Film cooling effectiveness from upstream purge slots of a turbine vane endwall: Experiment, modeling, and correlation

The design of an efficient cavity slot between assembled components, where purge air is injected, is especially crucial to the durability and efficiency of an aero-engine, since the purge air is relevant to sealing and film cooling of the hot component. In this paper, film cooling for purge flow injected from slots upstream the endwall of a turbine vane is systematically investigated in a linear cascade using Pressure-Sensitive Paint (PSP). The influence of the slot width (0.020-0.044 times vane axial chord length), position (0.11-0.24 times vane axial chord length in front of turbine passage inlets), and inclination angle (20- 45 degrees) is examined for coolant injection ratios of 0.3-2.0 %, with an attempt to develop a new correlation specifically for purge flow film cooling over a turbine endwall, since existing correlations in literature only work for slot injection on flat plates. The experimental tests are undertaken in extensive ranges of the slot geometry and the injection rate that are typically seen in a modern engine. For better understanding the impacts of the affecting parameters, five-hole probe and thermocouple measurements and numerical simulations were carried out as well to visualize the coolant-withmainstream mixing flows. The measured local film coverage, pitchwise- and area-averaged cooling effectiveness are presented and discussed, in combination with the probe-detected and numerically-modeled flow structures to elaborate the experimental observations. The current results sufficiently reveal the changing tendency of purge flow film cooling caused by the variations of the slot geometry. Additionally, the newlydeveloped correlation is well validated using own experimental data and datasets in literature, proving the capability of the correlation to predict film cooling for purge flow injected from slots with such geometrical parameter ranges. The correlation can be a helpful tool to support the selection of an efficient slot in its preliminary design stage.