Publications

Imaging of dissipative structures in the near field of a turbulent non-premixed jet flame

Kaiser, Sebastian A.; Frank, Jonathan H.

Two-dimensional laser Rayleigh measurements of thermal gradient structures are performed in a turbulent non-premixed jet flame. The measurements focus on the near field (10 nozzle diameters downstream of the jet exit) where traditional scaling laws from the self-similar far field of non-reacting jets are not necessarily applicable. The optical performance of the high-resolution imaging system is characterized. The square of the temperature gradient field is analyzed by calculating the power spectral density (PSD) and by directly measuring the thicknesses of the layer-like structures. Fully resolved spectra extending over three orders of magnitude in PSD are obtained using a new noise cancellation technique. Some spatial filtering (smoothing) is necessary to reliably measure the layer-normal structure widths in the images. The probability density function (PDF) of the layer widths is found to be approximately log-normal. The PDFs of the 20-percent-full-width layer thicknesses have peak values at 216 and 368 μm for rid = 0 and r/d=1, respectively. The peak of the layer-thickness probability density function (PDF) occurs at a length scale where the PSD is at approximately 0.5 percent of its maximum in both the low-temperature centerline region and the region near the maximum mean temperature. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.