Abstract
This work focuses on the evolution of a free plane laminar jet in the near-nozzle region. The jet is buoyant because it is driven by a continuous addition of both buoyancy and momentum at the source. Buoyancy is given by a temperature difference between the jet and the environment. To study the jet evolution, numerical simulations were performed for two Richardson numbers: the one corresponding to a temperature difference slightly near the validity of the Boussinesq approximation and the other one corresponding to a higher temperature difference. For this purpose, a time dependent numerical model is used to solve the fully dimensional Navier-Stokes equations. Density variations are given by the ideal gas law and flow properties as dynamic viscosity and thermal conductivity are considered nonconstant. Particular attention was paid to the implementation of the boundary conditions to ensure jet stability and flow rates control. The numerical simulations were also reproduced by using the Boussinesq approximation to find out more about its pertinence for this kind of flows. Finally, a stability diagram is also obtained to identify the onset of the unsteady state in the near-nozzle region by varying control parameters of momentum and buoyancy. It is found that, at the onset of the unsteady state, momentum effects decrease almost linearly when buoyancy effects increase.
Highlights
Jet flow occurs in a variety of industrial applications such as pulverization, thermal isolation, film cooling, solid straightening, welding in aerodynamic, and hydrodynamic fields
Some works on laminar jets are limited to analytical or numerical solutions of the governing equations in the developed region
An analytical solution for the transition region, with buoyancy forces and inertial forces of same order of magnitude, has been addressed by Yu et al [14] in laminar regime. These authors have introduced new parameters and used a change of variables. The equations they obtained were solved by taking into account the boundary conditions and the two integration constants derived from the momentum conservation and the heat flux
Summary
Jet flow occurs in a variety of industrial applications such as pulverization, thermal isolation, film cooling, solid straightening, welding in aerodynamic, and hydrodynamic fields. An analytical solution for the transition region, with buoyancy forces and inertial forces of same order of magnitude, has been addressed by Yu et al [14] in laminar regime These authors have introduced new parameters and used a change of variables. The equations they obtained were solved by taking into account the boundary conditions and the two integration constants derived from the momentum conservation and the heat flux. The jet flow configuration studied here is a free vertical plane jet, discharged from a rectangular nozzle, where the aspect ratio width/thickness is considered significant. A time dependent two-dimensional numerical model is used in the present work, where density variations are given by the ideal gas law and flow properties as dynamic viscosity and thermal conductivity are considered nonconstant. Some numerical tests were carried out to define the appropriate boundary conditions since stability and flow rates control must be ensured
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