Reynolds-averaged Navier-Stokes Turbulence Models Research Articles

Calculations of Steady and Pulsating Impinging Jets—An Assessment of 13 Widely used Turbulence Models

Computational fluid dynamics (CFD) calculations of impinging jets have been performed with 13 widely spread Reynolds-averaged Navier-Stokes (RANS) turbulence models using commercial CFD software. It was the aim of these calculation to assess how heat transfer and flow structure can be predicted at different Reynolds numbers and different nozzle-to-plate distances. The only model able to predict correctly the laminar–turbulent transition occurring at small nozzle-to-plate distance was the SST k − ω model (“transitional flow option”). Most of the other models can only satisfactorily predict heat transfer in the turbulent wall jet region. When the SST k − ω model with transitional flow option is applied for calculation of pulsating jets, the tendencies are predicted correctly.

Assessment of the RANS Turbulence Models for a Turbulent Flow and Heat Transfer in a Rod Bundle

A computational fluid dynamics (CFD) analysis has been performed to assess the Reynolds Average Navier-Stokes (RANS) turbulence models to predict a turbulent flow and heat transfer in a triangular rod bundle with pitch-to-diameter ratios (P/Ds) of 1.06 and 1.12. The CFD predictions using various turbulence models were compared with experimental results. Anisotropic turbulence models such as the nonlinear k - [curly epsilon] and the second-order closure models predicted the turbulence-driven secondary flow in the triangular channel and the distributions of the time mean velocity and temperature showing significantly improved agreement with the measurements from the linear standard k - [curly epsilon] model. The anisotropic turbulence models predicted the turbulence structure for a rod bundle with a large P/D fairly well but could not predict the very high turbulence intensity of the azimuthal velocity observed in the narrow flow region (gap) for a rod bundle with a small P/D.

Three-Dimensionality in Reynolds-Averaged Navier-Stokes Solutions Around Two-Dimensional Geometries.

The flow over two-dimensional geometries is studied via unsteady numerical simulations that are three dimensional, with periodic conditions applied along the spanwise coordinate. This framework is well accepted for direct numerical simulations (DNS), large-eddy simulations, and detached-eddy simulations (DES), but is here combined with standard Reynolds-averaged Navier-Stokes (RANS) turbulence models. This strategy, which is not new, is referred to as unsteady RANS (URANS). Limited previous evidence suggested that, in URANS, three dimensionality is suppressed by high eddy-viscosity levels. However, three dimensionality proves fairly easy to sustain with adequate initial conditions, in all three cases studied here: stalled airfoil, circular cylinder, and a rounded square, except that for one case three dimensionality failed to last from random-based initial perturbations and was sustained only when using a DES field as initial condition.

High-Resolution Large-Eddy Simulation of Flow Around Low-Pressure Turbine Blade

Large-eddy simulation ofcompressible Navier-Stokes equations is used to study flows where a laminar boundary-layer separation is followed by a turbulent reattachment. The aim of the present work is to predict and describe the transition process and its interaction with the wake dynamics for a subsonic blade turbine configuration. Indeed, a better knowledge of this mechanism can help to improve the accuracy of a Reynolds-averaged Navier-Stokes turbulence model for such a flow case. High-resolution large-eddy-simulation-type computations have been carried out for the T106 low-pressure blade turbine at inlet Mach number of 0.1 and chord Reynolds number of 1.6 x 10 5 based on the exit isentropic velocity. The simulated mean and turbulent quantities compare well with the available experimental data. The primary two-dimensional instability that originates from the free shear in the bubble is unstable via the Kelvin-Helmholtz mechanism. Then, the three-dimensional motions spread on the boundary layer, leading to full breakdown to turbulence after the reattachment point

On modelling turbulent flow in an oscillatory baffled column – RANS model or large‐eddy simulation?

AbstractOscillatory flow in a baffled column can achieve intensive and uniform mixing with lower shear rate in comparison to the traditional stirred tank reactors (STR). The flow in an oscillatory baffled column (OBC) is unsteady with periodicity in both time and space. Mixing is achieved by the formation of eddies. It is therefore very important to understand the turbulence in an OBC as it determines the degree of segregation, breakage of droplets and bubbles, and the efficiency of chemical/biochemical reactions. Modelling of turbulence is usually associated with the traditional Reynolds Averaged Navier–Stokes (RANS) model. Our results show that the RANS turbulence models, which are sufficiently good for simulating flows in STR, are very poor in predicting periodic flows in an OBC as the methodology of averaging in time in RANS has effectively removed the turbulence. In OBC, eddies of various sizes are the main ingredient for mixing, the large‐eddy simulation (LES) is particularly suitable for such type of flows. In this paper, we describe our understanding on the way in which the LES works.© 2003 Society of Chemical Industry