A two-fluid model of turbulence is presented and applied to flow in tundishes. The original fluid is modelled as a real power-law fluid, where we define the coefficients k and n of it. The problem was solved for isothermal and... more
A two-fluid model of turbulence is presented and applied to flow in tundishes. The original fluid is modelled as a real power-law fluid, where we define the coefficients k and n of it. The problem was solved for isothermal and non-isothermal conditions of continuous casting (CC) tundish. Transport equations are solved for the variables of each fluid, and empirical relations from prior works are used to compare the model results.
For the calculated real fluid, we compare the classic k-ε turbulence model and the new promised two scale k-ε turbulence model in isothermal and non-isothermal conditions.
We optimize our results by presenting a new estimation in mass transfer rate calculation and in the intermittency factor, which the last provides a measure of the extent of turbulence in the tundish. Finally, we defined then two-fluid empirical coefficients cf, ch, cm for a real non-isothermal fluid.
The paper presents a comparative study based on the 3D computational simulations of the flow around a circular cylinder fitted with vortex generators, benefiting from a series of dedicated model tests conducted in a large circulating... more
The paper presents a comparative study based on the 3D computational simulations of the flow around a circular cylinder fitted with vortex generators, benefiting from a series of dedicated model tests conducted in a large circulating water tunnel. The effect of the vortex generators is presented with comparisons including the bare cylinder with no vortex generator case and related experimental data Incompressible, unsteady Reynolds-Averaged-Navier-Stokes (URANS) computations were performed by using three different two-equation turbulence models, which were Realizable k-epsilon, Wilcox k-omega, and Shear-Stress-Transport k-omega models. The numerical calculations emphasized the effectiveness and the performance enhancing character of the vortex generators. Many key findings of the measurements such as the elongation of the near-wake, the extension of the shear layers, the decrease of the stress components and the weakening of the vortices were successfully reproduced with the computations. Significant drag reduction was observed in both experimental and computational study due to the application of the vortex generators.
Purpose: This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics. Design/methodology/approach : The nozzle configuration consists of a central nozzle surrounded by four nozzles.... more
Purpose: This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics.
Design/methodology/approach : The nozzle configuration consists of a central nozzle surrounded by four nozzles. All nozzles have same diameter and constant separation between nozzles. OpenFOAM® is used for simulating the jet flow. Reynolds Averaged Navier Stokes (RANS) equations are solved iteratively with a first order closure for turbulence. Pitot-static tube with differential pressure transducer is used for mean velocity measurements. The comparison of computed results with experimental data shows similar trend and acceptable validation.
Findings: According to the results, the momentum flux distribution significantly alters the near field of multiple turbulent round jets. Highly non-linear decay region in the near field is found for the cases having higher momentum in the outer jets. As a result of merging, increased positive pressure is found in the mixing region. Higher secondary flows and wider mixing region are reported as a result of momentum transfer from axial to lateral directions by Reynolds stresses.
Research limitations/implications : The present study is limited to isothermal flow of air jet in air medium.
Social implications: Optimum momentum flux distribution in multijet injector of a combustor can reap better mixing leading to better efficiency and lesser environmental pollution.
Originality/value: As summary, the contributions of this paper in the field of turbulent jets are following: simulations for various momentum distribution cases have been performed. In all the cases, the flow at the nozzle exit is subsonic along with constant velocity profile. To simulate proper flow field, a large cylinder type domain with structured grid is used with refinements towards the nozzle exit and jet axis. The results show that the non-linearity increases with increase in momentum of outer jets. Longer merging zones are reported for cases with higher momentum in outer nozzles using area averaged turbulent kinetic energy. Similarly, wider mixing regions are reported using secondary flow parameter and visualizations.
