In this study, a numerical simulationNumerical simulation of the actual operating conditions of a walking beam reheating furnaceReheating-furnace with direct flame, designed for the processing of conventional steel slabsSlab, was carried out. Two case studies were simulated: one with the slabsSlab in a static state and the other with the slabsSlab moving inside the furnace. For this purpose, the fluid dynamics, heat transferHeat transfer, chemical species and combustion fields were solved in a coupled manner, using a continuous adaptation of the computational domain by means of a dynamic meshDynamic-mesh. The simulation was validated by means of temperatureTemperature measurements averaged over 24 h of plant operation with 16 thermocouples, resulting in a minimum error of 0.15% and a maximum of 5.53% for case A and a minimum error of 0.71% and a maximum of 9.01% for case B. The use of a dynamic mesh allowed studying a more realistic thermal evolution of the slabSlab and comparing the thermal evolution with static slabsSlab for this research, natural gas was considered only as methane due to its predominance in the mixture. This research provides an interesting result for the analysis of the thermal evolution of slabsSlab without the need for the use of the dynamic meshDynamic-mesh model, this will accelerate subsequent studies due to the lower computational cost and reliability of this methodology.