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- Unsteadiness of a Ground Vortex FlowPublication . Silva, André; Barata, Jorge M M; Santos, Pedro J. T. C; Nunes, Ricardo F.; Durão, DiamantinoThe impact zone of a wall jet with a boundary layer is studied computationally using a Reynolds averaged Navier-Stokes (RANS) approach with the "κ-ε" turbulence model. The computational domain corresponds to complete experimental rig and the measured boundary conditions were used. It was found that the gross features of the flow are well predicted, and the fluctuations of the flowfield around the ground vortex occur in a very small region near the wall where the impact between each flow occurs. The computational results showed a cyclic formation of two small secondary vortexes that appear and disappear cyclically around the separation and maximum penetration points of the ground vortex.
- Laser-Doppler Analysis of the Separation Zone of the Ground Vortex FlowPublication . Silva, André; Durão, Diamantino; Barata, Jorge M M; Santos, Pedro José da Costa Teixeira; Ribeiro, SamuelLaser Doppler measurements are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The experiments were performed for a wall jet-to-boundary layer velocity ratio of 2, and include mean and turbulent velocity characteristics along the two normal directions contained in planes parallel to the nozzle axis. The results, which have relevance to flows encountered by powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow resulting from the collision of a wall jet with a boundary layer. The results revealed the existence of a very low-frequency instability. The source of this low frequency unsteadiness is probably associated with a small vortex located near the separation point. In the central zone of the upwash flow where the maximum values of the vertical velocity component occurs, additional distinct high frequency peaks were also identified.
- Laser Doppler Measurements of Twin Impinging Jets Aligned with a CrossflowPublication . Barata, Jorge M M; Carvalho, Pedro dos Santos Duarte; Neves, Fernando M. S. P.; Silva, André; Vieira, Diana; Durão, DiamantinoThis paper presents a detailed analysis of the complex flow beneath two impinging jets aligned with a low-velocity crossflow which is relevant for the future F-35 VSTOL configuration, and provides a quantitative picture of the main features of interest for impingement type of flows. The experiments were carried out for a Reynolds number based on the jet exit conditions of Rej = 4.3 104, an impingement height of 20.1 jet diameters and for a velocity ratio between the jet exit and the crossflow VR = Vj/Uo of 22.5. The rear jet is located at S = 6 D downstream of the first jet. The results show a large penetration of the first (upstream) jet that is deflected by the crossflow and impinges on the ground, giving rise to a ground vortex due to the collision of the radial wall and the crossflow that wraps around the impinging point like a scarf. The rear jet (located downstream) it is not so affected by the crossflow in terms of deflection, but due to the downstream wall jet that flows radially from the impinging point of the first jet it does not reach the ground. The results indicate a new flow pattern not yet reported so far, that for a VSTOL aircraft operating in ground vicinity with front wind or small forward movement may result in enhanced under pressures in the aft part of the aircraft causing a suction down force and a change of the pitching moment towards the ground.
- Turbulent Energy Budgets of a Ground Vortex FlowPublication . Barata, Jorge M M; Santos, Pedro José da Costa Teixeira; Silva, André; Durão, DiamantinoTurbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV (Laser Doppler Velocimetry) measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.
- Numerical study of single impinging jets through a crossflowPublication . Barata, Jorge M M; Durão, Diamantino; McGuirk, J. J.