Investigation of Turbulent Rectangular Shaped Contraction Nozzle Flow for IFMIF Target Application, Validation of Turbulence Models

The target assembly of the International Fusion Materials Irradiation Facility (IFMIF) consists of a nozzle, which has to form a stable lithium jet. Therefore, a flat uniform velocity distribution at the nozzle outlets cross-section with a simultaneously low turbulence intensity is required to ensure a safe operation. These boundary conditions necessitate a detailed knowledge on the turbulent flow in contraction nozzles in order identify turbulence models accurately predicting experimental findings within the velocity range of interest for nuclear target and hence can then act as design optimization tool.

In order to validate commercially available Computational Fluid dynamic codes (CFD) and the turbulence models incorporated in them a series of experiments using water as model fluid are conducted in the Liquid-Metal-Laboratory KALLA at the research center Karlsruhe. A number of turbulence models with different extensions for the near wall treatment were tested versus the experimentally obtained data. Based on this comparison a hydraulic analysis of the contraction nozzle flow is performed taking into account the relaminarization of the accelerated flow, the occurrence of secondary motions and their impact on the development of the boundary layer. In summary the V2F turbulence model exhibits the best agreement between numerical and experimental data and thus can be considered to be most suitable for the simulation of the accelerated nozzle flow for free surface target applications.