High pressure gas turbine components require advanced cooling schemes to manage thermal loading. The complex nature of the flow in the vicinity of the hub endwall requires careful design for proper film cooling coverage. The secondary vortex flows wash coolant across and away from the endwall while enhancing mixing of endwall boundary layer flow with the mainstream. Therefore, strong understanding of aero-thermal interactions associated with secondary flows and film cooling flows is important to assist in developing better cooling methods. Results of a numerical study of a first stage nozzle guide vane with an axisymmetrically-contoured endwall are presented. The model is of a linear, two-passage cascade that matches the geometry of a previous experimental study. The cascade model includes a film cooling slot on the endwall upstream of the passage inlet. Steady Reynolds Averaged Navier Stokes (RANS) equations are employed for this study using the commercial software ANSYS Fluent. The inlet conditions are forced to match the measured approach flow conditions of the experiment, which include an inlet temperature profile simulating the effects of the combustor liner coolant. Results for temperature fields and endwall adiabatic effectiveness distributions are compared with the corresponding experimental data. It is found that, while overall flow features are captured by the numerical model, the over-dissipative nature of the RANS turbulence model inaccurately under-predicts the turbulent mixing of film coolant with the mainstream flow. This results in an over-prediction of coolant coverage over the endwall. The results document the effects of a common problem with RANS modeling in large-length-scale, highly-turbulent, turbomachinery passage flows.