Numerical modelling of fluid flow and heat transfer in smooth and rough cooling channels

In the framework of liquid rocket engines, the huge amount of power released in a relatively small volume makes the design of the cooling system a rather challenging issue. The regenerative cooling technique, which is the technological background of this thesis, is the most employed cooling method. It uses onboard propellant to flow through narrow channels around the thrust chamber, preventing thermal failures by maintaining wall temperatures within safe limits. While widely employed, recent technological advancements in manufacturing and design demand a deeper physical understanding of the fluid flow and heat transfer phenomena occurring in the cooling channels. In this regard, crucial support is provided by computational fluid dynamic (CFD), given that suitable modelling is employed. Within this context, the present Ph.D thesis aims to evaluate the suitability of different numerical modelling solutions to predict the fluid flow and heat transfer in cooling channels, combining the use of high fidelity CFD tools, simplified models and experimental data. In the first part of the thesis, an analysis of smooth and rough cooling channels modelling is presented. A comparison activity between direct numerical simulations (DNS) and Reynolds averaged Navier Stokes simulations (RANS) is carried out, in order to evaluate the RANS turbulence model capabilities and past developed theories. To this goal, the model completeness is gradually increased and the effect of different fluid and geometrical parameters is investigated. The second part of the thesis addresses an experimental investigation on a multi-injection combustion chamber. Copper segments realized by additive layer manufacturing printing techniques are integrated and tested with the goal of characterizing heat transfer and pressure losses in the cooling circuit. Additionally, experimental data can be useful to get an insight into the effect of 3D printing and roughness levels and to be used as a benchmark for numerical simulations. In the last part, numerical simulations of a real oxygen-methane liquid rocket engine regenerative cooled thrust chamber are performed and compared with experimental data. Additionally, adopting a system-wide perspective of the engine, the studies conducted on the injection plate, turbopumps, and coking within the cooling channels are presented, alongside improvements made to the EcosimPro models for enhanced accuracy and predictive performances of pressure losses and heat transfer.