In order to obtain better performance, gas turbines always operate with high inlet temperature. This contributes to a high level of thermal load on the first stage vane endwall. To ensure safe operation of a gas turbine within a proper temperature range, the cooling performance of the vane endwall must be further investigated. In the present study, effects of the mainstream turbulence and upstream coolant flow direction on the endwall cooling and vane suction side surface phantom cooling were numerically investigated. Three-dimensional (3D) Reynolds-averaged Navier-Stokes (RANS) equations combined with shear stress transport (SST) k - omega turbulence model were solved to conduct the numerical simulations on basis of the validated turbulence model. The calculated results indicate that both the adiabatic cooling effectiveness on the endwall and the phantom cooling effectiveness on the vane suction side surface are significantly influenced by slot injection angle. For alpha = -30 degrees the coolant injection is driven towards the vane suction side, which contributes to the lowest adiabatic cooling effectiveness level on the pressure side endwall and the highest phantom cooling effectiveness level on the vane suction side surface. With the increase of the slot injection angle, the adiabatic cooling effectiveness level on the pressure side endwall is enhanced significantly. In contrast, the phantom cooling (when the vane suction side is cooled by coolant originating from the endwall) of the vane suction side surface is reduced significantly. This is because a large slot injection angle leads to a large coolant momentum towards the pressure side. Moreover, the case with a smaller slot injection angle obtains a slightly higher area-averaged adiabatic cooling effectiveness level around the leading edge due to a relatively larger portion of coolant being confined near the leading edge. In addition, the inlet turbulence intensity has a small impact on the overall endwall cooling and the phantom cooling of the vane suction side surface compared to the slot injection angle. (C) 2017 Elsevier Ltd. All rights reserved.