The wake behind a circular cylinder in water is visualized when colored solutions are injected through rows of holes pierced in the cylinder. When these solutions are viscoelastic, a drastic change of the shape of the wake is observed compared to that observed for water injections. The aspect ratio of the wake is decreased, the wavelength of the vortices is increased, and a large region of slow fluid motion is developed behind the cylinder. It is shown that these observations are consistent to a shear instability inhibition due to a local elasticity.

No abstract

No abstract

This results aims to improve the effectiveness of security systems by optimizing the interaction between technological components and organizational and human intervention. Objectives are to determine the specific laws governing indoor fire phenomena by means of experimental full-scale and numerical approaches, to get real-time information about the fire during operations. A second phase consists in a transformation of the usual passive-safety systems into intelligent and communicating systems, thereby optimizing and securing the human and organizational emergency response. The dual competence numerical /experimental data is essential in this type of study since the experimental data suffer from a lack of resolution (spatial, temporal) but nevertheless represent information necessary for validating the codes.

In compartment fires (houses, buildings, underground, warehouse, etc.), smokes are a major danger during firemen intervention. Most of the time, they are at high temperature (>800˚C) and they flow everywhere through many kinds of ducts, which leads to the propagation of the combustion by the creation other fires in places which may be far away from the initial fire. In this paper, we present a new approach of the problem, which allows to better follow the fire behavior and especially to detect the dangers that may appear and endanger firefighters. This approach consists in a mathematical analysis based on the comparison of moving averages centered in the past, calculated on the temperature recordings of the smokes. As a consequence, this method may allow to improve decision support in real time and therefore to improve the security and the efficiency of firefighters in their operations against that kind of fires.