Scalar time-series measurements in turbulent CH₄/H₂/N₂ nonpremixed flames: OH

Time-series measurements of OH concentrations are reported for simple jet diffusion flames using a fuel mixture of hydrogen, methane, and nitrogen. Five Reynolds numbers and two burner diameters are examined. Autocorrelation functions were computed from the time series and were used to calculate integral time scales for many axial and radial locations in each jet. The autocorrelation functions are found to collapse when normalized by the integral time scale, indicating that a single time scale adequately characterizes the full range of scalar fluctuations. The evolution of the integral time scales is assessed with respect to Reynolds number, axial height, radial location, and burner diameter. The time scales are found to decrease as Re^-1.4, which is in contrast to the usual Re^-1 dependence for mixture fraction and velocity in nonreacting jets. The OH time scales are found to be complicated functions of radial location and do not follow the scaling expected from nonreacting flows. Copyright (C) 2000 The Combustion Institute.