Wave Dynamic Mechanisms in Coaxial Hydrogen/Liquid-Oxygen Jet Flames

Abstract

Coaxial gaseous hydrogen/liquid-oxygen jet flames were studied experimentally as a function of the outer-toinner momentum flux ratio J using high-speed shadowgraphy and hydroxyl radical (OH ) chemiluminescence imaging at 25 kHz. Particular attention was paid to wave dynamic mechanisms that could be observed. It was found that large structures generated at the exit of the annular flow created a chain of events that had a strong effect on the flame. These structures were found to impinge on the liquid-oxygen core and created local increases in OH emission (interpreted as combustion waves), local troughs in the liquid-oxygen core caused by increased vaporization, and waves composed of expansion gases: all of which convected downstream at different velocities, with the combustion wave propagating the fastest. The combustion waves were found to sometimes merge, sometimes spontaneously disappear, or sometimes continue to propagate as pairs. Earlier results had shown the importance of large-scale structure dynamics in the outer flow to simpler nonreacting coaxial flow. These results also confirmed their importance in combusting flows.

Transverse Acoustic Forcing of Gaseous Hydrogen/Liquid Oxygen Turbulent Shear Coaxial Flames

“…Roa and Talley [25] were, to our knowledge, the first to identify the wave amplification mechanism described previously. The present Paper appears to be the first time it has been described under the influence of acoustic forcing of any kind, and transverse acoustic forcing in particular here.…”

“…The current Paper is an extension of that work, in which transverse acoustic forcing is added under the same conditions and variation in J. It will be found in the following that the wave amplification mechanism identified in [25] is preserved in the presence of acoustic forcing, but modified. Accordingly, it is appropriate to describe this mechanism in further detail next.…”

“…Roa and Talley [25] explored the wave dynamics present in high-pressure, two-phase, turbulent, gaseous hydrogen/LOX shear coaxial flames as a function of the gas-to-liquid momentum flux ratio J ρU 2 gas ∕ρU 2 liq in the absence of acoustic forcing. That study identified the presence of a naturally occurring dynamics called here a wave amplification mechanism, which, in addition to the turbulence, controlled much of the dynamics of the unforced flames.…”

“…The ambient pressure was 3.93 MPa (570 psi), and the gas-to-liquid momentum flux ratio J was 0.15. Further details of this flow condition are given in [25], but they are also approximately the same as Table 1 of this Paper for the same value of J because the experimental conditions in this Paper are very similar to those in [25] except that here transverse acoustic forcing was added. The imaging diagnostics are described further in Sec.…”

“…Experimental and computational research on shear coaxial injectors using a gaseous annular propellant and a central cryogenic jet for liquid rocket engine applications were carried out by Poinsot et al [4], Rey et al [5], Richecoeur et al [6][7][8], Méry et al [9], Hakim et al [10,11], Urbano et al [12], Gonzalez-Flesca et al [13], Urbano et al [14], Hardi et al [15,16], Gröning et al [17], Armbruster et al [18], Mayer and Krülle [19], Mayer and Tamura [20], Mayer et al [21], Oefelein and Yang [22], Zong and Yang [23,24], Roa and Talley [25], Roa et al [26], Forliti et al [27], Hua et al [28], Graham et al [29], Levya et al [30,31], Rodriguez et al [32], Wegener et al [33], and Davis and Chehroudi [34]. Aspects of those studies that focused largely on characterizing and understanding the atomization, flame locations, and average global behavior for shear coaxial flows that are not experiencing combustion instabilities were reviewed by Roa and Talley.…”