Self-similarity of hydroxyl-concentration temporal statistics in turbulent nonpremixed jet flames

Temporal statistics for hydroxyl concentrations in turbulent nonpremixed hydrogen/argon flames have recently been reported in the form of power spectral densities for a range of Reynolds numbers (2.8 × 10³-1.7 × 10⁴) and axial locations (x/D = 1-20). In the present investigation these data are examined further, and the two-time statistics are shown to collapse when scaled by the measured integral timescale. The resulting autocorrelation function is shown to be closely approximated by an exponential decay, as previously reported for mixture fraction. The measured integral timescales vary with Reynolds number and position within the reacting jet in accordance with a simple similarity scaling. The implications of this unexpected statistical similarity are examined with respect to the simulation of scalar fluctuations in turbulent nonpremixed flames.