Innovative Experimente an der TOPFLOW Versuchsanlage zur Verfikation und Validierung von CFD Codes

Innovative Experimente an der TOPFLOW Versuchsanlage zur Verfikation und Validierung von CFD Codes

Lucas, D.; Hampel, U.; Beyer, M.; Weiß, F.-P.

There is an increasing interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses related to Nuclear Reactor Safety (NRS). Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Also in nuclear reactor research CFD codes are successfully applied single phase flows, e.g. for problems related to boron mixing in the primary circuit of Pressure Water Reactors. On the other hand two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels which are characterized by large interfaces. For two-phase CFD codes additional closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Instead closure models have to be developed and validated basing on new experimental data with high resolution in space and time. Due to the independency of CFD codes on the geometry and scale it is not necessary to do such experiments in real geometries, but the local flow conditions should be similar the ones expected in praxis. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. This allows to conduct experiments at condition which are close to the nuclear application. On the other hand local data characterizing the micro- or meso-scale structure of the flow are required. For this reason unique measurement devices, such as high-pressure wire-mesh sensors and fast X-ray tomography are applied in TOPFLOW experiments. They provide CFD like data, which means data in high resolution in space and time. The TOPFLOW facility was used for different types of flow experiments in vertical test sections and a large pressure chamber. New experimental setups are currently under preparation. The paper gives a general overview on the experiments done at the facility and their importance for CFD model development and validation for two-phase flows. This is illustrated in detail on the example of poly-dispersed bubbly flows. In addition examples for experimental data useful for the CFD code qualification in case of stratified flows are given. Finally the complex flow situation in case two-phase Pressurized Thermal Shock (PTS) is discussed.

Keywords: two-phase flow; bubble; pipe flow; CCFL; experiment; CFD; wire-mseh sensor; X-ray tomography

  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12754