A PARALLEL NEWTON-KRYLOV METHOD FOR ROTORCRAFT FLOWFIELD CALCULATIONS

This paper explores the use of Krylov subspace iterative methods for implicit solution of rotary-wing flowfields on parallel computers. A Newton-Krylov scheme is proposed which couples conjugate gradient-like iterative methods within the baseline structured-grid Euler/Navier-Stokes flow solver TURNS (Transonic Unsteady Rotor Navier Stokes). Two Krylov methods are studied, Generalized Minimum Residual (GMRES) and Orthogonal s-Step Orthomin (OSOmin). Preconditioning is performed with a parallelized form of the Lower Upper-Symmetric Gauss Seidel (LU-SGS) operator. The scheme is implemented on the IBM SP2 multiprocessor and applied to three-dimensi onal computations of a rotor in forward flight. The main benefit of the Newton-Krylov scheme is found to be a higher level of time-accuracy in implicit timestepping. This increases the allowable timestep for time-accurate unsteady calculations, yielding a reduction in the overall solution time.

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