This paper describes some studies on flow separation and on the extended Cebeci-Smith turbulence and transition models, carried out using a three-dimensional turbulent boundary layer code developed at the Vikram Sarabhai Space Center (VSSC), Thiruvananthapuram, India. This code uses an orthogonal curvilinear surface fitted co-ordinate system. The governing equations are solved, by an implicit space marching numerical method called the Keller Box Scheme with suitable modifications for reverse crossflows. Initial data on two intersecting planes for starting the solution procedure, are obtained by solving the appropriate limiting form of the governing equations. Three transition models available in the Literature are studied. A few sample results are presented and compared with experimental measurements.