Gas Weber Number Research Articles

Feasibility of Using Polymers to Improve Foam Flow Performance in Vertical Pipes: Application to Liquid Unloading in Gas Wells

Foam unloading is a cost-effective technique for removing liquid from low-energy gas wells, but it faces challenges due to the instability of foam at the wellbore. Surfactants alone struggle to create and maintain durable foam films under wellbore conditions. Polymers are known to enhance foam stability by increasing lamella thickness and viscosity, but their impact on foam unloading has not been well explored. This study investigates the effects of Xanthan Gum (XG) and Polyvinylpyrrolidone (PVP) polymers on stability and unloading efficiency of the foams made by Alkyl Polyglycoside surfactant. The research evaluates foam stability and examines the bubble size and lamella thickness under varying salinity conditions. Additionally, the study evaluates foam unloading efficiency by determining unloaded mass rate, critical gas velocity and Weber number. Results show that polymer concentration, type and molecular weight significantly affect foam morphology and stability. Xanthan Gum at 1000 ppm demonstrated the smallest bubble size and greatest foam stability. This concentration also achieved the highest unloaded mass, 30% more than the surfactant-only case. Regarding the molecular weight of the polymers, HPVP demonstrated an ability to generate smaller bubbles in comparison with LPVP. Consequently, HPVP exhibited superior performance in liquid unloading, surpassing LPVP by a margin of 8.5%. The addition of polymers reduced critical gas velocity, with 1000 ppm of XG yielding the lowest value. Initially, the Weber numbers for polymer-stabilised foams were higher than the surfactant-only case (XG: 208.01, LPVP: 17.70, HPVP: 26.38 vs. APG: 2.25) due to the Marangoni effect but decreased during the unloading process (XG: 788.58, LPVP: 1850.26, HPVP: 1702.01 vs. base case: 4046.42), indicating improved stability and performance. Overall, the study demonstrates that polymers can significantly improve foam stability and performance, maintaining foam integrity throughout the unloading process if engineered properly prior to their application.

Morphology and dynamics of the liquid jet in high-speed gas-assisted atomization retrieved through synchrotron-based high-speed X-ray imaging

The breakup of a liquid jet by a surrounding high-speed gas jet with different liquid Reynolds numbers and gas Weber numbers was studied using high speed phase-contrast X-ray imaging technique. Focusing on the liquid core, the portion of liquid that is connected to the nozzle, four distinct morphologies were observed and can be associated with changes in the large-scale configurations of the two-phase flow are reported in a phase diagram. Gas-to-liquid kinetic energy balance arguments capture several transitions between the liquid core regimes. The temporal evolution of the center of mass of the liquid core is extracted to quantify its motion, whose statistics can be utilized as a signature to distinguish different regimes. At low to moderate gas Weber numbers, the dynamics are strongly influenced by flapping, while long-time dynamics develop at high Weber numbers, that give way to quasi-periodic motions when swirl is impeded to the gas jet.

Experimental study on the change of the orientation of high aspect ratio nozzle slit relative to the airflow

An experimental study to investigate the flow of liquid jet issued from a high aspect ratio nozzle slit into an incoming airflow by changing the orientation angle from the incoming free-stream was performed. A two-dimensional liquid sheet emerged from the narrow slit into the subsonic air crossflow. Different orientation angles between 0 and 90 degrees were studied. High-speed photography and shadowgraphy techniques were utilized to visualize the flow physics. The influence of the slit orientation angle on the flow morphology and the flow regimes of liquid sheets was investigated. Some fluid flow parameters were obtained by analyzing the images. The changes in breakup height of different orientations were measured. A model was offered for the breakup height of the liquid sheet based on the liquid-to-gas momentum ratio, gas Weber number, and a new non-dimensional parameter as a representation of the angle of slit orientation. Also, the defined sheet trajectory for each orientation angle was obtained, and the variations were examined. Empirical correlations for the defined trajectory of the sheet in terms of liquid to gas momentum ratio and gas Weber number for each orientation angle were proposed.

Breakup characteristics of a pulse jet issuing into a compressed gas environment under different injection conditions

The dynamics of jet breakup undergo significant alteration due to the influence of a compressed gas environment. In the first injection stage of an air-assisted fuel injector (AAFI), fuel is introduced into such an environment. Therefore, studying the influence of injection conditions on the jet breakup characteristics has significant importance for AAFI spray. This study utilized a high-speed camera to record the jet breakup images in a compressed gas environment. Subsequently, these images were analyzed using MATLAB to get the spray penetration distance and fuel projection area (FPA). The research findings indicate that both fuel injection pressure (FIP) and fuel–gas pressure drop (ΔP) exert influence on jet breakup characteristics, with ΔP exhibiting more significant influence. Maintaining ΔP at 1 bar, when FIP increased from 4 to 7 bar, gas Weber number (Weg) increased by 87%. While maintaining gas pressure at 5 bar, as ΔP increased from 1 to 3 bar, Weg escalated by 194%. Additionally, jet breakup length under different injection conditions followed a pattern as summarized by Bonhoeffer et al. [“Impact of formulation properties and process parameters on the dispensing and depositioning of drug nanosuspensions using micro-valve technology,” J. Pharm. Sci. 106(4), 1102–1110 (2017)]. The jet surface disturbance was enhanced by the increase in both FIP and ΔP. The detachment of the droplets from main jet stream induced by ΔP resulted in an increase in jet flow width. Furthermore, the effect of ΔP on FPA was more significant compared to FIP. As ΔP rose from 1 to 3 bar, the time-averaged FPA and area-to-mass ratio (Raq) increased 245% and 207%, respectively.

Effect of elevated crossflow temperature on jet primary atomization

Liquid jet in hot gas crossflow is widely employed in industrial combustion devices, especially in the propulsion systems. In this work, the effect of elevated crossflow temperature on the primary atomization of a liquid jet is experimentally investigated, including breakup regime, surface wavelength, column breakup height, and near-field trajectory. The experiments are conducted at crossflow temperatures of 300 K and 500 K, with gas Weber number ranging from 8.82 to 67.55 and momentum flux ratio from 10 to 50. The gas Weber number and momentum flux ratio are kept constant via increasing the crossflow velocity when crossflow temperature increases. The results show that the elevated crossflow temperature weakens surface breakup, particularly at high momentum flux ratios, which makes the transition of breakup regime from column breakup to surface breakup require higher gas Weber number or momentum flux ratio. Besides, the elevated crossflow temperature leads to a slight increase in surface wavelength, column breakup height and near-field trajectory, with the increase in trajectory being more pronounced at lower gas Weber numbers. Finally, an empirical correlation for the near-field trajectory is obtained, including the effects of crossflow temperature, gas Weber number, and momentum flux ratio.

Computational insights into gas atomization of FeCoNiCrMoBSi high-entropy alloy: From droplet formation to rapid solidification

The intricate processes governing the gas atomization of molten metal droplets and their subsequent solidification hold paramount significance in materials science. Computational fluid dynamics simulations have emerged as indispensable tools for unraveling the complexities inherent in metal melt atomization. This study employed the volume of fluid method and the shear-stress transport k-ω turbulence model to simulate the primary atomization process of a FeCoNiCrMoBSi high-entropy alloy. Subsequently, the discrete phase model and Taylor analogy breakup model, based on the gas Weber number and incorporating primary atomization outcomes as initial conditions, were utilized to simulate droplet formation during the secondary atomization process. Analysis of the particle size distribution at the outlet of the geometric model demonstrated excellent agreement with experimental data for gas-atomized FeCoNiCrMoBSi high-entropy alloy powder. Furthermore, comprehensive characterization analyses were conducted to probe the phase constitution and structure of FeCoNiCrMoBSi powder produced by gas atomization. The results revealed that, irrespective of particle size, the powder exhibited a face-centered cubic structure and distinctive eutectic microstructural characteristics. The numerical simulation provided insights into the solidification process of secondary droplets by integrating inverse pole figure data for gas-atomized powder across varying particle sizes. The estimated cooling rate of secondary droplets ranged from 1.22 × 104 K/s to 2.64 × 105 K/s. These findings significantly advance the understanding of the gas atomization mechanism of the FeCoNiCrMoBSi high-entropy alloy, paving the way for the development of more efficient manufacturing processes for advanced materials.

The breakup and instability structures of liquid jets in subsonic crossflows

The breakup of water and Jet A fuel jets injected transverse into elevated temperature (up to 425 °C), combustion pre-heated, subsonic crossflows was investigated by internally fluorescing the liquid jet column. The fluorescent dye seeded test liquids were illuminated by a pulsed laser light that was transmitted within the injector using a quartz rod light-guide. High-resolution images isolating the intact liquid column from light scattered by the surrounding dense spray facilitated precise measurement of the liquid column breakup position and the size and distribution of windward column instability waves. The injector geometry consisted of a 1 mm circular orifice with an orifice length of 20 mm with a tapered inlet. Liquid jet to gaseous crossflow momentum flux ratios were varied from 6 to 266 and the gas Weber number was varied from 10.7 to 228. Empirical correlations were derived for the liquid column breakup coordinates and breakup time in addition to the average and local maximum instability wavelength and amplitude on the liquid column windward surface. The reported correlations provided key insight into atomization physics and aim to support the quantitative validation of high-fidelity numerical simulations of the liquid jet in subsonic crossflow.

Experimental Study on Gas-Liquid Two-Phase Stratified Flow at High Pressure in a Horizontal Pipe

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced.

Spray characteristics of a self-aspirating ethanol ejector for high-efficiency combustion-based thermoelectric micropower generators

Low energy conversion efficiencies of combustion-based micropower generators due to parasitic losses continue to be a persistent challenge that limits their practical applications. This work puts forward a new strategy of liquid fuel delivery to a microcombustor with improved atomization and minimum parasitic energy losses. In the present work, a self-aspirating spray ejector is developed, providing continuous ethanol fuel delivery in the form of micron-sized droplets to a microcombustor of ∼ 1.0 kW thermal input capacity. The ejector base- setup works on the principle of generating a low-pressure zone through gas expansion, leading to the self-aspiration of ethanol fuel. The emerging annular ethanol film manifests a shear instability at the liquid–gas interface and subsequently breaks up into ligaments and fine micron-sized droplets. It was observed that the hydrostatic pressure of gas and aerodynamic Weber number (We) significantly affect the ethanol ejection rate, Sauter mean diameter (SMD), droplet distribution, and entrainment ratio of the spray ejector. The spray characteristics, such as mean droplet velocity and spray angle, are mainly governed by a single parameter, i.e., aerodynamic Weber number (We). The maximum power consumption for the spray ejector during the steady-state operation is ∼ 0.1 % of thermal input. The present investigation suggests that the self-aspirating spray ejector generates a fine and fully developed spray with ultra-low energy input requirement and, thus, can be a potential candidate for the development of high-efficiency combustion-based thermoelectric micropower generators.

Combined optical connectivity and optical flow velocimetry measurement of interfacial velocity of a liquid jet in gas crossflow

Liquid jet in crossflow (LJIC) is a process in which a high-speed gas crossflow deforms and shears a continuous liquid flow into tiny droplets. This study quantifies the liquid surface motion of LJIC during the primary breakup process, which has not been quantified due to the optical limitation close to the nozzle exit. The interfacial velocity of a breaking liquid jet indicates the local interaction of the gas and liquid flows and determines the initial velocity of the stripped droplets. The local interfacial liquid velocities of LJIC have only been estimated from theoretical and computational studies, which have not been evaluated from measurements. Optical Connectivity (OC) introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate the laser light inside the continuous liquid to record the instantaneous features of the interface of the continuous liquid during the primary atomisation at the near nozzle region through imaging of the emitted fluorescent intensity from the liquid flow. The current study combines Optical Connectivity with Optical Flow Velocimetry (OFV) to quantify the time-dependent, local interfacial velocity of the liquid interface structures of the LJIC for gas Weber numbers between 14.9 - 112.6 and liquid-to-gas momentum ratios between 2.1 - 36.4. The combined OC-OFV measurements of the spatial distribution of the mean and fluctuating values of the different components of the liquid interfacial velocity of LJIC demonstrate how the gaseous shear and liquid jet geometry interact to influence the atomisation process.

Experimental study of the injection angle impact on the column Waves: Wavelength, frequency and drop size

An experimental study was performed to investigate the influence of injection angle on further details of breakup of a circular liquid jet injected into an airstream. Wavelength and frequency of axial oscillations caused by column waves, drops size distribution, orientation and aspect ratio of these drops were measured and reported. Injection angles between 30 and 90 degrees were considered. High-speed photography and shadowgraphy techniques were utilized to visualize and record the flow. Experimental data were obtained by processing images with the help of an in-house developed code. We found that gas Weber number and the injection angle are influential on wavelength and frequency of the column waves. The wavelength decreased and the frequency increased with increasing gas Weber number or decreasing the injection angle. Also, momentum ratio, gas Weber number and injection angle were affecting drop's average diameter. By reducing the injection angle, the atomization process was prolonged and the produced drops were larger. Although the injection angle affected the average drop size and number, as long as the regime was not changed, the probability distribution of drop size was independent of the injection angle.We extended theory of Ng et al. [1] to estimate wavelength, frequency of column waves formed on the liquid jet that was injected into an airstream to account for injection angle. A relative gas Weber number was defined by using the relative velocity of the gas to that of the liquid along the flow direction. The introduced relative gas Weber number was found useful in classifying the breakup regimes of the flow. A relation was proposed to estimate these wavelengths with good agreement with our data at different injection angles and other previously published data at normal injection of liquid jets. Two separate correlations for SMD estimation were proposed for before and after bag formation in the flow.

Liquid jet breakup in gaseous crossflow injected through a large diameter nozzle

Near nozzle field behavior of round liquid jets injected through large injector diameter (ranging from 0.2 to 0.6 m) into subsonic uniform gaseous crossflows is numerically investigated using the Volume of Fluid (VoF) method. The liquid jet to gas momentum ratio is ranging from 4.3 to 39 with a gas Weber number ranging from 1.6×104 to 5.3×104. The large scale liquid water column main properties, such as primary breakup process, liquid column penetration height, liquid column expansion and column breakup point location are studied. Effects of several parameters on the liquid column evolution are investigated, namely the diameter injector, the liquid jet injection velocity and the gaseous crossflow velocity. It has been found that the surface breakup and column breakup mechanisms are both contributing to the liquid column fragmentation. The fragmentation at large scale is characterized by the generation of a significant number of well developed arm and leg structures that align with the airflow on the side and at the bottom of the liquid column. Correlations for the main liquid jet properties are proposed and compared with results previously obtained for smaller size liquid jet. Liquid column penetration height, width and column breakup height follow the same type of power laws that those observed for liquid jet at smaller size. The liquid jet evolution is compared to the water jet generated by the B747 airtanker.

Regimes of the length of a laminar liquid jet fragmented by a gas co-flow

Atomization occurs when a high-speed gas jet breaks a low-speed liquid jet coaxial to it, forming a spray via the production of ligaments, sheets, and drops. This mechanism has received a lot of attention and different fragmentation regimes have been identified qualitatively using imaging in the vicinity of the nozzle’s exit plane, as a proxy for the change of underlying break-up mechanisms. As the Weber number increases, i.e. as the gas aerodynamic stresses become larger with respect to the liquid surface tension, the liquid–gas interface suffers from instabilities that are governed by either capillarity, shear, or acceleration (or a combination of these). Several fragmentation regimes, in the low Weber number range, are typically deemed undesirable for applications such as propulsion or additive manufacturing, but no quantitative regime map is readily available. Using back-lit high-speed imaging in a multiscale approach, coaxial two-fluid fragmentation is studied in a broad range of gas Weber numbers that spans five fragmentation regimes. A fixed laminar liquid injection rate is maintained while the gas jet exit velocity is varied widely. The liquid core length, i.e. the extent of the liquid jet that is still fully connected to the nozzle, is an important metric of fragmentation, but most research has been focused on its average value in the bag break-up and fiber-type atomization regimes. The scaling laws of the first three statistical moments, the minimum value, and the correlation time of the liquid core length are reported across fragmentation regimes. The changes in scaling laws appear to be good indicators for several of the transitions explored.

Characterizations of gas-liquid interface distribution and slug evolution in a vertical pipe

Large vertical pipes are key structures connecting subsea wells to offshore platforms. However, existing studies mainly focus on small vertical pipes. In a vertical acrylic pipe with 80 mm inner diameter and 11 m height, a high-speed camera was used to visually research the influences of pipe diameters, liquid properties and inlet effect on air-water co-flow characteristic. Different flow regime maps of vertical pipes (diameters are in the range of 50–189 mm) were compared and the critical gas velocity of the transition boundary from bubble to slug flow tended to increase with the increase of diameters at D ≥ 80 mm. Drift-flux models were established in different flow regimes and liquid properties have a significant effect on drift coefficients of bubble flow and slug flow (void fraction α ≤ 0.4). The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D, where the flow was fully developed. Slug frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities (JL ≤ 0.31 m/s). And on the basis of this law, a new slug frequency correlation was proposed. It was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.

Spray Characterization of a Preheated Bio-Oil Surrogate at Elevated Pressures

Abstract Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in microgas turbines (MGTs), an aqueous surrogate of a preheated bio-oil, injected from an original equipment manufacturer (OEM) twin-fluid atomizer, is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI), phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. Over the range of conditions studied, it is found out that the cone angle of sprays is insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. Therefore, to estimate the Sauter mean diameter of spray droplets, D32, a correlation previously reported in the literature is modified by including the effect of system air density at elevated pressures, and a novel correlation is proposed based on four dimensionless groups, namely, gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio. The detailed results obtained in the present study could be used to define the optimal parameters required for twin-fluid atomization of high viscosity liquids with various atomization gases under realistic operating conditions and to enhance the capabilities of their numerical simulations.

Combined Optical Connectivity And Optical Flow Velocimetry For Measurement Of The Interfacial Velocity Of A Liquid Jet In Gas Cross-Flow

Liquid jet in crossflow (LJIC) is a process in which a high-speed gas crossflow deforms and shears a continuous liquid flow into tiny droplets. This study quantifies the liquid surface motion of LJIC during the primary breakup process, which has not been fully assessed due to limited optical access close to the nozzle exit. The interfacial velocity of a breaking liquid jet indicates the interaction of the gas and liquid flows and the initial velocity of the stripped droplets. However, the local interfacial liquid velocities have not been measured, since no measurement technique is available, and they have only been estimated from theoretical and computational studies. Optical Connectivity (OC) is a new optical technique, which introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate the laser light inside the continuous liquid. This allows the recording of the instantaneous features of the disintegrating continuous liquid and its interface during the primary atomisation at the near nozzle region through imaging of the emitted fluorescent intensity from the liquid flow. The current research reports time-dependent OC measurements of the temporal evolution of the liquid interface structures along a LJIC. The LJIC breakup behaviour is reported for different atomisation regimes, as determined by non-dimensional parameters. Optical Connectivity is combined with Optical Flow Velocimetry (OFV) to quantify the local interfacial liquid velocities of liquid interface structures of the LJIC for a range of gas Weber numbers between 14.9 - 112.6 and liquid-to-gas momentum ratios between 2.1 - 36.4. The combined OC-OFV measurements report the spatial distribution of interfacial velocities along the surface of LJIC and reveal the physics of the contribution of gaseous shear and liquid jet geometry on the atomisation process.

Spray trajectory and 3D droplets distribution of liquid jet in crossflow with digital inline holography

Liquid jet in crossflow (LJCF) has a wide application in the actual engine engineering. This article presents an experimental investigation of a water jet transversely injected into a subsonic crossflow through digital inline holographic imaging, and presents the relationship between the column trajectory and the downstream droplet distribution. A phenomenological analysis based on high-speed digital inline holography (DIH) with the frequency of 25 kHz is presented to interpret the source of droplets with different sizes in the bag breakup mode and the shear breakup mode. High-resolution DIH with a spatial resolution of 5.5μ m is applied to measure breakup point, droplet size, and location under 30 mm downstream of the orifice. The experiment is carried out under normal temperature and pressure. Gas Weber number Weg varies from 11 to 67, and the liquid to gas momentum ratio q changes from 10 to 28, which are mainly under bag breakup and multi-mode breakup regime. Crossflow velocity profiles are also measured. Liquid penetration were obtained and fitted through spray pattern under x/dj<10 and through downstream droplet statistics under 12<x/dj<70 separately. Under the cases studied, spray penetration evaluated by droplet statistics is larger than that evaluated through spray pattern. In addition, droplet size is relative large in the core region of the spray under higher Weg, possibly due to the presence of vortices in the core region and stronger aerodynamic effects at the periphery of spray. This research presents the quantification of the primary breakup process and corresponding three-dimensional (3D) downstream SMD distribution simultaneously, which helps improve the understanding of spray evolution in crossflow.

Taylor bubble formation and flowing in a straight millimetric channel with a cross-junction inlet geometry. Part I: Bubble dynamics

• Taylor bubble formation dynamics were studied at a cross-junction. • Filling and squeezing stage frequencies were not controlled by the same parameters. • Gas finger lengths were measured to identify different bubble pinch-off patterns. • A simple relationship linking relative bubble lengths with j G 0 / j L was established. The investigations of bubble formation dynamics at a cross-junction in a straight milli-channel were reported. The bubble formation process could be divided into the filling and squeezing stages, and their frequencies were compared at various conditions. It was found that the filling and squeezing frequencies were controlled mainly by the gas and liquid superficial velocities, respectively. The bubble formation frequencies could be related to the gas-liquid superficial velocity ratios, the liquid superficial velocities, and the bubble length. The bubble formation process was then analyzed considering the length of the gas finger right after the bubble pinch-off. Two patterns were identified depending on whether the pinch-off occurred inside of the cross-junction or not. The transition between these two patterns was described by a critical liquid Capillary number. Furthermore, the squeezing and dripping patterns were distinguished as the gas finger could fully block the channel or not. The transitions between the bubble formation patterns were determined by the gas Weber number and liquid Capillary number. Finally, the bubble length, the liquid slug length, and the bubble length normalized by the unit cell length could all be predicted based on the gas-liquid superficial velocity ratios η 0 .

Influence of injection angle on liquid jet in crossflow

The influence of changing the injection angle of a liquid jet injected into airstream in crossflow was investigated. The injection angles from 90 to 30 degrees were considered. Based on liquid velocity and air speed, liquid and gas Weber numbers from 8 to 600 and 0.2 to 27 were considered, respectively. Many flow parameters such as: Rayleigh-Taylor wavelengths, liquid jet trajectories, breakup lengths and penetration lengths by means of high-speed photography and shadowgraph technique were measured and reported. Based on the relative importance of the aerodynamic forces of the crossflow to the liquid momentum and surface tension forces different breakup regimes occurred. Using gas Weber number, the following liquid jet breakup regimes: column breakup, arc breakup, bag breakup and multimode breakup were observed at various injection angles. It was found that at lower injection angles the required gas Weber number to transition between regimes was slightly increased.At lower gas Weber number flows, increasing the injection angle caused the liquid jet to penetrate farther into the airstream and this process was gradual. However, at higher gas Weber number flows, there was a bifurcation in behavior: At the lower injection angles, the behavior was the same, but at the higher injection angles, the penetration behavior reversed and the penetration of liquid jet into airstream decreased as the injection angle was increased. We believe this phenomenon was due to switching of the breakup mechanism from Rayleigh-Taylor instability to shear breakup mechanisms at higher injection angles.Theoretical models for prediction of liquid jet trajectory and its breakup point taking the effect of injection angle into account were developed and presented. The models’ predictions were compared with our measurements and other published data resulting in good agreements.

Experimental and numerical investigations on the spray characteristics of liquid-gas pintle injector

The spray characteristics of a liquid-gas pintle injector at different total momentum ratios (TMR) are investigated by means of experiment and numerical simulation. Water and nitrogen are used as simulant for liquid fuel ejected out from radial gap and gas oxidizer ejected out from axial annular gap, respectively. A high-speed photography system and Malvern measuring instrument are used to study the spray pattern, spray angle, droplet diameter and spatial distribution. A coupling algorithm between Volume of Fluid and Lagrangian Particle Tracking (VOF-LPT) is applied for spray simulations implemented within the CFD software OpenFOAM. The results indicate that the spray pattern generated by the liquid-gas pintle injector is mainly influenced by gas weber number and divided into three types. The spray angle is dominated by the TMR, and the outer boundary of the spray field is enlarged with the increase of the TMR. In particular, a spray angle formula of liquid-gas pintle injector is given in: cos⁡θ=c/(c+TMR), and c=0.71 with considering the gas jet momentum loss. The droplet diameter and spatial distribution indicate that Sauter Mean Diameter (SMD) decreases in the spray intermediate area with the increase in the aerodynamic force action. The spray structure and diameter distribution obtained by numerical calculation agree well with the experimental results, and can be used to analyze the spray characteristics.