Computing flow field in igniting autonomous underwater vehicle using three-dimensional grids

We use the three-dimensional grid and the VOF (volume of fluids) multiphase flow model to compute the three-dimensional flow field during the ignition of a non-axisymmetric autonomous underwater vehicle with X-type rudders. But the larger number of three-dimensional grids increases the computational time; in this regard, the determination of a reasonable number of grids and reasonable parameters can help obtain precise computational results. We use more than 1 500 000 grids, the FLUENT software and the VOF multiphase flow model to compute the unsteady flow of the autonomous underwater vehicle, thus obtaining the changes in drag, exhausted gas bubbles and flow field at the beginning of its ignition process. The computational results, given in Figs. 2 through 5, and their analysis show preliminarily that the changes in exhausted gas bubbles exert some impact on the drag and flow field of the autonomous underwater vehicle. The results of comparison of our computational results with the experimental results, some of which are done by ourselves and some are from literatures, show that they are in general agreement, indicating that the computation with our method is reliable.