Temporal Behavior of Lifted Turbulent Jet Flames

Abstract

Measurements of the fluctuating liftoff height of turbulent jet flames were made using a linear photo-diode array. A wide range of experimental conditions was investigated, including varying the fuel, nozzle diameter and liftoff height. The amplitudes of the fluctuations in h were found to be of the order of the local large scale of the jet. There is a slight increase in normalized fluctuation level h′/h¯ with the mean liftoff height h¯ and there is some variation of h′/h¯ with fuel type. The dominant time scales of the fluctuations of h were found to be considerably longer than the local large-scale time of the turbulence defined as the local jet width divided by the centerline velocity, τ_δ ≡δ/U_(cl). By using fuels of different chemical times to vary τ_δ. the measured correlation time τ_(1/2) normalized by τ_δ was found to collapse with Richardson number ξ_h However, the Richardson numbers achieved are dependent largely on the chemical rates of the fuels. Also, experiments in which the nozzles were oriented horizontally showed no change in τ_(1/2).

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