Formation Of Recirculation Zone Research Articles

Innovative eco-friendly design solutions for energy demands using swirl- induced burner by jets

Addressing the need for innovative burner designs to optimize combustion characteristics and meet energy efficiency goals, this study introduces a novel concept rooted in swirl-induced flames. The proposed burner employs a unique approach to generate air and fuel swirl using four opposing slots in two sets, each set at distinct angles. Incorporating of a channel within the outer casing allows for fine-tuning of entry angles, optimizing the double swirling process. The objective of this research is to enhance combustion characteristics through the implementation of the swirl principle, introducing a tangential velocity component to the airflow or fuel-air mixture upon entry into the burner. Systematic measurements at various entry angles (0°, 15°, 30°, 45°, and 60°) are conducted to identify optimal or near-optimal conditions. The research covers a comparison between flow fields generated by traditional swirled vanes and swirl-induced injection ports at identical inlet conditions, revealing enhanced flame stability and combustion efficiency in the latter configuration. The formation of recirculation zones around the burner, facilitated by increased outer air jet velocities, promotes better mixing and stability. This research contributes valuable insights into burner design and optimization, with implications for improved combustion efficiency and environmental sustainability.

Numerical Computational of Blood Flow and Mass Transport in Stenosed Bifurcated Artery

Stenosis refers to the narrowing of blood vessels caused by atherosclerosis, which can lead to serious circulatory problems by obstructing blood flow and mass transfer to other organs and tissues in the body. The objective of this investigation is to numerically examine the mass transfer of blood flow in a stenosed bifurcated artery using COMSOL Multiphysics, based on the finite element method. The study takes into account the geometry of a bifurcated artery with stenosis present at the mother and daughter arteries. The blood vessel is modeled as a two-dimensional (2D) rigid wall, and the blood flow is assumed to follow a non-Newtonian Carreau fluid model, being incompressible, laminar, and steady. The continuity equation, momentum equation, and mass transfer equation, along with boundary conditions, will be solved using COMSOL Multiphysics based on the finite element method. The simulation results show that the formation of recirculation zones, as indicated by streamline patterns and mass concentration, can significantly impact the severity of stenosis and Reynolds numbers. Thus, individuals exposed to such recirculation zones may be at risk of developing cardiovascular diseases.

Characterizing Swirl Strength and Recirculation Zone Formation in Tangentially Injected Isothermal Flows

This paper presents a computational study characterizing the swirl intensity distribution and Internal Recirculation Zone (IRZ) formed in a cylindrical domain with tangential injections and isothermal flow. The range of inlet boundary conditions investigated is 5o to 25o for the injection angle and 7190 to 100711 for the bulk flow Reynolds number. The evolution of swirl intensity is presented with and without incorporating effects of the accompanying pressure variations. The Shear Stress Transport (SST) k-ω is used to model turbulence. Results show that the Swirl strength created by such tangential injections strongly depends on the injection angle but does not vary with bulk flow Reynolds number (Re), except for low Re values. The swirling flow is shown to result in IRZ formation at injection angles 6o and above or when asymptotic value of the maximum Swirl Number in the domain exceeds approximately 0.6, same as the transition value of inlet Swirl Number in swirling flows with axial injections. The IRZ length increases with injection angle and varies with Re for lower values of Re at a given injection angle but asymptotes for higher values above 40000. The conventional Swirl Number rises rapidly downstream of the injection plane followed by a slow decline. On the other hand, an alternative Swirl Number, which incorporates the gauge pressure variation, shows slow and consistent decay all the way downstream of the injection plane. The Swirl Number incorporated with gauge pressure term subsumes interconversions between the axial momentum and pressure in the regions of vortex breakdown and IRZ formation, thereby presenting an alternative picture of swirl intensity evolution in swirling flows.

Computational investigation to interpret the reacting flow conditions for two different fuels in the scramjet combustor

The scramjet engines use the atmospheric oxygen to complete the combustion process, therefore, known as Air breathing engines. It does not bear any active parts and operates at supersonic speed, so it becomes essential that the variables such as fuel, pressure, temperature, Mach number to create the necessary environment to initiate the combustion phenomenon. The supersonic combustion undergoes severe turbulence in the variables associated with combustion. Thus, the selection of the appropriate parameters in designing of a suitable combustor is indispensable. The research paper discusses the effects of two different fuel jets on the flow variables in a scramjet combustor under reacting flow conditions. The Computational Fluid Dynamics (CFD) simulations on the scramjet combustor are carried out using Ansys 15.0 software. To investigate the effect of fuels on the combustion characteristics, the effect of pressure, Mach number and species concentration are studied. The pressure distribution for both the fuels shows that the maximum pressure is seen for hydrogen fuel at Mach number 2.52. The Mach number contours for both fuels reveal that the recirculation zone formation is more pronounced for ethylene fuel. The performance assessment of the combustor show that the maximum combustion efficiency was 87.62% and 89.26% and mixing efficiency was 98.97% and 97.46% for hydrogen and ethylene fuel respectively at M-2.52. Thus, it is concluded that the current scramjet model operated more effectively at Mach 2.52 with hydrogen as a fuel.

Оценка влияния температурных условий на естественную вентиляцию глубоких карьеров Арктической зоны

The Arctic zone of Russia is a territory where such minerals as gold and other precious metals are concentrated. Most often, the development of such deposits is carried out by an open method. The conditions hindering its use should be considered: the depth of distribution of permafrost and significant amplitude of changes in atmospheric air temperature during the year, month and day. The consequence of the alternation in depth of temperature zones may be the formation of recirculation zones in which harmful substances accumulate. Purpose of work. Study of the formation of velocity and temperature fields in a quarry under natural ventilation, taking into account the complex dynamics of atmospheric air temperature. Research methods. Systematization, generalization and analysis of theoretical and experimental studies in this area, including those carried out at the considered fields. Analysis of the results of mathematical modeling of aerodynamic processes in a quarry. Results. It is noted that to assess the peculiarities of formation of the mine atmosphere parameters it is sufficient to carry out only mathematical modeling of aerodynamic processes allowing to define the conditions of temperature inversions formation and dimensions of recirculation zones being potentially dangerous for accumulation of pollutants. The methodology of aerodynamic processes modeling taking into account the geometry of the pit space, temperature gradient, speed and direction of the wind flow is proposed. It is shown that at positive and negative temperature differences for the two investigated air media the development of recirculation movement zones of air masses that assure the accumulation of pollutants which in turn leads to reduced efficiency of natural ventilation in the pit, is characteristic. The conclusion has been made on the necessity to apply additional engineering measures during the period of inversion formation with negative temperature gradient in order to normalize the pit air parameters.

A numerical investigation of recirculation in axisymmetric confined jets

• Confined jet similarity parameters from literature are disambiguated. • A numerically consistent confined jet similarity parameter is determined. • Linear fits to numerical data can predict recirculation in confined jets. The formation of recirculation zones in confined jet flows was investigated numerically using large eddy simulation (LES) with the wall-adapting local eddy-viscosity (WALE) subgrid model and Reynolds-Averaged Navier–Stokes (RANS) simulations with a k- ω shear stress transport (SST) turbulence model. Accuracy and robustness of the turbulence closure models were assessed through comparisons with confined jet experiments. Simulations were used to assess the effectiveness of various similarity parameters reported in the literature to predict the critical point, where the flow transitions from an attached jet flow to recirculation flow. A modern variation of the Craya-Curtet parameter was determined to be the most appropriate and could reliably predict the critical point over a wide range of diameter ratios and jet Reynold numbers. The effectiveness of the Craya-Curtet number at low diameter ratios, where the assumptions of the derivation of the similarity parameter break down, were also investigated.

Novel EDM deep hole drilling strategy using tubular electrode with orifice

Fabrication of deep holes (depth to diameter ratio >10) using electrical discharge drilling (EDD) has gained momentum in the areas of aerospace, automotive and biomedical industries. However, formation of recirculation zones in flushing channel causes accumulation of debris particles at higher depths of drilling. This leads to secondary discharges within the flushing channel resulting in excessive tool wear, dimensional inaccuracy and hole tapering. The present paper proposes a novel tool geometry having orifices at the bottom end of tool electrode with an aim to improve debris evacuation. The effectiveness of proposed method is established through CFD simulations and experiments.

Performance of turbulence models for flow prediction in a mould of continuous steel caster

The flow of molten steel in a mould during continuous casting process is nowadays most often studied using numerical approach. With such an approach, appropriate numerical tools have to be selected to achieve physically sound results. Within this work we focus on performance of different turbulence models for the case of casting of steel billets with single SEN port oriented in vertical, downward direction. Only fluid dynamics aspect of the casting process is considered, while all other phenomena are disregarded at this stage. Simulations were performed with commercial CFD package ANSYS Fluent with k-ε, k-ω and SAS turbulent models. The geometric model, material properties and process conditions are closely matched to those from our experimental water model studies, which is typically not done. Hence, the difference between the experiments and the numerical simulation originates only due to turbulence model performance. The experimental PIV data from the water model experimental system is used to benchmark the performance of various turbulence models. The models are compared based on lateral dispersion of the liquid jet exiting submerged entry nozzle (SEN) and formation of recirculation zones around the SEN. The results show that while all three models are capable of capturing general flow features, only the SAS model predicts finer turbulent structures and reasonably captures the flow behaviour in temporal domain.

Experimental and Numerical Investigations on the Local Direct Leakage Process of Rotary Regenerative Air Preheater

An inherent defect of the operating rotary air preheaters (RAPH) is known as leakage, which seriously hinders the efficient and safe operation of RAPH. It is significant for the estimation of the direct leakage to determine the effects of different structure parameters of sealing sheets and different operation parameters of a RAPH. A direct leakage set-up was built and a three-dimensional numerical model was established to explore the local direct air leaking process of rotary regenerative air preheater and study the effects of geometrical and operational parameters on the leakage. The numerical simulation using the transition k-kl-ω turbulence model was verified by the experimental results. The results show that the local direct air leakage mainly depends on the total pressure difference between the two sides of the seal instead of the one-side pressure. The air leakage can be significantly reduced by narrowing the leakage gap. The increase in the number of sealing sheets can reduce the air leakage own to the increase in the leakage resistance. The increase in the spacing between the adjacent sealing sheets can enlarge the recirculation zone and increase the energy loss of mainstream, greatly reducing the local direct air leakage. Due to the different size recirculation zone formation and streamline curvature induced by sealing sheet, the effect of bending angle on the direct air leakage varies. To obtain lower leakage rate, it is recommended for the rotor of tri-sectional air preheater to pass through flue gas section, secondary-air section, and primary-air section in sequence.

Experimental determination of turbulence models applicability limits for the fluid dynamic computation in rotary divergent flow

Such fundamental scientific problem arises in much industrial application. The turbulent fluid dynamic characteristics were analyzed experimentally in a rotary-divergent flow. The laser Doppler anemometry was used for turbulent mass transfer diagnostics. The verification of numerical calculations by computational hydrodynamics has been carried out according to the results of experimental studies. Verification has shown that turbulent models describe the rotational-divergent flow well only until generation of flow gaps and formation of recirculation zones.

Thermal Mixing of Impinging Laminar Streams of Shear-Thinning Fluids

Thermal mixing behavior of shear-thinning fluids with the specified heat flux boundary condition at mixing zone walls is studied numerically to investigate the effect of Reynolds number (10 to 50), power-law index (0.6161 to 1), Nusselt number (104 to 106) for external air flows and dimensionless ambient temperature (−2.7 to 1.3). The temperature is a passive tracer that quantifies the degree of mixing in this study. Detailed kinematics shows the formation of recirculation zones at the mixing channel walls. Length required to achieve the well mixed condition (i.e., a flat temperature profile across the channel height) is shorter at low Reynolds number, convective heat transfer coefficient and ambient temperature, and high power-law index values. In the impingement zone, a faster reduction in mixing index has been observed with respect to mixing length at high power-law index and low Reynolds numbers, while Nusselt number and ambient temperature exert only a weak influence. Under appropriate conditions, significant energy exchange between the system and surroundings can occur and has been analyzed in detail in this work. This work finds its applications in the improved mixing as practiced in the processing and production of food-stuffs, fine chemicals, personal care products, etc.

Hypersonic flow past a spherically blunted nose cone: A computational study

The present study investigates the aerodynamic characteristics of spherically blunted nose cone at a hypersonic Mach number of 5.8, numerically. The studies are conducted for different combinations of bluntness ratios and semi-cone angles, at zero angle of attack, in order to ascertain the nose cone parameters which provide minimum aerodynamic drag coefficient. The velocity vector shows the flow deceleration near the nose, re-acceleration through the sides as well the formation of recirculation zones. The structure of bow shock formed ahead of the nose as well as shock detachment distance is depicted by the Mach number contours. It is observed that the shock detachment distance follows linearly increasing behaviour with increase in bluntness ratios for all semi-cone angles studied. An empirical expression is developed for the shock detachment distance using the regression analysis, which reveals that it is mainly a function of bluntness ratio. It is observed that the aerodynamics drag coefficient attains a minimum value for smaller, bluntness ratios and semi-angle. Further, the aerodynamic drag coefficient is observed to be a strong function of bluntness ratios for smaller semi-cone angles.

Ferro hydro dynamic analysis of heat transfer and biomagnetic fluid flow in channel under the effect of two inclined permanent magnets

Abstract Peripheral vascular diseases is one of the main causes of death in the world. It is disorders that cause the blood vessels to narrow, block, or spasm. Here, effects of two inclined rectangular permanent magnets field on heat transfer and flow characteristics of blood fluid in a channel, as a model of straight part of the aorta, has been investigated using FerroHydroDynamics (FHD) principles. Thermally and hydrodynamically fully developed flow is considered at the inlet of the vessel. Governing equations have been discretized using the finite volume method and the SIMPLE algorithm. Simulations have been carried out for different inclination angles of magnets and saturated magnetization. From the results, the magnetic field of two inclined magnets leads to increase heat transfer of blood fluid flow toward the walls. Moreover, major energy loss, arising from mean wall shear stress, is decreased but local or minor energy loss, arising from generated vortices, is increased. Furthermore, the formation of recirculation zones near the wall, where the magnetic drug can be trapped there for uptake to tissue, is observed.

Convective-diffusion model of particle deposition in modeling of building structures

The problem of the motion of a swirling flow in a vortex chamber with particle deposition effects at the lateral surface is numerically investigated. Flowfields with formation of recirculation zones are analyzed on the basis of the Navier-Stokes equations. Two cases of the transport process for solid particles of different sizes with deposition on the lateral surface of the channel are studied (passive impurities are assumed). In the first case, the particles are injected into the peripheral part of the channel together with the swirling flow; in the second case, this process is performed through an annular slot without swirling. The results are compared with available experimental data and asymptotic solutions.

Impact of Rustication Joints on Lightweight Insulation in Ventilated Facade Systems

One of the problems of ventilated facades systems is the emission of heat-insulating layer. Emission is a process of separation or removal of material’s particles from insulation by virtue of different factors. In this article research of emission of contemporary light weight insulation in system of hinged ventilated facade (VF) with various design is carried out. Impact of design and hydraulic factors on insulation destruction is estimated. Quantitative characteristic of blast air through rustication joints in a vertical channel is given and, consequently, it is possible to determine control point of recirculation zone formation – the beginning of turbulent air flow. Particle’s removal in insulation and decline of its properties are most probable in case of tangential stress, that conform to turbulent air flow.

Effect of Varying the Retainer Angle on the Performance of Oil Burner

A research has been done to observe the effect of varying the retainer angle on the performance of oil burner in terms of exhaust gas emissions and temperatures. Retainer was a flame stabilizer used to stabilize the flame, improve mixing between air and fuel and affect the formation of emissions such as carbon monoxide (CO), carbon dioxide (CO2), oxides of nitrogen (NOX), and sulfur dioxide (SO2). These emissions can cause harm to the world ecosystem. One of the methods to reduce emissions was by varying the retainer's blade angle to certain angle that complete the combustion with high efficiencies and less emissions. In this research, an oil burner with four different retainer angles has been investigated using a combustor of one meter length. Tests were conducted using diesel as feedstock. Four different retainer angles used are 15°, 30° (baseline), 45°, and 60° with swirl number 0.2016, 0.4344, 0.7524, and 1.3032. From the experiment, data shown that swirling flow affect the formation of recirculation zone thus provides the aerodynamics blockage to stabilize the flame and emissions reduced due to varying the retainer angles and the best retainer angle was achieved by consider the exhaust gas emission reduction.

Experimental investigation and numerical analysis on flame stabilization of CH4/air mixture in a mesoscale channel with wall cavities

Behaviors of premixed CH4/air flame in mesoscale channels with and without cavities were experimentally investigated. No stable symmetric flame was observed in the channel without cavities and flame is prone to inclining and pulsating. In contrast, flame can be effectively anchored in the presence of cavities. When the inlet velocity is increased sufficiently high, curved fluctuating flame front appears. Blow-off limits of the channel with cavities are several times larger than the corresponding burning velocity of incoming CH4/air mixture, while the flashback limits are almost the same as the straight channel counterparts. These indicate that the cavities have a strong ability to extend the operational range of inlet velocity. Numerical simulation demonstrates that combined effects, i.e., the formation of recirculation zone and low velocity zone in the cavities, preferential diffusion effect, as well as the preheating effect of upstream inner walls, are major mechanisms responsible for flame stabilization. Furthermore, numerical result reveals that large strain rate and heat loss rate exist at the transition point between the ramped cavity wall and the downstream inner wall, which results in flame splitting at high inlet velocity due to local extinction, and eventually leads to flame blow-off. In summary, the combustion behaviors in the mesoscale channel with cavities strongly depend on the interactions between the reaction zone, conjugate heat exchange and flow field.

Numerical Modeling of Nonuniform Flow in Settling Basins

The settling basins for hydropower plants are designed to remove suspended sediments from the waterflow. The inlet geometry of the settling basin may cause formation of recirculation zones and high turbulence, which may lead to diminished trap efficiency, and as a consequence, turbine erosion. Most analytic approaches for calculating the trap efficiency of settling basins are based on the assumption of a uniform flow; hence, simplified one-dimensional equations are used to determine the velocity distribution and the turbulence characteristics of the flow. However, the velocity field in settling basins is often unevenly distributed, and the simplified equations are not always applicable. This study describes a new method for improving the assessment of settling basin performance. The idea is to extract values for the velocity distribution and the turbulence characteristics along the settling basins from computational fluid dynamic (CFD) models. The extracted CFD values are then used as input parameters to the standard analytical approaches for calculation of settling basin trap efficiency. This promising method is tested on a case study of a physical model of the settling basin for the Lower Manang Marsyangdi Hydropower Project in Nepal. The CFD calculations turn out to provide additional information to the sedimentation calculations in settling basins, and are useful for the assessment of different design alternatives at an early stage.DOI: http://dx.doi.org/10.3126/hn.v14i0.11251HYDRO Nepal JournalJournal of Water, Energy and EnvironmentVolume: 14, 2014, JanuaryPage: 27-35

Magnetic field impact on the high and low Reynolds number flows

The effect of a strong magnetic field on the temperature and velocity fields of laminar flow was examined. The magnetizing force and gravity term were included in the momentum conservation equation. Biot-Savart's law was applied to obtain the distribution of magnetic field. Three-dimensional computations were performed for straight pipe and pipe with elbow. The single circular magnetic coil was oriented perpendicularly to the flow axis and divided the straight pipe in two equal parts, while in the case of pipe with elbow was just at the beginning of elbow. The wall of the first straight part was adiabatic while the second was isothermal. Half of the elbow was heated, while the reamining part was adiabatic. Various boundary conditions were applied to estimate their influence on the velocity and temperature distributions. Low entrance velocity, high wall temperature and strong magnetic field led to deceleration of the flow in the central area, acceleration near the wall and formation of recirculation zone in between for the straight pipe. Flow structure and temperature field in the pipe with elbow were significantly modified by the magnetic force. Increasing entrance velocity reduced influence of magnetic field, therefore the flow was less modified. High temperature and magnetic induction resulted in significant changes of the velocity profile. The analysis was conducted with an application of software with special user-defined function. The magnetic field had an influence on the forced convection but its scale depended on the fluid and flow properties, boundary conditions and magnetic field induction.

Effect of the inertia terms in sliding bearing calculation problems

Viscous incompressible fluid flow in sliding bearings is calculated numerically for four configurations on the basis of the system of Navier-Stokes equations. Various flow regimes including those with the formation of recirculation zones are obtained. A parameter range over which the flow deviates considerably from the Stokes flow model is determined.