Open-Source 3D CFD of a Quadrotor Cyclogyro Aircraft

Abstract

This chapter provides a detailed method for building an unsteady 3D CFD model with multiple embedded and adjacent rotating geometries. This is done relying solely on open-source software from the OpenFOAM$^{\textregistered }$ package. An emphasis is placed on interface meshing and domain decomposition for parallel solutions. The purpose of the model is the aerodynamic analysis of a quadrotor cyclogyro. The challenging features of this aircraft consist of a series of pairwise counterrotating rotors, each consisting of blades that oscillate by roughly 90$^\circ$ about their own pivot point. The task is complicated by the presence of solid features in the vicinity of the rotating parts. Adequate mesh tuning is required to properly decompose the domain, which has two levels of sliding interfaces. The favored decomposition methods are either to simply divide the domain along the vertical and longitudinal axes or to manually create sets of cell faces that are designated to be held in a single processor domain. The model is validated with wind tunnel data from a past and finished project for a series of flight velocities. It agrees with the experiment in regard to the magnitude of vertical forces, but only in regard to the trend for longitudinal forces. Comparison of past wind tunnel video footage and CFD field snapshots validates the features of the flow. The model uses the laminar Euler equations and gives a nearly linear speedup on up to four processors, requiring 1 day to attain periodic stability.