooling in Neighboring Passages With Upstream Rotating Flow

Abstract

The distribution of film-cooling holes is considered to be the same between neighbouring high pressure turbine passages in most cascade experiments. Because of the difference in accounts of combustors and vanes, however, the flow fields of neighbouring passages are completely different. The secondary flow, especially the passage vortex, is dominated by the upstream inlet rotating flow whose relative flow direction is the reverse between the neighbouring vane passages. Specific rotating directions introduce new challenges in film-cooling design. The present experiment compares three groups of endwall film-cooling with anticlockwise rotating flow inlets at different clocking positions, and the film-cooling effect is analysed to investigate the effects of inlet rotating flow. The inlet flow condition of neighbouring passages is simulated by switching the position of the swirler by means of which rotating inlet flow conditions in different positions are achieved. The GE-E3 airfoil is used in the cascades, with a scaled-up factor of 2.2. The inlet Reynolds number is 3.5×105 and the Mach number is 0.1. The effects of the blowing ratio and relative positions of the swirler are investigated in the experiment. Adiabatic film-cooling effectiveness is probed by using pressure-sensitive painting (PSP). The coolant is simulated by nitrogen by which a density ratio of around 1.0 can be achieved. Fan-shaped film-cooling holes are introduced into the endwall surface as well as trailing edge discharge holes. The cooling performance of the combustor-turbine gap leakage flow is also considered simultaneously. Conclusions are as follows: (1) the anticlockwise direction of rotating flow influences the endwall film-cooling effectiveness, especially for the upstream part of the endwall which is mainly covered by the leakage flow; (2) the film-cooling effectiveness in the neighbouring passages differs depending on the position of the inlet rotating flow core; (3) the film-cooling performance at the downstream part of the endwall is partly influenced by the upstream rotating flow inlet as well.