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J-M. Brustet, B. Benech, and P. Waldteufel

Abstract

The possibility of applying infrared imagery to the study of a large, hot plume materialized by carbon particles resulting from the incomplete combustion of fuel oil is investigated.

In a specific case (the PROSERPINE experiment), due to the high carbon particle content, the lower part of the plume acts as a semi-opaque target. Using an infrared camera equipped with a detector sensitive in the 2–5.8 μm band, the thermal images are found to yield a plume geometry in good agreement with visible contours retrieved from visible photographs.

Thermal images provide access to the internal structure of a plume, down to scales which depend on the plume opacity. It appears that IR imagery is able to yield improved information concerning the turbulent fields of motion and temperature.

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B. Bénech, J. Noilhan, A. Druilhet, J. M. Brustet, and C. Charpentier

Abstract

The work reported here describes the environmental impact of emitting about 1000 MW of dry heat from a concentrated source into the atmosphere. It is based on a large field program conducted jointly by the Centre de Recherches Atmosphériques and Electricité de France. This program provided an opportunity to evaluate the actual environmental impacts of large-scale heat release and to obtain data required to develop parameterization schemes for use in modeling heat releases by intense sources such as dry cooling towers.

The heat source is an array of 105 fuel-oil burners distributed over 15 000 m2. An aerial assemblage suspended at two levels (25 and 50 m) over the burner array has been used to collect data (temperature and velocity fields) for analyzing aspects of both the mean and the turbulent components of the flow near the heat source.

The flow field near the heat source comprises a cold downdraft upwind zone which supplies the burner area with ambient air, a convective zone containing a hot vertical air stream with rotation effects, and a cold updraft downwind zone where numerous vortices are initiated.

In the upwind zone, the horizontal flow is accelerated, steady state and divergent. In the convective zone, temperature and vertical velocity are closely correlates, as are temperature and horizontal velocity. The downstream flow shows strong convergence (∼0.3 s−1) and contains two counter-rotating vortices. Cross-correlation and spectral analysis of temperature and vertical velocity in the convective zone show that the major spectral energy contribution is located at wavelengths between 30 and 70 m. The slope of the temperature spectra tends to increase with the standard deviation of the temperature fluctuations. The turbulence in the core of the convective zone is characterized by large values of the dissipation rate ε (∼1 m2 s−3) and of the temperature structure parameter CT 2 (∼10 m−⅔ K). The comparison between the turbulent and advective heat fluxes suggests that the turbulence is not yet fully developed at the vicinity of the heat source. Finally, an estimation of the mean initial conditions as a function of the wind is given.

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