Experiments on axisymmetrically pulsed turbulent jet flames

Lovett, Jeffery A.; Turns, Stephen R.

doi:10.2514/3.10350

Cited by 47 publications

(21 citation statements)

References 26 publications

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“…The unsteady perturbation decays faster as the frequency of the oscillation grows, and only for small Strouhal numbers is it possible to notice the effects of the forcing at large distances downstream. This effect has been observed previously in laminar [6,7] and turbulent flames [8,9].…”

Section: Resultssupporting

confidence: 83%

“…The flame response changes from the full modulation represented in Figure 2 for S = 0.1 to the almost unchanged pattern of Figure 5 at a relatively small Strouhal number S = 1; in the latter case, the oscillations do not disappear but are kept confined to the cold region located upstream of the flame. Similar results have been observed previously in the numerical solution of [10] and in the experimental works of [7][8][9].…”

Section: The Role Of Viscositysupporting

confidence: 91%

“…In the next section, we formúlate the problem; in Section 3, we introduce the numerical method used in computing the solutions; and in Section 4, we present the results. Specifically, we confirm the experimental observations of Strawa and Cantwell [6,7] and Lovett and Turns [8,9] and extend their explanation using some recent asymptotic and numerical work to analyze the influence of the pulsation on the máximum fíame temperature, fíame shape, and CO oxidation chemistry. In Section 5, we summarize the main conclusions of the work.…”

Section: Introductionsupporting

confidence: 84%

“…Finally, time-averaging the H T data demonstrates that the average flame heights of these forced flames are slightly shorter than their steady counterpart, fundamentally due to the enhanced mixing promoted by the oscillation. This phenomenon has also been observed experimentally [7,8] and numerically [21].…”

Section: Flame Pinch-offsupporting

confidence: 75%

“…They found that, by imposing a perturbation at a certain frequency, it was possible to produce a completely periodic, fully controllable flow that allowed the modification of the chemical reaction and the mixing process. The same conclusión was also later suggested by Lovett and Turns [8,9] for turbulent jets.…”

Section: Introductionsupporting

confidence: 80%

See 4 more Smart Citations

Influence of Strouhal number on pulsating methane–air coflow jet diffusion flames

Sánchez–Sanz

Bennett

Smooke

et al. 2010

Combustion Theory and Modelling

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Four periodically time-varying methane-air laminar coflow jet diffusion flames, each forced by pulsating the fuel jet's exit velocity U¡ sinusoidally with a different modulation frequency w¡ and with a 50% amplitude variation, have been computed. Combustión of methane has been modeled by using a chemical mechanism with 15 species and 42 reactions, and the solution of the unsteady Navier-Stokes equations has been obtained numerically by using a modified vorticity-velocity formulation in the limit of low Mach number. The effect of w¡ on temperature and chemistry has been studied in detail. Three different regimes are found depending on the flame's Strouhal number S = awj/Uj, with a denotingthe fuel jet radius. For small Strouhal number (S = 0.1), the modulation introduces a perturbation that travels very far downstream, and certain variables oscillate at the frequency imposed by the fuel jet modulation. As the Strouhal number grows, the nondimensional frequency approaches the natural frequency of oscillation of the flickering fíame (S -0.2). A coupling with the pulsation frequency enhances the effect of the imposed modulation and a vigorous pinch-off is observed for S = 0.25 and S = 0.5. Larger valúes of S confine the oscillation to the jet's near-exit región, and the effects of the pulsation are reduced to small wiggles in the temperature and concentration valúes. Temperature and species mass fractions change appreciably near the jet centerline, where variations of over 2% for the temperature and 15% and 40% for the CO and OH mass fractions, respectively, are found. Transverse to the jet movement, however, the variations almost disappear at radial distances on the order of the fuel jet radius, indicating a fast damping of the oscillation in the spanwise direction.

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