Loading...
6 results
Search Results
Now showing 1 - 6 of 6
- 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.
- The Turbulent Structure of a Ground VortexPublication . Barata, Jorge M M; Santos, Pedro; Silva, AndréLaser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are presented and discussed together with flow visualization. In the present study a velocity ratio between the boundary layer and the wall jet of 0.5 was used, and the results confirmed the existence of a very complex vortex flow region in the collision zone near the ground wall. Vorticity values were calculated from the experimental data and revealed negative (clockwise) vorticity near the stagnation point which is an indication of the presence of a small secondary vortex, also detected from the visualization studies but not sufficiently identified from the LDA measurements. 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.
- Experimental Study of the Collision Zone of a Boundary Layer with a Wall JetPublication . Barata, Jorge M M; Ribeiro, Samuel Dinis Galvão; Santos, Pedro; Silva, AndréLaser-Doppler measurements are presented for a highly curved flow resulting from the collision of plane turbulent wall jet with a boundary layer. This configuration can be found in the case of impinging jets of a V/STOL aircraft operating in ground vicinity. The experiments were carried out for boundary layer to wall jet velocity ratio of 0.5. The results include mean and turbulent velocity characteristics of the flow field as well as the characterization of the vorticity. The results revealed the existence of very small recirculation zones located upstream the separation point that co-exist and interact with the very well known VSTOL ground vortex. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
- Unsteady Computations of a Ground VortexPublication . Nunes, Ricardo F.; Silva, André; Barata, Jorge M MA computational study of the impact zone of a wall jet with a boundary layer was performed for a wide range of velocity ratios, VR, from 0.065 to 0.2. A ground vortex is formed and for intermediate velocity ratios the flowfield exhibits an oscillating behavior. The location and size of the ground vortex is almost constant during the complete sequence of oscillation, but secondary vortexes may also appear. For the case of very low velocity crossflow (small VR) the computations exhibit a stationary solution, which is in agreement with previous numerical and experimental results. For strong crossflows (large VR) the flow is also stationary, although there is a transition regime of some unsteadiness without any secondary vortex present.
- Experimental Study of a Ground VortexPublication . Barata, Jorge M M; Ribeiro, Samuel; Santos, Pedro José da Costa Teixeira; Silva, AndréLaser-Doppler measurements of the mean and turbulent components of the velocity flowfield resulting from the frontal collision of a wall jet with a boundary layer are presented and discussed, together with the visualization of the flow with direct photography and digital film imaging. The experiments were carried out for boundary-layer-to-wall- jet velocity ratios of 0.5 and 0.58. The results revealed the existence of a small counter-rotating recirculating zone located upstream (in the sense of the wall-jet flow) of the separation point, not reported before for this type of flow. This secondary vortex has an oscillating behavior observed in other ground-vortex flows, similar to that which can be observed, namely, through the bimodal histogram of the horizontal velocity (parallel to the wall) measurements, although the power spectra measurements do not exhibit any particular peaks.
- Influence of the Energy Dissipation in the Spray Impingement ModelingPublication . Rodrigues, Christian; Barata, Jorge M M; Silva, AndréSimulating the complex dynamic phenomena that occur during the spray droplets impact is of great interest in numerous applications. In this sense, refine flexible dispersion models that can be adjusted through the use of adapted and more suitable empirical correlations in order to fit specific configurations with minimum time constraints would be a great asset both for industry and researchers. In this work, it is intended to study the dissipative energy term in the splash event. Besides the original relationship proposed in the dispersion model used, other equations of energy dissipation based on investigations devoted to the study of this parameter are introduced in the simulation and the results are tested against experimental data. Comparing all the relationships evaluated, the ones drawn from the literature deviates from what was expected. Therefore, it is evident that further research are essential in this field in order to propose a sub-model that could accurately define the energy dissipation term during the splash regime, whereas the investigations carried out so far only considered the energy loss through viscous dissipation during the spread regime.