Axial Penetration Research Articles

Inflow Conditions and the Flow Behavior of Submerged Annular Viscoplastic Non-Newtonian Jets

Abstract Submerged annular viscoplastic jet flows were studied numerically within the steady laminar flow regime. The impacts of inner-to-outer annular nozzle diameter ratio, and yield number, for uniform and fully-developed inflow conditions, were investigated. The extent of the outer recirculation region and recirculation intensities of both the central and outer regions were found to substantially diminish with the yield number, resulting in the elimination of recirculation throughout the whole flow field at high yield numbers. The axial penetration of the jet decreases with both the yield number and the annular diameter ratio. The impact of inflow conditions on the flow structure and decay characteristics of the jet are more pronounced at low yield numbers.

Impact of Laval nozzle structure on the flow characteristics of supersonic gas-solid two-phase flow

This study introduces a mathematical coupling model within the Euler-Lagrange framework to conduct numerical simulations for supersonic gas-particles flow. After validating the model, the gas flow characteristics and particle dynamics within supersonic gas-particle flow under various nozzle configurations are investigated. The findings are as follows: (1) A Laval nozzle with a smoothly connected throat suppresses the generation of fan-shaped Prandtl-Meyer expansion waves and other complex wave systems, effectively mitigating significant changes in gas pressure at the throat and enhancing the stability of supersonic jets. (2) The presence of a particle-free zone in the nozzle divergent segment reduces the collision frequency between particles and the walls, thereby restricting the radial expansion of particles. (3) Utilizing an internally smooth-lined nozzle and expanding the radial divergence angle to 2.5–2.8 times, while ensuring particles maintain consistent axial penetration performance, increases the reflective contact area. This leads to an improvement in the utilization efficiency of particles. These findings provide valuable insights for optimizing nozzle configurations and enhancing the performance of supersonic gas-particle systems.

Gas-dynamic and mixing analysis of under-expanded hydrogen jets: effect of the cross section shape

Green hydrogen is expected to have a key role in the transition towards a carbon-neutral society, particularly in the transportation sector. Exploration of novel solutions for the direct injection of hydrogen in internal combustion engines (ICEs) is a main topic for both academia and industry. Here, the authors explore the gas-dynamic and mixing features of hydrogen under-expanded jets exiting from non-axisymmetric cross-sections, with the aim to provide guidelines for designing novel generations of ICE hydrogen injectors. Triangular and star shapes have been compared with elliptical and rectangular sections with different aspect ratios. Differences in the shock wave systems are reported, and explanations of the gas-dynamic mechanisms developed by each section are proposed. Non-uniformity in the radial expansion of the jet boundary has been noticed in all of the non-axisymmetric sections, leading to an axis switching of the jet in some cases. Differences in the radial mixing and axial jet penetration have been reported too, and a robust correlation with the vorticity distribution along the jet boundary has been observed.

Four-way coupled Eulerian-Lagrangian study of phase interaction mechanism in the supersonic gas-solid two-phase flow

Supersonic gas–solid jet injection has received much attention in many industrial applications such as pneumatic conveying, powdered drug delivery, steel refining process and thermal spray coating, but it is still a challenging topic due to the complex interphase interaction in compressible flows. In this work, supersonic gas–solid two-phase flow is numerically studied under the Eulerian-Lagrangian framework. After the model validation with the experimental measurement, the inherent mechanism of supersonic gas–solid flow under the conditions of different powder feeding rates and particle diameters is explored. The results demonstrate that increasing the powder feeding rate leads to the reduction of the axial velocity and penetration ability of the particles. Especially when powder feeding rate increases to 10 kg/s, serious blockage occurs in the nozzle divergence section and the conventional supersonic flow characteristic in Laval nozzle has been substantially changed. Moreover, particle diameter largely determines the dynamic and thermodynamic characteristics of the particles. Small-diameter particles exhibit better followability to the gas phase and large-diameter particles exert non-negligible impact on the gas flow, mainly reflects in weakening the expansion ability of the gas phase. The results obtained in this work provide meaningful insight for understanding the flow characteristics of supersonic gas–solid flow and benefit the operating parameters selection in industrial applications.

Cohesiveness and penetration performance of jet: Theoretical, numerical, and experimental studies

Jet formation was studied by performing theoretical analyses and numerical calculations, and a predictive model was proposed. X-ray experiments were conducted to verify the model and investigate the jet formation. Static penetration experiments were performed to study the penetration ability, and the microscopic topography of the penetration channel was observed to reveal the potential effect of jet cohesiveness on the penetration performance. The results showed that the proposed model can predict jet formation and help determine the proportion of non-cohesive segment of the jet. Because of the coexistence of cohesive and non-cohesive segments in the actual jet, determining an exact proportion of non-cohesive segment is beneficial for selecting the penetration model and improving calculation accuracy. In the theoretical model, pressure was considered as the main factor and the use of the collapse angle, which is difficult to measure accurately, was avoided, thereby effectively improving the engineering practicability of the model. The results of the penetration experiments showed that the radial dispersion of particles can weaken the axial penetration ability significantly but improve the damage efficiency (crater, hole, and caving). At a suitable stand-off, the non-cohesive jet can improve the damage efficiency and maintain a good penetration depth when penetrating the concrete. The results of this study provide new ideas for jet formation research and a reference for the development of high-damage warheads.

An earthworm-like modular soft robot for locomotion in multi-terrain environments

Robotic locomotion in subterranean environments is still unsolved, and it requires innovative designs and strategies to overcome the challenges of burrowing and moving in unstructured conditions with high pressure and friction at depths of a few centimeters. Inspired by antagonistic muscle contractions and constant volume coelomic chambers observed in earthworms, we designed and developed a modular soft robot based on a peristaltic soft actuator (PSA). The PSA demonstrates two active configurations from a neutral state by switching the input source between positive and negative pressure. PSA generates a longitudinal force for axial penetration and a radial force for anchorage, through bidirectional deformation of the central bellows-like structure, which demonstrates its versatility and ease of control. The performance of PSA depends on the amount and type of fluid confined in an elastomer chamber, generating different forces and displacements. The assembled robot with five PSA modules enabled to perform peristaltic locomotion in different media. The role of friction was also investigated during experimental locomotion tests by attaching passive scales like earthworm setae to the ventral side of the robot. This study proposes a new method for developing a peristaltic earthworm-like soft robot and provides a better understanding of locomotion in different environments.

Numerical Investigation on the Combustion and Emission Characteristics of Diesel Engine with Flexible Fuel Injection

As the main engineering power plant, diesel engines are irreplaceable in the future. However, the stringent emission regulations impose many tough requirements to their developments. Recently, flexible fuel injection strategy has been recognized as an effective technology in creating an advanced spray and mixture formation and improving combustion efficiency indirectly. However, the detailed combustion and emission behaviors under flexible fuel injection are still unknown. Therefore, this paper aims to investigate the combustion and emission characteristics under flexible fuel injection and explore an optimal injection strategy for high-efficiency combustion. A numerical simulation method is conducted by coupling the large-eddy simulation (LES) model and the SAGE combustion model. Then, the spray mixing, combustion flame propagation and emissions formation under various multiple-injection strategies are investigated. Results reveal that initial an ultrahigh injection pressure has a significant influence on the spray’s axial penetration while dwell time mainly affects the spray’s radial expansion. Under an initial ultrahigh injection pressure, the turbulence kinetic energy (TKE) becomes larger, and the vortex motions are stronger, contributing to a better spray turbulent mixing. Meanwhile, a snatchier flame structure with a favorable level of equivalence ratio and a homogeneous temperature distribution is obtained. In this way, the peak heat release rate (HRR) could increase by 46.7% with a 16.7% reduction in soot formation and a 31.4% reduction in NOx formation.

On convective instabilities in a rotating fluid with stably stratified layer and thermally heterogeneous boundary

The onset of convection in a rotating plane layer due to a vertical temperature gradient is studied in this paper. The background stratification is modulated by lateral temperature variations and stable stratification aimed at understating the Earth's outer core convection subject to thermal core–mantle interaction. At the top boundary, sinusoidal and Gaussian temperature variations are imposed apart from the reference case of isothermal condition used in the classical Rayleigh–Benard convection. The additional modulating conditions break the top–bottom flow symmetry leading to flow localization and asymmetry that exhibit modified temporal dynamics unlike that of the classical Rayleigh–Benard cells. The threshold for convection is lowered with flows occurring in surplus heat flux regions caused by the imposed conditions. Despite flow suppression in the stable layer, rapid rotation favors the penetration of convection rolls with smaller wavelengths. The lateral variations in temperature imposed at the top boundary enhance such axial penetration with a laterally varying penetrative extent resulting in a modified clustered flow structure unlike the reference case. With both modulating conditions imposed, the onset of overstable modes is favored for low Prandtl numbers, a regime which is relevant to the Earth's core conditions. With rapid rotation, a novel mode of traveling wave instability occurs at the onset of convection, the propagation direction of which is controlled by the lateral temperature gradients at the top boundary. The onset of oscillatory modes is suppressed by the imposition of the modulating conditions indicated by the significant lowering of the transition Prandtl number.

Numerical characterization of hydrogen under-expanded jets: influence of the nozzle cross-section shape

This historical moment is characterized by a great awareness regarding the need to reduce the Greenhouse Gas emissions (GHG), which are responsible for the climate change and its detrimental consequences. Green hydrogen produced by means of Power-to-Gas technologies from renewables is gaining momentum as a possible clean fuel for the future mobility. In such a context, traditional injectors for hydrocarbon fuels are currently being tailored to be used with hydrogen. The short time available for the injection process leads to the employment of a high inlet pressure, resulting in the formation of an under-expanded jet. In this work, the main characteristics of these jets are analyzed by means of Computational Fluid Dynamics (CFD) for a Nozzle Pressure Ratio (NPR) equal to 10. Then, to provide insights regarding the dependence of the air-hydrogen mixing on section shape of the nozzle, comparisons have been performed by changing the nozzle cross-section (circular, rectangular, and elliptical), keeping constant the mass flow rate to highlight the different levels of axial penetration and radial spread observed when varying the aspect ratio (1.5, 5.0, 8.0).

Characterizing and predicting 21700 NMC lithium-ion battery thermal runaway induced by nail penetration

• Pioneering CFD predictions of nail penetration induced TR in 21700 cylindrical cells. • Internal heat generation is coupled with external convective and radiative heat exchange. • New tests to establish the differences in radial and axial penetration of cylindrical cells. • Fill experimental gaps by quantify the effects of contact resistance and external heat transfer. • The generic nature of the CFD based predictive tool can be easily adapted for other cell types. Combined numerical and experimental studies are conducted to characterise 21,700 cylindrical lithium-ion battery (LIB) thermal runaway (TR) induced by nail penetration. Both radial and axial penetrations are considered for 4.8 Ah 21,700 NMC cell under 100% state of charge. Heat generation from the decomposition of the cell component materials are analysed. The maximum cell surface temperature rise and time to reach it in both types of penetration tests are compared. Snapshots from the video footages captured by three high definition and one high speed cameras shade light on the dynamic processes of spark ejection and flame evolution. A generic predictive tool is developed within the frame of the in-house version of open-source computational fluid dynamics code OpenFOAM for nail induced TR. The code treats the cell as a lumped block with anisotropic thermal conductivities and considers heat generation due to nail induced internal short circuit resistance, exothermic decomposition reactions and heat dissipation through convective and radiative heat transfer. Validation with the current measurements shows promising agreement. The predictions also provide insight on the magnitudes of heat generation due to internal short circuit resistance, decompositions of solid electrolyte interphase layer (SEI), anode, cathode and electrolyte. Parametric studies further quantify the effects of cell internal short circuit resistance, contact resistance between the nail and cell, convective heat transfer coefficient and cell surface emissivity on TR evolution.

Fast volumetric imaging with line-scan confocal microscopy by electrically tunable lens at resonant frequency.

In microscopic imaging of biological tissues, particularly real-time visualization of neuronal activities, rapid acquisition of volumetric images poses a prominent challenge. Typically, two-dimensional (2D) microscopy can be devised into an imaging system with 3D capability using any varifocal lens. Despite the conceptual simplicity, such an upgrade yet requires additional, complicated device components and usually suffers from a reduced acquisition rate, which is critical to properly document rapid neurophysiological dynamics. In this study, we implemented an electrically tunable lens (ETL) in the line-scan confocal microscopy (LSCM), enabling the volumetric acquisition at the rate of 20 frames per second with a maximum volume of interest of 315 × 315 × 80 µm3. The axial extent of point-spread-function (PSF) was 17.6 ± 1.6 µm and 90.4 ± 2.1 µm with the ETL operating in either stationary or resonant mode, respectively, revealing significant depth axial penetration by the resonant mode ETL microscopy. We further demonstrated the utilities of the ETL system by volume imaging of both cleared mouse brain ex vivo samples and in vivo brains. The current study showed a successful application of resonant ETL for constructing a high-performance 3D axially scanning LSCM (asLSCM) system. Such advances in rapid volumetric imaging would significantly enhance our understanding of various dynamic biological processes.

SIMULATION STUDY OF BREAKUP AND ATOMIZATION CHARACTERISTICS OF GASOLINE-ETHANOL (GASHOLS) FUEL BLENDS

To meet the increasingly stringent constraints on mobile and point emissions in the wake of the dwindling fortunes of fossil fuels, evaluation of hybrid fuels for application in combustion engines has become an imperative, especially in the third world countries. This paper presents, modeling of atomization characteristics of gasoline-ethanol fuel blends. Fuel breakup models and correlations between flow patterns and droplet characteristics were adopted and implemented in OpenFOAM Computational Fluid Dynamics (CFD) modeling suite for direct gasoline injector using a simple cylindrical mesh structure at constant volume. The Rosin Rammler distribution model was used to generate the number of spray particles injected into the cylinder. The spray modeling and atomization employed the use of blob sheet model and Kelvin-Helmholtz-Rayleigh-Taylor (KH-RT) model while the numerical technique for simulating atomization process by CFD included the use of governing equations such as Eulerian for gas phase, Lagrangian for disperse phase and turbulence modeling. The effects of fuel blends, injection pressure, ambient gas pressure and spray cone angle were evaluated on the axial spray tip penetration, spray width, and overall Sauter Mean Diameter (SMD). The SMD was seen to be affected by varying the degree of injection cone angle. The spray tip penetration lengths were larger for higher injection cone angles while higher penetration lengths were obtained at higher injection pressures. One salient conclusion drawn from the modeling is that as the number of particle increased, the density of clusters became smaller.

The influence of in-cylinder flows and bulk gas density on early Spray G injection in an optical research engine

A well-characterized multi-hole gasoline injector, the Engine Combustion Network’s (ECN) Spray G injector, was investigated in an optically accessible research engine under four motored operating conditions with early injection. The experiments were conducted at intake pressures of [Formula: see text] and [Formula: see text], nearly matching the ECN’s standard early injection operating conditions, Spray G2 (flash boiling) and Spray G3 (early injection), respectively. This was combined with two engine speeds at [Formula: see text] and [Formula: see text]. Using particle image velocimetry and volumetric Mie scatter imaging, the in-cylinder flows were evaluated and the effects on the spray morphology were characterized. The in-cylinder flow was evaluated to understand the spray-flow interaction, including the turbulent kinetic energy. Little effect on turbulent energy was observed in the region examined near the exit of the fuel injector nozzle shortly after injection. Mie scatter imaging was used to characterize the spray morphology and wall wetting was clearly visible on the spark plug. Cyclic variability of the sprays was found to be insignificant; and major differences in spray morphology are attributed to the in-cylinder velocity and intake pressure at the time of injection. Decreasing the bulk gas density by decreasing the intake pressure had a number of effects on the evolution of the spray including faster evaporation, increased axial liquid penetration, and decreased spray angle. Increasing the in-cylinder flow magnitudes by increasing the engine speed had a similar effect on spray morphology by also increasing the evaporation rate, increasing the axial penetration, and decreasing the spray opening angle. Comparison of the motored spray cases with a no-flow case (when the fuel is sprayed into the engine without the piston present) further illustrated the extent to which the intake flow influenced the spray shape.

Deformation and Failure Properties of Lithium-Ion Battery Under Axial Nail Penetration

Abstract As one of the commonly used power sources for electric vehicles, cell phones, and laptops, lithium-ion batteries (LIBs) have aroused more and more attention. Lithium-ion batteries will inevitably suffer from external abuse loading, triggering thermal runaway. Nail penetration is one of the most dangerous external loading methods, so it is meaningful to study the failure behaviors under this loading condition. In this article, the experimental study of 18650 cylindrical lithium-ion batteries (with nickel cobalt aluminum oxide cathode) under axial nail penetration is carried out. Force, temperature, and voltage data are recorded synchronously to learn its mechanical, thermal, and electrochemical behaviors, respectively. Then, the loading velocity effect is discussed, and the results show that the loading velocity has no obvious effect on failure properties of lithium-ion battery. Besides, deformation and failure properties of lithium-ion battery are discussed in detail. A simple homogenous computational model is established to predict the mechanical responses of the battery. The partially detailed model is also established to explore the failure mechanism. The batteries are disassembled after loading to better understand the failure morphologies. Two failure modes are discovered through experiments and computational model. The findings can contribute to a better understanding of the failure mechanism of lithium-ion battery under axial nail penetration, providing reference for battery safe design.

Near-field spray characterization of a spill return atomizer using a PIV laser sheet

The Combustion of liquid fuels is largely dependent on effective ways of atomization. The investigation of flow dynamics and atomization of alternative fuels is essential and supportive for combustion assessment. The current experimental investigation aims at providing a microscopic insight into the spray characteristics of the conventional (light diesel oil) fuel, a renewable fuel (waste cooking oil), and their blend together. A PIV laser measuring technique is used to provide detailed information on the fuel spray: droplets size, pattern, evaporation rate, instantaneous velocity, local cone angle, average axial velocity, penetration, and vorticity. The experiments cover four air to liquid ratios (ALR) of 0.8, 0.78, 0.65, and 0.57. A coaxial spill return atomizer is employed downwards as well as is surrounded by co-flowing air (kg/hr) of 48, 52.2, 55.8, and 60. The spray images are taken in an open atmosphere and the assessment of the fuel droplets velocity and size is obtained through PIV cross-correlation inside a glass room. The maximum evaporation rate is 48.1% for diesel fuel, 37% for waste cooking oil, and 44% for blended fuel at an ALR of 0.57. The application of co-flowing air (kg/hr) of 48 will reduce the local cone angle by 17%, 6%, and 4.3%. The interaction between waste cooking oil droplets with surrounding air is very difficult because of its high viscosity, density, lower evaporation rate, and larger droplets size than diesel fuel.

Numerical Simulations of Air Cavities in Inclined Plunging Jets

The dynamic process of circular water jets plunging into a quiescent pool was analyzed in this study based on the RNG k∼ε turbulence model and VOF method. The effects of jet velocity and inclination angles relative to horizontal on the cavity shapes and sizes were analyzed. The simulation successfully captured the formation, development, pinch-off, and disintegration phenomena of cavities. The shape of the cavity is mainly affected by the impact angle, while the impact velocity mainly affects the size of the cavity. The cavity pinch-off initially appears at a certain point in any direction for vertical jets, while the cavity in the opposite direction of flow pinch-off appears before the cavity in the direction of flow for inclined jets. Before cavity pinch-off, the maximum radial and axial sizes of the cavity generally increase with the impact velocity and the time after impingement. The axial penetration velocity of the cavity tip is approximately half of the impact velocity, which is consistent with previous research. Finally, based on the statistics of the cavity sizes, empirical formulas for predicting the maximum radial and axial sizes of the cavity were established.

A semi-empirical study of penetration of shaped charge jet into high and ultra-high strength reactive powder concrete targets

In this study, a semi-empirical model was proposed to calculate the penetration depth and cavity diameters generated by shaped charge jet into high and ultra-high strength concrete (H&UHSC) targets. A recently proposed axial penetration equation and the two-step mechanism of cavity growth were employed to determine the analysis. The predictions were validated with reference to the experiments conducted using a kind of H&UHSC named reactive powder concrete (RPC). Furthermore, the influences of the RPC compressive strength and the jet velocity on the penetration were analyzed. The results showed that the RPC targets had good protection efficiency for both penetration depth and cavity diameters as the compressive strength approaches approximately 250∼280MPa. Moreover, the radial cavity growth efficiency increased linearly with the increase of the jet velocity, while the axial penetration efficiency increased rapidly when the jet velocity was 1.0∼4.0km/s and reached the maximum at 4.0∼7.0km/s and tended to be stable as the jet velocity increased to greater than about 7.0km/s.

Visualization research on hydrogen jet characteristics of an outward-opening injector for direct injection hydrogen engines

The hydrogen jet characteristics have effect on the performance of direction injector (DI) hydrogen engines because they can influence the process of mixture formation and heat release. In this study, the hydrogen jet characteristics of an outward-opening injector were studied with high-speed schlieren imaging in a constant volume chamber at different injection and ambient pressure ratios (PRs), which ranged from 10 to 140. Results show that the hydrogen jet in the near-field is a conical structure, while the jet structure develops into a spherical vortex in the far-field. The jet axial penetration, radial penetration, and volume increase with the increasing of the PR. The jet spread angle is not sensitive to the PR except for the low PRs. The entrainment rate decreases with the increasing of the PR. The normalization analysis of jet penetration shows that the hydrogen jets have a good self-similarity under all PRs. A non-dimensional scaling correlation of axial penetration is proposed for this kind of hydrogen jets. In the scaling correlation, the exponents of the non-dimensional penetration and time term are 0.18 and 0.83, while the penetration constant is 13.18. The discovery of the above jet characteristics can predict the free jet shape under any PR in the range of 10 to140. These results can also promote the application of DI hydrogen engines.

Microscopic characteristics of supersonic natural gas jet in a constant volume chamber under different pressure ratios

The mixing effect of the gas–air mixture and the concentration distribution of supersonic gas jets for natural gas engines are affected by the microscopic characteristics of natural gas jets. In this study, the schlieren method was used to record the injection process of natural gas from an outward-opening injector. Results showed that the average equivalent ratio φ decreased as the pressure ratio (PR) increased, and the effect of PR on φ was smaller when PR was large. Further, φ was large at the beginning of the injection, then decreased rapidly and finally stabilized in the range of 1.7–3. The effect of PR on gas concentration was insignificant. The concentration distribution of natural gas jet was uneven along the axial direction. The mole fraction decreased with an increase in the axial penetration Zt and entered a stable range of 0.1–0.2 when Zt larger than 20 mm. The steady penetration constant Γ for an outward-opening injector was 1 ± 0.06, which was smaller than that of a single-hole injector. Γ increased rapidly with time and stabilized after the injector valve was fully opened. The steady Γ was slightly affected by the PR, but the moment Γ reached stability advanced with the increase in PR. The PR imposed a weak effect on the self-similarity index S of the outward-opening injector. The steady S of the outward-opening injector was 0.7, which was larger than that of a single-hole injector (S = 0.25 ± 0.05).

Experimental investigation on the microscopic characteristics of underexpanded transient hydrogen jets

The microscopic characteristics of hydrogen jet affect the concentration distribution and gas-air mixing of high-pressure gas jets for a hydrogen engine. In this study, the schlieren method was used to record the hydrogen jet for an outward-opening injector. The results showed that the jet asymmetricity was large in the initial stage of the jet development, then decreased rapidly as the jet developed, and finally entered a stable range of 13%–38% when the valve fully opened. The increase of the ambient pressure was beneficial to reduce the fluctuation range of the asymmetricity. The steady S of an outward-opening injector (S = 0.7 ± 0.03) is larger than that of a single-hole injector (S = 0.25 ± 0.05). The increase in injection pressure and the decrease in ambient pressure caused S to decrease to 1 faster. The steady Γ of an outward-opening injector was experimentally determined, and the value (Γ = 0.98 ± 0.1) was smaller than that of a single-hole injector. According to the transient Γ, the injection process can be divided into the developing phase and the self-similar phase. Γ increased rapidly with time and then stabilized after the injector valve reached its maximum lift position. The gas concentration distribution was uneven along the axial direction. The mole fraction decreased with the increase in axial penetration, and entered a stable range of 0.27–0.37 when axial penetration was greater than 20 mm. The average equivalent ratio was large at the beginning of injection under different pressure ratios, and then decreased and finally stabilized in the range of 1.4–5.