Three-Component Breakdown of Spurious Drag in Computational Fluid Dynamics

摘要

A three-component phenomenological breakdown of spurious pressure drag in computational fluid dynamics is derived, following a far-field formulation. The study is purposely restricted to solutions to the Euler equations, in which the spurious drag, also extant in viscous simulations, can best be detected and analyzed. The matter of far-field spurious-drag elimination, which must indeed be handled differently in viscous flow and in inviscid flow, is outside its scope. Each of the three spurious components is produced through a different process. The first two components, already identified in the past, are of an irreversible thermodynamic nature. The first one is related to vorticity normal to the velocity, as it appears in Crocco's relation. The second one is concomitant with destruction of vorticity parallel to the velocity. The third component, of a reversible nature, is purely due to the effect of the far-field boundary condition. It exists in two-dimensional flow as well as in three- dimensional flow, in which it is shown that it must be negative, while positive in two dimensions.