Computational fluid dynamics (CFD) of a three-inlet-Y-junction duct connected to a U-bend: Influence of inlet velocities on air and water flows subjected to cold fronts and turbulence

This study presents the movement of air and water flowing in a Y-junction duct with three connected inlets of a U-bend with attention to the impact of cold fronts. Analyses were carried out to observe the behavior of the fluids (air and water) at the duct axis, after the mixing zone (at 70 mm), just upstream of the bend and downstream, at the outlet. The realizable k-ε viscous turbulence model coupled with the energy equation were solved numerically using Ansys Fluent 2024R2. Three cases of cold front formation were studied according to the inlet velocities. An extended cold front appears when the cold fluid enters slowly from inlets 2 and 3, while a high velocity at inlet 1 (case II) can extend the front to outlet CS3. The U-bend acts as a turbulence amplifier, but the response of the fluid in question (air and water) depends both on their physical properties (density, kinematic viscosity, and inertia) and their physicochemical characteristics. The complex dynamics of these flows are explained not only by mechanical phenomena but also by intermolecular interactions: water (a polar molecule), capable of forming hydrogen bonds and susceptible to cold fronts, reacts differently from air, a mixture of non-polar gases with weak intermolecular interactions.