Session: 08-11: Computational Fluid Dynamics (CFD) and Applications - XI

Paper Number: 136058

136058 - Analysis of Flow Pulsations in Triangular and Square Rod Bundles 

Abstract: 

The majority of currently operating reactors are water-cooled reactors with fuel arranged in bundles. Two basic bundle types can be distinguished based on the fuel rods' geometrical configuration inside bundles, namely square or triangular arrays. In reality, rod bundles are characterised by very complex geometries with grid spacers. Such geometries are too complicated to investigate in detail different physical phenomena, such as secondary flows. As a remedy, scientists in their research (both experimental and numerical), are using simplified geometries to limit the impact of various factors. Thus, in the present study, a wide range of steady-state and Unsteady Reynolds Averaged Navier-Stokes (URANS) computations are performed to reproduce the turbulent flow and heat transfer conditions in a bare rod bundle with different array configurations. As a reference two well-known experiments have been considered. The first one is based on Krauss and Mayer experiments, in which turbulent flow in a bundle of heated 37 rods with a triangular array at two different pitch-to-diameter ratios (P/D = 1.12 and P/D = 1.06) was investigated. The four-rod models for each pitch-to-diameter ratio were defined and multiple meshes were tested. The second experiment concerned the square configuration and it referred to the hydraulic experiment of Hooper.  The six-rod array test section with a pitch-to-diameter ratio of P/D = 1.107 was built to model the fluid mechanics inside a large symmetrical square-pitch rod array. It is known that the pitch-to-diameter ratio is one of the most important geometrical parameters which could influence the main characteristics of the coolant flow (such as the existence of gap vortex street, dominant flow and thermal frequency or wavelength of the pulsations). Therefore, in the present research work, the parametric study of the turbulent flow and thermal quantities is performed systematically. As a first step, the macroscopic flow characteristics of both experiments are numerically reproduced. Secondly, the Reynolds numbers of the reference experimental cases were scaled down in such a way that the overall phenomenology of the flow field was preserved, using the existence of a gap vortex street. Special attention has been put forward to the possible reproduction of the gap vortex street in the laminar and transient flow regimes.  In addition, a parametric study for different passive scalars is performed to take into account the heat transfer analysis within the domain. These passive scalars correspond to the Prandtl numbers of three different working fluids, i.e., air, water and liquid metal. The heat transfer of these three fluids has been studied along with two different boundary conditions on the walls, i.e. a constant temperature on the rod wall and a constant heat flux. As a final result, the main flow and heat transfer characteristics from two different array configurations have been compared to each other. As a result, the performed study has allowed the design of a proper set-up for the higher-order turbulent model approaches using Large Eddy Simulations (LES) or even Direct Numerical Simulations (DNS).

Presenting Author: Tomasz Kwiatkowski National Centre for Nuclear Research

Presenting Author Biography: Dr Tomasz Kwiatkowski is a research fellow currently working at the National Centre for Nuclear Research (NCBJ), Poland. He has over 10 years of experience in the field of nuclear energy and in the new high-temperature reactor technologies. His main expertise scopes heat transfer, thermal design, computational fluid dynamics (CFD), and nuclear safety analyses. Currently responsible for CFD calculations for the designed HTGR-POLA high-temperature research reactor, which will be built at NCBJ. Additionally, he is involved in reliability analyses for future nuclear installations (the International Fusion Materials Irradiation Facility – Demo Oriented NEutron Source (IFMIF-DONES)).

Authors:

Tomasz Kwiatkowski National Centre for Nuclear Research
Anna Talarowska European Nuclear Society Young Generation Network
Afaque Shams King Fahd University of Petroleum and Minerals
Osman Siddiqui King Fahd University of Petroleum and Minerals