URANS computations for an oscillatory non‐isothermal triple‐jet using the k–ε and second moment closure turbulence models

Abstract

SUMMARYLow Reynolds number turbulence stress and heat flux equation models (LRSFM) have been developed to enhance predictive capabilities. A new method is proposed for providing the wall boundary condition for dissipation rate of turbulent kinetic energy, , to improve the model capability upon application of coarse meshes for practical use. The proposed method shows good agreement with accepted correlations and experimental data for ows with various Reynolds and Prandtl numbers including transitional regimes. Also, a mesh width about 5 times or larger than that used in existing models is applicable by using the present boundary condition. The present method thus enhanced computational e ciency in applying the complex turbulence model, LRSFM, to predictions of complicated ows. Unsteady Reynolds averaged Navier-Stokes (URANS) computations are conducted for an oscillatory non-isothermal quasiplanar triple-jet. Comparisons are made between an experiment and predictions with the LRSFM and the standard k-model. A water test facility with three vertical jets, the cold in between two hot jets, simulates temperature uctuations anticipated at the outlet of a liquid metal fast reactor core. The LRSFM shows good agreement with the experiment, with respect to mean proÿles and the oscillatory motion of the ow, while the k-model under-predicts the mixing due to the oscillation, such that a transverse mean temperature di erence remains far downstream.

Numerical assessment of hydrodynamic characteristics in chlorine contact tank

“…NUMERICAL COMPUTATION Several 3D steady-state and time-variable numerical simulations are performed using commercial CFD code in a contact tank geometry where a different number of baffles is considered. The CFD models are based on the fundamental equations for fluid flow, continuity, and momentum, known as Reynolds-averaged Navier-Stoke equations (RANS), as well as standard k-ε turbulence equations [15][16][17][18][19][20][21][22][23][24][25][26][27] to determine eddy viscosity and mixing coefficient, applying first-order accurate finite volume method. The governing equations of the CFD model and their solution procedure can be found in Stamou [9].…”

Large-eddy simulation of thermal striping in unsteady non-isothermal triple jet

“…The three channels were attached to the the base of the square duct, and the jets were issued from the nozzle. The experiment of Nam and Kim [10] was designed to be two-dimensional by using nozzles with a rectangular cross section, and the previous numerical studies used a two-dimensional grid [13][14][15]. In this study, we performed full three-dimensional numerical simulations using the LES technique.…”

“…High frequency thermal oscillations, albeit small amplitude, were predicted with the v 2 −f and SST k −ω models [15]. Nishimura and Kimura [13] probability density functions (pdf) from the fine grid LES and the two turbulence models are plotted in Figure 5 along with the experimental data. The pdf profile predicted in the LES is reasonably similar to the one in the experiment although the LES has a much broader peak than the experiment (see Table 1).…”

“…Many variants of turbulence models have been used in Reynolds-Averaged Navier-Stokes (RANS) simulations with some varying successes in terms of predicting mean velocity and thermal fields [8,[11][12][13][14][15][16]. Recently, Choi and Kim [15] performed numerical simulations of the triple jet experiments conducted by Nam and Kim [10].…”