Calculation of the Darcy friction factor in a periodic tube bundle by means of wall-resolved large eddy simulations at bulk Reynolds number of 40,000
Abstract
The knowledge and understanding of turbulent flows in tube bundles are of primary interest for the design of pressurized water reactors. In particular, the accurate prediction of the pressure drop coefficient steps into the closure
relationships of component thermalhydraulics codes, but is often difficult to address by an experimental approach.
Wall-modeled large eddy simulation (LES) has proven its benefit in providing useful insight on the average flow structure, such as the velocity distribution, secondary flow and pressure drop. However, the use of a wall function could be considered as questionable since it amounts to artificially placing the dimensionless velocity on the universal wall law.
On the other hand, wall-resolved LES allows an accurate resolution of the whole boundary layer despite a high computational cost. In the present study, wall-resolved large eddy simulations of a tri-periodic subchannel without mixing grids are performed with the WALE subgrid-scale model at a bulk Reynolds number of 40,000. The main features
of the average flow are extracted and analyzed. When the mesh size tends toward zero, the friction coefficient tends
toward the value that would be produced by a direct numerical simulation (DNS). Consequently, the DNS friction
coefficient is deduced from a series of LES performed on successively refined meshes, assuming that the discrepancy
between the LES and DNS coefficients varies as a power of the mesh size. The computed DNS friction factor exhibits
finally a good agreement with the correlation of Rehme and used in the FLICA4 subchannel code.
KE
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