Jet Mixing Process Research Articles

Simulation study on the breakup process of kerosene Gel Jet in transverse airflow

The gel propellant not only inherits the characteristics of liquid propellants, such as high specific impulse, multiple ignition capabilities, and adjustable thrust, but also offers an advantage type of solid propellants, including reduced risk of leakage, long-term storage feasibility, and ease of maintenance. In this study, numerical simulations were conducted to investigate the atomization and mixing process of kerosene gel jets in high-speed crossflows. The study reveals that the jet breakup process primarily involves two forms of breakup: columnar breakup dominated by Rayleigh Taylor’s unstable wave and surface breakup dominated by Kelvin Helmholtz’s unstable wave. These two forms coexist, complement each other, and interact with each other. The numerical simulation of the kerosene gel breakup process provides favorable support for studying its combustion characteristics in the rotating detonation engine.

Effect of ion collision on separation between light and heavy ions in multi-component vacuum arc

In multi-component vacuum arc discharge, light ions and heavy ions usually have different spatial distributions of density and velocity. Previous research has suggested that the difference in spatial distribution of light and heavy ions is due to the mixing effect of cathode spot jet. However, in this work, the ion collision is found to be an important factor leading to the separation of light and heavy ions. In this paper, multi-fluid model is used to study the effect of ion collisions on separation mechanism in multi-component vacuum arc. The simulation results show that, during the jet mixing process, the collisions between different ions will reduce the velocity of light ions, and greatly increase the density and temperature. As a result, the pressure expansion of light ions is significantly enhanced. In addition, the collision between different ions will also increase the size of jet mixing region for light ions, which makes the plasma jet of light ions mixing more fully. These effects make their isotropic expansion dominant, and the ion density at the center is not much different from that at the edge. However for heavy ions, the collision between different ions has little influence on their movement. The pressure is far less than the inertia force, so the density of heavy ion mainly distributes along the convection direction, and the center is greater than the edge. This is the main separation mechanism of ion angular flux. It is also found there are three main factors leading to the separation of light and heavy ions: ion mass, ion density and ion temperature. The separation effect can be enhanced by increasing ion temperature, decreasing ion density and selecting electrode components with significant differences in elemental mass. This paper provides an insight into the mechanism of ion separation in multi-component vacuum arc.

Study on the relationship between the length of mixing layer and the characteristic scale of mixing layer in multi-strut ejector

The flow structure of the multi-strut ejector based on jet segmentation has an obvious relationship with the transverse characteristic scale of the jet. Therefore, this paper studies the relationship between jet transverse characteristic size and mixing layer. Through the simulation of multi-strut ejectors with different number of struts, the development of mixing layer in the mixing process of jets with different transverse characteristic sizes is compared under the same boundary conditions. It is concluded that when there is no obvious coupling effect between the mixing layer and the shock & expansion wave, there is a linear relationship between the transverse characteristic scale of the jet and the mixing length of the flow direction, and the jet mixing with different transverse characteristic scales is consistent. When the shockwaves and expansion waves are strongly coupled with the mixing layer, the linear relationship between the jet transverse characteristic scale and the mixing layer length is not strong.

Evolution and Near-Wall Effect of the Vortex Structures Induced by In-Line Twin Synthetic Jets in a Crossflow

This paper aims to further the understanding of the mixing process of in-line twin synthetic jets (SJs) and their impact in the near-wall region in a flat-plate laminar boundary layer. A numerical study has been carried out, in which colored fluid particles and the Q criterion are used to track the SJ-induced vortex structures at the early stage of the evolution. Interacting vortex structures at four selected phase differences are presented and analyzed. It is found that the fluid injected at the early stage of the blowing stroke mainly contributes to the formation of the hairpin legs, the fluid injected near the maximum blowing mainly contributes to the formation of the hairpin head, and the fluid injected at the late stage of the blowing stroke contributes very little to the formation of the hairpin vortex. It is also confirmed that, irrespective of the phase difference, the hairpin vortex issued from the upstream actuator is more capable of maintaining its coherence than its counterpart issued from the downstream actuator. The influence of the interacting vortex structures on the boundary layer is also studied through investigating excess wall shear stress. In all cases, a pair of streaks of high wall shear stress can be observed with similar size. Among them, the streaks have the strongest wall shear stress, with the largest gap at phase difference 0 when partially interacting vortex structures are produced. The findings can provide valuable guiding information for the applications of synthetic jets in heat transfer, mixing control, and flow control in a crossflow.

Mixing enhancement mechanism of combined H2–Water jets in supersonic crossflows in a combustor with an expanded section

To obtain the mixing enhancement mechanism of H 2 –Water combined jets in supersonic crossflows in a combustor with expanded section for rotating detonation ramjet, the flow field shape and spray structure were studied by experimental and numerical methods. The Eulerian–Lagrangian method was used to investigate the diffusion mechanism and H 2 –Water interaction law of combined jets with different sequences. At the same time, high-speed photography and the schlieren technique were used to capture the flow field. The effects of jet pressure drop, orifice diameter, orifice spacing, incoming Mach number, and other parameters on the penetration depth of water jets were studied. The results of experiment and simulation show that using H 2 –Water combined jets, the penetration depth of the jet spray can be greatly increased and the jet mixing effect can be significantly improved, which will contribute to the engine's ignition and stable combustion. In the case of pre-water/post-H 2 , the penetration depth of the hydrogen jet is greater. In the case of pre-H 2 /post-water, the hydrogen jet raises the water spray mainly by protecting the integrity of the water column. • The mechanism of the mixing process of H2-Water combined jets in supersonic crossflows was investigated. • Eulerian-Lagrangian method was used to investigate the H2-Water interaction law in a combustor with an expanded section. • The penetration depth of water jets under different parameters was studied experimentally.

Study on the fuel jet evolution under trans/supercritical conditions and different environment pressure conditions

In Liquid Rocket Engines or Internal Combustion Engines, increasing the inlet fuels temperature or chamber pressure exceeding its critical point is capable of improving the combustion efficiency. Under these conditions, the thermophysical and transport properties have an important effect on fluids mixing and combustion process. In this study, the fuel of n-heptane injected into a multi-species environment are simulated by Large Eddy Simulations and the performance of the injected fuel temperature and different chamber conditions are compared in conjunction with high accuracy equation of state and transport properties. The results show that as the injected temperature or the chamber pressure increase, the penetration length and density gradient decrease, while the width of mixing layer increase. The results obtained in this investigation indicated that for the single injection condition, by increasing the fuel inlet temperature or chamber pressure, the essence is to reduce the initial density ratio, thereby reducing the density stratification between the jet and environment gas, which is beneficial to the jet mixing and combustion process.

Study on the fuel jet evolution under trans/supercritical conditions and different environment pressure conditions

In liquid rocket engines or internal combustion engines, increasing the inlet fuels temperature or chamber pressure exceeding its critical point is capable of improving the combustion efficiency. Under these conditions, the thermophysical and transport properties have an important effect on fluids mixing and combustion process. In this study, the fuel of n-heptane injected into a multi-species environment are simulated by large eddy simulations and the performance of the injected fuel temperature and different chamber conditions are compared in con-junction with high accuracy equation of state and transport properties. The results show that as the injected temperature or the chamber pressure increase, the penetration length and density gradient decrease, while the width of mixing layer increase. The results obtained in this investigation indicated that for the single injection condition, by increasing the fuel inlet temperature or chamber pressure, the essence is to reduce the initial density ratio, thereby reducing the density stratification between the jet and environment gas, which is beneficial to the jet mixing and combustion process.

Injection characteristics and fuel-air mixing process of ammonia jets in a constant volume vessel

The direct-injection of gaseous ammonia is a possible way to fuel engines to meet the scenario of zero-carbon emission. In this study, for the first time, the injection characteristics and fuel–air mixing process of ammonia jets are investigated. A Schlieren system is employed to characterize the macroscopic behavior of ammonia jets including the tip penetration and jet angle. Besides, the fuel concentrations of ammonia jets are quantitatively measured by LIBS to investigate the fuel–air mixing processes. According to the time evolutions of jet tip penetration, the three-stage behavior, namely the t, t0.5 and (t-τ)0.25 dependence corresponding to the early stage of injection, quasi-steady stage and after two times of injection duration respectively, are proposed and the mechanisms are discussed in detail. The effects of both injection and ambient pressures on the tip penetration and jet angle, as well as the fuel concentration distributions are investigated. The increased injection pressure leads to increases in the tip penetration and fuel concentration but decreases in the jet angle. The effects of ambient pressure are opposite, indicating that the ammonia jet development is governed by the injection-to-ambient pressure ratio. The comparisons between ammonia and methane jets are conducted. The results show they have quite similar tip penetrations and jet angles, as well as the nearly equivalent fuel mole fractions at the jet axis. However, the equivalence ratios in ammonia jets are significantly lower than those in methane jets, leading to the distinct flammable mixture distributions in ammonia and methane jets.

Effect of fuel injection distance and cavity depth on the mixing and combustion characteristics of a scramjet combustor with a rear-wall-expansion cavity

The mixing and combustion characteristics of a model scramjet combustor with a rear-wall-expansion cavity under a Mach 2.0 inflow are experimentally and numerically investigated. Two different cavity depths and two fuel injection distances are compared to show the effect of these parameters. High-speed imaging system is used to capture the oscillation of flamebase and the flame oscillation of cavity shear layer in the transversal direction. Numerical simulation is carried out to reveal the jet mixing process around the cavity. The experimental results show that the combustor with longer fuel injection distance and smaller cavity depth has weaker flame and lower wall pressure due to the significant oscillation. The oscillation of flamebase is found to be stronger in the shallower cavity due to its smaller volume. Cavity with short fuel injection distance and large depth could suppress the oscillation, and the combustor can achieve a robust and strong combustion. The simulation results show that under the shorter injection distance, the center of cavity shear layer is rolled up to the main stream; thus the shear layer can interact with the fuel jets more intensively, which improves the mixing efficiency and promotes strong combustion. Compared to the cavity with larger depth, the shear layer in the smaller cavity has a larger thickness and displays more significant shear layer oscillation in the transverse direction. The oscillation of the cavity shear layer can promote the mixing efficiency but is detrimental to combustion. Therefore, a proper cavity depth should be carefully considered during the design of a cavity flameholder.

Effect of nonideal fluid behavior on the jet mixing process under high-pressure and supersonic flow conditions

The mixing process of extremely underexpanded supercritical jets into a gaseous environment is studied. The focus lies on the influence of the nonideal fluid behavior on the mixing process. Numerical simulations are conducted for eight different injection conditions where experimental sound speed measurements are available. Overall, a very good agreement between simulations and experiments is found. A comparison of the real-gas and the ideal-gas closures shows the necessity to account for nonideal fluid behavior. The application of the ideal-gas law results in an incorrect energetic state which most prominently leads to an overestimation of the post-shock temperature by 70 K. The wrong energetic state yields erroneous thermodynamic properties in the mixing region. Finally, a mixture model is deduced enabling the prediction of mixture properties. As independent measurements of mass/mole fractions are not available, this evaluation procedure is a first attempt to numerically predict the mixture composition in underexpanded jets.

Investigation of Jet Mixing Characteristics Using Slotted Rectangular Tabs

This article discusses the jet mixing effectiveness of rectangular tab with slots to distort the jet, thereby creating vortices of differing sizes to enhance the mixing. This article numerically investigates the effectiveness of slanted slotted/perforated rectangular tabs with the slot connecting the adjacent faces of the tab to control Mach 0.4 jet. To intensify the jet mixing process, two similar tabs with equal blockage ratio of 7% are placed at diametrically opposite locations of the convergent nozzle exit. The jet flow development in the axial and radial directions of the jet are investigated in detail. To measure the effectiveness of the slotted tabs, the results are compared with the free jet and with the jet operated with solid rectangular tab. The percentage reduction in the core length obtained is 84.1 and 74% for the jet employed with the slotted tab and the solid tab, respectively, when compared with the free jet. The results exhibit that the slotted tab distorts the jet in the near field to a greater extent when compared with the solid rectangular tab.

Large-eddy simulation of methane direct injection using the full injector geometry

Understanding the mixing process of under-expanded gaseous-fuel jets from an outward opening injector is essential for developing Direct Injection (DI) internal combustion engines. This paper presents a Large-Eddy Simulation (LES) study of the DI of methane into a Constant Volume Chamber (CVC), considering the full, internal geometry of a prototype injector. Four cases at conditions relevant to Compressed Natural Gas (CNG) DI engines are investigated, with methane as a surrogate for CNG. A new post-processing method permits the 3D LES field to be projected into a 2D density gradient field that can be compared to a schlieren image. The LES results are then validated against high-speed, schlieren imaging experiments, demonstrating that the simulations are able to reproduce experimental trends. Three main regions of the external flow are observed: a recirculation zone just downstream of the injector tip, a stagnation zone and a far-mixing zone. The location of the stagnation zone increases as the CVC pressure decreases, consistent with a theory presented in the literature. The modelling of the full internal geometry of the injector leads to a determination of the injector pressure losses. Once the pressure loss within the injector is considered, a short version of the injector can reasonably represent the full injector for prediction of the external flow.

Characteristics analysis of the side-blown gas jet mixing process

The mixing performances of side-blown gas jets were studied by characterizing their manifold Betti numbers, namely 0-dimensional and 1-dimensional Betti numbers, through flow visualization and image processing techniques. The 0-dimensional Betti number reflects the mixing performance, and the 1-dimensional Betti number reflects the mixing unevenness degree. The mixing performances and flow fields were studied for different modified Froude numbers. As modified Froude numbers increase, the main flow was enhanced, promoting the macro-mixing of individual particles. The mixing performance of the stirring process was improved by a frequency conversion method, which destroyed the original flow pattern and promoted the micro-mixing process by chaotization.

A new LES approach to trans-critical mixing and combustion processes in high-pressure liquid-injectant engines

The understanding of flame holding mechanism is very important for combustor design. To elucidate the flame holding mechanism at the injector exit in liquid rocket engines, it is indispensable to know the underlying physics of trans-critical mixing process, because the flame holding location is exactly where trans-critical mixing process, which is still veiled, takes place. In the present paper, a new Large Eddy Simulation (LES) method is developed by gaining deeper physical insights into possible sub-grid-scale (SGS) thermodynamic and fluid dynamic instabilities excitable at thin large-density-gradient-magnitude portions to describe trans-critical processes. The presence of thin large-density-gradient-magnitude portions in trans-critical mixing process is troublesome for numerical stability of supercritical fluid flow LES from various points of view. Our idea is to utilize an SGS model functioning at the crossover between the liquid-like and gas-like supercritical fluids in a hybrid scheme of Lagrangian particle tracking and two-phase flow LES. Reduced dynamic viscosity at high pressure may cause SGS thermodynamic and hydrodynamic instabilities in the trans-critical mixing flow field. They are (1) phase separation due to thermodynamic instability, (2) Landau's hydrodynamic instability occurring at the pseudo-boiling location within a heated injector, and (3) Rayleigh–Taylor instability at the pseudo-boiling location, which is induced by Kelvin–Helmholtz instability vortices. These are analyzed and organized into new SGS models characterizing the trans-critical jet mixing process.

Effect of free stream angle on mixing performance of hydrogen multi-jets in supersonic combustion chamber

The fuel mixing process within the combustion chamber is a critical procedure for advance of scramjet engine. In current study, the influence of free stream angle on the fuel mixing process of multi jets was thoroughly investigated. This research attempts to applied computational technique to disclose the structure of multi-fuel jets when the supersonic air stream is not normal to the jet direction. The effect of both positive and negative supersonic free stream on the diffusion and penetration of multi-hydrogen jets is fully described. The attention of this research is the flow structure of the multi jets and their interaction in the presence of different free stream angle. Our results indicate that the positive free stream angle expands the mixing zone in the downstream while the negative angle of free stream limited jet distribution inside the combustor. Our results show that mixing efficiency increase approximately 50% when the angle of free stream augments from +20° to −20°. According to our findings, mixing efficiency surges up to 17% when the jet spaces are increased from 4Dj to 10 Dj.

Exhaust CO emissions of a laminar premixed propane–air flame interacting with cold gas jets

This study investigates a laminar premixed flame interacting with cold gas jets, at different cooling jet mass flow fractions (m˙jet*) and diluent types, namely air and N2. A novel burner and wall configuration is used to experimentally induce flame-cooling-air interaction (FCAI). Flame chemiluminescence imaging, exhaust temperature (Texh) and exhaust CO emissions ([CO]exh) measurements are conducted to characterise the flame shape and [CO]exh response to the cooling jets. Flame imaging reveals that the cooling jets greatly affect the flame shape. Measurements of [CO]exh demonstrate a direct correlation with Texh, as decreasing Texh is observed to occur with decreasing [CO]exh. Additionally, the air diluent case shows consistently lower [CO]exh values, relative to the N2 diluent case.Using a novel modelling approach, the cooling jets are simulated using one-dimensional (1D) fully resolved simulations (FRS). The effect of jet dilution, jet cooling and exhaust gas cooling are independently and jointly investigated in these simulations. The FRS results support the experimentally observed behaviour, and show that exhaust gas cooling and exhaust gas oxygenation produce decreased CO concentrations. Using a chemical reactor network (CRN), the jet mixing process is modelled by a perfectly stirred reactor (PSR), while the exhaust gas cooling process is modelled by a plug flow reactor (PFR). The CRN modelling shows that the jet mass flow rates dictated by m˙jet*, the dilution time (tdil) assumed for cooling jet mixing, and the exhaust gas cooling residence time (tcool), play an important role in determining the [CO]exh. An equilibrium analysis illustrates that the relationship between [CO]exh, Texh and exhaust O2, is due to the thermodynamically favoured equilibrium states. Timescale analyses demonstrate that appropriate modelling of jet mixing, and accounting for the rate of exhaust gas cooling, are important for estimations of [CO]exh.

Jet mixing when heating oil and fuel oil in storage tanks

This paper presents the research results of jet mixing and heating processes of crude oil of the Zachebashskoe field (Republic of Tatarstan) and fuel oil M100 in a tank with a capacity of 2000 m3. Circulation systems with nozzle inclination in the range from -25° up to 125° are considered. The presence and washing out of bottom sediments in the tank are modeled. The time required for removing the bottom sediments and for heating the tank to the optimum temperature is determined. The best heating for the tank with oil and fuel oil was observed at the nozzle inclination in the range from -25° up to 60°. The optimal nozzle inclination was 115° for washing out the bottom sediments in the oil tank. To remove sediment in a tank with fuel oil it is recommended to use the same nozzle inclinations as for heating.

Temperature Profile Measurement in Simulated Fuel Assembly Structure with Wire-Mesh Technology

When light water reactor (LWR) is subject to a cold shutdown, it needs to be cooled with pure water or seawater to prevent the core melting. To precisely evaluate the cooling characteristics in the fuel assembly, a measurement method capable of installing to the fuel assembly structure and determining the temperature distribution with high temporal resolution, high spatial resolution, and in multidimension is required. Furthermore, it is more practical if applicable to a pressure range up to the rated pressure 16 MPa of a pressurized water reactor (PWR). In this study, we applied the principle of the wire-mesh sensor technology used in the void fraction measurement to the temperature measurement and developed a simulated fuel assembly (bundle) test loop with installing the temperature profile sensors. To investigate the measurement performance in the bundle test section, it was confirmed that a predetermined temperature calibration line with respect to time-average impedance was calculated and became a function of temperature. To evaluate the followability of measurement in a transient temperature change process, we fabricated a 16 × 16 wire-mesh sensor device and measured the hot-water jet-mixing process into the cold-water pool in real time and calculated the temperature profile from the temperature calibration line obtained in advance from each measurement point. In addition, the sensors applied to three-dimensional temperature distribution measurement of a complex flow field in the bundle structure. The axial and cross-sectional profiles of temperature were quantified in the forced flow field with nonboiling when the 5×5 bundle was heated by energization.

Large eddy simulation and proper orthogonal decomposition analysis of fuel injection under trans/supercritical conditions

Heptane jets with subcritical and supercritical inlet temperatures injected into a supercritical environment filled with multi-component gas have been numerically investigated using large eddy simulation. Main attentions are paid on the effects of density-gradient, thermodynamic and transport properties on the jet flow evolution. It is found that large density-gradients are easier formed in transcritical injection and the larger specific heat has an effect of forming the density gradients, while the diffusion coefficients decrease in the larger density gradient regions, suggesting that large density gradient has the effects of suppressing the flow diffusion mixing. In addition, when the fluid transits across the pseudo boiling temperature, the specific heat reaches a maximum value, yet this value is suppressed by the dissolution effects, indicating that multi-component injection is different from the single species injection and a special investigation is needed. The disintegration features in transcritical and supercritical injections are different, and thermodynamic and transport properties are crucial in the disintegration process. A proper orthogonal decomposition analysis indicates that the turbulent kinetic energy is larger and vortexes are more easily formed in the supercritical injection. The vortex movement and paring significantly affect in the jet mixing process.

Large eddy simulation of reacting flow in a hydrogen jet into supersonic cross-flow combustor with an inlet compression ramp

Large eddy simulation (LES) has been performed to investigate transverse hydrogen jet mixing and combustion process in a scramjet combustor model with a compression ramp at inlet to generate shock train. Partially Stirred Reactor (PaSR) sub-grid combustion model with a skeleton of 19 reactions and 9 species hydrogen/air reaction mechanism was used. The numerical solver is implemented in an Open Source Field Operation and Manipulation (OpenFOAM) and validated against experimental data in terms of mean wall pressure. Effects of a shock train induced by the inlet compression ramp on the flame stabilization process are then studied. It can be observed that the interaction of the oblique shock and the jet mixing layer enhance the combustion and stabilize the flame. Symmetrical recirculation zone, which contributes to the flame anchoring of the supersonic transverse jet combustion, is observed in the near wall region of 10 < x/D < 20. The hydrogen fuel is transported from the center of jet plume to the near wall region on both sides of the central plane (z/D = 0) and thus intense combustion near the wall is observed due to the enhanced mixing and shock compression heating. Besides, the jet penetration in the reacting field is different from that in non-reacting case with the influence of the interaction between the reflected oblique shock and the jet shear layer on the windward side.