Numerical Study Of Flow Field Research Articles

Numerical Study of Flow Field and Particle Motion Characteristics on Raw Coal Vertical Roller Mill Circuits

In order to improve the motion characteristics of particles in vertical roller mills (VRMs), the assumption that different structures of helical guide blades affect the internal flow field of the VRMs was put forward. The distributions of fluid velocity and vorticity in VRMs were analyzed, and the mechanism affecting the motion of particles and the separation performance was studied. The study took the MMLM2550 (supplied by Jiangsu Dahuan Group, China; grinding table diameter of 2550 mm) VRM as the research object, whose structure was improved by adding helical guide blades. The results showed that, with the increase in the width of blade, the air flow trajectory and the distribution of vorticity improved, which was conducive to the transport of particles. However, changing the thickness of the blade had little effect on the internal physical field of the VRM and particle motion characteristics. Therefore, the influence of blade’s thickness on these factors was ignored. With the increase in the number of helical guide blade turns, the direction of the helical guide blade remained consistent with the trajectory of the movement of particles, making it more conducive to the discharge of particles from the VRM. The height of the helical guide blade had a great influence on the flow field and the particle motion characteristics. The smaller the blade height, the greater the reflux in the primary separation zone, and stronger the irregular circulatory motion of particles, thus increasing the movement time and the distance of particles. With the increase in the number of blades, the airflow speed increased in the flow channel, so that the particles moved with the airflow at high speed, while the movement time was effectively shortened. The study provides valuable guidance for the improvement of VRM structures, and serves as a reference for characterizing the motion of particles and enhancing the internal flow field in VRMs.

Numerical Study of Flow Field and Mixing Performance of a New Curved-Sheet Blade-Folded Static Mixer

Numerical Study of Flow Field and Mixing Performance of a New Curved-Sheet Blade-Folded Static Mixer

Numerical Study of Flow Field Over the Deck with Active Flow Control Method

When the destroyer is sailing on the sea, the turbulent ship airwake will be formed above the deck, due to the flow separation after the airflow passes through the edge of the hangar, and the most obvious vortex structure is the recirculation area, which will seriously affect the safety of take-off and landing of the ship-borne helicopter on the deck. Based on the means of flow control in fluid dynamics, this paper improves the quality of the flow field above the deck of the destroyer by adopting different blowing ways (3 blowing angles and 5 blowing speeds). The results show that for different blowing directions, the length of recirculation zone tends to decrease with the increase of blowing speed. The optimal blowing way is the blowing speed of 10m/s in the blowing direction of -45°, and the length of recirculation zone is reduced by 59.4%. This will obviously improve the landing safety of ship-borne helicopters and reduce the pilot's control load.

Numerical study of flow field in new design cyclones with different wall temperature profiles: Comparison with conventional ones

In this paper, numerical study of flow field in the new design cyclones with five different wall temperature profiles are investigated. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. In this paper, the five wall temperature profiles are as follows: (A) cooling with uniform distribution, (B) without temperature change, (C) heating with uniform distribution, (D) incremental linear heating, (E) reduction linear heating. Results are compared in new design and conventional cyclones. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW).Results show that generally, heating the bottom zone of the cyclones can improve the collection efficiency and reduce the pressure drop while heating the top zone of the cyclones marginally affects the flow field. Moreover, cooling the cyclones reduces the efficiency and causes a higher pressure drop. Among five different wall temperature profiles, C and E profiles can increase the efficiency about 8% and profile C reduces the pressure drop by about 9%. The mentioned values in different conditions including particle diameter, flow rate, etc. can be different.

A numerical study of flow field and particle deposition in nasal channels with deviant geometry

ABSTRACT Deviant geometry of nasal channels results in significant changes to nasal aerodynamics that alter flow resistance, sensation, and the ability to filter aerosols. The invasive, operative modification of nasal geometry might alter the intranasal flow patterns, and this must be considered in advance at the stage of surgical planning. The present work describes flow patterns, reproduced numerically for several nasal geometries. This includes the reference channel geometry without physiological modifications. Making use of the commercial CFD-package STAR-CCM+, we document a down to 51% reduction and up to a 280% increase in nasal flow resistance for enlarged and obstructed channel geometries. The study on particle deposition revealed an only 18% deposition efficiency for the enlarged nasal cavities, while this parameter was up to 58% for the normal and obstructed geometries.

Numerical Study of Flow Field in New Design Dynamic Cyclone Separators

In this paper the numerical simulation of flow field in the new design dynamic cyclone separator is investigated. The effects of different geometrical parameters such as impeller diameter, number of vanes, length and the location of impeller is investigated. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) were solved. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that in new design dynamic cyclone, the collection efficiency is higher and the pressure drop is lower in compare with other studied on cyclones. Installing impeller at the lower positions leads to a decrease in efficiency. With increase in impeller diameter, pressure drop in dynamic new design decreases. Finally, with increase in impeller length, efficiency increases and pressure drop decreases.

Numerical study of flow pattern around lateral intake in a curved channel

This paper deals with numerical study of flow field in a channel bend in presence of a lateral intake using three-dimensional numerical model SSIIM2. The effects of bend on the structure of the flow around the intake are investigated and compared with the experimental data. The tests are carried out in a U-shaped channel bend with a lateral intake. The intake is located at the outer bank of an 180∘ bend at position 115∘ with 45∘ diversion angle and the experimental data can be used to calibrate and validate numerical models. The results show that both the center-region and outer-bank cross-stream circulations are observed in the experiments while only the former is captured by the numerical model due to the limitations of the turbulence model. In the curved channel after the intake, both experimental and numerical results show another type of bi-cellular circulations in which clockwise center-region circulations and counterclockwise circulations near the inner bank and the free surface (inner-bank circulations) are captured. The study shows that the numerical model very satisfactorily predicts streamlines, velocity field and flow pattern in the channel and in vicinity of the intake. Investigation of flow pattern around lateral intake in channel bends shows that contrary to the case of flow diversion in straight channels, the width of the dividing stream surface near water surface level is greater than that of near bed level. Finally, the effects of position and diversion angle of the lateral intake, discharge ratio and upstream Froude number on the flow pattern are investigated.

Numerical study of flow field in new design cyclone separators with one, two and three tangential inlets

Numerical study of the fluid flow and particle dynamics is presented by numerical techniques to characterize the performance of new design cyclone separators with one, two and three tangential inlets. The design of this cyclone is based on the idea of improving cyclone performance by increasing the vortex length. This cyclone differs from a conventional cyclone with the separation space. Instead of conical part, the separation space of this cyclone consists of an outer cylinder and a vortex limiter. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved by use of the finite volume method based on the SIMPLE pressure correction algorithm in the computational domain. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). In the results the effects of number of inlets on the different important parameters such as pressure drop, collection efficiency, axial velocity and turbulence are investigated and deeply discussed. Contours of velocity, pressure and turbulent kinetic energy within these cyclones with different number of inlets are shown. The results show that the cyclone with three inlets has more collection efficiency, less pressure drop and less turbulence distribution with respect to cyclones with one and two inlets which is good in cyclones performance. Generally it is recommended to use the new cyclone designs with higher number of inlets.

Numerical study of flow field on molten iron desulfurization with mechanical stirring

The flow field of molten iron in the desulfurization process utilizing the mechanical stirring method under three different conditions was investigated using numerical simulation. The three conditions were central and eccentric stirring with the standard impeller and central stirring with the worn impeller, respectively. Three 1/20-scale numerical models were established and four inspection regions were set up on them. In all, 600 sets of instantaneous velocity fields for each model were exported and proper orthogonal decomposition technique was applied to deal with the data. The macroscopic flow field in the normal model operating under standard conditions was analyzed, which found that the mean flow has a relatively large fluctuation in flow field despite having a high proportion in total kinetic energy. A steady close relationship was revealed between the first two modes by studying the correlation of their coefficients. The first four modes were comparatively analyzed, which reflected that the change in the mean flow in the ladle using a worn impeller is slow and eccentric stirring is beneficial to desulfurization due to the asymmetry of the flow field on two sides.

Numerical study of flow field in new cyclone separators

Numerical study of the fluid flow and particle dynamics is presented by numerical techniques to characterize the performance of new cyclone separators. The design of this cyclone is based on the idea of improving cyclone performance by increasing the vortex length. This cyclone differs from a conventional cyclone with the separation space. Instead of conical part, the separation space of this cyclone consists of an outer cylinder and a vortex limiter. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved by use of the finite volume method based on the SIMPLE pressure correction algorithm in the computational domain. The Eulerian–Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). In the results the dependency of collection efficiency and pressure drop on different geometrical parameters is investigated. Contours of velocity, pressure and turbulent kinetic energy within these cyclones are shown. Tangential velocity profiles and velocity vectors in different sections are investigated.

Numerical Study of Flow Field and Aerodynamic Performance of Straight Bladed VAWT at Variable Tip Speed Ratios

This paper studies the relationship between unsteady flow features and instantaneous torque and power performance of straight bladed vertical axis wind turbine at variable tip speed ratios. The rotor unsteady flow field simulation was carried out by using computational fluid dynamics method. The flow physics and the principle of changing flow field acting on torque performance and power performance have been analyzed where the rotating rotor was the major concern. The results show that the flow feature alters from periodical blade dynamic stall vortexes generation, development and shedding at low tip speed ratio to cyclical formation, evolution and diffusion of blade wake flow with the rising tip speed ratio. Both vortex shedding around the blade and interaction of blade wakes degrade the rotor aerodynamic performance. It is suggested that, to absorb maximum wind energy, delay the blade vortex shedding and reduce the range of blade wake, evolution and diffusion should be included in the rotor aerodynamic design.

A numerical study of flow fields of lobed hailstones falling in air

The characteristics of the flow fields around six falling lobed hailstones of diameters 1 to 10cm are studied. The flow fields are obtained by numerically solving the time-dependent Navier–Stokes equations for flow past the six lobed hailstones created through a set of newly proposed mathematical expressions allowing us to precisely represent their shapes that can be easily meshed afterwards through stereolithography for the simulations performed herein. The range of Reynolds numbers is from 9560 to 388,000, which is believed to be close to the realistic physical range. The computed flow fields are characterized in terms of the streamtrace pattern, vertical velocity, pressure distribution, and vorticity fields. The computed results demonstrate that while the eddy lengths for the six lobed hailstones of equal size are almost the same, with more and longer lobes on a hailstone, the eddies inside the recirculation bubble shed more chaotically. In comparison with our previous numerical work, the spherical hailstones have higher drag coefficients than the three short lobed hailstones in the range of Reynolds numbers roughly between 25,000 and 122,000 while most long lobed hailstones we consider have greater drag coefficients than the spherical ones. However, compared with previous experimental data by others, the smooth spherical graupel and hailstone are both highly greater in drag coefficient than almost all the short and long lobed hailstones considered herein numerically.

A Numerical Study of Flow Field in a Hydrocyclone for Potash Ore Desliming

Despite the widespread use of hydrocyclone in the process of potash ore desliming, its accurate design is often difficult because the feed composition is complicated and the viscosity is high in the brine system. In this study, a numerical approach based on computational fluid dynamics (CFD) was performed to describe the flow field. The numerical simulation of flow pattern in hydrocyclones for potash ore desliming was presented. Some basic information concerning the velocity and pressure distribution is given, and the results can be used as the fundamental basis for its design.

A Numerical Study of Flow Field and Oil Water Separation in Vertical Deadlegs

Deadleg is a kind of blind pipe connected with a main pipe used for fluid transportation, which has distinct flow characteristics. This work aims to investigate the complex flow, oil/water separation and the relation between fluid flow and water concentration of a vertical deadleg. The investigation was based on the solution of algebraic slip mixture model, which calculated the continuity and momentum equations for the mixture of oil and water, and solved the volume fraction equation for the secondary phase. The computed results indicated that the mixing zone of the deadleg consists of two circulation vortexes and the whole mixing length depends on the inlet flow intensity. Furthermore, distinct oil/water stratification forms in the stagnant zone, and the maximum water volumetric concentration is related to the length of stagnant zone and also influenced by the flow intensity of the main pipe, which could increase from 25% to 72% with inlet velocity ranges from 0.75m/s to 5m/s.

Numerical study of flow fields in an airway closure model

The liquid lining in small human airways can become unstable and form liquid plugs that close off the airways. Direct numerical simulations are carried out on an airway model to study this airway instability and the flow-induced stresses on the airway walls. The equations governing the fluid motion and the interfacial boundary conditions are solved using the finite-volume method coupled with the sharp interface method for the free surface. The dynamics of the closure process is simulated for a viscous Newtonian film with constant surface tension and a passive core gas phase. In addition, a special case is examined that considers the core dynamics so that comparisons can be made with the experiments of Bian et al. (J. Fluid Mech., vol. 647, 2010, p. 391). The computed flow fields and stress distributions are consistent with the experimental findings. Within the short time span of the closure process, there are large fluctuations in the wall shear stress. Furthermore, dramatic velocity changes in the film during closure indicate a steep normal stress gradient on the airway wall. The computational results show that the wall shear stress, normal stress and their gradients during closure can be high enough to injure airway epithelial cells.

Numerical study of flow fields in an airway closure model

The liquid lining in small human airways can become unstable and form liquid plugs that close off the airways. Direct numerical simulations are carried out on an airway model to study this airway instability and the flow-induced stresses on the airway walls. The equations governing the fluid motion and the interfacial boundary conditions are solved using the finite-volume method coupled with the sharp interface method for the free surface. The dynamics of the closure process is simulated for a viscous Newtonian film with constant surface tension and a passive core gas phase. In addition, a special case is examined that considers the core dynamics so that comparisons can be made with the experiments of Bian et al. (J. Fluid Mech., vol. 647, 2010, p. 391). The computed flow fields and stress distributions are consistent with the experimental findings. Within the short time span of the closure process, there are large fluctuations in the wall shear stress. Furthermore, dramatic velocity changes in the film during closure indicate a steep normal stress gradient on the airway wall. The computational results show that the wall shear stress, normal stress and their gradients during closure can be high enough to injure airway epithelial cells.

Numerical study of flow field induced by a locomotive fish in the moving meshes

AbstractIn this paper, the equations of motion are solved together with the incompressible constraint condition to simulate the flow field induced by the two specified fish motions. Since the investigated flow/structure interaction varies with time, the analysis is conducted in the moving meshes. Within the arbitrary Lagrangian–Eulerian (ALE) framework, both the space conservation law and the geometric conservation law have been rigorously enforced on the discrete level. Grid points move along with the fish to facilitate the analysis of the induced flow field for revealing the interaction mechanism. The resulting wave and sinusoidal motions of the fish are addressed. Copyright © 2006 John Wiley & Sons, Ltd.

Numerical study of flow field in cyclones of different height

This paper presents the results of numerical simulation of flow pattern in cyclones of different height, which have recently been tested for separation efficiency without any information about flow field. Results show that the difference between tangential velocity in the upper cylinder and in the lower cone of a certain cyclone is not significant, suggesting that reduced cross-section in the cone does not lead to tangential velocity acceleration. Tangential velocity in cyclones of different height is quite different. Tangential velocity decreases with increasing cyclone height, and this should be responsible for the lower separation efficiency observed in long cyclones. However, if there exists considerable shortcut flow at the entrance of the gas exit tube, the higher tangential velocity will not give rise to the higher separation efficiency, for example, in the case of the shortest cyclone covered in this study, whose gas exit tube protrudes into the conical part.

Numerical Study of Flow Fields around Diffuser with Brim

Numerical Study of Flow Fields around Diffuser with Brim

Incompressible Navier-Stokes Computation of the NREL Airfoils Using a Symmetric Total Variational Diminishing Scheme

The purpose of this paper is to present a numerical study of flow fields for the NREL S805 and S809 airfoils using a spatially second-order symmetric total variational diminishing scheme. The steady two-dimensional flow is modeled as turbulent, viscous, and incompressible and is formulated in the pseudo-compressible form. The turbulent flow is closed by the Baldwin-Lomax algebraic turbulence model. Numerical solutions are obtained by the implicit approximate-factorization method. The accuracy of the numerical results is compared with the Delft two-dimensional wind tunnel test data. For comparison, the Eppler code results are also included. Numerical solutions of pressure and lift coefficients show good agreement with the experimental data, but not the drag coefficients. To properly simulate the post-stall flow field, a better turbulence model should be used.