High order simulation of unsteady compressible flows over interacting bodies with overset grids

A high order upwind scheme for first-principles based study of rotorcraft flowfields has been developed. The presence of highly concentrated vorticity regions plays a critical role in the determination of surface loads and in the design of rotor blades. A fifth order spatially accurate, second order temporally accurate, first-principles based Euler/Navier-Stokes analysis has been developed. The second order temporal accuracy has been achieved by the use of an iterative time integration scheme. This method has been applied to the study of two different rotors in hover and good agreement with experimental results has been obtained. The fifth order scheme is shown to capture the tip vortex accurately up to one revolution of the rotor, on relatively coarse grids.; To model complex rotor-airframe interaction, an overset grid methodology was adopted. An unsteady grid connectivity method has been developed for this purpose and has been closely integrated with the high order analysis. This overset grid method was used to study the unsteady flowfield around a rotor-airframe configuration that was tested at Georgia Tech. The various physical features of the flowfield were predicted well. Encouraging time averaged and instantaneous surface pressure correlations on the airframe have been obtained.; The fifth order analysis was used to study the evolution of the tip vortex from a wing. Downward and axial velocity profiles across the face of the tip vortex were computed using the high order scheme. These velocity profiles compared well with experimental values at various streamwise stations downstream of the wing trailing edge. The fifth order simulation predicted a complex evolution of the tip vortex system, with small, weak counter-rotating vortices moving around a strong vortex core.; The use of overset grids as a visualization tool for the study of the fine features of vortices was also investigated. It was found that the vortices can be transported over much larger distances without dissipation if overset grids were used instead of a single grid. The advantage of overset grids as a "microscope" for delineating fine flow features not visible in the baseline grid is clearly demonstrated.