Cold Supersonic Flow Research Articles

Effect of Kerosene Dual-Jet Spacing on the Mixing and Combustion Characteristics of a Scramjet Combustor.

As the core of a hypersonic propulsion system, the effective mixing efficiency of fuel and air in a supersonic combustor is crucial for its performance. This study focuses on a cold supersonic flow and employs computational fluid dynamics (CFD) techniques combined with Euler-Lagrange method's discrete-phase model (DPM) for multiphase flows, K-H and R-T (Kelvin-Helmholtz and Rayleigh-Taylor) mixing and atomization models, turbulence models, and surface evaporation models to investigate the injection, atomization, and mixing characteristics of kerosene in supersonic airflow. In order to enhance the mixing efficiency between kerosene and air while reducing flow losses, this study examines a staggered dual-jet injection scheme, with the dual jets arranged at the center of the cavity and having a dual-jet spacing of 10 and 20 mm, respectively. Starting from the interaction mechanism between jets, the impact of different staggered dual-jet spacings on the kerosene jet penetration height, span expansion area, angle of the shock wave, and Sauter mean diameter distribution was analyzed. The results show that a short dual-jet spacing (10 mm) leads to greater penetration height, wider span expansion, and a larger angle of the shock wave. When the dual-jet spacing is shorter, the interaction between the fuel jet and the cavity shear layer is stronger, resulting in an improved fuel mixing efficiency. The achievements of this study are consistent with previous experimental measurements and the literature, demonstrating a strong theoretical foundation for optimizing the design of hypersonic engines by deepening the understanding of the fundamental atomization mechanisms of kerosene jets in cold-state supersonic flows. Moreover, these results hold practical significance in improving the efficiency of kerosene combustion and enhancing the performance of flame stabilization devices.

Terrestrial ion escape and relevant circulation in space

Abstract. Observations of the terrestrial ion escape to space and the transport of escaping ions in the magnetosphere are reviewed, with the main stress on subjects that were not covered in reviews over past 2 decades, during which Cluster has significantly improved our knowledge of them. Here, outflowing ions from the ionosphere are classified in terms of energy rather than location: (1) as cold ions refilling the plasmasphere faster than Jeans escape, (2) as cold supersonic ions such as the polar wind, and (3) as suprathermal ions energized by wave–particle interaction or parallel potential acceleration, mainly starting from cold supersonic ions. The majority of the suprathermal ions above the ionosphere become “hot” at high altitudes, with much higher velocity than the escape velocity even for heavy ions. This makes heavy hot ions more abundant in the magnetosphere than heavy ions transported by cold refilling ions or cold supersonic flow. The immediate destination of these terrestrial ions varies from the plasmasphere, the inner magnetosphere including those entering the ionosphere in the other hemisphere and the tailward outer boundaries, the magnetotail, and the solar wind (magnetosheath, cusp, and plasma mantle). Due to time-variable return from the magnetotail, ions with different routes and energy meet in the inner magnetosphere, making it a zoo of different types of ions in both energy and energy distribution. While the mass-independent drift theory has successfully disentangled this zoo of ions, there are many poorly understood phenomena, e.g., mass-dependent energization. Half of the heavy ions in this zoo also finally escape to space, mainly due to magnetopause shadowing (overshooting of ion drift beyond the magnetopause) and charge exchange near the mirror altitude where the exospheric neutral density is at its highest. The amount of heavy ions mixing directly with the solar wind is already the same as or larger than that entering into the magnetotail and is large enough to extract the solar wind kinetic energy in the cusp–plasma mantle through the mass-loading effect and drive the current system near the cusp independently of the global current system. Considering the past solar and solar wind conditions, ion escape might even have influenced the evolution of the terrestrial biosphere.

Effect of Heat Release on a Gas Flow in a Channel with a Variable Cross Section

The influence of the longitudinal distribution of heat release in a supersonic combustion of propane under the conditions of an unsteady pulsed discharge on the gas flow regime in a rectangular channel with a variable cross section is studiecd. It is shown that, with an increase in the mass flow rate of propane, the thrust arising from the supersonic combustion of a lean hydrocarbon fuel in an expanding aerodynamic channel, the pressure jump in the combustion area, and the air temperature in the closed pressure chamber increase. It is revealed that there is a limiting amount of hydrocarbon fuel that can be burned in a supersonic combustion regime in an expanding rectangular aerodynamic channel with side expansion angles α = β = 5° without transition to a subsonic flow, while the ratio of the exit and entry sections S2/S1 is 12.7. The experimental results are in satisfactory agreement with the data of mathematical modeling with allowance for additional heating of the cold supersonic flow in the region of an unsteady pulsed discharge.

Numerical investigation of scale effect of various injection diameters on interaction in cold kerosene-fueled supersonic flow

The incident shock wave generally has a strong effect on the transversal injection field in cold kerosene-fueled supersonic flow, possibly due to its affecting the interaction between incoming flow and fuel through various operation conditions. This study is to address scale effect of various injection diameters on the interaction between incident shock wave and transversal cavity injection in a cold kerosene-fueled scramjet combustor. The injection diameters are separately specified as from 0.5 to 1.5mm in 0.5mm increments when other performance parameters, including the injection angle, velocity and pressure drop are all constant. A combined three dimensional Couple Level Set & Volume of Fluids (CLSVOF) approach with an improved K-H & R-T model is used to characterize penetration height, span expansion area, angle of shock wave and sauter mean diameter (SMD) distribution of the kerosene droplets with/without considering evaporation. Our results show that the injection orifice surely has a great scale effect on the transversal injection field in cold kerosene-fueled supersonic flows. Our findings show that the penetration depth, span angle and span expansion area of the transverse cavity jet are increased with the injection diameter, and that the kerosene droplets are more prone to breakup and atomization at the outlet of the combustor for the orifice diameter of 1.5mm. The calculation predictions are compared against the reported experimental measurements and literatures with good qualitative agreement. The simulation results obtained in this study can provide the evidences for better understanding the underlying mechanism of kerosene atomization in cold supersonic flow and scramjet design improvement.

하이퍼 혼합기를 사용한 저엔탈피 초음속 유동장 내연소 특성 연구

본 연구에서는 마하 2의 실험실 규모의 풍동장치에서 플라즈마 제트 토치를 점화기로 사용하여 강제점화에 대한 연소 특성을 연구하였다. 하이퍼 혼합기는 혼합기로 사용되었다. 수직분사의 경우, 하나는 하이퍼 혼합기의 웨지면에 충돌하도록 하였으며, 다른 하나는 차가운 주유동으로 바로 분사되도록 하였다. 하이퍼 혼합기와 충돌하는 경우 충돌된 연료는 분산되며 확산 혼합에 의해 혼합성능이 증대된다. 또한 혼합된 가스는 대부분 플라즈마 제트의 열원으로 유입되어 연소 성능을 증대시킨다. 하지만 주유동으로 직접 분사되는 경우는 초음속의 주유동 내에서 점화되지 못하고 많은 양의 연료가 소비된다. 따라서 강제점화방식의 연소의 경우에는 많은 양의 연료-공기 혼합물을 점화가 가능한 열원으로 공급하는 것이 중요하다. In this study, a forced ignition method with a plasma jet torch is studied in Mach 2 laboratory scaled wind-tunnel. The hyper-mixer is used as a mixer. For two normal injection cases, the one is collided against a wedge plate of the hyper-mixer and the other is directly injected into the cold main flow. For the first case, the hyper-mixer disperses the injected fuel, leading to the mixing enhancement. Furthermore, the fuel-air mixture is provided into the plasma hot gas, which enhances the combustion performance. However, the direct injection into the main flow method spends amount of fuel without ignition in the cold supersonic flow. In the end, for the forced combustion, it is important to supply the fuel-air mixture into the heat source.

Effects of plasma aerodynamic actuation on oblique shock wave in a cold supersonic flow

Wedge oblique shock wave control using an arc discharge plasma aerodynamic actuator was investigated both experimentally and theoretically. Schlieren photography measurements in a small-scale short-duration supersonic wind tunnel indicated that the shock wave angle decreased and its start point shifted upstream with the plasma aerodynamic actuation. Also the shock wave intensity weakened, as shown by the decrease in the gas static pressure ratio of flow downstream and upstream of the shock wave. Moreover, the shock wave control effect was intensified when a static magnetic field was applied. Under test conditions of Mach 2.2, magnetic control and input voltage 3 kV, the start point of the shock wave shifted 4 mm upstream, while its angle and intensity decreased 8.6% and 8.8%, respectively. A thermal choking model was proposed to deduce the change laws of oblique shock wave control by surface arc discharge. The theoretical result was consistent with the experimental result, which demonstrated that the thermal choking model can effectively forecast the effect of plasma actuation on an oblique shock wave in a cold supersonic flow.

Repetitively Pulsed Nonequilibrium Plasmas for Magnetohydrodynamic Flow Control and Plasma-Assisted Combustion

This paper demonstrates significant potential of the use of high-voltage, nanosecond pulse duration, high pulse repetition rate discharges for aerospace applications. The present results demonstrate key advantages of these discharges: 1) stability at high pressures, high flow Mach numbers, and high-energy loadings by the sustainer discharge, 2) high-energy fractions going to ionization and molecular dissociation, and 3) targeted energy addition capability provided by independent control of the reduced electric field of the direct current sustainer discharge. These unique capabilities make possible the generation of stable, volume-filling, low-temperature plasmas and their use for high-speed flow control, nonthermal flow ignition, and gasdynamic lasers. In particular, the crossed pulsersustainerdischargewasusedformagnetohydrodynamic flowcontrolincoldM � 3 flows,providing firstevidenceof cold supersonic flow deceleration by Lorentz force. The pulsed discharge (without sustainer) was used to produce plasma chemical fuel oxidation, ignition, and flameholding in premixed hydrocarbon–air flows, in a wide range of equivalence ratios and flow velocities and at low plasma temperatures, 150–300 � C. Finally, the pulser-sustainer discharge was used to generate singlet oxygen in an electric discharge excited oxygen–iodine laser. Laser gain and output power are measured in the M � 3 supersonic cavity.

Numerical study on self-sustained oscillation characteristics of cavity flameholders in a supersonic flow

Self-sustained oscillation characteristics of two-dimensional cavity-based flameholders in a cold supersonic flow were investigated in the present numerical study. The unsteady flowfields were calculated using hybrid Reynolds-averaged Navier—Stokes/large eddy simulation (RANS/LES) method. The key cavity parameters that were varied include cavity aft wall angle and cavity length to depth ratio. The hybrid model favourably captured the large scale unsteady characteristics and revealed the evolution process of cavity free shear layer. Pressure fluctuation spectra agreed well with theoretical predictions. The hybrid RANS/LES data indicate that cavity shape and size both have significant effects on the oscillation characteristics. As the cavity length to depth ratio decreases, oscillation frequency corresponding to maximum oscillation amplitude shifts to higher values. Most of the oscillation modes are greatly suppressed as the cavity aft wall angle decreases. Contrast to the steep aft wall cavity, only higher frequency modes remain in the oscillation of the cavity with small aft wall angle.

Low-temperature M=3 flow deceleration by Lorentz force

This paper presents results of cold magnetohydrodynamic (MHD) flow deceleration experiments using repetitively pulsed, short pulse duration, high voltage discharge to produce ionization in M=3 nitrogen and air flows in the presence of transverse direct current electric field and transverse magnetic field. MHD effect on the flow is detected from the flow static pressure measurements. Retarding Lorentz force applied to the flow produces a static pressure increase of up to 17%–20%, while accelerating force of the same magnitude results in static pressure increase of up to 5%–7%. The measured static pressure changes are compared with modeling calculations using quasi-one-dimensional MHD flow equations. Comparison of the experimental results with the modeling calculations shows that the retarding Lorentz force increases the static pressure rise produced by Joule heating of the flow, while the accelerating Lorentz force reduces the pressure rise. The effect is produced for two possible combinations of the magnetic field and transverse current directions producing the same Lorentz force direction (both for accelerating and retarding force). This demonstrates that the observed static pressure change is indeed due to the MHD interaction, and not due to Joule heating of the flow in the crossed discharge. No discharge polarity effect on the static pressure was detected in the absence of the magnetic field. The fraction of the discharge input power going into Joule heat in nitrogen and dry air, inferred from the present experiments, is low, α=0.1, primarily because energy remains frozen in the vibrational energy mode of nitrogen. This result provides first direct evidence of cold supersonic flow deceleration by Lorentz force.

710 水素-空気超音速混合層の時系列測定(OS7-3 計測・地上実験設備)(OS7 北海道における航空宇宙工学研究の進展と未来)

A hydrogen jet was injected into a cold supersonic flow in a parallel direction from a slit injector. The free stream Mach number was about 1.81. To organize mixing process of hydrogen-air supersonic mixing layer by time series, double wire probe, in which Pt and Ni wire were strung, was used. We have measured the electric power that supplied to constant temperature Pt and Ni wire in a supersonic mixing layer. The heat release due to the catalytic reaction, hydrogen concentration were measured. It was shown that the present measurement method was able to apply to the time series measurements on mixing condition of hydrogen-air supersonic mixing layer.

Evaluation of Supersonic Turbulent Mixing Using Catalytic Combustion of Constant Temperature Pt Wire.

Supersonic combustion using catalytic wire at constant temprature in a cold supersonic flow field was investigated in a square duct with a backward-facing step. The free stream Mach number was Mm=1.18. Hydrogen was injected transversely behind a backward-facing step into a cold air free-stream. The heat released from the catalytic combustion had no effect on the temperature of the catalyst. This indicates that the reaction rate of the catalytic combustion observed in this study was determined by the concentration of H2 and / or O2 on the surface of the catalyst. The spatial distribution of heat released from the catalytic combustion in supersonic turbulent mixing layer, corresponds to the spatial distribution of concentration of H2 and / or O2 in local, was obtained. It was found that the most suitable position for supersonic combustion was at the outer edge of the mixing layer.

Evaluation of Supersonic Turbulent Mixing Using Catalytic Combustion of Constant Temperature Pt Wire.

Supersonic combustion using catalytic wire at constant temperature in a cold supersonic flow field was investigated in a square duct with a backward-facing step. The free stream Mach number was of Mm=1.81. Hydrogen was injected transversely behind a backward-facing step into a cold air free stream. The heat release due to the catalytic combustion has no effect of the temperature of catalyst. It indicates that the reaction rate of the catalytic combustion observed in this study was determined by the consentration of H2 and/or O2 on the surface of the catalyst. The spatial distribution of heat release due to the catalytic combustion in supersonic turbulent mixing layer, that corresponds to the spatial distribution of consentration of H2 and or/O2 in local, was obtained. It was found that there exists the most suitable position for the supersonic combustion at the outer edge of mixing layer.

Catalytic Combustion of Transverse Hydrogen Jet Injection behind a Rear-Facing Step into a Cold Supersonic Flow.

Supersonic combustion using a catalytic combustion in a cold supersonic flow field was investigated in a square duct with a backward-facing step. The free stream Mech number was Mm=1.81. Hydrogen was injected transversely behind a backward-facing step into a cold air free stream. Using a catalyst in a cold supersonic turbulent mixing layer, it was found that hydrogen reacted stably to oxygen in the air flow. The relationship between the heat release due to catalytic combustion and supersonic flow properties, which influence the supersonic combustion, was clarified experimentally. The spatial distribution of heat release generated by catalytic combustion in the supersonic turbulent mixing layer is discussed. It was found that the heat release due to the catalytic combustion had a maximum at the outer edge of the mixing layer.