Numerical Simulation of Twin Impinging jets in Tandem through a Crossflow

Abstract

The flow field of ground vortex generated by twin impinging jets in tandem through a crossflow is numerically studied in detail. Numerical simulation and visualization are presented for two turbulent circular jets emerging into a low velocity cross stream, impinging after on a flat surface perpendicular to the geometrical jet nozzle axis. The numerical study is based in experimental studies done early, so all the features of the experimental flow were maintained when the numerical simulation was performed. The Reynolds number used was based on the jet exit conditions of 43,000 to 105,000, a jet to crossflow velocity ratio of 22.5 to 43.8, an impinging height of 20.1 jet diameters and an interject spacing's of S=5D and L=6D. The analysis of the flow was extended to regions and flow conditions for which no measurements have been obtained in last experimental studies, i.e., for velocity ratios of 15 to 90. The numerical results show that for the smallest velocity ratios the jets initially do not mix, but remain together in two layers. Three different types of flow regimes were identify, therefore when VSTOL aircrafts operating in ground vicinity, only the regime with strong impingement on ground and with a formation of a ground vortex is relevant. The numerical results allowed to extend the last experimental studies, and prove that the deflection of the rear jet is due to the competing influences the wake, the shear layer, the downstream wall jet of the first jet and the crossflow. NomenclatureCμ, C1, C2 = turbulent model constants D = diameter of the jet H = impinging height k = turbulent kinetic energy r = radius of cylindrical coordinates Re = Reynolds number S = distance between the jets axis Sϕ = source term U = horizontal velocity, U u  ' (Umean+u') V = vertical velocity, V v  ' (Vmean+v') VR = velocity ratio, Vj/Uo W = transverse ' w W  (Wmean+w') X = horizontal coordinate Y = vertical coordinate Z = transverse coordinate Greek symbols ϕ = transport coefficient ɛ = turbulent kinetic energy dissipation μT = turbulent viscosity ρ = density σk, σε = turbulent Prandtl/Schmidt numbers

Reynolds Number Effect on the Flow Demeanorin a Vertical Circular Free Turbulent Jet with Cross Flow

“…It was also deduced that the crossflow blocked and accelerates towards the upper part and contributes to a reinforced (or improved) mixing of all the secondary flows. In the continuity of her numerical investigations, Diana [8] discovered that for the configuration of tandem twin jets in crossflow, the second jet is driven by the first jet and not by the opposite flow and does not hit the ground. As for Ozmen [9], he carried out an experimental study oftwo jets coming from a low surface impacting a high surface.…”