ABSTRACT Title of Dissertation: Quad Tilt Rotor Simulations in Helicopter Mode using Computational Fluid Dynamics

The flow field around a simplified Quad Tilt Rotor (QTR) vehicle is simulated using com-putational fluid dynamics (CFD) for various low speed flight conditions in helicopter mode. A time-averaged rotor model is utilized, where the velocity field computed by CFD is cou-pled to blade element theory and a trim model to provide an equivalent time-averaged body force term in the compressible Navier-Stokes equations, instead of moving overset meshes; reducing the computational time while capturing the essential physics. Overset meshes are used to model the complicated geometry of the simplified aircraft fuselage and wings in order to ensure good resolution of viscous effects. The solution of the compressible Navier-Stokes equations are suitably modified using low Mach number preconditioning to properly scale the dissipation and enhance convergence. This approach is validated for the current work by comparison with experimental data for the downwash velocity underneath an isolated tilt rotor system as well as for the pressure distribution resulting on the surface of a single wing placed underneath such a tilt rotor system. A total of 8 grids with approximately 5.2 million grid points is then employed to simulate half of a simplified QTR geometry for a range of flight conditions. A high download (9 % of thrust) is obtained in hover, as expected, when th