1. A method for generating a multi-grid for fluid simulations, comprising: obtaining first level-set field values for a three-dimensional model of a fluid volume represented as a first two-dimensional grid of columns, wherein each column within the first two-dimensional grid comprises one or more regular cubic cells; downsampling the first level-set field values to generate second level-set field values for a second two-dimensional grid of columns that represents the three-dimensional model of the fluid volume and is coarser than the first two-dimensional grid of columns, wherein the downsampling increases the likelihood that air bubbles will persist in the second two-dimensional grid of columns; and downsampling the second level-set field values to generate third level-set field values for a third two-dimensional grid of columns that represents the three-dimensional model of the fluid volume and is coarser than the first two-dimensional grid of columns and the second two-dimensional grid of columns, wherein the downsampling increases the likelihood that air bubbles will not persist in the third two-dimensional grid of columns.