The guideline for wind tunnel tests by the Windtechnological Society e.V. (WTG) has long been considered a standard reference in wind engineering. In view of the increasing importance of CFD (Computational Fluid Dynamics) methods, a specific guideline for these numerical methods has now been developed. This guideline follows the Eurocode EN 1991-1-4, which permits both experimental and numerical methods, provided they are thoroughly validated. Validation is, therefore, the focus of the new technical bulletin. The Eurocode includes a flexibility clause that allows the use of wind tunnel tests and recognized numerical methods, as long as the structure and wind are correctly modeled. While the first validation must be carried out with particular care, the effort can be reduced for similar projects. The responsibility always lies with the user, not the software developer. The WTG bulletin is intended to serve as a guide for creators and clients of CFD simulations in wind engineering and to provide practical assistance. This manual aims to both clearly present the essential content of the WTG bulletin to practicing engineers and demonstrate its concrete application in and with RWIND through examples.