Browsing by Issue Date, starting with "2012-06-25"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- 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.
- 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.
- On the Modeling of a Spray Impinging on a SurfacePublication . Silva, André; Barata, Jorge M MThe present paper reports a numerical study of a spray impinging on a surface through a crossflow and is aimed at studying the fundamental aspects of the spray impingement phenomena in a three-dimensional configuration, which is relevant to practical engines. Different impinging models were used and the results are compared with measurements and predictions of other authors. The results show a general good agreement with the experiments, and reveal that the splash droplets are very important for the spray development. The performance of droplet impinging models depends strongly on the conditions of pre-impingement.
- Gago Coutinho and the Aircraft NavigationPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréGago Coutinho was one of the two Portuguese navigators that crossed by air the South Atlantic in the beginning of the 20th century. He developed a new model of sextant that could be used to measure the altitude of a star when flying without the need of the sea horizon. This new instrument was called "precision sextant" and used an artificial horizon line which was defined with the help of a water bubble. Due to his knowledge of Navigation, Astronomy, Geography and Mathematics he received from the Portuguese King D. Carlos I several assignments in Africa and Asia. Gago Coutinho received several important official medals and prizes, including the PhD Honoris Causa from the Universities of Lisbon and Oporto, and authored several scientific publications. He received the distinct position of Admiral of the Portuguese Navy in 1958, and died in the following year.