IMPLEMENTATION OF A NONLINEAR FILTER WITH A LAGRANGIAN FORMULATION FOR THE TREATMENT OF VERY HIGH-PRESSURE REFLECTED SHOCKS

The Engquist filter is implemented within the one-dimensional Lagrangi an gas dynamics code HAROLD. The conservation Version and the total va riation diminishing version of the filter are combined as proposed in the original paper, with filtering performed in characteristics space. The present results show that the fi Iter performs well in the Lagran gian system for very strong shocks. A new treatment of the wall bounda ry reflection for strong shocks that takes advantage of the filter is presented. Reflected shocks calculated using this technique show essen tially no overshoots typical of classical finite-difference codes. The se results show promise in applying the filter and the characteristics scheme to more complicated gas dynamics problems not only because of the high quality of the solutions, but also because the additional run time incurred due to the filter is minimal. Furthermore, it follows t hat older codes formulated using second-order finite difference method s utilizing artificial viscosity can be converted into accurate, moder n tools with a high potential for parallelizability. (C) 1995 Academic Press, Inc.