Modern computational fluid dynamics (CFD) methods are described. CFD simulations of whole compressor stages using the Reynolds-averaged Navier–Stokes equations (RANS), with a steady-state rotor–stator interaction model between the blade rows and a two-equation turbulence model, are the basis of aerodynamic calculations for the design of radial compressors. More detailed simulations using unsteady RANS (URANS) equations with unsteady rotor–stator interaction models are now used in a research environment. The source of errors and the importance of validating the CFD methods are described. The prediction of the turbulent flow is one of the main error sources in CFD simulations, and an overview is given of turbulence models. Up-to-date guidelines are provided on the use of CFD for the design and development of components in radial turbocompressors. A practical description of the CFD process is given, including the technologies used to support the calculations, such as geometry generation, mesh generation and postprocessing.