Abstract In order to investigate the acoustic oscillation characteristics of gas–liquid pintle rocket engines and elucidate the path by which spray combustion process provides energy to the combustor pressure oscillation, a LOX/GCH 4 pintle engine with rectangular combustor was designed. By adding transverse velocity disturbance for the first time, the acoustic response of spray combustion process was simulated, and the effect of excitation amplitude on acoustic response was researched. Numerical results show that the adopted transverse velocity disturbance can excite the first-order transverse acoustic oscillation with same excitation frequency in the engine combustor. The acoustic response maintenance mechanism under extrinsic excitation is summarized for pintle engines. Besides, the temperature distribution inside the engine combustor tends to be uniform, and the low-frequency oscillation caused by the flame transverse swing gradually disappears. The amplitude of combustor pressure oscillation is dominated by excitement amplitude and phase difference between the pressure and heat release in combustion reaction region. In addition, the time-averaged combustor pressure can be amplified mainly by transverse velocity disturbance. The research work can provide a reference for related fire tests on the acoustic response of a subscale gas–liquid pintle engine.
Kerosene-based turbo-pump is crucial to pump-fed expansion cycle scheme of the scramjet system in aerospace applications. An automatic simulation method was developed to conduct performance analysis of kerosene-based turbo-pump at low costs. Turbulence simulation combined with a multi-species surrogate model of kerosene was employed to study objective characteristics by simulating the flow-field inside the turbo-pump at 100000 rpm. Automatic simulation process, based on Design of Experiments technique, response surface model and high-fidelity numerical simulation, was applied for similarity analysis and Pareto front analysis, respectively. Results indicate that, all the characteristic curves of pump developed head (ΔHp) and turbine shaft power (Pt) with respect to mass flow rate at various rotating speeds, agree well with Similarity Criterion; ΔHp is negatively related to the efficiency of pump (ηp) in general, but the contrary is the case for Pt and the efficiency of turbine (ηt).
LOX/GCH 4 pintle injector is suitable for variable-thrust liquid rocket engines. In order to provide a reference for the later design and experiments, three-dimensional numerical simulations with the Euler-Lagrange method were performed to study the effect of the initial particle diameter on the combustion characteristics of a LOX/GCH 4 pintle rocket engine. Numerical results show that, as the momentum ratio between the radial LOX jet and the axial gas jet is 0.033, the angle between the LOX particle trace and the combustor axial is very small. Due to the large recirculation zones, premixed combustion mainly occurs in the injector wake region. As the initial LOX particle diameter increases, the LOX evaporation rate and the combustion efficiency decrease until the combustion terminates with the initial LOX particle diameter greater than 110 μ m. The oscillation amplitude of the combustor pressure increases significantly along with the increase of the initial LOX particle diameter, and the low-frequency unstable combustion occurs when the initial LOX particle diameter exceeds 60 μ m. The combustor pressure oscillation at about 40 Hz couples with the swinging process of spray and flame, while the unsteady LOX evaporation amplifies the combustor pressure oscillations at 80 Hz and its harmonic frequency.
The use of kerosene-based regenerative cooling for scramjet has been found widespread attention due to its inherent nature of high energy utilization efficiency and good thermal protection performance. In order to provide a reference for the later design and experiments, three-dimensional turbulence simulations and sensitivity analysis were performed to determine the effects of three operating mode parameters, heat flux, mass flow rate, and outlet pressure, on the regenerative cooling characteristics of kerosene scramjets. A single rectangular-shaped channel for regenerative cooling was assumed. The RNG k-ε turbulence model and kerosene cracking mechanism with single-step global reaction were applied for the supercritical-pressure heat transfer of kerosene flows in the channel. Conclusions can be drawn that as the kerosene temperature rises along the channel, the decrease of fluid density and viscosity contributes to increasing the fluid velocity and heat transfer. When the kerosene temperature is close to the pseudocritical temperature, the pyrolysis reaction results into the rapid increase of fluid velocity. However, the heat transfer deterioration occurs as the specific heat and thermal conductivity experience their turning points. The higher heat flux leads to lower heat transfer coefficient, and the latter stops rising when the wall temperature reaches the pseudocritical temperature. The same rising trend of the heat transfer coefficient is observed under different outlet pressures, but the heat transfer deterioration occurs earlier at smaller outlet pressure for the reason that the corresponding pseudocritical temperature decreases. The heat transfer coefficient increases significantly along with the rise of the mass flow rate, which is mainly attributable to the increase of Reynolds number. Quantitative results indicate that as the main influence factors, the heat flux and mass flow rate are respectively negatively and positively relative to the intensification of heat transfer, but outlet pressure always has little effects on cooling performance.
In order to understand the fragmentation and atomization characteristics of the liquid jet in transverse gas film, a pintle injection element using air and water as simulants is designed. The two-phase flow large eddy simulation and backlight imaging are used to study the liquid-jet breakup process and spray-field dynamic characteristics in the nearorifice area of pinte injection element under the atmospheric environment. The primary fragmentation process of the liquid jet dominated by surface wave is obtained by large eddy simulation, which reveals the establishment process of the spray field in near-orifice area of the gas-liquid pintle injector. After the subsonic airflow leaves the slit, it expands and accelerates into supersonic state. Then the deceleration and pressurization phenomenon occurs once the supersonic airflow passes through the detached bow shock upstream of the liquid jet. The liquid jet bends downstream due to the difference in pressure between upstream and downstream, and the Rayleigh-Taylor (R-T) unstable surface wave appears on the jet windward surface. As the surface wave develops, the penetration of the wave trough by airflow causes the continuous liquid jet to fragment. Proper orthogonal decomposition (POD) method can effectively reconstruct spray snapshot. The POD mode shows that the low-frequency spray oscillation in near-orifice area is caused by the overall expansion/contraction process of the spray field, while the high-frequency one is due to the “impact wave” movement of the liquid block or liquid mist group on the windward side. The latter is produced by the R-T unstable surface wave before the jet breakup, and can be categorized as traveling wave structure. The dimensionless traveling wave wavelength has a power-law relationship with Weber number.
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