Transitional Flow Research Articles

Numerical investigation of flow patterns in cuttings transport for extended-reach horizontal wells with rotation drillpipe

During the drilling process of extended-reach horizontal wells, the formation of the cuttings bed at the bottom of the wellbore is prone to cause drilling sticking and pump accidents. A coupled method of Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) is used here to study the flow patterns and transition of cuttings transport. Firstly, the model is validated with experimental results, which shows a good agreement. Then, the impact of the rotation speed, eccentricity, and conveying velocity on cuttings flow pattern are analyze. The total Reynolds number is introduced here to established a curve with dimensionless pressure drop, which divides the parameter interval of each flow pattern, and the change rule of cuttings flow pattern is also revealed. This study will establish a theoretical foundation for enhancing borehole cleaning efficiency and hold practical significance in guiding the drilling field construction of extended-reach wells.

Comparative Study of Air–Water and Air–Oil Frictional Pressure Drops in Horizontal Pipe Flow

Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore. Experiments were carried out over a wide range of flow conditions of superficial liquid and gas velocities that were varied from 0.05 to 1.5 m/s and 2 to 23 m/s, respectively. Pressure drops were measured using pressure transducers and a differential pressure (DP) cell. A hitherto unreported finding was achieved, as the pressure drop in air–oil flow can be lower than that in air–water flow for the higher range of flow conditions. Using flow visualization to explain this phenomenon, it was found that it is related to the higher liquid holdup that occurs in the case of air–oil around the annular flow transition and the resulting interfacial friction. This additional key finding can have applications in flow assurance to improve the efficiency of oil and gas transportation in pipelines. Models and correlations from the open literature were tested against the present data.

EFFECT OF INNER BOUNDARIES GEOMETRY ON NATURALCONVECTION HEAT TRANSFER IN HORIZONTAL ANNULI

An analytical modeling of natural convection in physically-based analysis is developed for investigate free convective heat transfer in horizontal eccentric annulus between a circular outer cylinder and heated different shape inner envelope with used four models of the shapes of the inner cross section of (circular, triangular, square and hexagon inner boundary). The main objective of this paper was taking a composite model based on asymptotic solutions for three limiting cases: pure conduction, laminar boundary layer convection and transition flow convection. Laminar conditions up to Rayleigh number RaPi of 5×104 were investigated. By using data from MATLAB simulations for a wide range of two cylinder temperature difference in order to study the effects of annulus diameter ratio, Rayleigh number, and the cross section geometries of inner cylinder on the Nusslte number and the ratio of thermal conductivity. The numerical result illustrated for the circular the increasing the Rayleigh number leading to slightly increasing the non-dimensional Nusslte number with various value of annulus diameter ratio and when used the high annulus perimeter ratio (Po/Pi( about (4.5,2.6,1.6 and 1.175). There is rapid increasing in the non-dimensional ratio of thermal conductivity with increasing the Rayleigh number at the high values of (Po/Pi(, and the result showed that the non-dimensional ratio of thermal conductivity and the Nusslte number values of the (triangular, square and hexagon) less than in the case of circular inner boundary, but the hexagon model showed the Nusslte number more that than in the (triangular and square). the mathematical results compared with model developed by pervious numerical the model and data are in good agreement, with an average RMS difference of 10.6% for the circular annulus of dimensional Nusselt number (NuPi) and less than 4.9 % and 9.8% for the square inner geometry non-dimensional ratio thermal conductivity.

Chain Recurrence and Selgrade’s Theorem for Affine Flows

AbstractAffine flows on vector bundles with chain transitive base flow are lifted to linear flows and the decomposition into exponentially separated subbundles provided by Selgrade’s theorem is determined. The results are illustrated by an application to affine control systems with bounded control range.

Turbulence generation in the transitional wake flow behind a sphere

Turbulence generation in the transitional flow in the wake behind a sphere is studied with numerical simulations. The filtered Navier–Stokes equation and the large eddy simulation method are employed as the governing equation and the numerical method, respectively. The ΩR̃ vortex identification method is used to trace the evolution of vortices in the wake flow. The energy gradient theory is used to analyze the spike formation in the wake flow. The simulation results show that the vortex structure in the wake flow is the type of hairpin vortices, which is similar to that in a boundary layer flow. Ejection and sweep motions exist around the hairpin vortices. There are two most unstable regions in the wake where turbulence “burst” is first produced, one is near the center of the vortex head and the other is between the two vortex legs. There is a high-pressure zone above the vortex head due to the decrease in the streamwise velocity, and a soliton-like coherent structure exists in this area. The mechanism of turbulence generation in the wake is the discontinuity of the streamwise velocity, which makes the Navier–Stokes equation be singular. This singularity leads to the formation of the “negative spike” in the streamwise velocity. The amplitude of the “negative spike” reaches up to 60% of the incoming velocity, which is close to the situation in a boundary layer flow on a flat plate. It is concluded that the mechanism of turbulence generation in the wake flow is the same as that in the boundary layer flow.

Exploring the boundary layer transition of hypersonic flow over a compound delta wing

The boundary layer transition on a compound delta wing for Mach 6 has been studied experimentally and numerically. The experiment was performed at Peking University quiet wind tunnel using the Rayleigh scattering flow visualization and infrared thermography. Direct numerical simulations, under the same flow conditions, are applied to analyze the transition mechanism. The results show that the traveling cross flow vortices first appear near the leading edge of compound delta wing. These vortices modulate the mean profile of the flow due to which a rope-like structure appear in the streamwise direction, which is typical of Mack's second-mode. As Mack's second-mode grows to a sufficiently large amplitude, it triggers secondary instability, which behaves as secondary finger like structures. At the end of the transition process, low-frequency waves are excited by Mack's second-mode through an interaction mechanism with their phase speed approaching each other. It is also found that increasing the unit Reynolds number greatly promotes the aerodynamic heating as well as local hot streaks appear on both sides of the compound delta wing in the streamwise direction. The appearance of hot streaks on the compound delta wing is strongly correlated with Mack's second-mode.

Influence of magnetic field on dynamic behavior of double-diffusive convection

Double-diffusive convection under an external magnetic field has several industrial applications, and how the magnetic field affects flow and heat and mass transfer is a research focus. This paper studies the dynamical behavior of two-dimensional double-diffusive convection in a uniform magnetic field is investigated using a high-accuracy numerical method. The effects of the magnetic field strength on the flow and on the heat and mass transfer are analyzed, and the process of flow transition in the presence of a magnetic field is studied. The results show that, as the strength of the magnetic field increases, the flow is gradually inhibited, and most of the heat transfer occurs through conduction. For a fixed magnetic field strength, the temperature-dominated flow changes from periodic to chaotic, and finally back to periodic, as the orientation of the magnetic field increases. Two types of periodic flow occur in the transition route, namely, a simple periodic flow with an integer multiple of the fundamental frequency and a complex periodic flow with multiple lower-frequency subharmonic waves. In the presence of a strong magnetic field, the effect of the magnetic field orientation on the flow is significant. At high Rayleigh numbers and a fixed magnetic field strength, the heat transfer efficiency of a vertical magnetic field surpasses that of a horizontal magnetic field by approximately 50% when temperature is dominant, achieving a mass transfer efficiency of about 100%. In cases when concentration is dominant, the heat transfer efficiency of a vertical magnetic field is 20% higher than that of a horizontal magnetic field, and the mass transfer efficiency is approximately 60% higher for the vertical magnetic field compared to the horizontal magnetic field. The flow transitions from chaotic or periodic to steady as the Prandtl number increases. The solution branch bifurcates at certain Prandtl numbers, and hysteresis appears when Prandtl number is equal to 0.023. For low Rayleigh numbers, the heat and mass transfer efficiencies increase monotonically with increasing Prandtl number under a weak magnetic field but remain constant for various Prandtl numbers under a strong magnetic field.

The evolution of second harmonic waves in oblique transition

The evolution of second harmonic waves in oblique transition

The architecture of basalt reservoirs in the North Atlantic Igneous Province with implications for basalt carbon sequestration

Abstract Offshore CO 2 sequestration in basaltic formations of the North Atlantic Igneous Province may allow permanent storage of large volumes of CO 2 through rapid carbonate mineralization. Characterizing the internal architecture of such reservoirs is key to assessing the storage potential. In this study, six photogrammetry models and three boreholes on the Faroe Islands have been used to characterize the internal lava sequence architectures as a direct analogue to potential offshore North Atlantic Igneous Province storage sites. The studied formations are dominated by c. 5 to 50 m thick simple and compound lava flows, with drill core observations documenting a transition from pāhoehoe moving towards ‘a’ā lava flow types interbedded with thin (<5 m thick) volcaniclastic rock units. The identification of flow margin breccias is potentially important as these units form excellent reservoirs in several other localities globally. Stacked, thick simple flows may present sealing units associated with dense flow interiors. Connected porous and permeable lava flow crusts present potential reservoirs; however, the degree of secondary mineralization and alteration can alter initially good reservoir units to impermeable barriers for fluid flow. Large-scale reservoir volumes may be present mainly within both vesicular, fractured pāhoehoe and brecciated flow margins of transitional simple lava flows.

Tollmien–Schlichting waves in the subsonic regime

AbstractThe Tollmien–Schlichting (T‐S) waves play a key role in the early stages of boundary layer transition. In a breakthrough work, Grenier, Guo, and Nguyen gave the first rigorous construction of the T‐S waves of temporal mode for the incompressible fluid. Yang and Zhang recently made an important contribution by constructing the compressible T‐S waves of temporal mode for certain boundary layer profiles with Mach number . In this paper, we construct the T‐S waves of both temporal mode and spatial mode to the linearized compressible Navier–Stokes system around the boundary layer flow in the whole subsonic regime , including the Blasius profile. Our approach is based on a novel iteration scheme between the quasi‐incompressible and quasi‐compressible systems, with a key ingredient being the solution of an Orr–Sommerfeld‐type equation using a new Airy–Airy–Rayleigh iteration instead of Rayleigh–Airy iteration introduced by Grenier, Guo, and Nguyen. We believe that the method developed in this work can be applied in solving other related problems for subsonic flows.

Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

The numerical investigation focuses on the flow patterns around a rectangular cylinder with three aspect ratios ( $L/D=5$ , $10$ , $15$ ) at a Reynolds number of $1000$ . The study delves into the dynamics of vortices, their associated frequencies, the evolution of the boundary layer and the decay of the wake. Kelvin–Helmholtz (KH) vortices originate from the leading edge (LE) shear layer and transform into hairpin vortices. Specifically, at $L/D=5$ , three KH vortices merge into a single LE vortex. However, at $L/D=10$ and $15$ , two KH vortices combine to form a LE vortex, with the rapid formation of hairpin vortex packets. A fractional harmonic arises due to feedback from the split LE shear layer moving upstream, triggering interaction with the reverse flow. Trailing edge (TE) vortices shed, creating a Kármán-like street in the wake. The intensity of wake oscillation at $L/D=5$ surpasses that in the other two cases. Boundary layer transition occurs after the saturation of disturbance energy for $L/D=10$ and $15$ , but not for $L/D=5$ . The low-frequency disturbances are selected to generate streaks inside the boundary layer. The TE vortex shedding induces the formation of a favourable pressure gradient, accelerating the flow and fostering boundary layer relaminarization. The self-similarity of the velocity defect is observed in all three wakes, accompanied by the decay of disturbance energy. Importantly, the decrease in the shedding frequency of LE (TE) vortices significantly contributes to the overall decay of disturbance energy. This comprehensive exploration provides insights into complex flow phenomena and their underlying dynamics.

Characterization of the Macroscopic Impact of Diverse Microscale Transport Mechanisms of Gas in Micro-Nano Pores and Fractures

The objective of this study is to construct a refined microscopic transport model that elucidates the transport mechanisms of gas flow within micro-nano pores and fractures. The collective impact of various microscopic transport mechanisms was explained through the apparent permeability model, specifically related to gases such as methane and carbon dioxide, within the shale matrix. The apparent permeability models, taking into account microscopic transport mechanisms such as slippage flow, Knudsen diffusion, transition flow, and surface diffusion, were established individually. Subsequently, the influencing factors on apparent permeability were analyzed. The results demonstrate that the apparent permeability of the shale reservoir matrix is significantly influenced by pore pressure, temperature, pore size, and total organic carbon (TOC). As pressure decreases, the apparent permeability of Knudsen diffusion and surface diffusion increases, while the apparent permeability of slippage flow decreases. In addition, the apparent permeability of the reservoir matrix initially decreases and then increases. With increasing temperature, the apparent permeability of slippage flow, Knudsen diffusion, and surface diffusion all increase, as does the apparent permeability of the reservoir matrix. As pore size increases, the apparent permeability of surface diffusion and Knudsen diffusion decreases, while the apparent permeability of slippage flow and the reservoir matrix increases. Furthermore, an increase in TOC leads to no change in the apparent permeability of slippage flow and Knudsen diffusion, but an increase in the apparent permeability of surface diffusion and the reservoir matrix. The model presented in this paper enhances the multi-scale characterization of gas microflow mechanisms in shale and establishes the macroscopic application of these micro-mechanisms. Moreover, this study provides a theoretical foundation for the implementation of carbon capture, utilization, and storage (CCUS) in shale gas production.

Impacts of aquifer heterogeneity on subsidence resulting from engineering dewatering in the Lower Yangtze River plains

Study regionLower Yangtze River alluvial plain, China. Study focusThe uneven subsidence caused by dewatering in underground engineering constructions in densely populated areas of alluvial plains with an unevenly distributed medium has caused increased concerns. This study applied the transition probability geostatistical software (T-PROGS) geostatistical models based on data from 31 boreholes to characterize a three-dimensional (3D) heterogeneous aquifer (8.8×105 m2 in area and 56 m in depth) in an underground construction area in the alluvial plain of the lower Yangtze River. The SUB model was constructed to simulate the pumping-induced subsidence processes based on a reliable MODFLOW transit flow model. New hydrological insightsThe simulation results indicated that surface subsidence increased with pumping and reached a maximum of 33 mm by the end of the extraction (the 14th day). Surface subsidence development exhibited spatial anisotropy around the pumping center, consistent with the observations. Furthermore, the proposed model indicates that hydraulic head evolution and soil compressibility distributions significantly influence the spatial–temporal development of subsidence, implying the significance of the aquifer heterogeneity. The compressible soft soil overlying the pumping section was identified as a vulnerable subsidence zone, suggesting its significance for engineering geological surveys and dewatering designs in underground construction in alluvial plains.

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.

Impact of hydraulic tortuosity on microporous and nanoporous media flow.

Using two-dimensional porous structures made up of homogeneously arranged solid obstacles, we examine the effects of rarefaction on the hydraulic tortuosity in the slip and early transition flow regimes via extended lattice Boltzmann method. We observed that modification in either the obstacle's arrangement or the porosity led to a power-law relation between the porosity-tortuosity. Along with this, we also found that in the slip-flow regime, the exponent of this relation contains the effect of finite Knudsen number (Kn). In addition, we observed that on properly scaling Kn with porosity and hydraulic tortuosity, a generalized correlation can be obtained for apparent permeability.

Laminar to turbulent transitions of pipe flows by resonances of natural frequencies of components of test sections

This investigation analyses special papers and doctoral theses that treat transitions of pipe flows as a resonance phenomenon of wave frequencies. These frequencies are natural frequencies of pipe flows, of components of the test section and of vortex ring formations. Resonance conditions are derived that show how the critical Reynolds number, Rec , depends on the volume of the plenum chamber, the pipe diameter, the pipe length, etc. The derived resonance relations were verified experimentally using the experimental data of the third author, yielding R e c ∼ 1 / V ple , R e c ∼ 1 / ( L D ) and other interesting results. These findings suggest that the laminar-to-turbulent transition has various modes and transitive dependences. To understand this fully, it is necessary to take all components of the test section involved into account. The test section considered in this paper consists of a mass flow controller to supply the airflow and a plenum chamber, followed by the actual pipe of interest. It is shown that all the components can contribute to the measured value of the critical Reynolds number of pipe flow transition.

Laminar Separation Control for Eppler 387 Airfoil Based on Resolvent Analysis

By actively controlling laminar separation, the aerodynamic loading can be increased. In the context of turbomachinery, an increased loading allows for more power to be extracted or for a lower part count. Active flow control can be made more effective and efficient if the actuator location and forcing frequency are chosen well. Large-eddy simulations of the flow over an E387 airfoil were carried out for a chord Reynolds number of 100,000. For an angle of attack of zero degrees, the suction-side boundary layer separates laminar to form a large separation bubble. With 1% freestream turbulence intensity, the boundary layer reattaches earlier, and the length of the separated region is in better agreement with available measurements. A resolvent analysis suggests that forcing immediately upstream of separation with an angular frequency of 50 (based on freestream velocity and chord length) provides the maximum forcing-response gain. Guided by the resolvent analysis, active flow control by wall-normal blowing and suction was then investigated in the simulation. Forcing introduces laminar, two-dimensional “rollers” that effectively suppress separation. Without freestream turbulence, transition occurs close to the trailing edge. With freestream turbulence, the flow transitions further upstream and active flow control is less effective.

An improved laminar–turbulent transition cavitation model using the IDDES method

Prediction of the detachment positions of sheet cavitation remains an unsolved problem, being not only dependent on local pressure but also closely related to the boundary layer transition. For hydrofoils, traditional cavitation models tend to predict premature cavity detachment positions. In the study reported here, to obtain cavity detachment positions that match experimental results, improvements are made to both turbulence models and cavitation models. A scale-resolving transition turbulence model is established by incorporating transport equations to represent boundary layer transition that are based on the improved delayed detached eddy simulation (IDDES) method. The intermittency γ, representing the probability of turbulence at a specific point in space, is introduced into the homogeneous cavitation model to account for the influence of the laminar–turbulent transition on the sheet cavitation detachment position. Numerical results show that the IDDES-based transition turbulence model combines transition and scale-resolving capabilities. The improved turbulence transition cavitation model proposed here is shown to be able to accurately predict the detachment position of sheet cavitation around two-dimensional hydrofoils and a typical axisymmetric ITTC body.

Aerodynamic and Aeroacoustic Effects of Different Transition Mechanisms on an Airfoil

The paper delves into the detailed sound generation and propagation mechanisms associated with tripping-induced flow perturbations and trailing-edge scattering using wall-resolved large-eddy simulations. Two distinct boundary-layer tripping techniques, namely a geometrically resolved stair strip and an artificially modeled trip using suction and blowing, are investigated. To facilitate comparison, the natural boundary-layer transition is also simulated as a baseline scenario. The analysis takes into account a Reynolds number of 4×105, a Mach number of 0.058, and a nonzero angle of attack of 6.25° over a NACA 0012 airfoil configuration. The mechanisms for sound generation and propagation related to trailing-edge noise remain consistent across the three transition scenarios. However, boundary-layer tripping notably leads to intricate, scenario-specific noise generation: there is an interaction between the laminar separation bubble and tripping for the stair strip case, whereas laminar boundary-layer instability is evident for the suction and blowing scenario. Aerodynamic flowfields involving acoustic noise sources, their propagating natures near the wall, and far-field acoustics are cross-examined in detail. The comprehensive analysis of observed phenomena provides valuable insights for understanding nonlinear flow and acoustic interactions relevant to airfoil noise and designing new types of trips under adverse pressure gradient flows.

Gas Kinetic Scheme Coupled with High-Speed Modifications for Hypersonic Transition Flow Simulations.

The issue of hypersonic boundary layer transition prediction is a critical aerodynamic concern that must be addressed during the aerodynamic design process of high-speed vehicles. In this context, we propose an advanced mesoscopic method that couples the gas kinetic scheme (GKS) with the Langtry-Menter transition model, including its three high-speed modification methods, tailored for accurate predictions of high-speed transition flows. The new method incorporates the turbulent kinetic energy term into the Maxwellian velocity distribution function, and it couples the effects of high-speed modifications on turbulent kinetic energy within the computational framework of the GKS solver. This integration elevates both the transition model and its high-speed enhancements to the mesoscopic level, enhancing the method's predictive capability. The GKS-coupled mesoscopic method is validated through a series of test cases, including supersonic flat plate simulation, multiple hypersonic cone cases, the Hypersonic International Flight Research Experimentation (HIFiRE)-1 flight test, and the HIFiRE-5 case. The computational results obtained from these cases exhibit favorable agreement with experimental data. In comparison with the conventional Godunov method, the new approach encompasses a broader range of physical mechanisms, yielding computational results that closely align with the true physical phenomena and marking a notable elevation in computational fidelity and accuracy. This innovative method potentially satisfies the compelling demand for developing a precise and rapid method for predicting hypersonic boundary layer transition, which can be readily used in engineering applications.