Radiation Intensity Measurements and Computations of an Impinging Turbulent Buoyant Diffusion Flame

Studies of radiation emissions from turbulent buoyant diffusion flames impinging on structural elements have applications to the development of fire models and estimation of structural integrity under large heat loads. An experimental and numerical study of radiation emissions from turbulent buoyant diffusion flames with and without impingement on a flat plate is reported. The steel plate was suspended above a buoyant flame at a select axial location above the fuel exit. Time-dependent images of the narrowband radiation intensity from the flames with and without impingement were measured using a high speed infrared camera. Fire dynamics simulations were performed using a mixture fraction based combustion model and state relationships obtained from a steady laminar flamelet model. The computed temperature and species concentrations were used in conjunction with a narrowband radiation model to calculate the radiation intensities by solving the radiative transfer equation. The computed radiation intensities were rendered in the form of images and qualitatively and quantitatively compared with the measurements. The measured and the computed images reveal flame necking and bulging with a characteristic frequency of 7 Hz and 9 Hz respectively which is in agreement with previous empirical correlations. The experimental and computational results show stagnation point flame stabilization and high radiation heat loading on the steel plate. Turbulent radiation statistics such as the normalized root mean square and temporal correlations indicate that the plate reduces the magnitude of the normalized intensity fluctuations and oscillations in the impinging flame. The results demonstrate that the plate has an upstream propagation effect on impinging flame radiation.