One Validation Case of the CFD Software Fluent: Part of the Development Effort of a New Reactor Analysis Tool

To model Generation IV reactor systems in detail, INEEL is currently developing a new thermal hydraulic analysis tool coupling RELAP5-3D / ATHENA© and the computational fluid dynamics (CFD) software, Fluent. One of the first steps in this endeavor is extensive validation and verification (V&V) of Fluent for various situations of interest, such as the abrupt expansion of a gas entering a gas-cooled reactor core. Fluent results were compared to validation data provided by Baughn, et al. on turbulent air flow through an axisymmetric pipe expansion with constant wall heat flux [1] and uniform wall temperature [2]. Fluent peak Nusselt numbers varied 25% from validation data—well outside experimental uncertainties of 5%. However, non-peak Nusselt numbers varied only 10% from validation data and fully-developed Nusselt numbers were in good agreement with widely-accepted empirical relations such as the Dittus-Boelter Correlation.