In this study, overall cooling effectiveness of a vane endwall for a high-pressure turbine of an aero-engine is investigated using combined experimental and numerical methods. In particular, the influence of purge flow upstream of the endwall is examined on the conjugate endwall for various coolant mass flow rates and mainstream flow Reynolds numbers of 1.4 x 10(5)-4.2 x 10(5). The cooling configuration investigated incorporates internal jet impingement cooling and external purge flow and film cooling. Purge flow is injected at an inclination angle of 20 deg from a slot at 12% axial chord length upstream of the vane leading edge and film coolant is injection from three rows of discrete holes within the vane passage on the endwall. Geometric and flow parameters of the engine turbine vane are matched to engine conditions to obtain engine-relevant non-dimensional temperatures. Computational results with and without purge flow are compared to the experimental data, showing good agreement with one another, with an overall averaged error of less than 5.0%. Both measurements and predictions indicate that purge flow has profound enhancement effects on endwall overall cooling effectiveness, particularly improving cooling uniformity. Improvement due to purge flow increases with increases of purge flow rate. Since Reynolds number impacts the external and internal heat transfer simultaneously, the Reynolds number effects depend on which one dominates, but passage inlet Reynolds number globally has little effects on endwall overall cooling performance compared to the effects of coolant mass flow rates. In addition, the numerical results are analyzed to better describe thermal fields in the solid and fluid and, mixing between coolant injection and mainstream flows. (C) 2019 Elsevier Ltd. All rights reserved.