The fundamental study of near-wall turbulent structures is extremely important due to its dominant role in several different engineering applications. In turbulent flows, structures with different scales interact among themselves through a complex phenomenon, characterized by a continuous and self-sustainable process. Although the presence of coherent patterns seems to be responsible for the maintance of turbulence, the evolution and interaction of these structures are not yet completely understood. In order to investigate such phenomena, experimental tests of turbulent flow over a flat plate were conducted in a wind tunnel. Experiments were also conducted in a square channel flow, representing a couple of near-wall flow studies. The present work employed a tomographic particle image velocimetry technique, TomoPIV, with high temporal resolution for measuring 3D velocity fields, allowing the determination of the complete velocity gradient tensor, as well as the reconstruction of the temporal history of the turbulent structures. Processing procedures for the TomoPIV technique were optimized in order to improve the algorithm performance and precision of the measured vectorial fields. The conducted measurements allowed for the attainment of conditional statistics for the typical turbulent boundary layer coherent structures, such as (high and low) velocity streaks, vortices sweeps and ejections, thus providing quantitative information on such structures. The statistical analyses were accomplished through the use of a data post-processing code, especially developed for the current research. Results have shown vortices distributed all over the flow; those were concentrated, however, in the neighborhood of low velocities and ejections. These vortices have presented a variety of angles (inclinations) and a wide range of size scales. The results have indicated that the vortices were indirectly correlated with the turbulence production process, despite being the mainly accountable for dissipation of turbulent energy. Ejections and sweeps, associated to the regions of low and high velocities, respectively, were seen as the structures which contribute the most for turbulence production.
Mechanical Engineering Postgraduate Program at PUC-Rio is ranked once more at the highest level, 7, in the triennial CAPES evaluation. Besides PUC-Rio, three other programs were ranked 7 in the Engineering III group.
Online enrollment for Masters / PhD programs in Mechanical Engineering at PUC-Rio are open from October 01 to November 30, through the PUC-Rio website.
In 2014, the mechanical engineering postgraduate program at PUC-Rio celebrates 50 years of existance. The very first master’s thesis was written in 1965 by Guilherme de la Penha. The Mechanical Engineering Department will celebrate this important date with an event at the RDC Auditorium, at 15 pm, november 27.
Watch the short movie about these 50 years of the department’s postgraduate program:
The addition of small amounts of polymer molecules to internal turbulent flows can result in significant drag reduction, which in turn can reduce pumping costs in transport systems, for example. The goal of this project is to study in detail the interaction of the polymer molecules with the near-wall turbulent structures in a channel flow. These local interactions are the key to a better understanding of the global drag-reducing effect that is observed in practice. Discussions in the literature are open and point to the need of further investigation.
Thus, the task here is to perform three-component velocity field measurements, in a thick plane, focusing attention on the small-scale turbulent structures present in that region. The technique employed is the Stereoscopic Particle Image Velocimetry.
The thesis work will consist, in principle, of the following steps:
– Bibliographic update
– Implementation of updates and improvements in reconstruction / processing / velocity field calculation software, already pre-developed in C++
– Final hologram acquisition, with and without polymers
– Processing of raw data and physical analysis of the results
– Preparation of thesis manuscript
Students graduated in Mechanical Engineering or Physics, interested in at least one of the following fields of knowledge: fluid mechanics, optics, image processing, programming, and with good academic performance.
CAPES/Cnpq scolarship and possibility of supplementary grant.
Luis Fernando A. Azevedo email@example.com (021) 3527-1181
Leonardo Fernandes – firstname.lastname@example.org (21) 97218-1245