The performance of a showerhead arrangement of film cooling in the leading edge region of a first-stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45 deg toward the tip. The blowing ratios tested are BR = 2.0, 3.0, and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of thermochromic liquid crystals (TLC) technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the computational fluid dynamics (CFD) calculations were conducted by simulating the whole vane. Within the Reynolds-averaged Navier–Stokes (RANS) framework, the very widely used realizable k–ε (Rke) and the shear stress transport k–ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e., Rke, was selected for running detached eddy simulation (DES) at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise directions, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C = 0.2.