Average Velocity Distribution Research Articles

Investigating heat transfer in an upward flow of liquid metal in the mercury facility with a loop of natural circulation

Research of heat transfer is performed in an upward flow of liquid metal in a vertical channel of rectangular cross-section under the condition of one-sided heating and in a vertical pipe in a mercury circuit with a natural circulation loop. Natural circulation loop enables measurements in mixed turbulent convection modes, which are inaccessible on a contour with a forced convection, that is, in the region of small Reynolds (Peclet) numbers of characteristics. Using a two-coordinate probe with a microthermocouple correlation sensor, profiles of averaged velocity and temperature and distribution of a wall temperature are obtained, and heat transfer coefficients are determined. Criterion dependences of Nusselt number on Peclet and Richardson are built. Experimental data on heat transfer are compared with similar data obtained earlier in a loop with a forced flow of mercury.

Permeability Characteristics of Water-Sand Seepage in Fracture by Experiment

Studies on the seepage characteristics of water-sand cracks are of great significance to reveal the mechanisms of water and sand inrush. Using a self-made water-sand fracture seepage test instrument, a water-sand seepage test was carried out, and the permeability of water and sand in the fracture was determined. The hysteresis characteristics of water-sand flow in the fracture were obtained after the required permeability was attained. The results show that the hysteresis curve changes from type I to type IV with the increase in sand particle size and concentration. The hysteresis parameters are described by the maximum hysteresis Gp ∗ and the hysteresis area S, both of which show an increasing trend with the increase in sand particle size and concentration; however, this increase is not synchronous. The average velocity and turbulent kinetic energy distribution of the water-sand fluid on the fracture cross section are greatly affected by the particle size and concentration of the volume of sand. This study can provide a reference for further study of water inrush from a shallow coal seam. Through simulation, it is found that the particle size has a great influence on the seepage velocity, and the influence near the side wall surface is greater than that in the middle position.

Assessment of MULTALL as Computational Fluid Dynamics Code for the Analysis of Tube-Axial Fans

Abstract This work deals with the application of the open-source computational fluid dynamics (CFD) code MULTALL to the analysis of tube-axial fans. The code has been widely validated in the literature for high-speed turbomachine flows but not applied yet to low-speed tutbomachines. The aim of this work is to assess the degree of reliability of MULTALL as a tool for simulating the internal flow in industrial axial-flow fan rotors. To this end, the predictions of the steady-state air-flow field in the annular sector of a 315 mm tube-axial fan obtained by MULTALL 18.3 are compared with those obtained by two state-of-the-art CFD codes and experimental data of the global aerodynamic performance of the fan and the pitch-wise averaged velocity distribution downstream of the rotor. All the steady-state Reynolds-averaged Navier–Stokes (RANS) calculations were performed on either fully structured hexahedron or hexa-dominant grids using classical formulations of algebraic turbulence models. The pressure curve and the trend of the aeraulic efficiency in the stable operation range of the fan predicted by MULTALL show very good agreement with both the experimental data and the other CFD results. Although the estimation of the fan efficiency predicted by MULTALL can be noticeably improved by the more sophisticated state-of-the-art CFD codes, the analysis of the velocity distribution at the rotor exit supports the use of MULTALL as a reliable CFD analysis tool for designers of low-speed axial fans.

Microtremor exploration at strong motion stations in Aydin and Denizli provinces, western Turkey

This paper reports the results of a case study of the application of the microtremor exploration method in western Turkey. We have conducted microtremor surveys at strong motion stations in Aydin and Denizli provinces to derive shallow S-wave velocity profiles. Array records of vertical microtremor motion were acquired at 12 and 15 stations in Aydin and Denizli provinces, respectively. A spatial autocorrelation analysis was applied to the records to estimate Rayleigh wave phase velocities in the frequency range of 3–30 Hz. Then, the phase velocity dispersion at each station was inverted to a one-dimensional S-wave profile down to a maximum depth of about 50 m. The soil models at 5 and 11 stations in Aydin and Denizli provinces, respectively, have a bedrock with an S-wave velocity of 400–600 m/s at depths less than 10 m. The spatial distribution of average S-wave velocities in the top 30 m of the revealed profiles shows low values in the Büyük Menderes Graben and the Denizli Basin, and high values in the surrounding hill or mountain areas. We compared our S-wave profiles with those from previous surface-wave studies. S-wave velocities in shallow parts to a depth of 5–10 m are similar in the two studies. However, S-wave velocities in deep parts are different at some of the stations.

The structure of turbulent flow behind the NACA 0012 airfoil at high angles of attack and low Reynolds number

This paper shows the results of a study of the turbulent structure behind the NACA 0012 airfoil. During the experiment, the flow velocity was 20 m·s−1. That corresponds the Reynolds number 1.3·105. The point behind the trailing edge was chosen for experimental studies. Measurements were performed at six angles of attack α = 0°, 15°, 30°, 45°, 60°, 75° and various cases of positioning the measuring section. Namely at a constant crosssection and a constant distance behind the airfoil. The NetScanner pressure system and hot-wire technique were used for experimental studies. The obtained data allowed us to investigate the wake topology. The average velocity and standard deviation distributions are clearly grouped depending on the angle of attack. Thus, flowing around the airfoil is better up to α ≤15°. Distributions by power density and dissipation spectra also have a similar grouping tendency. Finally, we investigated the turbulent structure according to the research program. We found that at α ≥45°, depending on the measurement case, there is a clear difference in the distribution of standard deviation, Eulerian length scale, Taylor micro-scale, and Reynolds number based on the Taylor micro-scale. The obtained values at the constant distance, in contrast to the constant cross-section, are reduced.

Information technologies for the study of the planned and profile model of the flux creep in the transit channel

The article presents the inlet chamber computer models for the Beloyarskyin take structure: a computer model of the depth distribution and a computer model of the water level distribution for determining the hydrodynamic structure of the flux creep in the transit channel. To build a computer model, the depth survey of the inlet chamber was used during hydro meteorological surveys. The water level at the survey time is 15.30 m. The construction of a depth distribution computer model in the inlet chamber at the intake structure for the water supply of the Beloyarsky city was carried out by the finite element method on a personal computer in the Multiphysics software product. The uneven distribution of average velocities on the verticals, both along the channel width and length, is explained by the significant expansion of the inlet chamber in the intermediate sections 2-2, 3-3, 4-4, 5-5 in relation to the input 1-1 and output sections. Deepening the channel in the entrance section 1-1 by an average of 1.3-1.5 m will increase its flow rate to 10, 2m3/s or 10 times with an increase in the average speeds on the verticals by 2.0-2.5 times. Such an increase in the flow rate in the input section will lead to an increase in the average speeds in other sections 2-2, 3-3, etc. Hence, the passage of increased flow through the transit channel after clearing a number of shallow areas will create better conditions for preventing algae spread.

Molecular simulation of N2 and CO2 injection into a coal model containing adsorbed methane at different temperatures

To research the dynamic mechanism of nitrogen and carbon dioxide displacement of methane, we used the grand canonical Monte Carlo (GCMC) simulation method to determine the lowest energy coal model containing adsorbed methane. The desorption behavior of CH4 after the injection of N2 and CO2 at different temperatures was studied. Results show that CO2 and N2 were mainly used to drive off methane gas by occupying adsorption sites. The total energy of the CH4-CO2 model was lower than that of the CH4-N2 model. With the increased of temperature, the average relative concentration and motion velocity of CH4 in the vacuum layer increased. The relationship of the average relative concentration and average velocity distribution of the three gases in the vacuum layer was CH4>CO2>N2. Under the same time conditions, the relationship between the mean square displacement and diffusion coefficient of CH4, CO2, and N2 in different models was CH4>CO2>N2, and they all increased with temperature. The diffusion activation energy of CH4 in the model injected with CO2 was reduced by 20.53%, and the effect of injecting CO2 to promote the desorption of methane was better than that of N2.

Thermo-Fluid Dynamics Analysis of Fire Smoke Dispersion and Control Strategy in Buildings

Smoke is the main threat of death in fires. For this reason, it becomes extremely important to understand the dispersion of this pollutant and to verify the influence of different control systems on its spread through buildings, in order to avoid or minimize its effects on living beings. Thus, this work aims to perform thermo-fluid dynamic study of smoke dispersion in a closed environment. All numerical analysis was performed using the Fire Dynamics Simulator (FDS) software. Different simulations were carried out to evaluate the influence of the exhaust system (natural or mechanical), the heat release rate (HRR), ventilation and the smoke curtain in the pollutant dispersion. Results of the smoke layer interface height, temperature profile, average exhaust volumetric flow rate, pressure and velocity distribution are presented and discussed. The results indicate that an increase in the natural exhaust area increases the smoke layer interface height, only for the well-ventilated compartment (open windows); an increase in the HRR accelerates the downward vertical displacement of the smoke layer and that the 3 m smoke curtain is efficient in exhausting smoke, only in the case of poorly ventilated compartments (i.e., with closed windows).

Comparison of Turbulence Models in the Turbulent Wave Boundary Layer for Cnoidal Waves

Turbulent structures in the bottom boundary layer beneath the wave motion have an important role in the nearshore sediment transport modeling and its analyses. Cnoidal waves can be used as a representative of asymmetry waves in the ocean. This paper is aimed to observe the structure of turbulent boundary layer under cnoidal waves as a representative of asymmetry waves in which the effect of asymmetric is actualized along wave cycle related with the wave asymmetric parameter, Ni. The turbulent boundary layer characteristics beneath cnoidal waves motion (i.e. mean velocity and turbulent intensity) are given in the results of experimental results and turbulent numerical models (i.e. the k-ε, the k-ω, the BSL k-ω and the SST k-ω model). Turbulent properties prediction of cnoidal waves from each turbulence model is compared among them and that of experimental results. A laser Doppler velocimeter (LDV) is used to measure the profiles of velocity distribution in the tunnel of oscillating wind over rough bed beneath cnoidal waves motion. From the comparison of the average velocity distribution between all the models of turbulence and the results of experimental for the cases of cnoidal waves in general, it has been obtained that the model of BSL k-ω is superior to predict which is followed by the model of k-ε, the model of k-ω and the model of SST k-ω.

Прогнозування деформацій на заплавах з урахуванням опору при обтіканні мостових опор

Introduction. Eroded processes on the plains are substantially different from riverbed deformations, due not only to their geological structure but also to the presence of vegetation. A large number of experimental and numerical studies on the distribution of the high-speed structure and depth have been carried out in order to predict the blurred processes on the flood plains in the area affected by bridge crossings. The question remains as to how many features of flood plains in the area of the bridge opening should be taken into account. Problems. In the design of bridge crossings, the most interesting value is the maximum deformation that can occur while the operation of a bridge during a design flood or flood. Accordingly, in calculating the deformations not only in the bed but also in the floodplain in the area of the opening of the bridge, it is important to establish the maximum depths, which reasonably determine the required depth of laying the foundations of the bridge supports. The aim of the work. Forecasting of maximum swells in flood plains, taking into account the force of resistance at the fairing of bridge supports. Materials and methods. This paper is based on the theory of mechanics of a continuous environment, heterogeneous flows and the theory of shallow water, mathematical modeling methods, numerical modeling methods. The calculation in the zone of influence of bridge supports is carried out according to the equation of the transfer of the speed of floodplain flow with grass vegetation, taking into account the force of the resistance during the flow of bridge supports. The numerical implementation of the proposed mathematical models on iterative methods for calculating the hydrodynamic characteristics of floodplains with vegetation has necessitated the formulation of initial and boundary conditions to take into account the characteristic features of flood fluxes in the zone impact of bridge crossings. Results. A two-dimensional mathematical model has been developed that makes it possible to take into account the features of the flood plains concerning the distribution of vegetation, the winding and the resistance when the bridge supports are rounded. According to the proposed method, the hydrodynamic indicators of the flood plains of Severski Donets on the T-05-14 road in the Donetsk region were determined, including the longitudinal velocity, taking into account the resistance force of the fairing of the bridge supports and the marking of the bottom region after the passage of the flood down the design staircase. The maximum longitudinal velocity at the beginning of the dip varies between 2.45 m / from 2.32 m / s, respectively, on smaller and larger plains. The depth of the bottom erosion varies from 0.19 m to 1.91 m in the lower floodplain and from 0.035 m to 2.75 m in the greater floodplain. Conclusions. The proposed two-dimensional mathematical model of the floodplain flow makes it possible to determine the distribution of average velocities and depths in accordance with the consistency with the pressure field and taking into account the characteristics of the area under investigation with supports on the floodplain sections in the bridge bridge bridge tail. On the basis of the results of its numerical implementation in the section of r. Severskiy Donets, the value of the maximum dilution has been established, which is the starting point for the determination of the depth of laying the foundations of the bridge supports. The maximum melting depth at the higher floodplain is 2.75 m, and at the lower plain is 1.91 m, which is due to the effect of the drag on the fairing of bridge supports and the compression of the flow between them.

A simple diagnostic model for the cross-channel distribution of the depth average velocity in curved open channels

ABSTRACT A simple diagnostic narrow channel shallow water model for the cross-channel distribution of the depth average velocity is developed. It is diagnostic, because the slope of the stream-wise free surface is specified and it models the cross-channel distribution of the depth average velocity without any knowledge of the velocity field. A non-dimensional parameter that encapsulates the channel dimensions and the relative importance of bottom friction to horizontal eddy viscosity is defined. Numerical solutions for the cross-channel distribution of the depth average velocity are obtained using values of this non-dimensional parameter for different cross-channel topographies. Numerical solutions for the depth average velocity are in turn used to find the cross-channel distribution for secondary flow and vertical velocity. Two-dimensional distributions of the vertical velocity in the n–z-plane show that changes in topography dominate the vertical velocity distribution. Three-dimensional tracers in a hypothetical open channel using scaling values from geophysical observations show that secondary circulation has a loose helical flow pattern of approximately one full rotation for every of curvature. It is not unreasonable to suggest that this 1:1 relationship describes the looseness of secondary circulation in geophysical data.

Aerodynamic Performance and Flow Structure Investigation of Contra-rotating Wind Turbines by CFD and Experimental Methods

Wind tunnel experiment was carried out to measure mechanical power of the contra-rotating wind turbine (CRWT) and single rotor wind turbine (SRWT) under various working conditions. Particle Image Velocimetry (PIV) device was employed to measure the transient flow field on the meridional plane of the rotors. The azimuthal velocity vector, magnitude and streamline were obtained by the average PIV image of ten intervals in a rotation cycle. CFD model of steady flow was developed to predict aerodynamic performance and flow structure of the CRWTs using S-A turbulent model. The single channel model was employed with periodic boundary condition. CFD results were validated with wind tunnel test in literature and experiment in this paper. Results show that CFD method has a satisfied accuracy in power prediction, with a relative error less than 34%. The azimuthal average velocity distributions predicted by experimental and CFD methods are close and the maximum value are approximate to each other. Results demonstrate a high velocity zone at the outside of the front rotor tip and a low velocity zone near the middle of the rear rotor. CRWT has a complicated flow structure. Particularly at the rear rotor, flow becomes uneven and streamline curvatures are more ununiformed.

Experimental study and numerical simulation of mean longshore current for mild slope

In this paper, experimental and numerical studies were performed to investigate the characteristics of longshore current under two mild slopes, the results of which may complement the existing studies, which have mainly focused on steep slopes. The experimental results revealed that the average velocity distribution of the longshore current was significantly different under the two different mild slopes. Under the slope of 1:100, the distribution of the averaged longshore current velocity had a downward concave trend at the nearshore side, while under the slope of 1:40 the trend became convex. In addition, the analysis of the numerical results showed that the distribution of the averaged longshore current velocity was affected by the distribution of the wave height within the surf zone and the bottom friction equations, with the influence of the latter being more significant. For the slope of 1:100, the cross-shore variability of alongshore variability can be calculated using the flow-type bottom friction equation, while for the slope of 1:40, the wave-type bottom friction equation can be used instead. Finally, the secondary breaking wave heights for mild slopes and the distribution of wave set-up are also shown in the study.

DEM study on the effects of pellet characteristics on particle flow in rectangular hopper

In this work, a non-cohesive and multi-element particle model of discrete element method (DEM) was constructed, which was used in combination with experiments to investigate the particle flow characteristics in retangular hopper equipped with the screw discharging machine. On this basis, different diameter pellets (dp = 20 mm, 25.02 mm) with various sphericities (φ = 0.868, 0.985, 1) and particle size distribution (a = 0:1, 0.1:0.9, 0.15:0.85, 0.2:0.8) were selected to examine the effects of sphericity and particle size distribution on the distribution of particle average velocity, motion distance and voidage. Our results showed that as the a increased, the particle average vertical velocity was first decreased and then increased. The motion distance of particles at 1/2 bed height was relatively stable. Furthermore, the average voidage of cylindrical particles was the largest and that of ellipsoidal particles was the smallest. Finally, the specific position of the lag of particle motion is revealed.

The effect of river flow velocity distribution on indications of the occurrence of degradation of the Tambong River basin

Floods that have high flow velocity can be indicated that there is degradation in the riverbed. If the deterioration of the riverbed is allowed to continue, it can cause damage to the existing building infrastructure around the river. Tambong River, located in the Kabat District of Banyuwangi, has experienced river overflowing. Process of measuring flow velocity uses the current meter. To determine the shape and contour of the Tambong River flow velocity distribution using the Surfer Software. In the Tambong River basin, the middle river of the downstream has the highest river flow velocity distribution of 0.92 m/sec, with a discharge of 1.75 m3/sec. It was indicated that the Tambong River Basin in the middle of the downstream would experience river bed degradation by showing a Reynold of 426, 997.33 and a Froude value of 0.55 so that it includes turbulent flow types and flow types subcritical. Average flow velocity distribution in the middle of the Tambong River basin is 0.901 m/sec and was indicated to have degraded as thick as 2.10 m/year. It can be concluded that the middle part of the Tambong river is a flood-prone zone due to the considerable velocity of the river flow.

Poboljšanje mešanja zrna pšenice na dnu dozatora laboratorijske mešalice primenom simulacija metodom diskretnih elemenata

In the agricultural industry, the conservation of wheat grains in silos after stocking is a hard task. This is because when stocking a large crop, hot aeration from the bottom of the silo is not sufficient to preserve the crop and avoid losses due to the manifestation of moisture between grains and grains-wall. As a concern, engineers, as well as inspectors, challenged day-to-day issues whenever packing such granular material. A screw could be a good solution to improve the dryness of the particles and mix the bed material in case of stocking different types of grains. Mainly, the complexity does emanate from the model used to predict accurately the mixing performance. Emerging generation of simulation codes using the discrete element method (e.g., EDEM®, LIGGGHTS, etc.) have brought an intact solution to the problem of particulate flow and particles inhomogeneity. The present work has sought to develop predictive models for average mixing index and particles velocity distribution assessments in mixing of wheat granules in a small-scaled hopper base screw mixer. A screw-mated-horizontal-ploughs has been utilized to improve the agitation of grains rather than a simple screw. 1, 2 and 4 mated ploughs to the screw axle has been used, also the tilt angle of the 4 mated ploughs case has been varied as follows; 20°, 45° and 70° then evaluated. Next, findings regarding bed homogeneity are calculated using the Lacey method [1] for quantitative analysis and visual observations have been read out for qualitative assessment. Particles inhomogeneity is at its minimum when more ploughs mated to the screw were used.

Experimental Investigation of Rotors Hovering above Inclined Surfaces

Particle image velocity measurements were taken to document the wake generated by a rotor operating in ground effect above inclined surfaces. In particular, the current work focused on the average wake structure and axial velocity distribution through the rotor. A two-bladed rotor was operated at a height of one rotor radius above a ground plane that was inclined at angles from 0° to 30°. Rotor performance measurements were also taken, using a six-axis load cell, to examine the effect ground plane angle had on the thrust produced and power required. The wake structure was found to be very sensitive to ground plane angle causing the radial distribution of axial velocity through the rotor to increase inboard and decrease outboard with increasing ground plane angle. As compared to the level ground case, the peak figure of merit of the rotor decreased by approximately 10% for a ground plane inclination angle of 30°.

THEORETICAL CALCULATION OF THE VALUE OF THE VON KARMAN CONSTANT

The article considers various approaches to assessing the physical essence of the von Karman constant characterizing the vertical distribution of the flow velocity. On the one hand, the von Karman constant is a proportionality coefficient between the length of the mixing length and the depth; on the other hand, it characterizes the tilt angle of the vertical velocity profile. It is considered that this parameter is universal, that means it is constant as long as the averaged velocity distribution is constant. However, depending on estimation way of this constant, its values under the same conditions may differ to 2 orders. Two methods for estimating the von Karman constant are considered. In the first case, determination of the von Karman constant is on the grounds of direct measurements of the maximum and average flow velocities, depth and slope of the water surface in a particular area. Propagation of the obtained value to other objects will lead to errors. In the second case, the parameter is defined as a function of the coefficient of hydraulic friction. The authors showed that the von Karman constant is a function of the coefficient of turbulent exchange (viscosity) and indirectly is a function of the depth. As a result of the calculations, it was shown that the maximum values of the von Karman constant observed on the bottom. Additionally, the authors propose a new version of the calculation of the von Karman constant through the tension shift for a turbulent flow. It is concluded that since for velocities <1 meter per second the changes in the von Karman constant values from 0.27 to 0.38 the maximum velocity with variation do not exceed 3%, which fits into the accuracy of the velocity measurements, it is practically impossible to estimate the value of von Karman constant by first method for flat rivers even with multiple measurements with standard hydrometric equipment. Keywords: the von Karman constant; coefficient of turbulent exchange (viscosity); Reynolds number; coefficient of hydraulic friction; velocity distribution diagram; turbulent mode

Investigation of aerodynamics of improved four-vortex furnace device

In this work, the inner aerodynamics of a perspective vortex furnace device with a four-vortex burner layout scheme is experimentally investigated. Using the contactless optical flow diagnostics method (PIV), the averaged velocity distributions are obtained in a number of cross sections of the furnace model for various modes. The spatial structure of the flow is studied. It is found that the flow consists of four vertical vortices with curved rotation axes.

Studying the Flow Structure in a Promising Vortex Furnace

The internal aerodynamics of an isothermal laboratory model of a modified four-vortex furnace for a pulverized coal boiler have been experimentally studied. The digital tracer imaging (particle image velocimetry) technique was used to determine average flow velocity distributions and streamline projections in several sections of the model in various regimes of furnace operation determined by the velocity ratio of flows supplied via primary (main) and secondary nozzles. Conditions for the formation of a stable flow structure with four symmetric conjugated vortices in the entire volume of the furnace, as well as the domain of parameters leading to a nonregular spatial vortex structure, were determined.