Efficient time-resolved thermal characterization of single and multi-injector rocket combustion chambers

In this work, an efficient methodology for the time-resolved thermal characterization of rocket combustion chambers at reasonable computational cost is presented. The multi-scale and multi-physics numerical framework tackles simultaneously an arbitrary number of contiguous domains, either fluid or solid, and takes advantage of several modeling solutions aimed at stiffness reduction. Non-premixed turbulent combustion is handled through a flamelet-based approach accounting for non adiabatic and non equilibrium effects, thermal wall functions adapted for rocket operating conditions are employed to overcome the stiffness induced by the boundary layer, and a coupling strategy is implemented to guarantee temperature and heat flux continuity across the interfaces. The coupling strategy is based on a Conjugate Heat Transfer (CHT) condition, yielding the interface temperature as a result of a heat flux continuity constraint, and is then reformulated for convection-dominated phenomena, allowing for a further reduction of the computational cost. This allows for the simulation of long time windows, of industrial and experimental relevance. In particular, the solution of the chemically reactive flow is initialized with a CHT condition, and replaced, upon attainment of a statistical fluid dynamic steady state, by an equivalent convective boundary condition. The numerical framework is validated and tested by means of several 2D and 3D cases, the latter consisting in both single-element and multi-element experimental combustor chambers operating in rocket-like conditions.