Tangential Velocity Components Research Articles

Erosion under turbulent slurry flow: An experimental determination of particle impact angle, impact direction, and distribution thereof by image processing

In turbulent flows, the extent of erosive wear is given by particle impacts caused deviated from nominal flow by turbulent fluctuations. This paper describes an experimental determination of particle impact angle and impact direction distributions from collective wear scar features by image analysis. A slurry pot is used to produce wear damage on copper in exposure to a dilute slurry of glass beads. Degradation is evaluated by weight loss, and topography data for the image analysis is acquired by non-contact 3D profilometry. The results reveal that most of the kinetic energy is transferred by the tangential component of the impact velocity at shallow impact angles, regardless the particle size. Particle impact conditions do not distribute Gaussian and a statistical cut-off angle is established.

Experimental and Numerical Analysis of a Streamwise Vortex Downstream of a Delta Wing

The present paper analyzes the vortical flow downstream of a delta wing. The delta wing is designed to generate a vortex that resembles the vortex of a nacelle strake. The experimental results of stereoscopic particle image velocimetry measurements performed at different positions downstream of the delta wing display the streamwise development of the vortex. Details of the postprocessing of the measurement data and a quantification of the uncertainties are presented. The evaluation of the mean axial and tangential velocity components and Reynolds stresses provides insights to the vortex characteristics and their development in the streamwise direction. In addition, results of numerical simulations with the DLR TAU-code applying the Menter-Shear Stress Transport (SST) eddy viscosity model and the Speziale-Sarkar-Gatski/Launder-Reece-Rodi (SSG/LRR)- Reynolds stress model show the ability of the turbulence models to capture the vortex development. The experimental results indicate a preservation of the vortex strength and structure downstream of the delta wing. The Menter-SST model does not predict this preservation; rather it computes a rapid decay of vortex strength and an increase in vortex size. In contrast, the results of the SSG/LRR- model are in good agreement with the experiments concerning the mean flow development. However, both turbulence models underpredict the turbulence in the vortex core.

Numerical study of inlet air swirl intensity effect of a Methane-Air Diffusion Flame on its combustion characteristics

In this paper, the effect of inlet air swirl number of a Methane-Air Diffusion Flame on dynamic flow behavior, temperature, and radiation heat flux distribution was investigated using ANSYS-Fluent CFD code. Based on the swirling effect on dynamic flow behavior, a specific equation in terms of axial and tangential velocity components was used to reach the swirl number. The modeling of the chemical reaction was carried out by applying the Eddy Dissipation Model (EDM). Furthermore, radiation heat flux and turbulent flow characteristics were performed by using P-1 and standard k-ϵ models.The results showed that the elevating swirl number of the inlet air from 0.0 to 0.6 develops the furnace internal recirculation zone which leads to producing the combustion products in the internal recirculation zone. Consequently, fuel and air are mixed more efficiently, which results in the enhancement of combustion efficiency by removing the high-temperature zones as the leading cause of producing nitrogen oxides (NOx). Moreover, as the swirl number increases, the radial flow distribution improves, and the flame heat exchange area enhances regardless of the maximum flame temperature reduction, which will increase the flux radiation efficiency by 36.5% and reduces the pollutant NOx by 58.6%.

Shape effects of molybdenum disulfide (nm) micro-rotating particles in crosswise transport of hydrogen oxide: (MoS2–H2O) nano polymer gel

Nano polymers have emerged as a new development offering promising durability, anti-corrosion and thermal efficiency. Nanoparticles shape, size and volume fraction plays critical part in improved performance of heat exchanger systems involving modern manufacturing processes of nano-rheological materials. Molybdenum Disulfide nanostructures finds significant applications in desulfurization processes, in thermoelectric appliances and many more. Motivated by elaborating in further detail, the present article presents a mathematical and computational study on steady, two-dimensional, non-aligned thermo-fluid transport of Molybdenum Disulfide doped-Hydrogen oxide (H2O) based micropolar fluid. To simulate real nano polymer dynamics, the Tiwari-Das model for nano particle concentration and Maxwell-Garnet model for nanofluid thermal conductivity is exploited. The conservation equations for mass, momentum (normal and tangential) and energy are normalized by employing suitable transformations. Numerical solutions are attained via Keller Box method in MATLAB symbolic software. The impact of key emerging dimensionless parameter i.e. nanoparticles volume fraction and various shape effects of molybdenum disulfide nanoparticles on non-dimensional normal and tangential velocity components, micro rotation profile, temperature, shear stress at the wall and local heat flux is explored graphically. Local heat flux and micro-rotation profile is boosted while tangential skin friction coefficient depletes with the insertion of blade shaped nanoparticles. Moreover greatest thermal conductivity is achieved with the insertion of blade shape nanoparticles.

Computational and Physical Examination About the Aspects of Fluid Flow Between Two Coaxially Rotated Disks by Capitalizing Non-fourier Heat Flux Theory: Finite Difference Approach

This pagination is executed to exemplify flow features exhibited by viscous fluid between two coaxially rotated disks. Thermal analysis is performed by using Cattaneo-Christov heat flux theory. Porosity aspects are also taken in to account. Mathematically structured non-linear PDEs are transmuted into non-linear ODEs by employing Karman transformations. Afterwards, solution is heeded by applying implicit finite difference scheme renowned as Keller box method. Interpretation of flow controlling parameters on axial, tangential and radial components of velocity, thermal distribution is exhibited. Assurance of computed data is done by managing comparison for skin friction coefficients at walls of disks. From the attained outcomes it is addressed that the magnitude of axial and radial velocities diminishes at lower disk contrary to upper disk for intensifying magnitude of Reynold number. Increment in tangential component of velocity is also demonstrated for uplifts values of Reynold number. It is also concluded that thermal field decrements for increasing of Pr and thermal relaxation parameter. It is worthy to mention that shear drag coefficient at wall of lower disk decreases conversely to the wall shear coefficient magnitude at wall of upper disk.

Dynamics of dislocations in the domain structure of the nematic liquid crystal

Dynamics and interaction of classical dislocations in the domain structure of π/2 nematic liquid crystal is studied. A feature of twisted nematics is that hydrodynamic flows in Williams domains, together with the tangential component of velocity, also have an axial component, the direction of which is opposite in neighboring domains. Dislocations can move both perpendicular (glide) to Williams domains, and along (climb) them. It was found that when dislocations collide with opposite topological charges S = ±1 at given voltage, their speed increases. It has been shown that dynamics and interaction of dislocations with topological charges S = ±1 are qualitatively well described by the perturbed sine-Gordon equation.

A Microscale Mathematical Blood Flow Model for Understanding Cardiovascular Diseases.

The blood plasma flow through a swarm of red blood cells in capillaries is modeled as an axisymmetric Stokes flow within inverted prolate spheroidal solid-fluid unitary cells. The solid internal spheroid represents a particle of the swarm, while the external spheroid surrounds the spheroidal particle and contains the analogous amount of fluid that corresponds to the fluid volume fraction of the swarm. Analytical expansions for the components of the flow velocity are obtained by introducing a stream function ψ which satisfies the fourth-order partial differential equation E4ψ=0. We assume nonslip conditions on the internal inverted spheroidal boundary which is also impermeable, while on the external spheroidal surface, we assume continuity of the tangential velocity component and nil vorticity. In order to solve the problem at hand, we employ the method of Kelvin inversion, under which, the initial problem, formulated in the inverted prolate spheroidal coordinates, is transformed to an equivalent one in the prolate spheroidal coordinates, where the solution space of the equation E4ψ=0 is already known from our previously published work. The solution for the original problem is obtained by using the inverse Kelvin transformation and the effect of this transform to the Stokes operator (Dassios, IMA J Appl Math 74:427-438, 2009). Finally, the analytical solution for the stream function ψ is given through a series expansion of specific combinations of Gegenbauer functions of mixed order, multiplied by the Euclidean distance on the first and on the third power, in a so-called R-separable form.

Binary collisions and coalescence of droplets in low-pressure fuel injector

The phenomena of binary collisions and coalescence of droplets was investigated from experimental studies but still are missing from real applications such as from fuel injector. The main purpose of the current study is to investigate the phenomena of binary collisions and coalescence of droplets from a practical port fuel injector (PFI). To accomplish this, direct microscopic images are taken from high-speed video camera coupled with a long-distance microscope and Barlow lens using the backlighting method. Experimental optimization of the spatial resolution and the depth -of -field of the long-distance microscope and Barlow lens are achieved. Experimental results from the direct microscopic images are compared with predictions from empirical equations for different collision regimes. Droplet sizes and velocities of experimental coalescence droplets from collisions are compared with the values predicted by the equations. The main results of this study are: The probability of collision and coalescence is very low in a PFI. The tangential velocity components of small droplets play an essential role in shape deformation during collisions and coalescence of the droplets. The previous published empirical equations to calculate dimensionless parameters, the Weber number (We), the droplet diameter ratio (?), and impact parameter (B) are applicable to the coalescence of droplets in a PFI.

Entropy-induced Separation of Binary Semiflexible Ring Polymer Mixtures in Spherical Confinement.

Coarse-grained molecular dynamics simulations are used to investigate the conformations of binary semiflexible ring polymers (SRPs) of two different lengths confined in a hard sphere. Segregated structures of SRPs in binary mixtures are strongly dependent upon the number density of system (ρ), the bending energy of long SRPs (Kb, long), and the chain length ratio of long to short SRPs (α). With a low ρ or a weak Kb, long at a small ratio α, long SRPs are immersed randomly in the matrix of short SRPs. As ρ and bending energy of long SRPs (Kb, long) are increased up to a certain value for a large ratio α, a nearly complete segregation between long and short SRPs is observed, which can be further characterized by the ratio of tangential and radial components of long SRPs velocity. These explicit segregated structures of the two components in spherical confinement are induced by a delicate competition between the entropic excluded volume (depletion) effects and bending contributions.

Analysis of a propeller turbine operated in a full load operating point

A full load operating point of a propeller turbine is investigated both numerically and experimentally. Steady state and unsteady flow simulations, using four different turbulence models with grid sizes up to 100 million elements, are validated with experimental results which are performed according to IEC 60193 standard. Due to the high swirl number of S = -0.175 at the runner outlet, steady state and unsteady RANS simulations are no longer capable to predict the correct flow field in the draft tube of the turbine. Hence, unsteady simulations with scale-resolving turbulence models, are performed. As a result of the high swirl a full load vortex rope is generated starting at the runner hub developing in the center of the draft tube. The integral quantities head and torque as well as the axial and tangential velocity components at five evaluation lines in the draft tube are validated with experimental results. Velocity components are both time- and phase-averaged, using the runner as trigger signal. Additionally, a comparison of local quantities, head loss in the draft tube and the pressure recovery factor is carried out. The turbulence quantities of the different approaches are evaluated at the evaluation lines applying the viscosity ratio or energy spectra at discrete points in the draft tube of the turbine.

Laser diagnostics of the instability onset in the confined vortex flows

This paper focus is the application of optical methods of pulsating vortex flow diagnostics on the example of swirling flow instability in a cylinder with rotating lid and aspect ratio h = 3.3, 3.4. To obtain a complete picture of auto-generated pulsations development, long-term LDV measurements of the tangential velocity component were carried out with a continuous method of the Reynolds number variation from 2000 to 3500 over 8 hours (30,000 seconds). In the view of the smallness of the Reynolds number increase rate ΔRe / Δt = 0.05 s−1, this process can be considered as quasi-equilibrium. A comparison with the widely used discrete method of the Reynolds number variation is made, given range of the Reynolds numbers was studied with a step ΔRe = 50 for 20 minutes per point. It was found that at the same h, Re different vortex structures are formed depending on the Reynolds number variation method. In the case of discrete the Reynolds number variation, the development of pulsations may require up to 2000 rotating lid revolutions or 500 seconds, it should be considered conducting the experiments.

Effect of gravity in wheel/terrain interaction models

AbstractPredicting the motion of wheeled robots in unstructured environments is an important and challenging problem. The study of planetary exploration rovers on soft terrain introduces the additional need to consider the effect of nonterrestrial gravitational fields on the forces and torques developed at the wheel/terrain interface. Simply reducing the wheel load under Earth's gravity overestimates the traveled distance and predicts better performance than is actually observed in reduced‐gravity measurements. In this paper, we study the effect of gravity on wheel/terrain interaction. Experiments were conducted to assess the effect of reduced gravity on the velocity profile of the soil under the wheel, as well as on the traction force and sinkage developed by the wheel. It was shown that in the velocity field of the soil, the decay of the tangential velocity component becomes gradual with reducing gravity, and the decay of the normal to rim velocity is slower in Lunar gravity. It was also found that wheel flexibility can have an important effect on the dynamics as the contact patch and effective radius vary periodically. These results were then used together with traditional semiempirical terramechanics models to determine and validate the simulated drawbar pull values. The developed simulation model includes the effect of wheel flexibility, dynamic sinkage, and gravity.

Fog harvesting from cooling towers using metal mesh: Effects of aerodynamic, deposition, and drainage efficiencies

Fog harvesting is recognized as an important alternate source of fresh water. Industrial fog can supplement water for industrial requirement. Collection of fog (drift droplets) from cooling tower plumes is a viable mode of industrial fog harvesting. The present study delves deeper into the findings of our earlier pilot investigation, on cooling tower fog harvesting and unravels how the collection efficiency depends on interaction of the mesh with the oncoming flow and the deposited fog droplets. Herein, we quantify the fog collection and explain the rationale of the individual contributions of aerodynamic, deposition, and drainage efficiencies on the overall collection efficiency. The effect of the mesh orientations and the tangential velocity component of the cooling tower plume (arising out of the cooling tower-fan rotation) are considered. Aerodynamic efficiency of the mesh and pressure drop across is estimated through computational fluid dynamic analysis. Also, an analysis of the force interaction between the mesh wires, deposited droplet, and the fog stream is carried out to identify the salient deterring factors like re-entrainment, clogging, and premature dripping of collected water droplets, based on which the regime of collection is mapped. The best collection configuration is found at an inclination of 15° with the vertical, with an overall collection efficiency of about 16%. The best configuration would allow recovery of re-usable fresh water at a nominal energy penalty of ∼3.9 kWh/m3. Our results offer the design bases for developing full-scale fog harvesting setups for industrial cooling towers.

On the substantiation of the effectiveness of air-centrifugal separation and dust cleaning of seed heap of herbs after the grate device

The agrobiological and physico-mechanical properties of leguminous seed plants do not allow them to be harvested without loss exclusively by combine technologies. One way to increase the productivity of the seed production process is to include stationary machines in the assembly technology for wiping and separating seed heaps. Combining these important operations with one machine will further increase the efficiency of legume seed production technologies. This work is devoted to considering ways to increase the efficiency of air-centrifugal separation and dust cleaning seed heaps. A review of recent studies and publications has shown that there is a sufficient methodological basis for determining the parameters of the process of separation of the heap and purification of the exhaust air. An analysis of the publications made it possible to determine the purpose of the research, which is to increase the efficiency of the grater-separation unit by substantiating its scheme and the method of theoretical determination of the parameters of the separation process. According to the results of previous studies, a structural scheme of the grater-separating device is proposed. The main elements of the block are a grater device, which consists of a motionless and movable corrugated discs of the separating device with separate channels for the exit of seeds, straw part of the heap, air. To increase the efficiency of the cleaning process, a blade swirler and a louvre nozzle are placed in the separating device, which provide the air flow with rotational movement around the axis of the cyclone body. In theoretical studies of the motion of particles in a rotational air flow, the simplified assumption was adopted: the particles are spherical, do not deform, and do not interact with each other, the inertia force is directed along the radius of the cyclonic chamber, the tangential and axial components of the particle velocity are equal to the corresponding components of the air velocity, and the particle resistance force determined by the Stokes law, the force of attraction is much less than the centrifugal force, so we neglect it. The obtained formulas allow one to approximately determine the parameters of the cyclone device that will ensure the separation of the seeds of legumes.

Material removal efficiency improvement by orientation control of CMP pad surface asperities

This paper presents a novel method of improving material removal efficiency in the chemical mechanical polishing (CMP) process by optimizing the surface asperity orientation with respect to polishing motion. Feret's diameter plays a key role in increasing the number of working abrasives. Based on Feret's diameter model, an optimization method is proposed for the conditioning motion of a diamond dresser against a CMP pad. The radial velocity component of the dresser on the CMP pad is maximized by considering its direction of motion based on kinematic motion simulation. In addition, the pad cut rate profile is optimized to be uniform. Analytical and experimental investigations show that the ratio of radial and tangential velocity components is improved, yielding a larger Feret's diameter and 15% increase in the material removal rate.

Трехмерный газодинамический расчет соплового аппарата малорасходной центростремительной турбины

The article describes the low-consumption turbines as reliable, productive, small-sized actuating mechanisms in various units and machines. Experience in production and use 
 of low-cost turbine stages contributes to improving the efficiency along with simplifying and re-ducing the cost of manufacturing of the blades and the stage in general. Improving the efficiency 
 of low-consumption turbines requires solving the problem of aerodynamic improvement of the flow part and the calculated determination of the optimal geometry and operating modes of the impeller flow. One of the innovative ways to improve the design efficiency of low-consumption turbines is the automation of the development process using modern modeling systems based on the developed software systems. Due to the small size of the design, the design calculations of turbine stages of this type have been made in a one-dimensional formulation with the involvement of various analogies with classical stages. Using three-dimensional gas dynamic calculations based on the ANSYS CFX platform will significantly improve the quality of design of flow parts of low-flow turbines. Implementation of three-dimensional gas-dynamic calculation of the nozzle unit using the software package ANSYS CFX low-consumption turbine stage can solve this problem. The geometric model is built using AutoCAD software, the grid is selected, the boundary conditions are set. The values of the experimental coefficients of the nozzle velocity, neck velocity and the tangential component of velocity at the nozzle outlet have been compared with the coefficients obtained when using the software package. There have been built the velocity fields and made conclusions about feasibility of using the ANSYS CFX software package to determine the main parameters of a three-dimensional flow of the turbine stage.

Creeping flow of fluid sphere contained in a spherical envelope: magnetic effect

The characteristic of creeping flow past a fluid sphere enclosed in a spherical envelope bearing fluid of different viscosity has been studied under the impact of transverse magnetic field. Stream functions related to modified Bessel functions are used in order to calculate the solution in closed form. The problem is considered to be parted into two flow regions as inner fluid and outer fluid region respectively, which are supposed to be governed using Stokes equations with different Hartmann number. At the contact layer of outer and inner fluid sphere, we assume the vanishing of normal components of velocity along with continuity of tangential components of velocity and stress respectively as boundary conditions. The condition of vanishing of vorticity (Kuwabara model) is considered to be applicable at the outer layer of fluid envelope. Expression for drag acting on the inner fluid sphere is presented. In limiting cases, several significant results accessible in literature are evaluated.

Eulerian conditional statistics of turbulent flow in a macroscale multi-inlet vortex chemical reactor

The conditional velocity time averages (⟨Ui|ξ⟩) and conditional mixture fraction time averages (⟨Φ|ωi⟩) were computed based on the Eulerian approach from the experimental data measured in a macroscale multi-inlet vortex chemical reactor. The conditioning events were determined by equally sized intervals of the sample space variable for the mixture fraction (ξ) and the velocity vector (ωi). The experimental data, which consisted of instantaneous velocities and concentration fields for two Reynolds numbers (Re = 3250 and 8125), were acquired using the simultaneous stereoscopic particle image velocimetry (stereo-PIV) and planar laser induced fluorescence techniques. Two mathematical models, the linear approximation and probability density function (PDF) gradient diffusion, were validated by experimental results. The results of the velocity conditioned on the mixture fraction demonstrated that the linear model works well in a low turbulence region away from the reactor center. Near the reactor center, high velocity gradients coupled with low concentration gradients reduce the accuracy of the linear model predictions. Nevertheless, an excellent agreement was found for the conditional events within ±2Φrms (mixture fraction root mean square). Due to lower concentration gradient in the tangential direction, the linear model better predicted the tangential velocity component for all locations investigated. The PDF model with an isotropic turbulent diffusivity performed inadequately for the tangential and axial velocity components. A modified version of the PDF model that considers the three components of the turbulent diffusivity produced a better agreement with the experimental data especially in the spiral arms regions of significant concentration gradients. Furthermore, the mixture fraction conditioned on the velocity vector components showed a more linear behavior near the reactor center, where the PDF of the mixture fraction is a Gaussian distribution. As the concentration gradients became prominent away from the reactor, ⟨Φ|ωi⟩ also deviated from the linear pattern. This was especially remarkable for the mixture fraction conditioned on the tangential velocity. The overall prediction of ⟨Φ|ωi⟩ improves at higher Reynolds number as the fluid mixing is enhanced.

Analysis of entrance region flow of Bingham nanofluid in concentric annuli with rotating inner cylinder

This work analyses the entrance region flow of Bingham nanofluids in cylindrical concentric annuli. In this discussion, water is used as the base fluid which is embedded with the silver(Ag) and copper(Cu) nanoparticles coalescing with Bingham fluid. The investigation has been carried out by rotating the inner cylinder, while the outer cylinder is assumed to be at rest. A finite-difference analysis is used to obtain the axial, radial, tangential velocity components and the pressure along the radial direction. With the Prandtl's boundary layer assumptions, the continuity and momentum equations are solved iteratively using a finite difference method. Computational results are obtained for various non-Newtonian flow parameters, different volume fraction parameters and geometrical considerations. This work’s main interest is to study the development of velocity profiles and pressure drop in the entrance region of the annuli. The present results are compared with the results available in the literature for various particular cases and it is found to be in good agreement.

Complex Dynamics of the Cascade of Kink—Antikink Interactions in a Linear Defect of the Electroconvective Structure of a Nematic Liquid Crystal

The complex dynamics of an ensemble of dislocations in a linear defect appearing in a one-dimensional electroconvective structure of a π/2-twisted nematic liquid crystal has been studied. This type of defects is characterized by a quite extended strain field or degree of “dissociation.” Hydrodynamic flows in domains of the twisted nematic liquid crystal have not only the tangential velocity component but also the axial component whose directions in neighboring domains are opposite. Under the action of an applied voltage, the linear defect with the topological charge S = −1 begins to oscillate and decays into an odd number of dislocations with the conservation of the total topological charge. The further dynamics of dislocations in the core of the defect is established such that it ensures the continuity of the flow of an anisotropic liquid in domains. The spatiotemporal dynamics of the cascade of interacting dislocations is qualitatively well described by the multikink solution of the sine-Gordon equation. The fundamental possibility of creating new model objects with a given number of interacting dislocations has been shown.