A new implicit fictitious domain method for the simulation of flow in complex geometries with heat transfer

A numerical algorithm for the simulation of flow past immersed objects with heat transfer is proposed and validated which conforms with the ideas of the fictitious domain method. A momentum source term is added to account for the presence of the object and a heat source term is proposed to impose the Dirichlet boundary condition on the surface of the objects. The algorithm is an implicit fictitious domain based method where the entire fluid-immersed object domain assumed to be an incompressible fluid. The flow domain is constrained to be divergence free, whereas a rigidity constraint is imposed on the body domain. Heat transfer is similarly considered by assuming that the object domain is filled with a fluid with different thermal properties. The SIMPLE algorithm with a collocated grid arrangement is used for pressure–velocity coupling which is unconditionally stable. The algorithm is validated by considering stationary, forced motion and freely moving objects with both isothermal and freely variable temperature inside the object. Good agreement with previous numerical and experimental studies for all the test cases is observed

Fully-resolved simulations of heat transfer in particle-laden flows

Solid particles suspended in a fluid flow are encountered in many industrial applications, environmental processes and natural systems, such as fluidized beds, cloud formation, dust and pollutants dispersion, industrial mixers, oceanic plankton and many others. In the present dissertation we carry out fully resolved numerical simulations of several problems in this general area both with and without particles-fluid heat transfer. An important aspect of the work is that the finite size of the particles is properly accounted for and that the fluid dynamic forces acting on them are based on an accurate solution of the fluid equations rather than parameterized. The general approach used in this study is based on the PHYSALIS method. This method uses local analytic solutions as “bridges" between the particle surfaces and a fixed underlying Cartesian grid. For the isothermal case, we study the rotational dynamics of a particle free to rotate around a fixed center in a turbulent flow. Fixing the particle center and carrying out parallel simulations of the flow without the particle enables us to fully characterize the flow incident on the particle. We determine the scales of eddies interacting most with the particle and explore the effect of vortex shedding on the rotational dynamics. The Magnus mechanism is not found to play a significant role. To account for particles-fluid heat transfer phenomena, we have extended PHYSALIS to deal with the energy equation. This new direct numerical simulation method for non-isothermal systems is described in detail and extensively validated against experimental studies and analytical solutions. The method is implemented numerically on a GPU-centric code, which is compatible with BLUEBOTTLE – a highly efficient GPU-centric computational fluid dynamics framework. An example of particles transported by a Rayleigh-Bénard convective flow is shown to demonstrate the potential applications of our method. A further application to the thermal wake of particles in turbulent flow is also given