Development of CFD Algorithms for Transient and Steady Aerodynamics

Research carried out in the United States and in Europe over the last 20 years has led to the development of the advanced propeller, a small-diameter, highly-loaded, multi-bladed, swept, variable-pitch propeller, that can achieve potential fuel savings of 30% over an equivalent technology turbofan engine at competitive speed and altitudes. In this work an implicit finite-volume algorithm is developed for predicting the transient flow around an advanced propeller under asymmetric inflow conditions. The development of the unsteady propeller algorithm evolves from a family of methods for progressively more complex applications. In total six algorithms are developed: three steady and three unsteady. Each solves the Euler equations using a cell-centered, central-difference, finite-volume scheme in transformed space. Adaptive artificial dissipation terms are added both for stability and for accuracy. The steady methods employ an explicit, multistage, time-stepping scheme. A fully implicit time discretisation is employed in the time-dependent algorithms to avoid the maximum time step limitation typical of explicit schemes. The implicit equations are iteratively inverted at each physical time step by casting them in a modified steady form and marching to steady-state in a pseudo time. Local time-stepping, implicit residual averaging and multigrid are employed for convergence acceleration. Results from a range of test cases computed by each of the algorithms are presented and compared with wind tunnel data and with the predictions of other researchers. The unsteady propeller algorithm is used to compute the flowfields around advanced propellers at incidence. The results demonstrate that this family of algorithms is useful for in viscid flowfield analyses and that the unsteady propeller algorithm can provide further insight into the aerodynamics of advanced propellers.