Development of advanced immersed-boundary methods for multiphysics

The purpose of this work is to develop and test an accurate and efficient tool for computing three-dimensional complex flows past fixed or moving geometries, for a wide range of Reynolds and Mach numbers. Firstly, an accurate and efficient Immersed-Boundary (IB) method, using a state-of-the-art Unsteady Reynolds-Averaged Navier–Stokes (URANS) parallel Cartesian solver, has been improved, by means of a new IB treatment, extended to three space dimensions, and validated versus several test cases of increasing complexity. Then, a code for solving heat conduction (HC) equation that uses the same spatial discretization and time-marching scheme as the URANS solver has been developed and coupled with it to obtain an efficient tool for solving Conjugate-Heat-Transfer (CHT) problems: the Cartesian grid presents both fluid and solid zones: the URANS equations are solved at all fluid cells and the HC equation is solved at all solid cells; the two solutions are coupled by the interface conditions requiring that both the temperature and heat-flux be the same at all (fluid-solid) boundary points. Finally, a surface-based structural solver that simulates the dynamics of deformable geometries, discretized by triangulated Lagrangian meshes, has been coupled with the basic IB-URANS method to provide an efficient tool for solving Fluid-Structure-Interaction (FSI) problems: the forces exerted by the fluid onto the solid surface are used to determine its motion, which is fed as a kinematic boundary condition for the flow, via an iterative procedure implemented within the dual time stepping procedure of the URANS solver. The two coupled solvers have been validated versus CHT and FSI problems, such as the flow through an air cooled gas turbine cascade and the low Reynolds shear flow past a deformable sphere, proving to be promising research and development tools for industrial and medical applications.