P. Bournot

Numerical Analysis of Recirculation Bubble Sizes of Turbulent Co-Flowing Jet

Abstract This paper deals with the numerical prediction of an axisymmetric turbulent jet discharged into a co-flowing stream. Two computational codes have been employed, in-house code using the standard k-ɛ model and commercial CFD software including the standard k-ɛ and the RSM model. The main object of our research is to investigate the recirculation phenomena induced by the change of the inlet and boundary conditions. We observed different recirculating regions (central and corner) induced by the inclusion of the nozzle thickness δe. The size and the strength of these recirculation bubbles are intensified by increasing δe. We also observed that the co-flowing jet emitted with a different velocity profile generates a wide central recirculation bubble and a small corner vortex. However, the formation of the recirculation bubble is destroyed by decreasing Froude number. Furthermore, the analysis of the size and strength of the recirculation bubbles is necessary in the case of the jet pump and the flame in combustion chambers.

Investigation of a turbulent wall jet in forced convection issuing into a directed coflow stream

ABSTRACT In the present paper, we have studied numerically the directed coflow stream effects on mean and turbulent flow properties of a turbulent plane wall jet in forced convection emerging into a directed coflow stream. The system of equations governing the studied configuration is solved with a finite difference scheme using a staggered grid for numerical stability, not uniform in the two directions of the flow. The modified version of the first-order low Reynolds number k–ϵ turbulence model is used and compared to existing experimental findings. It is found that predicted results are in satisfactory agreement with the experimental data and that the wall jet fluid decays faster in presence of a directed coflow stream. Results show also that the increase of coflow deviation angles causes an increase of the growth rates of the dynamic and thermal half-width of the jet and enhances the turbulent mixing. It is found that the longitudinal development of normalised forms of the jet characteristics parameters at different directed coflow velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale.

Numerical Study of Wall Horizontal Turbulent Jet of Freshwater in a Homogeneous Co-flow Stream of Saltwater

The disposal of effluents in nature and more particularly in the sea is a very frequent practice. The discharge of wastewater into a receiving environment such as seawater is generally in the form of a turbulent jet. The efficiency of the dispersion of the jet depends on its characteristics of mixing with the ambient environment and when the latter is in motion, it is significantly modified. This paper investigates a numerical study about buoyant wall turbulent jet in co-flow stream. A light fluid of freshwater is injected horizontally and tangentially to a plane wall into homogenous moving environment of saltwater. Since the domain temperature is assumed to be constant, the density of the mixture is a function of the salt concentration only. The mathematical model is based on the finite volume method and reports on an application of standard turbulence model k-e for steady flow with densimetric Froude number of 11 and Reynolds number of 3800. The aim of this work is to predict the influence of the co-flow stream on the dispersion of the jet and the mixing processes between freshwater jet and ambient saltwater. The concentration contours, the cling length, and the central trajectory of the jet are determined. It is found that the jet behavior depends on the co-flow-to-jet velocity ratio.

Turbulent-Heated Plane Compressible Jet Emerging in a Directed Co-Flowing Stream

In this present work, we have studied the directed co-flow effects on mean and turbulent flow properties of a turbulent heated plane jet with variable density discharging into a directed co-flowing stream. The first order k-eturbulence model is applied and has been compared with the existing experimental data. The Finite Volume Method (FVM) is used to discretize governing equations. First of all, it is found that predicted results are in satisfactory agreement with the experimental findings. Moreover, the numerical results of the mean and turbulent quantities has been presented and discussed in this work. The major interest of presenting this model is that to show the importance of the directed co-flow with a positive angle, which is enhancing the mixing. Furthermore, a qualitative analysis of the air entrainment would suggest that the higher inlet hot air jet temperature affect more the lateral in flow of air into the jet and jet lateral expansion is augmented when the inlet hot air jet temperature increases. Therefore, the increase of the inlet hot air jet temperature decreases faster the axial mean velocity and thus more entrainment air is required.