Stagnant Zones Research Articles

Effect of Nozzle Shape on Fluid Flow and Heat Transfer characteristics of an Impinging Jet System – A Numerical Study

Impinging jet is one of the most efficient techniques to achieve a high heat transfer coefficient and is used in many engineering applications. The present study focuses on the effect of nozzle shape on fluid behavior and heat transfer characteristics. For the current investigation, circular, square, rectangular, and elliptical nozzles with identical hydraulic diameters are used with Reynolds number Re ranging from 15,000–35,000. The circular nozzle results are validated with the published numerical and experimental data. In the current study, it is found that as the Reynolds number increases, the value of the averaged Nusselt number increases in all circumstances. When examining the different nozzle shapes, the value of the averaged Nusselt number is higher when an elliptical nozzle is used. The contours of the surface Nusselt number and velocity streamlines are also presented. The contour shows that the heat flux is highest in the stagnation zone and gradually decreases to the sides because they are outside the impingent coverage. Moreover, the area between the jets has a low heat flux. The heat transfer in the impinging zone is initially raised as the jet-induced crossflow increases and achieves a peak value, and then reduced stream-wise because of the crossflow effect.

ИССЛЕДОВАНИЕ ВЕТРОВОГО РЕЖИМА СУЩЕСТВУЮЩЕЙ ЖИЛОЙ ЗАСТРОЙКИ В УСЛОВИЯХ ЖАРКОГО КЛИМАТА

The article focuses on the microclimate of dense residential buildings in a hot climate and ensuring the wind comfort of people there. It considers the aeration of a complex built up with high-rise and low-rise residential and public buildings. The numerical simulation method is used in the ANSYS Discovery Live software package. The paper presents the analysis of the comfort of the wind regime on the territory of the residential complex with the allocation of aeration zones according to wind speed and gives recommendations to reduce stagnant aeration zones. It also considers the aeration of a residential complex improved by the installation of wind screens. The results obtained and the revealed patterns will help to better assess the architectural and planning solutions of residential buildings, including buildings within existing districts, in terms of the comfort of people staying in these territories.

Wind influence on the spent nuclear fuel safety in dry cask storage

This article examines the effect of wind load on the safety of spent fuel storage in a naturally ventilated building. To assess the influence of wind influences characteristic of the Akkuyu NPP site on the temperature of fuel rod cladding, a CFD model of the spent fuel storage building was developed. Reynolds-averaged governing equations of motion (RANS model) with a k-ε turbulence model were used. Computational grid included about 17 million cells. The CFD model allowed us to study different directions and intensities of wind loads, estimate the temperature around the containers and identify stagnant zones. Based on the modeling results, the dependences of the influence of wind load on the thermal fields in the building were obtained. These dependencies allowed for design decisions to be made that guaranteed safety and ensured the continuation of construction of the building.

ABOUT SOME PROBLEMS OF WATERFLOODING IN CARBONATE RESERVOIRS

The features of waterflooding of carbonate (fractured-porous) rocks, caused by the interaction of the system of fractures with the matrix (blocks) of the rock, are considered. It is shown that the slower propagation of the pressure pulse in the rock matrix in comparison with the propagation of this pulse along the fracture system of the formation leads to compression of the rock blocks in the near-wellbore zone of the injection well, as a result of which stress concentration occurs at the ends of vertical fractures, which increases the likelihood of these fractures growing into the roof of the productive formation. It is shown that in order to prevent the development of this process, the growth rate of water injection pressure should be limited in accordance with the time of liquid pressure equalization in the pore space of the rock matrix and in the fracture system. When developing production wells drilled in fractured porous media, in order to prevent the development of the process of closing fractures in the bottomhole zones of these wells, the drawdown reduction rate must also be limited in a similar way. It is noted that when applying technologies for non-stationary flooding of productive reservoirs, the main factor determining their effectiveness is the change in the direction of filtration flows in the reservoir. This leads to the activation of filtration processes in the stagnant zones of the formation and the intensification of the processes of capillary impregnation of low-permeability interlayers with water from more flooded highpermeability interlayers.At the same time, it is important to take into account that when changing the direction of filtration flows at a late stage of development of carbonate reservoirs, in order to prevent reimpregnation of hydrophobic rock blocks with oil, it is more expedient to change the operating modes of production rather than injection wells. It is shown that water flooding of hydrophobic carbonate reservoirs results in incomplete water displacement of oil as a wetting phase from rock blocks. To reduce the residual oil saturation of rock blocks, it is advisable to increase the displacement pressure gradient in the reservoir in combination with a change in the direction of filtration flows in it.

The evolution of the compaction process and the deformed state of porous blanks during their hot forging in the open die

The article presents the results of the study of the evolution of the deformed state of the workpieces, the energetic parameters of the process and the distribution of porosity over the volume of the forging at all stages of hot forging of porous powder forgings in an open die. Modeling of the process was carried out using the finite element method using the DEFORM 2D/3D software complex. As a result of the simulation, it was found that at the initial stage of the process, the blank is mainly compacted with minimal radial flow of the material. Noticeable flow of metal into the groove groove area begins only when the forging material reaches an average relative density exceeding 90%. A significantly different nature of the distribution of axial er and radial ez deformations over the volume of the forging was noted. A zone with increased levels of values of axial deformations is formed in the central layer of the forging, equidistant from the upper and lower surfaces of the die cavity, and the values of radial deformations decrease with distance from the zone bordering the free side surface of the workpiece in the radial (to-center) direction. The minimum values of ez and er appear in the upper and lower angular stagnant zones of the forging. It is shown that the graph of the dependence of the deformation force on the displacement of the punch is marked by the presence of at least three characteristic sections due to the relationship between the processes of compaction and forging shape change at each stage of the process.

The force and dynamic response of low-velocity projectile impact into 3D dense wet granular media

The presence of liquid bridges between particles in a wet granular media gives rise to capillary forces at the microscopic scale that dramatically alters the material's microstructure and macroscopic responses. Previous experimental studies show significant differences in the penetration depth of the projectile into assemblies of dry or wet particles. Still, there is a lack of fundamental understanding of the difference induced by the presence of liquid bridges in dynamic regimes. In this study, the contact model parameters of wet glass beads are calibrated employing the angle of repose tests and cylinder lifting tests, and a series of three-dimensional discrete element method simulations of spheres impact into wet granular packings are conducted. The dynamic characteristics of the projectile are obtained numerically and found to be in good agreement with the experimental data. The analyses indicate that the final penetration depth in the wet granular media is linearly related to the initial velocity and has a power function relationship with the impact energy. The generalized Poncelet law is suitable for wet granular materials, but the presence of liquid significantly affects the values of the parameters. There is a velocity “stagnation zone” at the initial stage of the wet granular impact, and the final penetration depth and the duration interaction time are smaller than that of the dry case. The difference can be attributed to the resistance evolution of the projectile exerted by particles and gives the parameter scaling law of the peak impact force. Further, a macro-micro transition technique is employed to characterize the velocity field, pressure field, and stress field inside the wet granular media and the spatial distribution is quantified based on stress theory.

JUSTIFICATION OF THE DESIGN AND TECHNOLOGICAL PARAMETERS OF THE ROTOR MIXER OF PERIODIC ACTION COMBINED FEED

The last stage of preparation of fodder mixtures is mixing of components with the help of special devices - mixers of continuous or periodic action. From the point of view of zootechnics, it is important not only to include in the fodder mixture the components provided for by the diet in the required ratio, but also to ensure an even distribution of all components throughout the volume of the mixture. The homogeneity of the mixture ensures the same nutritional value of the feed in all parts of its volume. Currently, when creating a new generation of mixers for dry fodder mixtures, preference is given to rotating mixers. The advantages of mixers of this type compared to stationary intermittent mixers of any type are: a reduction in feed unloading time, a fully automated chamber cleaning cycle, the absence of stagnant zones and rubbing parts. The purpose of the research is to determine the rational structural and technological parameters of the intermittent rotary mixer and to study the change in the homogeneity of the mixture when varying their values. Research was conducted in two stages: numerical modeling and experimental research. Numerical simulation was implemented in the Simcenter Star-CCM+ software package. As research factors, we accept the following parameters: angle of inclination of the blade α (0 °, 45 °, 90 °), mass of material m (0.1 kg, 0.2 kg, 0.3 kg), rotation frequency n (30 rpm min, 60 rpm, 90 rpm), mixing duration t (1 min, 3 min, 5 min). Experimental studies were carried out on a laboratory installation of a periodic rotary mixer. As a result of numerical modeling and experimental studies of the mixing process in a rotary mixer of batch feed, the dependences of the change in the homogeneity coefficient of the mixture in the mixer h on the angle of inclination of the blade α, the mass of the material m, the rotation frequency n, and the duration of mixing t were established. By fulfilling the condition of maximizing the homogeneity of the mixture in the Wolfram Cloud software package, the rational parameters of the rotary compound feed mixer of periodic action were obtained: α = 50.5 °, t = 4.415 min., m = 0.11 kg, n = 43.9 rpm. At the same time, the homogeneity coefficient is h = 0.98.

Insights into the thermal characteristics and dynamics of stagnant blood conveying titanium oxide, alumina, and silver nanoparticles subject to Lorentz force and internal heating over a curved surface

Abstract It is very significant and practical to explore a triple hybrid nanofluid flow across the stuck zone of a stretching/shrinking curved surface with impacts from stuck and Lorentz force factors. The combination (Ag–TiO2–Al2O3/blood) hybrid nanofluid is studied herein as it moves across a stagnation zone of a stretching/shrinking surface that curves under the impact of pressure and Lorentz force. Exact unsolvable nonlinear partial differential equations can be transformed into ordinary differential equations that can be solved numerically by similarity transformation. It was discovered that predominant heat transfers and movement characteristics of quaternary hybrid nanofluids are dramatically affected. Numerous data were collected from this study to illustrate how parameters of flow affect the temperature, velocity, heat transmission, and skin friction characteristics. The axial and radial velocities for both fluids (Newtonian and ternary hybrid nanofluid) are increased due to the increasing function of the curvature parameter, magnetic field, and suction parameter. Additionally, the direct relationship between the temperature and heat transfer decreases the heat transfer rate by the curvature parameter, magnetic field, suction parameter, Prandtl number, and heat source/sink. The higher the values of the curvature parameter, the higher the shear stress and velocity.

Flow and thermal behavior of solar air heater with grooved roughness

A simple and eco-friendly solar air heater (SAH) converts renewable solar energy into useful thermal energy. The implementation of roughness on the absorber plate of a solar air heater improves its air heating capability. The hot air thus produced is used in different applications such as agricultural, dairy, food processing, and cement industries. Towards that, a 2D numerical study is carried out with rectangular groove as a roughness with the RNG k−Ɛ turbulent model. The study has been carried out to find a SAH with higher performance. Two thermodynamic models are adopted to identify and qualify the best channel. The performance of the best SAH channel has been identified by the highest thermal enhancement factor (TEF) and to increase the exergetic ratio (Ɛth). A detailed study of introducing rectangular groove on heat transfer, pressure drop, thermal enhancement factor (TEF) and exergetic ratio (Ɛth) is conducted, by varying the geometrical parameters of rectangular grooves in the range of Re from 7000 to 17000. Geometrical parameters such as relative length (α), relative pitch (β) and relative height (λ) are varied in the range of 0.0067–0.040, 0.0333 to 0.10, and 0.1 to 0.5, respectively, to optimize the performance of the SAH. Higher exergetic ratio is found around the same parametric values where we get the highest TEF value. The maximum TEF is found around 1.455 at α = 0.020, β = 0.0667, and λ = 0.30 at Re of 17000 and the corresponding exergetic ratio is found around 0.9949. The length of the groove is found to augment both heat transfer and pressure drop of the solar air heater due to increased disruption of thermal and hydrodynamic boundary layers. Rate of augmentation of heat transfer decreases in case of α≥ 0.0333 due to formation of an additional stagnant zone inside the groove. The flow and thermal analysis shows that although local heat transfer within the rectangular groove is less, the rectangular groove improves the channel's overall heat transfer. Convective heat transfer coefficient is found relatively higher where there is a change in shear stress gradient.

Improving leading edge cooling through transpiration with partitioned porous injectors and a jet

This study proposes a novel transpiration cooling layout that improves the cooling effect in the stagnation region and downstream zones for a sharp leading edge. Large-eddy simulation is conducted using our in-house recursive-regularized thermal lattice Boltzmann method (RR-TLBM) and high-resolution grids with 2.33 × 108 nodes. The RR-TLBM method shows low numerical dissipation, which is crucial in studying the transpiration-cooled leading edge with small-scale flow structures. A proper size of transpiration area in a single porous injector can extend the effective cooling area, with about 62.2 % of the wall area cooled at the same coolant consumption. Moreover, the opposing jet can reduce the local heat flux in the stagnation region, especially for the sharp leading edges. The proposed combinational cooling method shows an improvement of about 20 % in the cooling performance of the stagnation zone, while there is a 25 % improvement downstream of the stagnation region when compared to that of the porous layout with partitioned injectors. Furthermore, turbulent mixing can impair the improvement in cooling performance downstream, and the extended effective cooling area is related to low turbulent fluctuation. The RR-TLBM solver shows great potential in capturing the 3D coherent structures in the transpiration-cooled leading edge, based on high-resolution grids and a desktop-level computer with three Tesla V100 graphics processing units (GPUs).

The Influence of Supply Channel Design on the Gas-Dynamic Structure of Air Flow in a Vertical Conical Diffuser

Vertical conical diffusers are used in power engineering, chemical industry, technological processes, and other industries. The efficiency of many machines and pieces of equipment is determined by the gas-dynamic and heat-exchange perfection of processes in diffusers. This study assesses the influence of the air supply method on flow structure in a diffuser. The studies were carried out on a test bench with thermal imaging for air flow rates ranging from 0.018 to 0.057 m3/s (42,500 < Re < 150,000). Two designs were examined: (1) a conventional air supply through one channel from below and (2) a nozzle air supply through four tubes at an angle of 45° to the vertical axis. In addition, the influence of the cross-sectional shape of the supply channels of both designs was studied. It is established that the use of a conventional air supply through one channel leads to the generation of a pronounced central flow along the vertical axis (all configurations of the supply channel) and the creation of stagnant zones in the corners of the diffuser (round and triangular channels; the use of a square supply channel causes the most uniform air distribution throughout the entire volume of the diffuser (while maintaining the central flow). It is found that with nozzle air supply, there are no stagnant zones in the corners and intense air movement generation in the centre of the diffuser (round and triangular tubes) can be observed; the use of square nozzle tubes causes intense flow movement at the base of the diffuser, which quickly collapses upstream, uniformly filling the entire volume of the diffuser’s cylindrical part. The presented data can be useful for designing various machines and pieces of equipment with vertical conical diffusers.

Simulation of Illumination and Wind Conditions for Green and Fed Cities Using CFD Software

To avoid ecological catastrophe, most cities are moving toward green building. The critical component is greening – conventional and green structures. Urban agriculture is a very prospective direction. Green roofs, terraces, and rooftop greenhouses are the most promising places for growing. This solves multiple tasks: heat loss recovery for planting (for rooftop greenhouses), additional thermal insulation, optimized logistics, increasing pollinator populations, avoiding pests, etc. In different-height districts, there are problems with natural illumination and winds. No good urban wind theory has been developed. The winds can be simulated in CFD software using a 3D model of a district. Most of the software can simulate solar radiation for thermotechnical calculations only. It should be simulated in other special software. The approach to calculating solar radiation is proposed using CFD software without additional needs. The unique "integrator" material should be added to the engineering database. Its thermotechnical properties can be set to obtain a temperature numerically equal to the exciting parameter. Application is shown in an example of a different-height building with a green roof. The results show areas most favorable for growing photophilous and shade-tolerant plants and placing cleaning and phytoncidal plants for maximum air quality in stagnation zones.

Mixture modeling to simulate helium boiling: Helium gas bubble trapped in high magnetic field

Multi-phase flow hydrodynamics is an essential theoretical foundation for modernizing engineering and is important in guiding and developing modernizing engineering. In the realm of superconducting power technology, it is imperative to submerge and cool high-field superconducting magnets and superconducting cables, constructed from superconducting materials, in cryogenic fluids in order to maintain a superconducting state. Even minor thermal disturbances can induce boiling of the cryogenic fluid, leading to a two-phase flow regime. In the case of high-field superconducting magnets, the presence of liquid helium as the cooling medium gives rise to a diamagnetic effect. Consequently, the formation of a bubble resulting from boiling is confined in close proximity to the central aperture of the magnet owing to the influence of the magnetic field force. This confinement adversely affects the heat transmission properties of the magnet. This work presents a comprehensive analysis of the flow state during the boiling process of liquid helium, using the finite element approach and the mixture model. The heat transfer in a two-phase flow is analyzed by treating the system as a single pseudo-fluid. The model is consistent with empirical formulations of liquid helium boiling in large vessels and is also suitable for modeling the effect of heating surface orientation on the critical heat flux. Consequently, the analysis of the retention of helium bubbles generated by boiling in a high-field magnet has been further examined, using this particular model. The results of numerical hydrodynamic studies show that the width of the helium bubble stagnation zone is larger compared to the results of hydrostatic calculations. This poses a major challenge for superconducting magnets operating at high magnetic fields and high temperatures. The paper further analyses the effect of supercooled liquid helium on helium bubble stagnation, thus providing valuable insight into the construction of superconducting magnets with high magnetic fields.

Effect of energy input on flotation of particles with different sizes: Perspective of hydrodynamics characteristics

By employing a torque sensor to measure energy input in a flotation machine, this paper investigates the flotation behavior of modified quartz particles with different sizes but similar surface hydrophobicity under various energy input conditions. Numerical simulations of the mechanical flotation machine were conducted to obtain the fluid dynamic characteristics including the flow velocity, turbulence kinetic energy, and turbulent eddy scale. With the flotation results and numerical simulations combined, the potential collision, attachment, and detachment behaviors of fine particles (―45 µm), intermediate particles (45―74 µm), and coarse particles (74―125 µm) were analyzed. The results demonstrate that under different conditions of energy input, the recovery of intermediate-sized particles was optimal for the above size fractions. As the particle size increases, the energy input required to achieve optimal recovery decreases. The flotation rate constants increase nearly linearly with energy input. Compared to the medium-sized particles in the range of 45―74 µm, finer and larger particles exhibit lower floatability. When the energy input exceeds a certain range, no stagnation zone is observed. The rupture of bubble-particle aggregates becomes more pronounced, which may be a reason why flotation recovery begins to decrease. Increasing energy input enhances turbulence energy dissipation and reduces the Kolmogorov turbulence length scale, in this study, the ―45 µm, 45―74 µm, and 74―125 µm particle sizes reached the optimal flotation performance at dp / η values of 1.35, 1.83, 2.54, respectively. The particle diameter-to-integral length scale ratio (dp/L) is also discussed as an important parameter for turbulent dispersion.

Multi-objective optimization of a combined heat sink with triangular protrusion and corrugated surface impinged by a nanofluid slit-confined jet

Improving temperature uniformity and heat transfer capacity is crucial for the application of a jet-impingement heat sink in dissipating heat from high-power electronic devices. Therefore, a combined heat sink with a triangular protrusion in the stagnation zone, a corrugated surface in the wall-jet zone, and an oblique angle of the upper plate impinged by a nanofluid jet is proposed. A two-dimensional model is established, using Al2O3-H2O nanofluid as coolant. The effects of the structural parameters of the heat sink, the volume fraction of the nanofluid on the temperature uniformity of the heat sink and the jet-impingement heat transfer were studied numerically. Meanwhile, the structure of the heat sink is optimized by the NSGA-II genetic algorithm. The results indicate that the three structures can enhance both the temperature uniformity and the heat-transfer capacity. Using nanofluids with a 3%volume fraction and a Reynolds number of 8,000, the average Nusselt number of the optimal structure is 26 % greater than that of a jet impingement flat heat sink, the temperature standard deviation is 67 % less, and the friction coefficient and thermal-hydraulic performance factor are greater by 55 % and 9 %, respectively. Meanwhile, the optimized structure exhibits excellent heat dissipation and temperature uniformity at higher heat flux. The allowable maximum heat flux reaches 341 W/cm2 when the junction temperature of the hot spot does not exceed 348 K, and the temperature standard deviation is 2.926, which are increase by 83 % and decrease by 36 % compared with that of jet-impingement plate heat sink, respectively.

Enhancing crop yield in hydroponic greenhouses: Integrating latent heat storage and forced ventilation systems for improved thermal stratification

Greenhouses play a crucial role in modern agriculture, creating an ideal environment for plant growth. Nevertheless, maintaining air temperature distribution inside a greenhouse remains a significant challenge due to the inherent tendency of warm air to stratify. This paper proposes an innovative integrated system that combines both heating and ventilation mechanisms. Its primary objective is to tackle the issue of air temperature stratification inside greenhouses, ultimately enhancing the microclimate to optimize crop production. The heating system comprises of a solar air heater with latent heat storage energy and a ventilation system designed to promote air circulation while eliminating stagnant zones. An experimental study was conducted to assess the performance of the integrated heating and ventilation systems in various greenhouse scenarios. The study begins by examining the thermal performance of the solar collector and its subsequent impact on the indoor environment of the hydroponic greenhouse. The results showed that the solar collector has a remarkable thermal performance with a daily energy efficiency between 32 % and 44 %. Incorporating the heating system into the greenhouse led to significant improvements in temperature stability, particularly during nighttime hours, when temperatures ranged from 17 °C to 20 °C. This translated to a temperature increase of 2 °C to 6 °C compared to greenhouses without heating, effectively illustrating the benefits of incorporating phase change materials into the heating system. The combination the heating and ventilation systems, resulted in a reduction of over 3 °C in the temperature difference between actual and desired levels.

Local structure effects on hydrodynamics in slender fixed bed reactors: Spheres and rings

Fixed bed reactors play a crucial role in the chemical industry, and their performance is influenced by the unique structural effects observed in the small tube-to-particle diameter ratio range (1.5<D/dp<9.3). Experimental void fraction data for beds made of spherical and ring-shaped particles reveal sudden changes, deviating significantly from theoretical calculations. These effects, categorized into four zones for spherical particles, i.e., single particle string, central channel, annular gap, and central channel + annular gaps, exhibit varying impacts on pressure drop. To describe this, the factors of the Ergun equation are modified accordingly. Furthermore, tortuosity is introduced as an additional parameter to describe the structural effects on fixed bed behavior. Classic correlations prove inadequate, leading to the adaptation of the Millington correlation for random beds, as well as those with a central channel and/or annular gaps. With particle-resolved Computational Fluid Dynamics (PRCFD) simulations, the residence time behavior is quantified of differently structured beds of spheres and rings, revealing deviations from plug flow and the presence of stagnation zones in beds containing a central channel. Notably, beds with an annular gap displays residence time behavior akin to plug flow, with lower pressure drop and an ordered, reproducible structure. These results highlight the importance of the D/dp ratio as an additional descriptor to characterize transport phenomena in slender fixed bed reactors.

Effects of regional groundwater discharge on transverse hyporheic exchange in compound channels

Previous studies of transverse hyporheic exchange in compound rivers mainly focused on processes driven by riverbed morphology, and neglected the effects of regional groundwater discharge (RGD). This study numerically investigated the transverse hyporheic exchange subjected to the joint influences of bedform and RGD in a conceptual compound channel. The results show the existence of an interfacial exchange zone (IEZ) across compound riverbeds even in the presence of RGD. A stagnation zone forms at the intersection of hyporheic flow and discharging groundwater flow when RGD flux is large, implying localized inactive nutrient processing within this zone. RGD sharply reduces the scale of IEZ whereas the flow rate of IEZ decreases slightly, consequently resulting in shorter residence times. The flux, depth and mean residence time of IEZ linearly, exponentially and exponentially decrease with RGD, respectively. RGD is likely to hinder solute transport depth and mass accumulation through IEZ depth and control transfer rate by mean residence time of IEZ. Therefore, a larger RGD would decrease the maximum solute transport depth, accompanied by less amount accumulation and a lower transfer rate in the bed. For a given bedform, a power model can describe how solute amount accumulation depends on hyporheic fluxes, while the solute accumulation dependence can be described by a linear model when the RGD condition is fixed. Findings from this study would help better understand the various mechanisms underlying hyporheic zones in compound channels.

The method of non-stationary flooding and the conditions for its effective use in the operation of an oil field

The article describes the essence of unsteady waterflooding, which is one of the most effective methods of increasing the oil recovery factor, used to change the direction of filtration flows, which makes it possible to engage in the development of undeveloped oil reserves and reduce the rate of watering of the deposit in productive reservoirs. A common technological method of unsteady water flooding is the use of cyclic modes of operation of injection wells. The essence of this method is that at an unsteady state in the oil deposit, there are conditions for the continuous manifestation of elastic forces of the reservoir system. In a heterogeneous reservoir between different zones, channels, and fluid flows there are gradients of hydrodynamic pressures, due to which there can be fluid flows from one layer to another, from fractures to blocks, as well as changes in flow directions. During unsteady flooding of heterogeneous formations, a part of oil reserves in low-permeability layers or zones remains uncovered by injected water. The waterflooded reservoir appears as an unsystematic alternation of watered and oil-saturated microflows. While creating in such reservoirs alternately changing in value and direction of pressure gradients, conditions for injection water penetration into stagnant oil-saturated low-permeable zones and channels appear in the oil reservoir and oil movement from them to active drainage zones. As a result of the analysis, the positive effect of the implementation of unsteady waterflooding technology was revealed, and recommendations for improving its application at other operational facilities of oil fields were given.

Tests for Validation Problems of Anomalous Separated Flow and Heat Transfer Enhancement on Structured Surfaces with Extraordinary Pressure Drops

New tests are presented for application packages and turbulence models for validation problems of high-intensity vortex flows near structured energy-efficient surfaces. The idea of testing is based on the discovery of anomalous intensification of separated flows and heat transfer in inclined grooves on plates and channel walls. In the grooves, due to the extraordinary pressure drops, confirmed by experiments, swirling flows are generated with high velocities of the return and secondary flow, comparable to the speed of the external flow. Also, high-gradient zones with friction and heat transfer are formed inside the grooves, many times (from 1.5–2 to 7–9 times) exceeding friction and heat transfer on a flat wall. As an example, the VP2/3 package, developed on the basis of original multi-block computing technologies and using multi-scale intersecting grids, is being tested. Comparison of numerical predictions with Zubin’s experiments confirmed high static pressure drops between the stagnation zone on the windward slope of the inclined groove and the negative pressure region at the site of generation of a tornado-like flow on the inlet spherical segment, and also demonstrated the acceptability of the RANS approach for predicting the characteristics of high-intensity swirling flows.