During atmospheric entry, the hypersonic flow environment around capsules or space debris is characterized by strong shock waves, complex fluid thermochemistry, and gas-surface interactions (GSI). Such interactions could induce material decomposition and mass loss, referred to as ablation, which alters the shape of the flying object as its surface recedes. Understanding the influence of these phenomena is crucial in the design of future spacecraft. Ground testing is inadequate for simultaneously replicating all aspects of these types of flows. Hence, proper computational modeling and simulations are essential, yet usually resource-intensive and methodologically demanding. This talk will give a brief overview of some of the recent developments at the Aerodynamics Group of the TU Delft Aerospace Engineering Faculty regarding the computational fluid dynamics (CFD) simulations enabled by high performance computing (HPC) to study high-speed high-temperature flows with gas and surface reactions with an emphasis on the prediction and analysis of laminar to turbulent transition.