TY - JOUR
T1 - Numerical simulation of stable and unstable ram-mode operation of an axisymmetric ethylene-fueled inlet-isolator-combustor configuration
AU - Hash, Caleb A.
AU - Drummond, Paige M.
AU - Edwards, Jack R.
AU - Kato, Nozomu
AU - Lee, Tonghun
N1 - This work is supported by the Air Force Office of Scientific Research under grants FA9550-20-1-0408 and FA9550-21-1-0072, monitored by Dr. Chiping Li. Computer time has been provided by the DoD's High Performance Computing Modernization Program.
PY - 2022/8
Y1 - 2022/8
N2 - Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois's ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations (HyChem FFCM 2.0). Conjugate heat-transfer models based on an assumed penetration depth of the applied heating load are used to account for localized wall heating during the short durations (∼0.2 to 0.3 s) of the parts of the experiments simulated in this work. The results show a marked sensitivity to trace levels of atomic oxygen (∼1% by mass) in the free stream, a consequence of the arc-heating process. Atomic oxygen significantly reduces ignition delay at the relatively low pressures present within the configuration. With 1% atomic oxygen in the free stream, a jet-wake stabilized, partially-premixed flame structure emerges during thermal-throat ramjet operation at an equivalence ratio of 1.24, in accord with available experimental pressure and imaging measurements. Considering the free stream as pure air results in a cavity-wake stabilized, rich premixed flame. Simulations of unstable ram-mode operation leading to inlet unstart at an equivalence ratio of 1.97 also indicate a sensitivity to the free-stream composition. A reduction in atomic oxygen concentration to 0.8% by mass yields good agreement with the experimentally-observed isolator shock-train propagation speed. Both the computational and experimental results indicate that the shock train accelerates before being disgorged from the inlet. This acceleration stems from a rapid increase in the sizes of regions of low speed, sometimes separated flow behind Mach disks that form as the shock train proceeds upstream.
AB - Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois's ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations (HyChem FFCM 2.0). Conjugate heat-transfer models based on an assumed penetration depth of the applied heating load are used to account for localized wall heating during the short durations (∼0.2 to 0.3 s) of the parts of the experiments simulated in this work. The results show a marked sensitivity to trace levels of atomic oxygen (∼1% by mass) in the free stream, a consequence of the arc-heating process. Atomic oxygen significantly reduces ignition delay at the relatively low pressures present within the configuration. With 1% atomic oxygen in the free stream, a jet-wake stabilized, partially-premixed flame structure emerges during thermal-throat ramjet operation at an equivalence ratio of 1.24, in accord with available experimental pressure and imaging measurements. Considering the free stream as pure air results in a cavity-wake stabilized, rich premixed flame. Simulations of unstable ram-mode operation leading to inlet unstart at an equivalence ratio of 1.97 also indicate a sensitivity to the free-stream composition. A reduction in atomic oxygen concentration to 0.8% by mass yields good agreement with the experimentally-observed isolator shock-train propagation speed. Both the computational and experimental results indicate that the shock train accelerates before being disgorged from the inlet. This acceleration stems from a rapid increase in the sizes of regions of low speed, sometimes separated flow behind Mach disks that form as the shock train proceeds upstream.
KW - Isolator shock train
KW - Large eddy simulation
KW - Partially-premixed combustion
KW - Thermal-throat ramjet
UR - http://www.scopus.com/inward/record.url?scp=85129297458&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85129297458&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2022.112157
DO - 10.1016/j.combustflame.2022.112157
M3 - Article
AN - SCOPUS:85129297458
SN - 0010-2180
VL - 242
JO - Combustion and Flame
JF - Combustion and Flame
M1 - 112157
ER -