An internal, 3-D, viscous numerical flow simulation was performed on the rectangular-to-circular transition, bifurcated, 2D high speed civil transport engine inlet at takeoff. The objective of the study was to obtain the causes of flow distortion at the inlet fan face. The inlet was modeled with the centerbody in the fully collapsed takeoff position. A single block, 14Ox40x40 Polar grid topology of a 1/4 symmetry volume of the inlet was used in the simulation. The calculation employed the well established, robust PARC3D CFD code, which uses the full three-dimensional, Reynolds averaged, Navier-Stokes equations in strong conservation form. The flow was considered to be turbulent over the entire flow region. The turbulence model incorporated into PARC3D is the algebraic Baldwin Lomax model. Limitations existed in the local region where the flow interacts with the nose cone due to the inherent limitations of the turbulence model. The results showed that the flow throughout the inlet was well behaved. The turbulent boundary layers were thin and stayed attached to the surfaces of the inlet throughout the entire flowfield. A high pressure recovery was observed at the fan face. Radial distortion at the fan face was caused by thin boundary layers on the nose cone and cowl surfaces. Circumferential distortion was caused by pressure gradients produced by the wake of the splitter plate, located just upstream of the fan. / Master of Science