Megaflow - Numerical Flow Simulation for Aircraft Design is a specialized book that addresses the advanced numerical simulation tools increasingly used in the early design phase of the aerospace industry. This work presents the results of a German initiative that brings together numerous CFD development activities from the German Aerospace Center (DLR), universities, and the aircraft industry. It provides detailed insights into numerical algorithms for structured and hybrid Navier-Stokes solvers and demonstrates the software's capabilities for complex industrial applications. The publication highlights recent improvements and extensions of the Megaflow software system, including the block-structured Navier-Stokes code FLOWer and the unstructured Navier-Stokes code TAU. It also discusses the validation activities that demonstrate these codes' ability to predict viscous flows around complex, industrially relevant configurations for the transport aircraft design process. The high maturity of both codes is underscored by their extensive use in the German aerospace industry.