21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-2.2.2

EFFICIENCY IMPROVEMENT OF CFD CODES USING ANALYTICAL FAR-FIELD BOUNDARY CONDITIONS

Verhoff A.
Boeing, USA

Keywords: cfd codes, analytical far-field boundary conditions

Higher-order far-field computational boundary conditions have been developed for CFD (Computational Fluid Dynamics) calculation of inviscid external flows. They are derived from analytical solutions of an asymptotic form of the steady state Euler equations and have improved accuracy compared to commonly-used characteristic boundary conditions. The analytical solutions provide for a smooth transition across the boundary to the true far-field conditions at infinity. The Euler equations are asymptotically linearized about this constant pressure, rectilinear flow condition. Because the Euler equations are used to develop the boundary conditions, the flow crossing the boundary can be rotational (i.e., applicable to transonic flow calculations). The boundary conditions can be used with any numerical Euler solution method and allow computational boundaries to be located very close to the nonlinear region of interest. This leads to a significant reduction in the number of grid points required for a CFD solution. Because of the proximity of the boundaries, convergence rate of the solution is also increased because fewer iteration steps are required to propagate information between upstream and downstream boundaries. If viscous dissipation is neglected in the far field, the boundary conditions can also be used with Navier-Stokes CFD codes. The procedure also demonstrates the synergism that can be realized from coupling analytical and computational methods.

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