Combined immersed-boundary finite-difference methods for three-dimensionalcomplex flow simulations

A second-order accurate, highly efficient method is developed for simulatin g unsteady three-dimensional incompressible flows in complex geometries. Th is is achieved by using boundary body forces that allow the imposition of t he boundary conditions on a given surface not coinciding with the computati onal grid. The governing equations, therefore, can be discretized and solve d on a regular mesh thus retaining the advantages and the efficiency of the standard solution procedures. Two different forcings are tested showing th at while the quality of the results is essentially the same in both cases, the efficiency of the calculation strongly depends on the particular expres sion. A major issue is the interpolation of the forcing over the grid that determines the accuracy of the scheme; this ranges from zeroth-order for th e most commonly used interpolations up to second-order for an ad hoc veloci ty interpolation. The present scheme has been used to simulate several hows whose results have been validated by experiments and other results availab le in the literature. Finally in the last example we show the flow inside a n IC piston/cylinder assembly at high Reynolds number; to our knowledge thi s is the first example in which the immersed boundary technique is applied to a full three-dimensional complex how with moving boundaries and with a R eynolds number high enough to require a subgrid-scale turbulence model. (C) 2000 Academic Press.