Gas Weber Number Research Articles

Online Measurement of Gas and Liquid Flow Rates in Wet Gas Using Vortex Flowmeter Coupled With Conductance Ring Sensor

Wet gas flow commonly exists in several industries. The online measurement of gas and liquid flow rate is beneficial for economic efficiency. A combination of vortex flowmeter and liquid film sensor was proposed for two-phase flow measurement of wet gas. The specific form is as follows: the dual-modality sensing system was designed and calibrated by an annular mist flow loop. The fluid materials are pure air and water liquid. The ranges of operating pressure, the superficial gas velocity, and superficial liquid velocity are 1.5 bar–3.5 bar, 18.86–37.73 m/s, and 0.0028–0.028 m/s. Then the function relations of liquid film thickness and vortex frequency, with gas and liquid Weber numbers were built, respectively. Finally, a novel model for calculating gas and liquid flow rates in wet gas measurement was established, and solved by the Newton iterative algorithm. It showed that the percentage error (PE) of gas flow rate predicted by the model is within ±1.5%, and the mean absolute percentage error (MAPE) is 0.55%. The full-scale PE of liquid flow rate is within ±5% and the MAPE is 3.48%. The data show that this solution for gas and liquid flow rates measurement of wet gas by combining a vortex flowmeter with a conductance ring sensor is feasible.

Dynamic Characteristic Analysis of a Gas–Liquid Swirl Injector Using Planar Laser Imaging

The oscillation of the mass flow rate of the input propellant in liquid rocket engines may induce a periodic heat energy release within the combustion chamber, resulting in operational instability. Since propellant components are discharged from the injector head, the injectors can play a role as a source of oscillation in the dynamic system of a liquid rocket engine. Prior studies confirmed that if the liquid spray and gas flow intersect by using gas-centered dual-swirl injector with tangential inlet in the gas flow path, droplets are generated with periodicity (fracture frequency). In this study, the characteristics and mechanisms of this periodicity were analyzed using longitudinal cross-section spray images. Since the multiple scattering signal that inhibits clarity is non-modulated components, it can be removed by using two modulated images with a phase difference of 180 deg (two-phase structured laser illumination planar imaging technique). And the dynamic characteristics of the gas–liquid spray were analyzed by applying the fast Fourier transform method. It was confirmed by this method that the fracture frequency was related to the impinging velocity of gas and hydrodynamic feature of liquid film. That is, it can be said that fracture frequency of the liquid film is dependent on the liquid Weber number and gas Weber number as the entrainment effect and impact force by gas flow are applied to the liquid film.

Characterization of bubbles dynamics in aperiodic formation

Bubble-bubble interactions are relevant to industrial applications, for which air is injected at different flowrates from submerged orifice. These interactions provoke aperiodic bubble formation that affects their departure and size distribution, which is revealed through our experimental data. Air is injected and regulated at flow rate between 10−4 m3.s−1 and10−3 m3.s−1 from a submerged orifice of inner diameter 12 mm, corresponding to a gas Weber number between 0.16 and 16. Image analysis is carried out to track the formation and departing of bubbles, as well as the formation of a globule, which is a large bubble formed after the bubbles coalescence. Upon increasing the flowrate, the different patterns of bubbling observed have been classified according to the variation of the coalescence position. In a conventional method, bubbles volumes are determined by inspecting the departure frequency and assuming single bubbling spherical pattern. Using the same assumptions and method, we find a good agreement with literature models. Owing to the phenomenological description of the flow, the frequency and volume of globules are characterized. A contrast between the conventional and phenomenological approaches is exposed, revealing a weak applicability of conventional models in estimating bubbles sizes at high flow rates.

Pressure drop and flow patterns of boiling flows in Mini-Channels with Semi-Circular Cross-Section

• Boiling flow characteristics in a semi-circular mini-channel are demonstrated. • Suppression of the increase in pressure drop was observed for the 0.55 mm channel. • Bubble nucleation at the corners affects the flow patterns and pressure drop. • An annular flow transition occurs at a high gas Weber number. • A new equation based on a separated flow model is proposed for the pressure drop. Frictional pressure drop and flow patterns of vertically upward boiling flows in semi-circular mini-channels with the hydraulic diameters of 1.04 mm and 0.55 mm were experimentally investigated using R-245fa as the working fluid. Measurements were conducted at a saturation temperature of 30 °C with a mass flux of 100 to 400 kg/(m 2 s) at an inlet subcooling degree of 10 K. The working fluid was heated with hot water flowing in the counter-direction. It was found that the gas Weber number at the flow pattern transition to annular flow increased with an increasing mass flux and a decreasing hydraulic diameter. While the film thickness in the corner of the cross-section became thick in the 0.55 mm channel, nucleate boiling leading to strong fluctuation of the gas–liquid interface was observed owing to the higher heat flux. For the 0.55 mm channel, the gas–liquid interface was relatively smooth. Moreover, the increase in the frictional pressure drop was suppressed at a moderate outlet quality with a low mass flux. A new correlation equation based on a separate flow model could estimate the frictional pressure drop with mean absolute errors of 21.4% and 34.0% for the 1.04 mm and 0.55 mm channels, respectively.

Experimental investigation on atomization properties of impaction-pin nozzle using imaging method analysis

The impaction-pin spray nozzle is widely used in chemical and process industries. To study the atomization characteristics of the impaction-pin nozzle, a high-pressure atomization apparatus was developed and an optical imaging system for the measurement of droplet parameters was proposed. The droplet size and velocity vector were extracted from the shadowgraph images and the influence of liquid pressure drop especially nozzle orifice diameter on atomization was analyzed in detail. Finally, prediction models for Sauter mean diameter were proposed and the atomization efficiency was analyzed. The results indicate that the range of droplet Sauter mean diameter is 8.55–37.5 μm while arithmetic mean velocity is 0.483–1.921 m/s at the pressure drop range of 0.525–4.95 MPa for PJ6. For PJ8, the range of diameter is 20.6–53.9 μm while velocity is 0.746–2.879 m/s at the pressure drop range of 0.43–3.32 MPa. The size and velocity of atomized droplets both follow the law of logarithmic normal distribution. The droplet diameter is negatively and the velocity is positively related to the pressure drop, while both of the diameter and velocity are positively related to the nozzle orifice diameter. The atomization efficiency declines with the rise of pressure drop and orifice diameter. Besides, empirical correlation models related to gas Weber number and liquid Reynolds number for droplet size and the atomization efficiency were also built accurately. The research provides guides for studies on atomization properties of spray nozzles and their applications.

Effects of nanoparticles on the instability of liquid jets in a gaseous crossflow

Nanofluids have attracted interest for their high performance in enhancing heat transfer and improving combustion. However, few studies have investigated the influences of nanoparticles on spray processes. In this study, the surface waves, liquid column oscillation, and droplet size distribution of a nanofluid transverse jet were investigated at low gas Weber number. A new statistical image-processing method was proposed to identify the surface wavelength and jet oscillation amplitude. A new power index parameter was proposed to account for the effect of nanoparticles, and then introduced to correlate with the upwind wavelength and Sauter mean diameter (SMD) of nanofluid droplets in the far field. The results show that in bag breakup and multimode breakup, the wavelengths decrease along the jet flow direction while the amplitudes gradually increase in the initial stage. The characteristic wavelength and SMD diminish with the increase of nanoparticle concentration, and the oscillation angle of liquid column increases correspondingly. The nanoparticle additive at low concentration obviously enhances the flow instability and cavitation inside the jet. Therefore, the fineness and uniformity of nanofluid atomization in the far field are significantly improved.

Simulation of primary breakup of molten slag in the gas quenching dry granulation process

Gas quenching dry slag granulation process is an energy-saving environmental protection method for waste utilization and waste heat recovery of molten slag, and the molten slag is broken up by supersonic airflow into droplets in this process. This paper performed the numerical investigations on the breakup behavior of slag by the coupled level-set and volume of fluid (CLSVOF) methodology and gain a deep insight into the breakup mechanism of the primary breakup and influence of gas Weber number (We) and liquid Reynolds number (Re) on the primary breakup. The results indicated that the primary breakup include flat film breakup and spherical cap film breakup, the both are typical perforation breakup; Aerodynamic force cause K-H (Kelvin Helmholtz) instability, K-H surface waves are the root cause of film breakup; The wavelength and the film thickness decrease with increasing We which is conducive to reducing the ligament diameter; The wavelength and the film thickness decrease first and then increase with increasing Re which is optimum in the range of 1068–1280; The empirical formula of the ligament diameter is obtained. The ligament diameter decrease with increasing airflow velocity and slag density and increase with increasing slag mass flow rate and slag viscosity.

Experimental analysis of the flow characteristics of a pressure-atomised spray

An experimental setup has been created to allow measurements of the properties of the gas phase, the liquid phase and the mixture in a pressure-atomised spray of water, in terms of both mean quantities and Reynolds stresses. This setup involves laser Doppler velocimetry for determining the velocity of either the gas or liquid phase, according to the parameters used, such as seeding or no-seeding of the ambient air, laser source power, or photo-multiplier gains, droplet tracking velocimetry for determining the velocity and characteristic size of the droplets, and a single optical probe for determining the mean volume fraction of the liquid, from which the liquid mean mass fraction and the mean density of the mixture are inferred. The experimental conditions, in particular in terms of liquid and gas Weber numbers, were chosen in a range for which the liquid phase turbulent kinetic energy should be mainly responsible for the liquid-jet primary break-up, these flow conditions lying within the second wind-induced atomization regime. Results reported herein are more specifically focused on the region ranging from 400 nozzle diameters to 800 nozzle diameters, where the liquid core is disrupted. They provide new information about the formation and properties of such pressure-atomised sprays, in particular in terms of the role played by the Reynolds stresses resulting from the slip velocity between the liquid and the gas. The mean slip velocity is directly related to the turbulent flux of liquid. Such information will be used in the future to develop new turbulence models since very limited experimental information is so far available for these terms.

Breakup Processes and Droplet Characteristics of Liquid Jets Injected into Low-Speed Air Crossflow

The breakup processes and droplet characteristics of a liquid jet injected into a low-speed air crossflow in the finite space were experimentally investigated. The liquid jet breakup processes were recorded by high-speed photography, and phase-Doppler anemometry (PDA) was employed to measure the droplet sizes and droplet velocities. Through the instantaneous image observation, the liquid jet breakup mode could be divided into bump breakup, arcade breakup and bag breakup modes, and the experimental regime map of primary breakup processes was summarized. The transition boundaries between different breakup modes were found. The gas Weber number (Weg) could be considered as the most sensitive dimensionless parameter for the breakup mode. There was a Weg transition point, and droplet size distribution was able to change from the oblique-I-type to the C-type with an increase in Weg. The liquid jet Weber number (Wej) had little effect on droplet size distribution, and droplet size was in the range of 50–150 μm. If Weg > 7.55, the atomization efficiency would be very considerable. Droplet velocity increased significantly with an increase in Weg of the air crossflow, but the change in droplet velocity was not obvious with the increase in Wej. Weg had a decisive effect on the droplet velocity distribution in the outlet section of test tube.

Retracted: “Symmetric and Asymmetric Disturbances in the Rayleigh Zone of an Air-Assisted Liquid Sheet: Theoretical and Experimental Analysis,” [ASME Journal of Fluids Engineering, 2020, 142(7), p. 071302; DOI: 10.1115/1.4045998

AbstractThe temporal analysis of symmetric (dilatational) and asymmetric (sinusoidal) perturbations at the interface of a water sheet in a coflowing air stream focuses on low gas Weber number region (Weg < 0.4), namely, Rayleigh breakup zone. The motive for this investigation is to acquire a better insight of breakup phenomena involved, rather than technical relevance, by utilizing Kelvin–Helmholtz instability. Accordingly, perturbations are introduced on the basic flow whose stability is to be examined by the method of normal (Fourier) modes. The temporal growth-rate of perturbations is traced to extract the wavenumber associated with maximum growth-rate. Thus, the critical wavelength, in conjunction with the phase velocity of the disturbance will facilitate to obtain the corresponding breakup frequency of the liquid sheet. The analytical findings on liquid sheet breakup frequency with increasing Weber number ratio exhibit the dominance of symmetric wave over asymmetric wave. It also shows independent evolution of breakup frequency with respect to Weber number ratio for the respective perturbation modes, which appears to be a pointed profile. That is, the frequency contour for dilatational mode dips, whereas it rises for the sinusoidal mode and at the Weber number ratio of 0.518 the crossover occur. The theoretical results were substantiated by high-speed flow visualization studies that discern the coexistence of low-frequency (primary) and high-frequency (intermediate) breakup events. Furthermore, the empirical average frequency data track reasonably well with the dilatational instability.

Liquid jet penetration and breakup in a free supersonic gas jet

The interaction of a coherent liquid jet with a free supersonic gas jet is of importance in cooling high-temperature exhaust plumes generated by ground rocket tests. Further, the associated phenomena are distinct from the well-studied jet in supersonic crossflow due to the unbounded nature of the gas jet, its shock train structure, and the relative sizes of the two jets. This work utilizes non-intrusive diagnostics including focused color Schlieren, high-speed diffused backlit imaging, and volume-illuminated imaging to study the interaction process of a high Reynolds number water jet with a free supersonic air jet. The effect of the water jet on the shock train structure and its dependence on water injection location and pressure are studied. The ensuing water jet breakup mode is investigated and found to exhibit distinguishing characteristics from known breakup modes observed at high Reynolds and gas Weber numbers. Finally, the water jet penetration height is quantified, and the ability of existing correlations from the literature to predict the penetration height are investigated.

Liquid jet primary breakup in a turbulent cross-airflow at low Weber number

The influence of turbulence characteristics of a cross-airflow including its velocity fluctuations and integral length and time scales on the primary breakup regime, trajectory and breakup height and time of a transversely injected liquid jet was investigated experimentally. Turbulence intensity of the incoming airflow was varied from $u_{rms}/u_{g}=1.5\,\%$ to 5.5 % (where $u_{g}$ is cross-airflow streamwise mean velocity and $u_{rms}$ is the r.m.s. of the corresponding cross-airflow streamwise mean velocity fluctuation) by placing at the inlet of the test section a perforated plate/grid with a solidity ratio of $S=50\,\%$. Over the range of gas Weber number, $3.1<We_{g}<7.14$, the ensuing liquid jet exhibited more fluctuations and late breakup transitional behaviour under turbulent airflow conditions than in a uniform cross-airflow. Proper orthogonal decomposition of the liquid jet dynamics revealed that the use of grid caused a rise in the wavelength of travelling waves along the liquid jet, which hindered the transition of the liquid jet primary breakup regime from enhanced capillary breakup to the bag breakup mode. The quantitative results demonstrated that, at a constant airflow mean velocity, turbulent cross-airflow caused the liquid jet to bend earlier compared with its uniform counterpart. A power-law empirical correlation was proposed for the prediction of the liquid jet trajectory which takes into account the effect of turbulent Reynolds number. The liquid jet breakup height (in the $y$-axis direction) normalized by the jet diameter, and accordingly the liquid jet breakup time normalized by the airflow integral time scale, were found to decrease with increasing the airflow turbulence intensity. Two power-law empirical correlations were proposed to predict the liquid jet breakup height and time.

Wave characteristics of vertical upward adiabatic annular flow in pipes

Annular flow exists in many engineering applications, such as refrigerators, oil extraction, nuclear reactors and so on, due to its high heat and mass transfer efficiencies. Annular flow is characterized by liquid film on the wall and gas core at the center of the flow duct. The interface between the gas and liquid is composed of many different waves that play important role in mass, momentum and energy transfers between gas and liquid phases. Here three important parameters regarding wave characteristics, namely, wave velocity, base film thickness and wave height have been studied. For wave velocity, correlation has been proposed by two methods which are derived from liquid interfacial velocity and interfacial shear stress, respectively. For correlations of base film thickness and wave height, they are proposed in similar forms as that of average film thickness previously developed by the authors. These newly proposed correlations are functions of gas and liquid Weber numbers, and are simpler and more straightforward to use as compared to the existing ones. The newly proposed wave velocity, base film thickness and wave height correlations, respectively, have mean absolute percentage errors of 9.56%, 14.6% and 12.1% compared to current databases. They have shown an improved prediction accuracy compared to the other correlations in the literature.

Vorticity dynamics in a spatially developing liquid jet inside a co-flowing gas

A three-dimensional transient round liquid jet within a low-speed coaxial outer gas flow is numerically simulated and analysed via vortex dynamics ($\unicode[STIX]{x1D706}_{2}$ analysis). Two types of surface deformations are distinguished, which are separated by a large indentation on the jet stem. First, there are those inside the recirculation zone behind the leading cap – directly affecting the cap dynamics and well explained by the local vortices. Second, deformations upstream of the cap are mainly driven by the Kelvin–Helmholtz (KH) instability, unaffected by the vortices in the behind-the-cap region (BCR), and are important in the eventual atomization process. Different atomization mechanisms are identified and are delineated on a gas Weber number ($We_{g}$) versus liquid Reynolds number ($Re_{l}$) map based on the relative gas–liquid velocity. In a frame moving with the liquid velocity, this result is consistent with prior temporal studies. A simpler and clearer portrait of similarity of the atomization domains is shown by using the relative gas–liquid axial velocity, i.e. $We_{r}$ and $Re_{r}$, and avoiding the widely used velocity ratio as a third key parameter. A detailed comparison of vorticity along the axis in an Eulerian frame versus a frame fixed to a surface wave reveals that the vortex development and surface deformations are periodic in the upstream region, but this periodicity is lost closer to the BCR. In the practical range of the density ratio and for early times in the process, axial vorticity is mainly generated by baroclinicity while streamwise vortex stretching becomes more important at later times and only at lower relative velocities when pressure gradients are reduced. The inertia, vortex, pressure, viscous and surface tension forces are analysed to delineate the dominant causes of the three-dimensional instability of the axisymmetric KH structure due to surface acceleration in the axial, radial and azimuthal directions. The inertia force related to the axial gradient of kinetic energy is the main cause of the axial acceleration of the waves, while the azimuthal acceleration is mainly caused by the pressure and viscous forces. The viscous forces are negligible in the radial direction and away from the nozzle exit in the axial direction. It is interesting to note that azimuthal viscous forces are important even at high $Re_{l}$, indicating that inertia is not totally dominant in this instability occurring early in the atomization cascade.

Experimental investigation of spray characteristics of a liquid jet in a turbulent subsonic gaseous crossflow

Two perforated plates with different solidity ratios, S=50% and 67%, were used to investigate the effect of the velocity fluctuations of a subsonic gaseous crossflow on the spray characteristics of a liquid jet including droplet size and velocity distributions. The experiments were conducted over a range of jet-to-crossflow momentum flux ratio of q=16.5-172, and two gas Weber numbers of Weg=2.7 and 5.9, corresponding to the enhanced capillary breakup and bag breakup regimes, respectively. The experimental results of this study revealed that the distribution of droplets size associated with a turbulent and a uniform crossflow for each specific breakup regime were approximately identical. The bimodal and single peak distributions of droplets size, respectively, associated with enhanced capillary and bag breakup regimes were generally consistent with the literature reports. However, the transition of the liquid primary breakup regime from enhanced capillary to bag breakup mode was delayed in a turbulent crossflow compared to its uniform counterpart. The general behavior of droplets size-velocity profiles were also consistent with the literature reports. Nonetheless, complex variations in the distribution of droplets velocity when changing the crossflow turbulence intensity were observed and linked with the presence of instabilities on the liquid jet's surface. Finally, the present experiments allowed shedding more light on the reason why the breakup mechanisms of a liquid jet in a conventional uniform crossflow should not be generalized to predict the distinct breakup process of a liquid jet in a turbulent crossflow.

Understanding liquid-jet atomization cascades via vortex dynamics

Temporal instabilities of a planar liquid jet are studied using direct numerical simulation (DNS) of the incompressible Navier–Stokes equations with level-set (LS) and volume-of-fluid (VoF) surface tracking methods. $\unicode[STIX]{x1D706}_{2}$ contours are used to relate the vortex dynamics to the surface dynamics at different stages of the jet breakup – namely, lobe formation, lobe perforation, ligament formation, stretching and tearing. Three distinct breakup mechanisms are identified in the primary breakup, which are well categorized on the parameter space of gas Weber number ($We_{g}$) versus liquid Reynolds number ($Re_{l}$). These mechanisms are analysed here from a vortex dynamics perspective. Vortex dynamics explains the hairpin formation, and the interaction between the hairpins and the Kelvin–Helmholtz (KH) roller explains the perforation of the lobes, which is attributed to the streamwise overlapping of two oppositely oriented hairpin vortices on top and bottom of the lobe. The formation of corrugations on the lobe front edge at high $Re_{l}$ is also related to the location and structure of the hairpins with respect to the KH vortex. The lobe perforation and corrugation formation are inhibited at low $Re_{l}$ and low $We_{g}$ due to the high surface tension and viscous forces, which damp the small-scale corrugations and resist hole formation. Streamwise vorticity generation – resulting in three-dimensional instabilities – is mainly caused by vortex stretching and baroclinic torque at high and low density ratios, respectively. Generation of streamwise vortices and their interaction with spanwise vortices produce the liquid structures seen at various flow conditions. Understanding the liquid sheet breakup and the related vortex dynamics are crucial for controlling the droplet-size distribution in primary atomization.

Annular liquid film thickness prediction in a vertical 180° return bend

Annular flow is predominant in gas wells. Liquid may be present in form of entrained droplets as well as in the liquid film on pipe wall. The knowledge of the average liquid film thickness is vital for detailed mechanistic modelling of churn–annular flow in engineering applications. So far, the models for liquid film thickness prediction are limited to vertical and horizontal pipes. These models were based on limited ranges of experimental data. In addition, exhaustive iterations are needed when these models are used to estimate liquid film thickness. In this work, a new correlation to predict liquid film thickness in a 180° bend under gas–liquid annular conditions was successfully proposed. The correlation was based on dimensionless numbers (modified gas and liquid Weber numbers and gas Froude number) which reflect the underlined physics governing gas–liquid interaction in the bend. The Weber numbers capture the two important forces (inertial and surface tension forces) which govern the formation of the liquid film thickness within the system while gas Froude number quantifies the interaction of two important forces (centrifugal and gravitational forces) which determines the distribution of the phases across a bend. The proposed liquid film thickness correlation was based on the experimental data obtained from a wide range of operating conditions. The liquid superficial velocities ranges from 0.02 to 0.2 m/s and gas superficial velocities from 3.5 to 16 m/s at different measurement locations of 45°, 90° and 135° of the bend with a diameter of 127 mm. The liquid film thickness in air–water and helium–water annular flow can be predicted by δ=28.4061(WeL)0.10318(WeG)-0.30954(FrG)-0.31423. The validation of the proposed correlation used to predict liquid film thickness in gas–liquid annular systems with different pipe diameters were examined against the available data in the literature. Good agreement was found between the predicted values of liquid film thickness with the experimental data at different measuring locations of the bend.

Planar liquid jet: Early deformation and atomization cascades

The temporal evolution of three-dimensional instabilities on a planar liquid sheet segment is studied using direct numerical simulation, and the level-set and volume-of-fluid methods for the liquid-gas interface tracking. Three atomization cascades are distinguished at early breakup, which are well categorized on a gas Weber number (Weg) versus liquid Reynolds number (Rel) map. These atomization processes include lobe stretching that occurs at low Rel and low Weg, hole and bridge formation that occurs at moderate Rel and high Weg, and lobe corrugation occurring at high Rel and low Weg. Qualitative comparison between the sizes of the ligaments and droplets that result from each process is presented. A transitional region between the prescribed atomization domains is found. At high Rel, the transitional boundary is a constant Ohnesorge line defined based on gas We and liquid Re (Ohm≡Weg∕Rel). At low Rel, the transitional region follows a hyperbolic line on the Weg–Rel plot. These atomization processes are qualitatively independent of the jet geometry—seen in both planar and round liquid jets. At a constant density ratio, characteristic times for the hole formation and for the lobe and ligament stretching are different—the former depending on surface tension and the latter on liquid viscosity. In the transitional region, both characteristic times are of the same order.

Analysis of roll wave characteristics under low liquid loading two‐phase flow conditions

An experimental study is conducted using a 0.152‐m ID facility to investigate the wave characteristics of two‐phase stratified wavy flow in horizontal pipelines. The experiments are conducted under low liquid loading condition, which is very commonly observed in wet gas pipelines. The experiments are conducted with water as the liquid phase, and repeated with 51 wt % of monoethylene glycol (MEG) in the aqueous phase to analyze the effects of MEG presence on wave characteristics. The experimental range of this study covers superficial gas velocity, vSg, values of 9–23 m/s and superficial liquid velocity, vSL, values of 0.01–0.02 m/s. Similar test matrices are completed for the cases with and without MEG in the aqueous phase. A conductivity probe system is used to measure the wave characteristics at the liquid–gas interface. These characteristics include the wave celerity, frequency, amplitude, length, and liquid film thickness. The experimental oil–air wave characteristics data of Gawas et al. (Int J Multiphase Flow. 2014;63:93–104) is also used for comparison purposes. The trends in the resulting wave characteristics with respect to input parameters are investigated, for oil, water, or MEG–water mixture as the liquid phase. Common predictive methods for interfacial wave celerity, including shallow water theory, Watson (Proceedings of the 4th International Conference in Multi‐Phase Flows, Nice, France. 1989:495–512), Paras et al. (Int J Multiphase Flow. 1994;20(5):939–956), Al‐Sarkhi et al. (AIChE J. 2012;58(4):1018–1029), and Gawas et al. (Int J Multiphase Flow. 2014;63:93–104) are evaluated in comparison with the experimental data. The results of the wave frequency correlation of Al‐Sarkhi et al. (AIChE J. 2012;58(4):1018–1029) are also compared with the experimental wave frequency data. Lastly, a correlation is developed to predict the relative wave amplitude, as a function of superficial gas Weber number and liquid velocity number. Most of the commonly used two‐phase stratified flow models are developed with the assumption of steady‐state conditions, and neglect the transient wave effects. This study provides valuable experimental results on wave characteristics of stratified wavy flow for different types of liquid phase. Moreover, a comprehensive analysis of the parameters affecting the wave characteristics of stratified wavy flow is presented. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3177–3186, 2017

High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers

Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the high liquid-gas density ratio across the sharp interfaces encountered in these flows are key reasons for this. In this work we challenge this status quo by presenting a numerical model able to deal with these challenges, employing it in simulations of liquid jet in crossflow atomization and performing extensive validation of its results against a carefully executed experiment with detailed measurements in the atomization region. We then proceed to the detailed analysis of the flow physics. The computational model employs the coupled level set and volume of fluid approach to directly capture the spatiotemporal evolution of the liquid-gas interface and the sharp-interface ghost fluid method to stably handle high liquid-air density ratio. Adaptive mesh refinement and Lagrangian droplet models are shown to be viable options for computational cost reduction. Moreover, high performance computing is leveraged to manage the computational cost. The experiment selected for validation eliminates the impact of inlet liquid and gas turbulence and focuses on the impact of the crossflow aerodynamic forces on the atomization physics. Validation is demonstrated by comparing column surface wavelengths, deformation, breakup locations, column trajectories and droplet sizes, velocities, and mass rates for a range of intermediate Weber numbers. Analysis of the physics is performed in terms of the instability and breakup characteristics and the features of downstream flow recirculation, and vortex shedding. Formation of “Λ” shape windward column waves is observed and explained by the combined upward and lateral surface motion. The existence of Rayleigh-Taylor instability as the primary mechanism for the windward column waves is verified for this case by comparing wavelengths from the simulations to those predicted by linear stability analyses. Physical arguments are employed to postulate that the type of instability manifested may be related to conditions such as the gas Weber number and the inlet turbulence level. The decreased column wavelength with increasing Weber number is found to cause enhanced surface stripping and early depletion of liquid core at higher Weber number. A peculiar “three-streak-two-membrane” liquid structure is identified at the lowest Weber number and explained as the consequence of the symmetric recirculation zones behind the jet column. It is found that the vortical flow downstream of the liquid column resembles a von Karman vortex street and that the coupling between the gas flow and droplet transport is weak for the conditions explored.