Direct numerical simulation is a computational methodology used in scientific research to investigate complex physical systems, particularly fluid dynamics and turbulence, by directly resolving all relevant spatial and temporal scales of motion without employing models for the unresolved scales. This approach, characterized by its high computational cost, provides high-fidelity data that are invaluable for gaining fundamental insights into underlying physical processes, validating theoretical models, and serving as benchmark data for the development and evaluation of lower-fidelity simulation techniques.