Tangential Velocity Distribution Research Articles

Numerical investigation on particles separation using an enhanced cyclone with shunt device: Effect of vortex finder lengths

To improve the performance of the enhanced cyclone with shunt device (ECSD), the vortex finder lengths optimization for the ECSD is carried out by numerical investigation. Reynolds stress model and discrete phase model are adopted. The results show that the separation ability of the ECSD can be improved by longer vortex finder, which is contrary to the generally accepted conclusion that the vortex finder length of the traditional cyclone should not be longer than cylindrical section length. When the ratio of vortex finder length to cylindrical section length reaches 1.5 (225 mm vortex finder), the total separation efficiency, reduced separation efficiency and comprehensive separation efficiency are 90.7%, 89.7%, and 80.6%, respectively, which are the highest. The tangential velocity distribution is one of the most important reasons that the separation efficiency increases with the increase of the vortex finder length in general. The tangential velocity in the conical section of the ECSD increased with the increase of vortex finder length. When the length of vortex finder is the same as that of cylindrical section, the overall energy consumption and split ratio of the ECSD are the largest of 1.88 kPa and 12.4%, respectively, which is detrimental to the overall performance of ECSD.

Effects of key structure parameters on flow field and sensitivity analysis for a bubble separator in MSR

In order to investigate the separation mechanism and provide some guidance for the separator design, the single-phase flow field of the bubble separator for the Molten Salt Reactor is simulated numerically by Reynolds Stress Model. The results show that a low-pressure and high-velocity region is induced under the obstruction of the guiding vanes in the flowing channel and the tangential velocity distribution resembles the Rankine vortex. Besides, the swirl number along the axial position increases first and then decreases due to the improvement of the first light phase outlet. Moreover, the effects of the key structure parameter of the generating swirler including deflection angle, the guiding vane number and the hub ratio on the flow field are investigated and their sensitivity analyses are conducted at the same time. It demonstrates that the deflection has the largest influence on the flow field and the hub ratio is the second.

Numerical and Experiment Investigation on Novel Guide Vane Structures of Turbo Air Classifier

In this paper, three types of air guide vanes are designed: direct-type, L-type, and logarithmic spiral type, respectively. ANSYS-FLUENT 20.0 is used to numerically simulate the internal flow field of turbo air classifier by novel different structures. The numerical results show that the guide vane structures have a good effect on the flow field stability of the annular function zone in the classifying chamber. The distribution of tangential velocity and radial velocity verified the logarithmic spiral guide vane, and makes the airflow flow along the rotor cage circumferentially uniformly. In addition, the turbulent dissipation rate and energy loss decreases in the rotor cage region, which also shows that the guide vane is beneficial to improve classification performance. The tromp curve of the numerical simulation shows that the logarithmic spiral guide vane reduced the cutting size by 6.3% and 23.7% at two different process parameters, and is obviously better than other guide vane structures in improving the classification sharpness index (K). Finally, the reliability of numerical simulation is verified by material experiment. The research results have certain theoretical significance and guidance for the structural design of the guide vanes of the turbo air classifier.

Effect of gas-induced inlet design on flow pattern and energy loss for small-scale countercurrent vortex reactor: Numerical simulation and experimental investigation

Small-scale vortex reactors have gained attention in the fields of gas-particle multiphase reactions because of the great potential of process intensification. Their performances highly depend upon the vortex flow-induced structure. However, its role has not yet been completely understood. To address the effect of the vortex flow-induced design of a small-scale countercurrent vortex reactor, the gas-induced inlet design with varying aspect ratio (the ratio of inlet height to inlet width of 0.56, 2.25, and 5.06) was designed to numerically and experimentally investigate the flow distribution, energy loss, and process intensification. It was found that for a given flow rate (inlet velocity), and with increasing aspect ratio the maximum tangential velocity is increased whereas the decay of the vortex flow is decreased. The semi-empirical equations were further developed to characterize the spatial distribution of the gas tangential velocity. There is no significant differentiation in axial velocity, but the static pressure near the wall increases significantly. Moreover, the pressure drop of the reactor increases as the inlet aspect ratio increases. Finally, an aspect ratio of 2.25 was found to be optimum for potential multiphase mixing and mass transfer. The results may provide a positive reference for the vortex-flow-based process intensification.

Flow Field Simulation of Swirling Abrasive Jet Nozzle for Hard Rock Breaking

Radial jet drilling (RJD) technology has been proved to be an economical and efficient stimulation technology for oil and gas, geothermal, hydrate, etc. but conventional RJD technology adopts pure water jet to break rock and form laterals, which has low rock breaking efficiency and is unable to effectively break hard rock such as shale. Swirling abrasive jet is proposed to promote the development of RJD. Here, the characteristics of the flow field of the swirling abrasive jet nozzle and the influence of the key impeller parameters are studied by numerical simulation. The distribution and development of axial velocity, tangential velocity, and radial velocity of water and abrasive are analyzed. The results show that the swirling abrasive jet has no constant velocity core, has stronger diffusivity, and can form a larger impact area than the direct jet. Abrasive particles and water can acquire large tangential and radial velocity which can break rock under the action of shear and tensile stress efficiently. With the increase of the spinning angle, the axial velocity of the fluid decreases, and the tangential velocity increases gradually. With the increase of blade thickness, the axial velocity decreases, and the tangential velocity increases. With the increase of the number of blades, the axial velocity decreases, and the tangential velocity increases. The spinning direction almost has no effect on the flow field. Therefore, the spinning angle is recommended to be no less than 270°, blade thickness is 2.5 mm, and number of blades are 3. The research results provide theoretical guidance for the structural design of swirling abrasive jet nozzles.

The inner/outer self-cleaning phenomenon in the granular bed filter-cyclone coupled separator

This paper presented an experimental study for a noticeable phenomenon named by the self-cleaning in a granular bed filter-cyclone coupled gas–solid separator. This phenomenon brought about positive effects on the dust cake destruction and the operating time extension in the separation process. It was analyzed under different inlet gas velocity, inlet dust concentration as well as the bed operating modes. The inner tangential velocity distribution was also measured with the five-hole probe. The dust cake porosity was deduced by combing the pressure, the deposited dust mass as well as the proposed correlations in published literatures. The experimental results showed that the inner/outer self-cleaning phenomenon resulted in significant improvement on the collection efficiency and the pressure drop. The tangential velocity played the most important role in the outer self-cleaning. The friction effect induced by the downward-moving collector particles was the other key to restrain the formation of the dust cake on the inner Johnson screen, which was conducive to the inner self-cleaning phenomenon. Only the dense particle packed dusts left on the screen surface under the full-bed operating mode and a high collection efficiency was achieved by the self-cleaning phenomenon.

Determination of the characteristics of a jet pump during its asymmetric rotation in a well

The hydraulic model of low-pressure jet pump working process for conditions of its asymmetric rotation is proposed on the basis of law of conservation of liquid momentum of parallel mixed potential flows with linear distribution of tangential velocities and radial displacement relative to borehole axis. In the process of derivation of the equation of pressure characteristic of low pressure jet pump at its asymmetrical rotation in a borehole the law of conservation of flow energy in the form of Bernoulli's equation and the law of continuity conservation of mixed currents have been used. To characterize uneven distribution of kinematic parameters in the mixing chamber of jet pump, the unevenness coefficient in the form of ratio of average and axial circumferential velocities of mixed flows is introduced. Flow rates of working, ejected and mixed streams are determined by integration of the adopted velocity profiles in the inlet and outlet sections of the mixing chamber of the jet pump. The developed hydraulic model allowed obtaining a dimensionless relative form of equation for determining the additional head of the jet pump caused by its asymmetric rotation in the borehole. The magnitude of the additional dynamic head increases as the peripheral velocity increases and the operating flow rate decreases. The total head produced by the jet pump is calculated by summing the additional head and the head obtained for the stationary ejector system. The rotation of the borehole ejection system causes the head and the efficiency of the jet pump to increase. The proposed hydraulic model can be used to improve the efficiency of jet pump mode prediction as a part of assemblies for drilling and bottomhole cleaning.

Radiative bioconvection nanofluid squeezing flow between rotating circular plates: Semi-numerical study with the DTM-Padé approach

Modern biomedical and tribological systems are increasingly deploying combinations of nanofluids and bioconvecting microorganisms which enable improved control of thermal management. Motivated by these developments, in this study, a new mathematical model is developed for the combined nanofluid bioconvection axisymmetric squeezing flow between rotating circular plates (an important configuration in, for example, rotating bioreactors and lubrication systems). The Buongiorno two-component nanoscale model is deployed, and swimming gyrotactic microorganisms are considered which do not interact with the nanoparticles. Thermal radiation is also included, and a Rosseland diffusion flux approximation is utilized. Appropriate similarity transformations are implemented to transform the nonlinear, coupled partial differential conservation equations for mass, momentum, energy, nanoparticle species and motile microorganism species under suitable boundary conditions from a cylindrical coordinate system into a dimensionless nonlinear ordinary differential boundary value problem. An efficient scheme known as differential transform method (DTM) combined with Padé-approximations is then applied to solve the emerging nonlinear similarity equations. The impact of different non-dimensional parameters i.e. squeezing Reynolds number, rotational Reynolds number, Prandtl number, thermophoresis parameter, Brownian dynamics parameter, thermal radiation parameter, Schmidt number, bioconvection number and Péclet number on velocity, temperature, nanoparticle concentration and motile gyrotactic microorganism density number distributions is computed and visualized graphically. The torque effects on both plates, i.e. the lower and the upper plate, are also determined. From the graphical results, it is seen that momentum in the squeezing regime is suppressed clearly as the upper disk approaches the lower disk. This inhibits the axial flow and produces axial flow retardation. Similarly, by enhancing the value of squeezing Reynolds number, the tangential velocity distribution also decreases. More rigorous squeezing clearly therefore also inhibits tangential momentum development in the regime and leads to tangential flow deceleration. Tables are also provided for multiple values of flow parameters. The numerical values obtained by DTM-Padé computation show very good agreement with shooting quadrature. DTM-Padé is shown to be a precise and stable semi-numerical methodology for studying rotating multi-physical flow problems. Radiative heat transfer has an important influence on the transport characteristics. When radiation is neglected, different results are obtained. It is important therefore to include radiative flux in models of rotating bioreactors and squeezing lubrication dual disk damper technologies since high temperatures associated with radiative flux can impact significantly on combined nanofluid bioconvection which enables more accurate prediction of actual thermofluidic characteristics. Corrosion and surface degradation effects may therefore be mitigated in designs.

Comparison of Different Impellers for Gas Dispersion in Power-Law Fluids

The 3D multiphase computational fluid dynamic (CFD) models have been developed for gas–liquid systems in a standard baffled stirred tank reactor (diameter 0.3 m) for non-Newtonian power-law fluids. The standard k-ε model has been used to model the turbulence, and drag has been modeled with the Grace drag model with Brucato modifications. CFD simulations have been carried out for three impellers, namely, the Rushton turbine, pitched blade turbine, and hydrofoil impeller. The effects of impeller design, power input per unit volume of the fluid (P/V) (1200–5200 W/m3), fluid rheology (K = 0–0.1561 Pa·sn, n = 0.687–1.000), and superficial gas velocity (7.1–28.3 mm/s) have been analyzed. The CFD model has been validated with the local distribution of axial, radial, and tangential velocities and overall gas holdup data reported in the literature. The CFD model has been used to predict the regime transition from flooding to loading and complete dispersion. A good agreement was observed for the prediction of regime transition for the Rushton turbine when compared with the experimental data. The average value of absolute error for the prediction of the gas holdup is 20%, which indicates that the developed CFD model can be successfully used to predict the gas holdup and regime transition in stirred tank reactors. Among the impellers studied, the hydrofoil impeller shows the highest gas holdup and uniform gas distribution in the vessel at low power consumption.

Numerical investigation of transient thermo-fluid processes in a Ranque-Hilsch vortex tube

A 2D numerical investigation is performed to better understand the transient thermo-fluid processes in a vortex tube for a cold mass fraction equal to0.44. The results along the Ranque-Hilsch vortex tube reveal a close agreement with past numerical and experimental data. The distribution of axial, radial, and tangential velocities as well as the stagnation pressure and temperature are examined at different positions for different time steps. The results indicate that the tangential velocity is the most significant velocity component and dominates the heat transfer and energy conversion processes. In addition, it is evident that the core of the cold end experiences the highest pressure gradient along with almost zero tangential and radial velocities. The maximum axial velocity appears close to the inlet and its value increases with higher cold mass fractions due to higher pressure gradient which may lead to the enlargement of the inner vortex. The impact of different cold mass fractions in the range of 0.22−0.82 at tube length ratios x/L equal to 0.05, 0.5, and 0.9 for different time steps are examined. The results indicate that there is relatively no vortex decomposition near the cold outlet.

Gas and particle instantaneous velocity measurement in swirling particle-laden turbulent reacting flow

Experimental study of particle-laden turbulent reacting flow was conducted on a test facility for swirl combustor. The Three-Dimension Particle Dynamic Analyzer (PDA) was employed to measure the gas and particle instantaneous velocities. The measured results provide the distributions of time-averaged axial and tangential velocities, root mean square of axial and tangential fluctuating velocities, and correlation moments of axial-tangential fluctuating velocities for both gas and particle phases and the distribution of particle mean diameter. The Probability Density Functions (PDF) for the instantaneous particle axial and tangential velocities are also obtained at each measuring location. The gas and particle axial and tangential velocities as well as axial and tangential fluctuating velocities are large in the upstream central region of the combustor. Differences are found evidently between the gas and particle fluctuating velocity components.

Hall currents effect on squeezing flow of non-Newtonian nanofluid through a porous medium between two parallel plates

An analysis is carried out to study the problem of unsteady squeezing flow of a non-Newtonian nanofluid through a porous medium between two parallel plates. The effects of Hall currents and heat source are taken into consideration. The governing partial differential equations are transformed into a set of nonlinear ordinary differential equations by using similarity transformations. A homotopy perturbation method is performed to obtain analytical solutions for that system of equations. The behaviors of the tangential velocity, normal velocity, temperature, and nanoparticles concentrations distributions are discussed analytically and graphically under the effect of different entering parameters. Physically, our model corresponds to squeezing problems in tunnelling such as study the relation between rock types and its depths in squeezing cases and time dependent stress induced problem in sandstone. This problem provides interesting results which may have many applications in chemistry, biology, and medicine.

Fluid flow and convection heat transfer in concentric and eccentric cylindrical annuli of different radii ratios for Taylor-Couette-Poiseuille flow

This paper presents the results of fluid flow and convection heat transfer in concentric and eccentric annuli between two cylinders using a three-dimensional computational fluid dynamics model. Effects of rotational speed ( n = 0, 150, 300, and 400 rpm) and eccentricity (ε = 0, 0.15, 0.3, 0.45, and 0.6) on axial and tangential velocity distribution, pressure drop and forced convection heat transfer are investigated for radii ratios (η) of 0.2, 0.4, 0.6, and 0.8, Reynolds number 2.0 × 103–1.236 × 105, Taylor number 1.47 × 106–1.6 × 1010, and Prandtl number 3.71–6.94. The parameters cover many applications, including rotary heat exchangers, mixers, agitators, etc. Nusselt numbers and friction factors for stationary and rotated concentric and eccentric annuli are correlated with four dimensionless numbers. The results revealed that when the speed of the inner cylinder increases from 0 to 400 rpm, the friction factor increases by 7.7%–103% for concentric and 8.2%–148% for eccentric annuli, whereas Nusselt number enhances by 37%–333% for concentric and 44%–340% for eccentric annuli. The radius ratio has a substantial effect on the heat transfer and pressure drop in annuli. The eccentricity enhances the heat transfer up to 12%, whereas its effect on the friction factor is not monotonic as it depends on Reynolds number, radii ratios, and rotational speed.

Study on multiphase flow field in Falcon separator by CFD simulation

ABSTRACT Flow field characteristics of Falcon separator are studied by CFD simulation based on Euler-Euler model as multiphase flow model and Reynolds stress model as turbulence model, including particle movement state in delamination area and separation area, three phase (Tangential, radial and axial directions) velocity distribution and turbulence field distribution. Simulation results show that particle movement trajectory is a three-dimensional helical structure with circular motion in groove, which can be regarded as “a circular harmonic motion of a roller coaster”; velocity distribution in the delamination area is almost same as other centrifugal separators but it is quite different in the groove; with feeding of recoil water, the turbulence intensity in the separation area is increased obviously, but it has a lower influence on the disturbance at upper layer of convective membrane, which enhanced the separation effect.

The Gaia view of the Cepheus flare

ABSTRACT We present a new census of candidate pre-main-sequence stars in the Cepheus flare star-forming region, based on Gaia EDR3 parallaxes, proper motions, and colour–magnitude diagrams. We identified new candidate members of the previously known young stellar groups associated with NGC 7023, L1177, L1217/L1219, L1228, L1235, and L1251. We studied the 3D structure of the star-forming complex and the distribution of tangential velocities of the young stars. The young stellar groups are located between 330 and 368 pc from the Sun, divided into three kinematic subgroups, and have ages between 1 and 5 million yr. The results confirm the scenario of propagating star formation, suggested by previous studies. In addition to the bulk pre-main-sequence star population between 330 and 370 pc, there is a scattered and more evolved pre-main-sequence population around 150–180 pc. We found new candidate members of the nearby Cepheus Association, and identified a new moving group of 46, 15–20 million yr old pre-main-sequence stars located at a distance of 178 pc, around the A0-type star HD 190833. A few pre-main-sequence stars are located at 800–900 pc, indicative of star-forming regions associated with the Galactic local arm above the Galactic latitude of +10°.

LES INVESTIGATION ON THE INFLUENCE OF CAVITATION ON THE EVOLUTION AND CHARACTERISTICS OF TIP LEAKAGE VORTEX

In the present paper, the tip-leakage vortex (TLV) cavitation around a NACA0009 hydrofoil is numerically investigated with large eddy simulation method combined with a new Euler-Lagrangian cavitation model, which takes into account the effect of nuclei on tip-leakage cavitating flow. A satisfying agreement between the numerical and experimental results is obtained. Based on the numerical data, the evolution behavior of TLV cavitation with different gap sizes and its influence on the strength and radius of TLV, the nuclei distribution in the vortex core and the distribution of tangential velocity are discussed in detail. The results show that once cavitation occurs, the intensity of TLV is mainly affected by the evolution behavior of the sheet cavitation, while the tip-leakage cavitating flow has little effect on the strength of TLV. In addition, the results suggest that a smaller gap size will result in a more unstable sheet cavity, and the strength of TLV in turn presents corresponding quasi-periodic fluctuation as influenced by the evolution of the sheet cavitation. As the tip clearance progressively increases, the strength of the sheet cavitation gradually decreases with the reduction of instability, and the intensity of TLV gradually returns to the level without cavitation, together with its fluctuation level. Cavitation has a more significant influence on the nuclei distribution in the vortex core, and its degree of influence depends on the spatial stability of TLV and the intensity of TLV cavitation after the occurrence of cavitation. Moreover, the numerical results obtained by our simulations also indicate that cavitation has a significant influence on the radius of TLV. After cavitation occurs, the radius of TLV increases to a certain extent, and a ``rigid body rotation'' tangential velocity distribution is formed on the periphery of cavitation region, which is mainly caused by the expansion process induced by cavitation growth and the viscous effect of flow.

Numerical simulation of two-phase flow and droplet breakage of glycerin-water mixture and kerosene in the cyclone reactor

• The static pressure distribution conformed with the rules of the eddy field. • The vortex motion near the side wall was intense. • The droplet deformed, stretched, and broken. • The small surface tension and large Weber number promoted droplet breakage. A liquid-liquid cyclone reactor (LLCR) was designed to achieve mixing-reaction-separation integration during isobutane alkylation catalyzed by ionic liquids. However, studies of the droplets deformation and breakage in the kind of reactors are lacking. In this work, the research studied the velocity distribution, pressure field, and turbulent field to investigate the flow pattern and the main energy loss location in the LLCR through the computational fluid dynamics (CFD) method. The simulation results were verified by experiemnts to prove the correctness of the model. Then the deformation and breakage process of droplets, and the influencing factors of droplets breakage were studied by remodeling which was based on the tangential velocity distribution result of the three dimensional model. The three dimensional simulation results clearly showed that the pressure of the LLCR was mainly concentrated in the cone section and fluid turbulent motion was the most intense near the lateral wall. The reconstruct the results of the two dimensional model clearly showed that the deformation and breakage location of droplets were mainly occurred in the velocity boundary layer, while it was difficult to break in the mainstream region. In addition, low surface tension and high Weber number had a positive effect on droplet breakage.

Numerical analysis of hydrodynamic characteristics and interphase coupling in a gas‐solid cyclone reactor

AbstractA down‐flow gas‐solid cyclone reactor (GSCR) for fluidized catalytic cracking process was proposed to solve the side reactions. Comprehensive three‐dimensional numerical models were established to interpret its gas‐solid flow features, where the continuous phase and dispersed phase were modelled in the Eulerian grid and Lagrangian framework, respectively. Simulation results show that the four‐way approach has a better prediction of gas‐solid flow hydrodynamics in GSCR than the two‐way approach, and the numerical pressure drop agreed well with the experimental data. Most catalysts accumulated on the wall when descending and the phase interface structure composed of internal pure gas and external mixtures was subsequently formed. The radial distribution of tangential velocity was almost hump shaped. Tangential and axial kinetic energies accounted for 92.49%–95.45% of total kinetic energy and were thus dominant. In the dilute condition, the oscillatory behaviour of particle concentration was more severe than that of gas velocities, and particle concentration and gas tangential velocity had the same dominant frequency (~2.6 Hz). As the particulate loading increased tenfold, the hydrodynamic characteristics became rather complex.

Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage

Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow control and performance improvement. First, the numerical results are validated against the experimental data, and flow conditions inside the inlet chambers with different structures are compared. They indicate that, in the non-guide vane scheme, sudden expansions, tangential flows and flow separations in the spiral and annular convergent channels are the major causes of flow loss and distortions, while using guide vanes could introduce additional flow impacts, separations and wakes. Based on the flow analysis, structure improvements have been carried out on the radial inlet chamber, and an average increase of 4.97% has been achieved in the inlet chamber efficiencies over different operating conditions. However, the results further reveal that the increases in the performance and overall flow uniformity just in the radial inlet chamber do not necessarily mean a performance improvement in the downstream components, and the distribution of the positive tangential velocity at the impeller inlet might be a more essential factor for the efficiency of the whole compressor.

Understanding the Velocity Distribution of the Galactic Bulge with APOGEE and Gaia

Abstract We revisit the stellar velocity distribution in the Galactic bulge/bar region with Apache Point Observatory Galactic Evolution Experiment DR16 and Gaia DR2, focusing in particular on the possible high-velocity (HV) peaks and their physical origin. We fit the velocity distributions with two different models, namely with Gauss–Hermite polynomials and Gaussian mixture models (GMMs). The result of the fit using Gauss–Hermite polynomials reveals a positive correlation between the mean velocity ( ) and the “skewness” (h 3) of the velocity distribution, possibly caused by the Galactic bar. The n = 2 GMM fitting reveals a symmetric longitudinal trend of ∣μ 2∣ and σ 2 (the mean velocity and the standard deviation of the secondary component), which is inconsistent with the x 2 orbital family predictions. Cold secondary peaks could be seen at ∣l∣ ∼ 6°. However, with the additional tangential information from Gaia, we find that the HV stars in the bulge show similar patterns in the radial–tangential velocity distribution (V R–V T), regardless of the existence of a distinct cold HV peak. The observed V R–V T (or V GSR–μ l ) distributions are consistent with the predictions of a simple Milky Way bar model. The chemical abundances and ages inferred from ASPCAP and CANNON suggest that the HV stars in the bulge/bar are generally as old as, if not older than, the other stars in the bulge/bar region.