Urgent generation of turbulence models for Computational Fluid Dynamics (CFD) enabled accurate simulation of fully turbulent flows in industry for decades, however, prediction accuracy for laminar-to-turbulent transitional flow lags significantly. Transitional turbulence models are still either in development or validation phase and not sufficiently mature for regular use in industrial computational fluid dynamics (CFD). In this Thesis validation of the Langtry-Menter k-Omega SST, a transitional 4 equation turbulence model is presented. The Langtry-Menter k-Omega SST, also known as the gamma-Re_theta model, is a 4 equation correlation-based transition model built strictly on local variables. Transitional turbulence model gamma-Re_theta is compared with the well known k-Omega SST model by Menter. The k-Omega SST is a 2 equation eddy-viscosity model. 2D validation is carried out for a Flat Plate geometry and the Eppler 387 airfoil geometry. Systematic mesh refinement study is performed for every geometry, with 9 meshes of different resolution. Flow quantities selected for comparison with experimental data include mean horizontal velocity profile, at three locations and skin friction coefficient for the Flat Plate geometry and pressure coefficient for Eppler 387 airfoil geometry. Furthermore, numerical uncertainty of the results, with regard to mesh density, is evaluated in accordance with Eca and Hoekstra. Simulation results for most of the 2D test cases show accurate transition behaviour and high correspondence with the experimental data.