The aim of this work is to perform a numerical investigation (CFD) of the dual-mode ramjet combustor tested at the ONERA LAERTE facility within the European LAPCAT-II (Long-Term Advanced Propulsion Concepts and Technologies II) project. LAPCAT-II explored advanced propulsion concepts for reducing the duration of an- tipodal flights by combining high-speed performance and sustainability. The proposed configuration relies on hydrogen fuel and consists of an Air Turbo Rocket (ATR) for the acceleration phase, followed by a dual-mode ramjet capable of transitioning from ramjet to scramjet operation, enabling cruise conditions up to Mach 8. The study is based on high-fidelity reactive Large Eddy Simulations (RLES), which resolve the largest turbulent structures while modeling the smaller scales.