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- 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.
- Experimental Study of Instabilities and Secondary Effects of a Ground Vortex FlowPublication . Barata, Jorge M M; Ribeiro, Samuel Dinis Galvão; Santos, Pedro; Silva, André; Silvestre, M.A.R.Laser-Doppler measurements of velocity characteristics of the flowfield resulting from the collision of a wall jet with a boundary layer are presented and discussed together with visualization of the flow. The experiments have been carried out for boundary layer to wall jet velocity ratios of 0.5 and 0.58. Direct photography, digital film imaging, and mean and turbulent laser Doppler measurements were obtained to characterize this type of flows. For the present conditions the results revealed the existence of a small counter-rotating recirculating zone located upstream the separation point not yet reported before for this type of flows. The results show that this secondary vortex has a similar oscillating behavior observed in some configurations leading to ground vortex flows, where they are also probably present, but due the geometric and characteristic parameters could not be identified separately. A particular ordered sequence was recognized for the small recirculation zone, and can be confirmed by the bimodal histogram of the horizontal velocity measurements obtained. In spite of the apparent organized sequence of the turbulent structure of the collision zone, the power spectra measurements did not exhibit any evident particular peaks.
- 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.