Roll Flow Research Articles

Gas-liquid flow regimes in a novel rocking and rolling flow loop

Predicting two-phase flow pattern characteristics and flow transition is fundamental to address several industrial problems, e.g. for the oil and gas industry. In order to fulfil the upscaling from the laboratory to the industrial scale, resource-efficient flow testing facilities which closely replicate industrial flow characteristics are needed. To address this, we introduce a new experimental device named as the Rocking and Rolling Ring Flow Loop (3RFL), which is size, cost, and time-efficient. In the present work, we employ the 3RFL apparatus at atmospheric pressure and temperature, with air and water as working fluids. However, the ultimate goal of our work is to build an experimental set-up capable of capturing the under-pressure reactive multiphase flow (gas-liquid–solid) dynamics typical of flow assurance in oil production and transportation. At the moment, the 3RFL can induce different flow regimes by adjusting the system control parameters such as rocking angle, rocking rate, and liquid volume fraction, all without requiring a pump. We observe three flow regimes, and analyse the impact of control parameters on their emergence. Our findings reveal that flow regime transitions are influenced by the competition between gravitational and centrifugal forces, which arise due to the curvature of the tube. Among three employed modelling strategies, namely mechanistic modelling, total energy minimization and a combined approach, we find that the total energy minimization model best compares to the experimental liquid height.

Interfacial Effects of Nanostructured Doubly Reentrant Surfaces on the Evolution of Local Concentration and Fluid Flow in an Evaporating Droplet.

Surface modification, such as bioinspired nanostructured doubly reentrant surfaces that have presented superhydrophobic wettability even under low-surface-tension liquid, is a very promising technology for controlling droplet dynamics, heat transfer, and evaporation. In this article, we investigate the interfacial effects of nanostructured doubly reentrant surfaces on the flow behaviors and local concentration evolution during the evaporation of an ethanol/water multicomponent droplet. Using particle image velocimetry (PIV) and novel aggregate-induced emission-based (AIE) techniques, the flow patterns and local concentration distributions on both hydrophobic and nanostructured doubly reentrant surfaces were probed and compared. It is found that in addition to the established Marangoni flow-dominated stage, transition stage, and buoyancy-induced flow-dominated stage, a new transition stage and a rolling stage for the nanostructured doubly reentrant surface are detected in the late evaporation period. Differences in the local concentration distribution evolution occur depending on the hydrophobicity of the surface on which the droplet is placed. For the hydrophobic surface, a nonuniform local concentration distribution exists consistently, with a high water fraction in a shell-shaped region near the liquid-air interface and a secondary concentration gradient within this shell-shaped region. The concentration distribution on the nanostructured doubly reentrant surface evolves in a more complex manner, with a strip-shaped region of high water fraction forming in the intermediate stage and then reorganized by rolling flow in the late stage. Finally, theoretical analysis combining PIV and AIE visualization results reveals that the variations in droplet concentration distributions on surfaces with different hydrophobicities exert a significant impact on evaporative behaviors. These behaviors, in turn, affect the evolution of the local concentration distribution.

Numerical Study on Characteristic Positions and Transition of Flow Patterns in a Slab Continuous Casting Mold

The flow pattern in an opaque mold cannot be readily visible, and worker experience plays a major role in controlling it, even though it has a significant impact on slab quality in a continuous casting (CC) mold. An Eulerian–Eulerian two‐fluid model is used to comprehensively study the two‐phase flow of argon and molten steel in a slab CC mold. The positions of vortex centers in upper/lower recirculation zones and the impingement point of jet flow on the narrow face of mold are identified and their distribution is analyzed. The interactive effects of casting speed, argon flow rate, and immersion depth of the submerged entry nozzle (SEN) on the flow pattern inside the mold are revealed. 2D and 3D flow pattern regimes are plotted and the boundary lines and boundary surfaces are fit with exponential functions and ternary functions, respectively. To obtain a double roll flow in the slab CC mold investigated, the relation among argon flow rate (), casting speed (), and the immersion depth of the SEN () should satisfy, .

Effects of inclination angle on Rayleigh–Bénard convection under non-Oberbeck–Boussinesq approximation in air

This study employs direct numerical simulations to explore the combined effects of inclination angles (ϕ) and non-Oberbeck–Boussinesq (NOB) conditions on heat transfer and flow patterns in inclined Rayleigh–Bénard convection (RBC). The simulations, conducted in air, classify flow behavior into seven regimes based on roll number and flow state. Heat-transport efficiency is found to be higher in the single-roll state. The study investigates the influence of NOB and inclination on top-bottom symmetry in a fluid-filled cavity, with systematic analysis revealing complex non-monotonic behaviors of the Nusselt number (Nu) and Reynolds number (Re) under different conditions. The effects of ϕ on heat transfer are significant in the modest to moderate range of Rayleigh numbers, becoming less pronounced as these values increase. The study finds that power-law scalings of Nu and Re are sensitive to the inclination angle and robust against NOB effects for ϕ≥40∘. Moreover, in NOB scenarios, the distributions of the local thermal boundary layers (BLs) along the hot and cold walls exhibit a lack of antisymmetry. As a result, there is an obvious deviation between the hot and cold global thermal BLs, which is further influenced by the inclination angle.

Partially saturated granular flow in a rotating drum: The role of cohesion

Partially saturated granular flows are common in various natural and industrial processes, such as landslides, mineral handling, and food processing. We conduct experiments and apply the discrete element method to study granular flows in rotating drums under partially saturated conditions. We focus on varying the strength of cohesion (surface tension) and rotation rate within the modes of rolling flow and cascading flow. With an increase in surface tension, a rolling mode can possess a steeper slope and correspondingly needs a higher rotation rate to transition to a cascading. The depth of the flowing region increases with increasing cohesion, while the sensitivity is reduced for cases of high cohesion. We propose a dimensionless number CE that captures the combined effects of rotation, gravity, and cohesion on the dynamic angle of repose and flow depth. In addition, we extract statistical information on the formation of clusters within the flow. We find a power law relation between the cluster size distribution and its probability, which indicates that stronger cohesion can promote the formation of larger clusters, and we discuss how cohesion impact on flows manifested by cluster formation.

Energy stable finite element strategy for simulating spreading, sliding and rolling flow dynamics of viscoelastic droplets

Moving mesh finite element method (FEM) for simulating dynamics of viscoelastic droplets on inclined surfaces is proposed. Viscoelasticity is incorporated into the governing system employing the Oldroyd–B constitutive model. The supporting (inclined) surface is allowed to have non–homogeneous properties incorporated into the mathematical model through the generalized Navier boundary conditions (GNBC). The droplet motion (sliding and/or rolling) is handled by employing arbitrary Lagrangian Eulerian (ALE) framework. Energy balance is derived from the governing system and it is a starting point in the derivation of the numerical scheme. The overall numerical strategy is designed in such a way that a counterpart of the (continuous) energy balance holds on the discrete level. This ensures that no spurious energy is introduced into the discrete system which, in turn, guarantees the stability of the scheme in the energy norm. The framework proposed is very general and encapsulates both two and three dimensional scenarios. Numerical studies in this work focus primarily on the three dimensional scenarios since such are significantly more challenging and seem to be much scarcer in the literature. The newly proposed numerical strategy is validated on several examples to confirm the theoretical predictions. The role of viscoelasticity in the overall droplet dynamics is briefly investigated and the behaviors of Newtonian and non–Newtonian droplets are compared.

Effect of powder morphology on flowability and spreading behavior in powder bed fusion additive manufacturing process: A particle-scale modeling study

Improving the quality of the powder bed is of great interest in the powder bed fusion-based additive manufacturing (PBF-AM) process to reduce micro-defects in the final product. We investigated the influence of particle morphology on flowability and spreading behavior using a discrete element method (DEM) simulation with multi-sphere modeling. The addition of non-spherical particles effectively decreased the flowability under gravity and rotation, resulting in a transition from rolling flow to cascading flow in the rotating condition. In the powder spreading process, the quality of the powder bed was decreased by adding elongated particles, owing to the frequent force-arch formation and additional wall effect caused by strong particle interlocking. Furthermore, the high spreading velocity facilitated loose powder packing owing to the frequent force arch and wide rearrangement area. In conclusion, spherical particles with a low spreading velocity are desirable for improving the quality of the powder bed, such as packing density and surface roughness, in the PBF-AM process.

A 3D Mathematical Modeling on Meniscus Solidification and Heat Transfer in Continuous Casting Chamfered Mold of Slab

Herein, a 3D mathematical model is established to elucidate the meniscus solidification and heat transfer in the chamfered mold. The fluid flow, heat transfer, the solidification of steel, the oscillation of the mold, and the steel–slag interfacial tension are considered, and the meniscus behavior on different longitudinal sections and cross sections is discussed. Under the influence of the upper roll flow, the height of the steel level increases from submerged entry nozzle to narrow face, which affects the distribution of the oscillation mark on the surface of the shell. With the mold chamfer and two new corners, the thickness of the slag film at the corner 1 with angle of 123.7° is the largest, and the shell thickness is the smallest, which is related to the 3D profile of the meniscus near the corner. The largest heat flux is located at 10–14 mm below the initial level of liquid steel and is below 3.0 MW m−2. The heat flux at the corner 1 with small obtuse angle is the smallest on the same cross section, indicating that small obtuse angle near the corner resulted in the low heat transfer.

Pattern selection and heat transfer in the Rayleigh–Bénard convection near the vicinity of the convection onset with viscoelastic fluids

The effect of viscoelasticity on the flow and heat transport in the Rayleigh–Bénard convection (RBC), a frequently encountered phenomenon in nature and industry, in a rectangular enclosure with horizontal periodic boundary is investigated via direct numerical simulation. The working fluid is described by a finitely extensible nonlinear elastic-Peterlin constitutive model almost all important features of viscoelastic fluid flow. Numerical simulations are conducted at a low concentration β=0.9, where β=μs/μ0, μs is the solvent viscosity, and μ0=μs+μp is the sum of μs and the polymer viscosity μp. A parametric analysis is performed to understand the influence of the Weissenberg number Wi, the viscosity ratio β, and the extension length L on the oscillating mode of the viscoelastic RBC. The results indicate that both Wi and β weakly inhibit the convection onset and the transition from steady to oscillatory convection. The amplitude and frequency of the oscillations in the oscillatory flow regime are both suppressed. However, the strongly elastic nonlinearity makes the flow transition irregular and even brings about the relaminarization or lead to the convection cells traveling in the horizontal direction. The increasing extension length L induces multiple pairs of roll flow patterns at a specific setting of (Ra, Wi). Heat transport is reduced (up to 8.5%) by elasticity but still obeys the power law with Ra if the flow pattern has one pair of rolls. However, heat transfer enhancement occurs if multiple pairs of rolls are induced.

Investigation of the secondary flow by convergent–divergent riblets in a supersonic turbulent boundary layer over a compression ramp

In this paper, the effect of the secondary flow induced by convergent–divergent riblets in supersonic turbulent boundary layers over a 24° compression ramp at Mach number 2.9 is studied via direct numerical simulation. Two riblet cases with the wavelength Λ being 1.1δ and 1.65δ (δ is the boundary layer thickness) are conducted to examine their impact on the secondary rolling motion, momentum transfer, turbulent fluctuations, flow separation, and unsteady shock motion. As the flow develops over the riblet section, both the size and intensity of the secondary rolling motion tend to increase. For the riblet case with Λ/δ=1.1, a single rolling mode is observed within a half wavelength, while a pair of co-rotating vortical structures is obtained for Λ/δ=1.65. Both rolling patterns lead to an apparent spanwise variation of the flow field. The results reveal that the secondary flow contributes to the increase of both the mean momentum flux and turbulent fluctuations. By using the spanwise averaging, the mean momentum flux contributed from the dispersive stress and compressible effect caused by the secondary flow is identified. Both components appear to enhance the near-wall momentum mixing, and a larger enhancement is observed for Λ/δ=1.1, where the intensity of the secondary flow is stronger. Compared to the baseline case, the area of the separation zone at Λ/δ=1.1 and Λ/δ=1.65 is decreased by 56% and 38%, respectively. For all the cases, the low-frequency motion near the foot of the shock is observed. In comparison, the frequency of the low-frequency motion for the riblet case is two times higher than that in the baseline case, owing to the reduction of the separation area and length.

Flow patterns in Rayleigh-Benard convection with variable thermal conductivity

The letter presents a numerical study of Rayleigh-Benard convection under strong non-Boussinesq conditions caused by variable thermal diffusivity. For Prandtl number in the range [0.001,10], bifurcations between hexagonal and roll flows controlled by the Prandtl number are investigated in the vicinity of critical Rayleigh number. The impact of the non-Boussinesq effects and their strength on the transition values of Prandtl number is analyzed. New non-integral criterion to select physically realizable states of motion is deduced from a comparative study of full-scale 3D simulation and model 2D runs.

Numerical investigation of flow characteristics in a rearing tank aboard an aquaculture vessel

The mobile aquaculture vessel is expected to be a sustainable way for future nutritious food due to its mobility, potential production rates and environment preservation. The flow field in fish rearing tanks aboard the vessel is a prerequisite for fish welfare. In this paper, the flow field characteristics in an aquaculture tank was numerically investigated. The fish fitting guaranteed rate (FFGR) based on the statistical cumulative distribution probability is presented and used to analyze water flow. A typical rolling condition of an aquaculture tank from the analyses of response amplitude operator (RAO) was used for the flow field analysis. The wavelet and fast Fourier transformation on the mass averaged mean kinetic energy reveals a steady-state of the rolling flow condition after 100 oscillating periods. Statistical analysis on the water velocity indicates that the period-averaged FFGR increases with velocity. Based on the FFGR, the flow field of aquaculture vessel in rolling oscillations are evaluated for six fish species, including Atlantic salmon and Pseudosciaena crocea.

Effects of rolling motion on transient flow behaviors of gas-liquid two-phase flow in horizontal pipes

The investigation of transient flow behaviors of gas-liquid two-phase flow under ocean conditions is vital to the application of gas-liquid transport in ocean engineering area. In this paper, the gas-liquid two-phase flow numerical model of rolling horizontal pipe is established based on CFD code combined with user-defined functions (UDF). The three-dimensional rolling flow fields are simulated using the volume of fluid (VOF) model, RNG k−ε turbulence model and additional inertia force method. First, the simulation results are compared with the experimental data, which revealed a reasonable agreement. Then, the variation in transient flow behaviors by horizontal pipe (L = 2.0 m, D = 0.035 m) with varying rolling conditions (θm = 2°-6°, T = 0.5–4.0 s) and flow velocities (jG = 0.1–10.0 m/s, jL = 0.1–0.5 m/s) are investigated. The results showed that the rolling motion caused agglomeration of dispersed bubbles and gas slugs into a continuous gas column, increased the cross-sectional void fraction significantly. The variation of additional inertial force and pressure drop increased with the increase of rolling angle and the decrease of the rolling period. Compared with the rolling angle, the transient flow behaviors are more sensitive to the rolling period. In addition, as the initial gas volume fraction increased, the effects of rolling motion on the transient flow behaviors decreased gradually. These qualitative conclusions may serve as a reference for gas-liquid transport simulations under rolling conditions.

Study of the weakly-compressible SPH method for improving pressure distribution of violent fluid-structure impact flows

Abstract When a traditional Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) model is used to simulate free surface flow with a large Reynolds number, an unstable numerical calculation due to high random pressure oscillations will result, while an accurate pressure field is of vital significance for simulating violent fluid-structure interactions. Riemann-based SPH and Delta-SPH are widely used to solve this problem. In this paper, to enhance computational efficiency, the SPH method is implemented on a General Processing Unit (GPU) platform using Compute Unified Device Architecture (CUDA). Parallelized SPH programs including the standard SPH method, Riemann-based SPH and Delta-SPH are verified by a dam break model with large Reynolds number and violent deformation of free surfaces. The results show that all SPH methods can vividly reflect the whole process of splashing, rolling and backward jet flow; both the Riemann-based SPH and the Delta-SPH methods are effective in alleviating the problem of inhomogeneous pressure distribution in the simulation process; the Riemann-based SPH method has better stability even with relatively large particle spacing, and it has higher accuracy in simulating impact pressure. When the number of particles reaches 100,000, compared with a single-thread Central Processing Unit (CPU) implementation, the speedups obtained with NVIDIA Titan V with high computing cores and Quadro K2200 with low computing cores are thousands and hundreds, respectively.

Metal Flow and Defect Development in Rough Rolling on a Universal Rail Mill

Metal Flow and Defect Development in Rough Rolling on a Universal Rail Mill

Prediction on the three-dimensional spatial distribution of the number density of inclusions on the entire cross section of a steel continuous casting slab

In the current study, the LES turbulent model, heat transfer, solidification, species transport model, and discrete phase model (DPM) were coupled to investigate the three-dimensional transient flow, temperature, solidification, segregation, and inclusion transport during the slab continuous casting (CC) process. The number, size, and spatial distribution of inclusions on the entire cross section of the CC slab were successfully predicted using the coupled full solidification model, DPM, and capture criteria at the solidification front. The improved capture criteria that considering the primary dendrite arm spacing (PDAS), different forces acting on inclusions, and the critical capture speed, successfully eliminated the banded distribution characteristics of inclusions under the simple capture criterion. The prediction results were in good agreement with the detection results. Four accumulation zones of inclusions along the thickness of the CC slab were predicted, including the 1/4 thickness and 3/4 thickness from the loose side, and the layer beneath the surface of the CC slab. Two accumulation zones near the layer beneath the surface of the CC slab were issued from the double roll flow pattern in the CC strand. The probability of inclusions contacting the solidification front in the upper recirculation zone increased, increasing the entrapment rate. The accumulation zones near the 1/4 thickness and 3/4 thickness from the loose side were corresponded to the peak value of the Marangoni force on inclusions at the 1/4 thickness and 3/4 thickness from the loose side. The Marangoni force increased the probability of inclusions being pushed to the solidification front. In addition, the accumulation near the 1/4 thickness from the loose side became more severe as the diameter of the inclusions increased due to the buoyancy.

Numerical Simulation of the Fluid Flow, Heat Transfer, and Solidification in Ultrahigh Speed Continuous Casting Billet Mold

Ultrahigh‐speed casting is the most remarkable feature of billet high‐efficiency continuous casting. The transient fluid flow, heat transfer, and solidification behavior under different casting speeds, submerged entry nozzle (SEN) parameters, and mold electromagnetic stirring (M‐EMS) are investigated using a 3D transient mathematical model. The results show that a typical roll flow pattern is generated for all casting speeds, while a third small recirculation zone developed near the solidified shell at the casting speed of 6.0 m min−1. When the casting speed increases, the impact depth of the molten steel increases from 0.748 to 0.844 m, the velocity and level fluctuation at the steel/slag interface increases, the high‐temperature zone moves downward, and the shell thickness is reduced from 16.2 to 11.1 mm. As the SEN inner diameter and immersion depth increases, the impact depth increases, the velocity and level fluctuation at the steel/slag interface decreases, and the shell thickness at the mold exit is ≈11.0 mm. When the SEN immersion depth and inner diameter are 120 and 40 mm, respectively, the flow and temperature fields in the mold are the most appropriate. In addition, the M‐EMS have a great effect on the fluid flow and heat transfer behavior.

CFD Simulation of Particles Mixing and Segregation in a Rotary Coating Disk: Influence of Drag Models and Restitution Coefficient

In this paper, the dynamics of a transverse plane of a rotary coating disk of a binary mixture system comprising sand and urea particles were simulated using the two-fluid model along with the kinetic theory of granular flow in Fluent 19.1. Although some parameters relating to the material properties and size of the rotary coating disk have been researched, the effects of both drag force and restitution coefficient on the flow characteristics have yet to be examined. Thus, this paper numerically examines the effect of the inclusion of drag models and particle-particle restitution coefficients on particle dynamics in a rotary disk operating in the rolling regime of the granular bed. Three particle-particle drag models were considered: the Schiller-Naumann, Syamlal-O’Brien, and Gidaspow. The Syamlal-O’Brien and Gidaspow models were both able to successfully simulate particle segregation in a perfect rolling regime, whereas the Schiller-Naumann drag model appeared to be unable to predict the segregation of the particles and the rolling flow regime under the assumed conditions. Four different values of the restitution coefficient were also investigated: 0.7, 0.8, 0.9, and 0.95. The higher restitution values of 0.9 and 0.95 were found to substantially affect flow characteristics, ensuring suitable rolling regime behaviour for the bed during the rotational movement. The lower restitution coefficients of 0.7 and 0.8, on the other hand, indicated that irregular velocity vectors could be obtained in the active region of the granular bed.

URANSE-Based Numerical Prediction for the Free Roll Decay of the DTMB Ship Model

In the present study, Computational Fluid Dynamics (CFD) is used to investigate the roll decay of the benchmark surface combatant DTMB-5512 ship model appended with bilge keels, sailing in calm water at different speeds (Fr = 0.0, 0.138, 0.2, 0.28 and 0.41) and with different initial roll angles. The numerical simulations are carried out using the viscous flow solver ISIS-CFD of the FINETM/Marine software provided by NUMECA. The solver uses the finite volume method to build the spatial discretization of the transport equation to solve the unsteady Reynolds-Averaged Navier–Stokes equations. Two-phase flow approach is applied to model the air–water interface, where the free surface is captured using the volume of fluid method. The closure to turbulence is achieved by making use of the blended Menter shear stress transport and the explicit algebraic Reynolds stress models. First, a systematic validation against the experimental data at medium speed and initial roll angle of 10° are performed; then, the effect of the initial roll angle and ship speed is later studied. Numerical errors and uncertainties are assessed using grid and time step convergence study based on Richardson Extrapolation method. A special focus on the flow in the vicinity of the bilge keels during the simulation is also investigated and presented in the form of velocity contours and vortical structure formations. The resemblance between the CFD results and experimental data for roll motion and flow characteristics are within a satisfactory congruence; however, some discrepancies are recorded for the over predicted roll amplitudes in the second and, sometimes, the third roll cycle, which appeared mostly in the cases with high initial roll angles.

Flow Field in Slab Continuous Casting Mold with Large Width Optimized with High Temperature Quantitative Measurement and Numerical Calculation

In this paper, the rod deflection method was applied to quantitatively measure velocity near the mold surface at high temperatures and the k-ε model coupled with a discrete phase model (DPM) was adopted to simulate the flow field in the mold. The calculated results match very well with the measured results under all the present conditions. Under the conditions of the large mold width of 1800 mm, 1.1 m/min casting speed and 140 mm submerged entry nozzle (SEN) immersion depth, the velocity near the mold surface decreases with increasing the argon gas flow rate. When the argon gas flow rate is 6 L/min, the flow pattern is the double roll flow (DRF). When the argon gas flow rate is increased to 10 L/min and 14 L/min, the flow pattern is the single roll flow (SRF), and the risk of slag entrainment increases. With an argon gas flow rate of 10 L/min, and an immersion depth of 160 mm, the velocity near the mold surface sensitively increases with increasing the casting speed. When the casting speed is 1.1 m/min, an intermediate flow (IF) is formed with the intensified mold surface fluctuation, which can easily result in slag entrainment defects. When the casting speed is only increased to 1.2 m/min, the velocity near the mold surface changes drastically and is close to the upper limit velocity of 0.4 m/s. When the casting speed is 1.1 m/min, and the argon gas flow rate is 10 L/min, the velocity near the mold surface is obviously increased with increasing the immersion depth. When the immersion depth of the nozzle increases from 140 mm and 160 mm to 180 mm, the flow pattern changes from SRF or IF to DRF. When the bottom shape of the SEN changes from mountain to well, the velocity near the mold surface decreases. We suggest adopting the well-bottom nozzle to reduce the risk of slag entrainment.