Streamlines Research Articles

Indoor Corridor Wideband Radio Propagation Measurements and Channel Models for 5G Millimeter Wave Wireless Communications at 19 GHz, 28 GHz, and 38 GHz Bands

This paper presents millimeter wave (mmWave) measurements in an indoor environment. The high demands for the future applications in the 5G system require more capacity. In the microwave band below 6 GHz, most of the available bands are occupied; hence, the microwave band above 6 GHz and mmWave band can be used for the 5G system to cover the bandwidth required for all 5G applications. In this paper, the propagation characteristics at three different bands above 6 GHz (19, 28, and 38 GHz) are investigated in an indoor corridor environment for line of sight (LOS) and non‐LOS (NLOS) scenarios. Five different path loss models are studied for this environment, namely, close‐in (CI) free space path loss, floating‐intercept (FI), frequency attenuation (FA) path loss, alpha‐beta‐gamma (ABG), and close‐in free space reference distance with frequency weighting (CIF) models. Important statistical properties, such as power delay profile (PDP), root mean square (RMS) delay spread, and azimuth angle spread, are obtained and compared for different bands. The results for the path loss model found that the path loss exponent (PLE) and line slope values for all models are less than the free space path loss exponent of 2. The RMS delay spread for all bands is low for the LOS scenario, and only the directed path is contributed in some spatial locations. For the NLOS scenario, the angle of arrival (AOA) is extensively investigated, and the results indicated that the channel propagation for 5G using high directional antenna should be used in the beamforming technique to receive the signal and collect all multipath components from different angles in a particular mobile location.

Linear and Weak Nonlinear Double Diffusive Convection in a Viscoelastic Fluid Saturated Anisotropic Porous Medium with Internal Heat Source

This paper deals linear and weak nonlinear stability analysis of double-diffusive convection in an anisotropic porous layer with internal heat source saturated by viscoelastic fluid. For linear stability analysis we use normal mode technique and obtained the expression for oscillatory thermal Rayleigh number which is used to plot neutral stability curve for oscillatory case. For nonlinear analysis truncated representation of Fourier series upto two terms is used. The system of time dependent nonlinear equation is solved numerically and plot the curve for heat transfer and mass transfer with respect to time for different parameters. Effect of thermal anisotropy parameter, mechanical anisotropy parameter, relaxation parameter, retardation parameter, internal heat source parameter, solute Rayleigh number, diffusivity ratio, Darcy-Prandtl number on the onset of convection, heat and mass transfers have been discussed. We also draw the stream lines, isotherms, isohalines at different times.

Numerical study of an asymmetrically heated rectangular duct with suspended cylinders

An asymmetrically heated (only one side of the duct is heated) solar air heater duct is numerically investigated using openFOAM to study the effect of passive turbulators (suspended cylinders) installed within the boundary layer close to the absorber plate to enhance heat transfer from it. Vortex flow is created behind the suspended cylinders, which disturbs the boundary layer and causes mixing of hot stream lines near the surface with relatively cold stream away from the absorber plate. Diameter of the suspended cylinders and its distance from the absorber plate is varied to study its effect on wall temperature of absorber plate in the turbulent flow regime.

Effect of Hartmann Number on Free Convective Flow of MHD Fluid in a Square Cavity with a Heated Cone of Different Orientation

This paper presents the effect of magnetic field, indicated by Hartmann number (Ha), on the free convective flow of Magneto-hydro-dynamic (MHD) fluid in a square cavity with a heated cone of different orientation. Although similar studies abound, the novelty of this work lies in the presence of the heated cone, whose orientation is varied at different angles. The mathematical model includes the system of governing mass, momentum and energy equations. The system is solved by finite element method. The calculations are performed for Prandtl number Pr = 0.71; the Rayleigh number Ra = 10, 1000, 100,000; and for Hartmann number Ha = 0, 20, 50, 100. The results are illustrated with streamlines, velocity profiles and isotherms. From the results, it is found that for the present configuration, magnetic field (Hartmann number) has no effect on the shape of the streamlines for low Rayleigh numbers. However, for high values of Ra, the effect of Ha becomes quite visible. Magnetic field affects the flow by retarding the fluid movement, and thus affects convective heat transfer. At low Ra, the fluid movement and heat transfer rate are already slowing, thus impressing a magnetic field does not produce much effect. At high Ra, fluid particles move at high velocity and change the stream lines, in absence of any magnetic force. Impressing magnetic field in this situation produced noticeable effect by slowing down the fluid movement and changing the streamlines back to low Ra situations. It is noted that a combination of low Ra with zero or low Ha produces similar effects with the combination of high Ra and high Ha. It can be concluded that with increasing Ha, heat transfer mode in MHD fluid gradually changes toward conduction from convection. It can be surmised that sufficiently large Ha can potentially stop the fluid movement altogether. In that case, heat transfer would be fully by conduction.

Heat transfer enhancement using U-shaped flow routing plates in cooling printed circuit boards

This study presents a numerical investigation on the effect of the U-shaped flow routing plate to laminar mixed convection heat transfer from protruded heat sources at the side walls of a horizontal channel. The air was used as a cooling fluid and protruded heat sources were equipped as 4 × 8 rows into the rectangular channel with insulated walls. Numerical investigations are carried out for the plate width/channel width ratio (LP/W) of 3/20, 1/10, 1/20 and plate angles (α) of 0°, 30°, 60° at different Reynolds (Re), modified Grashof (Gr*) and Richardson (Ri) numbers. In the study, periodic plate placement was analyzed numerically and the effects of a plate placement array on heat transfer enhancement were investigated. The highest heat transfer enhancement (180%) was observed for the values of α = 30° LP/W = 3/20 at all the Re, Gr* and Ri number values. The predominance of natural convection increases the use of the flow routing plate effectiveness but causes a decrease in the heat transfer enhancement after a certain number of Ri. Therefore, the increase in natural convection needs to be controlled. Theoretical fan power (Nfan) requirements due to pressure loss are also investigated. Depending on the parameters used in the numerical study, as a result of the plate usage, the pressure losses increased according to the case without a plate. It is observed that the most important factor affecting the pressure loss was the Re number and this case indicated that the plate placement was more appropriate for low values of Re. The findings obtained during the numerical studies were presented in detail as graphics of the row averaged Nusselt number (Nurow ave.) and the heater temperatures, surface stream lines, and temperature contours.

Unsteady Behavior of Necklace Vortex Produced by a Square Plate Protrusion

In this study, the unsteady behavior of necklace vortices formed in front of a square flat plate was experimentally investigated by flow visualization and PIV analysis by using a water channel. As a result, the necklace vortices started to oscillate when the Reynolds number increased beyond approximately 2000. Then, an amalgamation behavior of the necklace vortices took place when the Reynolds number increased beyond approximately 2650. Furthermore, in the same Reynolds number range, a breakaway behavior appeared when the relative height of the square plate was beyond approximately h/δ = 4.0. The features of the necklace vortices behaviors in the oscillation, amalgamation and breakaway states were explained by observing the time-series image of path lines and by analyzing the frequency of velocity fluctuation.

Evaluation of material deformability and pressure distribution on die surface around centerline of tool travel in friction-stir forming

Friction-stir forming (FSF) is a friction-stir process developed for fabricating product shapes. In FSF, friction stirring is conducted on the back surface of a material plate that is put on the die. The material deforms and fills the cavity of the die due to high pressure and heat caused by friction stirring, and it often has outstanding deformability and moldability. Conventional studies on friction-stir welding have not sufficiently clarified it as a metal-forming process. In this paper, material deformability along the tool travel path of friction-stir forming was investigated using a die having hole-cavities with various diameters on a straight line. The authors conducted FSF on 3 mm-thick A5083P-O aluminum plates on parallel-offsetting paths from the centerline of holes and evaluated the height of cylindrical extrusions to determine the deformability distribution of the material around the centerline of the tool movement path. In addition, forming pressure distribution on the die surface was evaluated using an embedded pressure pin connected with a load sensor. The authors conducted FSF on offsetting path lines from the center of the pin repeatedly as well as deformability tests and recorded the change of forming pressure with tool position, which was compiled from the bearing load of the pin, and mapped it two-dimensionally.

Influence of hole geometry on film cooling effectiveness for a constant exit flow area

Film cooling is an effective method which can protect the surface from the high temperature environment. Most previous studies have used the same mass flux ratio with different coolant exit flow area for different holes. A better comparison of the film cooling effectiveness would keep the coolant mass flow rate and exit area the same. The present study investigated the effect of hole geometry on the film cooling effectiveness for a constant film cooling exit flow area experimentally and numerically. Four kinds of film cooling holes, the cylindrical hole, the fan-shaped hole, the double jet holes and the hole with sister holes were studied with blowing ratio varied from 0.3 to 1.5. In the experiment, plate surface temperature was measured by an infrared camera and the main flow and coolant flow temperature were measured by thermocouples. To investigate the flow characters, numerical calculation using RNG k−ε turbulence model was performed. Protected wall temperature, film cooling effectiveness and coolant flow stream lines were studied to illustrate the difference between the coolant jets from the four kinds of hole geometries. The results show that film cooling with the other three kinds of holes have an obvious advantage compared to the cylindrical hole. The reason is that for the cylindrical hole, the coolant flow forms a strong vortex pair in the main flow which pulls the hot main flow underneath the coolant flow to lift the coolant jet from the wall, so the cooling effectiveness is very low. For the other three kinds of holes, the mixing between the main flow and the coolant jet forms a complex vortex structure which keeps the coolant jet on the wall, thus improves the cooling effectiveness.

Study of Snow Accumulation on Bogies Based on the DPM

During winters, the high-speed train in the northern of China, are struck by the recurring problems related to the snow and ice on the bogies. To understand the cause of snow packing in the high-speed train’s bogie regions clearly, a DPM discrete phase model were used to investigate the flow field carried snow particles in a single high-speed train bogie region and monitor the movement of snow particles. The results show that when air flows into the region which is a cavity, the airflow will rise and impact on the wheels, brakes, electromotors and other parts of bogie regions. The snow particles in the flow field will follow the path line of the air; while the air direction changes sharply, the snow particles will keep the movement due to the inertia. Afterwards, the snow is packed in the bogie region. In front of the obstacles the streamlines of the air flow and the particle path lines are basically the same. However, due to the inertia of mass particles, the following characteristics of the snow particles with the air are not obvious in the bogie leeward side, so there is much less snow.

Design and simulation of a microfluidic device for acoustic cell separation

Experimental acoustic cell separation methods have been widely used to perform separation for different types of blood cells. However, numerical simulation of acoustic cell separation has not gained enough attention and needs further investigation since by using numerical methods, it is possible to optimize different parameters involved in the design of an acoustic device and calculate particle trajectories in a simple and low cost manner before spending time and effort for fabricating these devices. In this study, we present a comprehensive finite element-based simulation of acoustic separation of platelets, red blood cells and white blood cells, using standing surface acoustic waves (SSAWs). A microfluidic channel with three inlets, including the middle inlet for sheath flow and two symmetrical tilted angle inlets for the cells were used to drive the cells through the channel. Two interdigital transducers were also considered in this device and by implementing an alternating voltage to the transducers, an acoustic field was created which can exert the acoustic radiation force to the cells. Since this force is dependent to the size of the cells, the cells are pushed towards the midline of the channel with different path lines. Particle trajectories for different cells were obtained and compared with a theoretical equation. Two types of separations were observed as a result of varying the amplitude of the acoustic field. In the first mode of separation, white blood cells were sorted out through the middle outlet and in the second mode of separation, platelets were sorted out through the side outlets. Depending on the clinical needs and by using the studied microfluidic device, each of these modes can be applied to separate the desired cells.

Modelling the generation of temperature inhomogeneities by a premixed flame

The response of a laminar, premixed flame to perturbations of upstream equivalence ratio is investigated and modelled, with emphasis on the generation of ‘entropy waves’, i.e. entropic inhomogeneities of downstream temperature. Transient computational fluid dynamics simulations of two adiabatic lean methane-air flames of different Péclet numbers provide guidance and validation data for subsequent modelling. The respective entropy transfer functions, which describe the production of temperature inhomogeneities, as well as transfer functions for the variation of the heat release, are determined from the computational fluid dynamics time series data by means of system identification. The processes governing the dynamics of the entropy transfer functions are segregated into two sub-problems: (1) heat release due to chemical reaction at the flame front and (2) advective and diffusive transport. By adopting a formulation in terms of a mixture fraction variable, these two sub-problems can be treated independently from each other. Models for both phenomena are derived and analysed using simple 0- and 1-dimensional configurations. The heat release process (1) is represented by a fast-reaction-zone model, which takes into account variations of the specific heat capacity with equivalence ratio in order to evaluate the magnitude of downstream temperature fluctuations with quantitative accuracy. For the transport processes (2), two types of models based on mean field data from the computational fluid dynamics simulation are proposed: A semi-analytical, low-order formulation based on stream lines, and a state-space formulation, which is constructed by Finite Elements discretisation of the transport equation for mixture fraction. Model predictions for the entropy transfer functions are found to agree well with the computational fluid dynamics reference data at very low computational costs.

Investigation of the fluid flow dynamic parameters for Newtonian and non-Newtonian materials: an approach to understanding the fluid flow-like structures within fault zones

To understand the fault zone fluid flow-like structure, namely the ductile deformation structure, often observed in the geological field (e.g., Ramsay and Huber The techniques of modern structure geology, vol. 1: strain analysis, Academia Press, London, 1983; Hobbs and Ord Structure geology: the mechanics of deforming metamorphic rocks, Vol. I: principles, Elsevier, Amsterdam, 2015), we applied a theoretical approach to estimate the rate of deformation, the shear stress and the time to form a streak-line pattern in the boundary layer of viscous fluids. We model the dynamics of streak lines in laminar boundary layers for Newtonian and pseudoplastic fluids and compare the results to those obtained via laboratory experiments. The structure of deformed streak lines obtained using our model is consistent with experimental observations, indicating that our model is appropriate for understanding the shear rate, flow time and shear stress based on the profile of deformed streak lines in the boundary layer in Newtonian and pseudoplastic viscous materials. This study improves our understanding of the transportation processes in fluids and of the transformation processes in fluid-like materials. Further application of this model could facilitate understanding the shear stress and time history of the fluid flow-like structure of fault zones observed in the field.

Numerical investigation of Cattanneo-Christov heat flux in CNT suspended nanofluid flow over a stretching porous surface with suction and injection

The present study analyzes the heat energy transfer in nano fluids flow through the porous stretching surface. Cattanneo-Christov heat flux model is employed to study the heat energy transfer. Darcy law is used to discuss the flow characteristics over the different types of permeable sheets with suction and injection. Nanofluids is considered as water based single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) nanofluids. A comparative study for SWCNT and MWCNT is also made. Governing equations are transformed into set of ordinary differential equations using similarity transformations. The computational results are obtained by using Runge-Kutta fourth order method along with shooting technique. Numerical and graphical results are presented to discuss the effects of various physical parameters on velocity profile, temperature profile, Nusselt number, Sherwood number and skin friction coefficient for different type of nanoparticles for suction and injection cases. Stream lines and isotherms are also plotted for three different cases viz. permeable sheet with suction, impermeable sheet and permeable sheet with injection. A comparative analysis with existing results is tabulated which validate that the numerical results of present study have good correlation with existing results. The outcomes of the results show that skin friction coefficient is more for SWCNT in caparison of MWCNT and the boundary layer thickness is maximum for permeable stretching sheet with suction parameter.

Numerical simulation of friction extrusion process

A three-dimensional computational fluid dynamics model with consideration of both heat transfer and material flow has been developed. The heat generation model from a previous study was adopted. The temperature predictions have a good agreement with experimental measurements, showing that material flow during the friction extrusion process has limited influence on heat transfer. Small solid particles were used as tracked markers in the fluid in the modeling to capture the material flow pattern. The path lines of the particles compare well with experimental observations. The material in the central region is pushed spirally upwards toward the extrusion hole to form the extrusion wire, the near material moves spirally to fill the central region, and there is a dead zone in the process chamber where the material always stays in the chamber and will not be extruded out.

Study of Snow Accumulation on a High-Speed Train’s Bogies Based on the Discrete Phase Model

During winters, the high-speed train travels in the northern of China is struck by to the snow, ice and coldness, massive snow accumulating on the bogies. To understand the cause of snow packing on the high-speed train’s bogies clearly, the 3-D unsteady Reynolds-averaged Navier-Stokes equations with a RNG double-equations turbulence model and a DPM discrete phase model were used to investigate the flow field carried snow particles in a single high-speed train bogie region and monitor the movement of snow particles. And, the numerical simulation was verified by the wind tunnel test. The results show that when air flows into the region, the airflow will rise and impact on the wheels, brakes, electromotors and other parts of bogie regions. The snow particles will follow the air, while the air direction changes sharply the particles will keep the movement due to the inertia. Afterwards, the snow packs on the bogie. In front of the bogies the streamlines of the air and the particle path lines are basically the same. However, due to the inertia of mass particles, the following characteristics of the snow particles with the air are not obvious in the bogie leeward side. Different structures of the end plates will affect the snow accumulation in the bogie regions.

Formation and evolution of target patterns in Cahn-Hilliard flows

We study the evolution of the concentration field in a single eddy in the two-dimensional (2D) Cahn-Hilliard system to better understand scalar mixing processes in that system. This study extends investigations of the classic studies of flux expulsion in 2D magnetohydrodynamics and homogenization of potential vorticity in 2D fluids. Simulation results show that there are three stages in the evolution: (A) formation of a "jelly roll" pattern, for which the concentration field is constant along spirals; (B) a change in isoconcentration contour topology; and (C) formation of a target pattern, for which the isoconcentration contours follow concentric annuli. In the final target pattern stage, the isoconcentration bands align with stream lines. The results indicate that the target pattern is a metastable state. The band merger process continues on a time scale exponentially long relative to the eddy turnover time. The band merger process resembles step merger in drift-ZF staircases; this is characteristic of the long-time evolution of phase-separated patterns described by the Cahn-Hilliard equation.

Poststagnation Retreat of Kamb Ice Stream's Grounding Zone

AbstractDespite the importance of grounding zone sedimentation for ice sheet stability and ice sheet history, evidence for sedimentary deposits beneath West Antarctica's modern grounding zone remains sparse. Seismic surveying shows that Kamb Ice Stream has no detectable grounding zone deposit. As grounding zone deposition relies strongly on ice flow, the absence of a deposit suggests that the transition from the ice stream to the ice shelf has moved after stagnation of Kamb Ice Stream. Further support for a recent grounding zone occupation comes from satellite imagery of sub‐ice shelf channel features that likely originated at previous grounding‐zone locations. These features begin 25 km seaward of the current grounding zone and cut across ice flow streak lines. We estimate that retreat to the modern grounding‐zone position was abrupt at rates >0.2 km a−1.

Irrigation return flows in a mediterranean aquifer inferred from combined chloride and stable isotopes mass balances

The supply of irrigation water often overcomes crop evapotranspiration, and the resulting return flow may infiltrate and significantly contribute to an aquifer water budget. Despite its crucial importance for water resource management, the proportion of irrigation water that contributes to groundwater recharge, namely the return flow coefficient, often remains difficult to assess. Here, a chloride mass balance is combined with an isotopic mixing model (δ18O and δD) to quantify return flow coefficients, in the Crau alluvial-type aquifer (Southern France), characterized by a long-term traditional practice of flood irrigation. Local groundwater compositions are interpreted in terms of average recharge along different flow paths. The high isotopic contrast between irrigation water and regional precipitation allows the partitioning of recharge between rainfall infiltration and irrigation return flows. Isotopic mixing proportions are then used to decipher the chloride concentration of groundwater purely recharged by return flow. This allows an original application of the chloride mass balance approach to estimate return flow coefficients, which doesn't rely on any atmospheric chloride survey. Values around 0.53 ± 0.16 were found for well defined stream lines averaging the functioning of the upstream aquifer, which leads to a return flow rate of 1190 ± 140 mm yr−1. These results are consistent with a local daily time series of recharge fluxes derived from the water-table fluctuation method over the 2003-2009 period, and in line with the spatial average previously quantified over the whole aquifer. This study confirms the ability of geochemical tracers to provide recharge rates fully independent from flux measurements. They can be further used to assess the irrigation efficiency in other similar systems, or to monitor the variations of irrigation return flow, which will result from the future modifications of land use, irrigation practices and climate.

Experimental and numerical methodology to analyze flows in a coronary bifurcation

Atherosclerosis is frequently associated to disturbed flow patterns in regions of the arteries with geometrical complexity. To understand atherosclerosis development, the hydrodynamic characteristics of the blood flow in arteries, such as the velocity and wall shear stress, must be studied and quantified. To investigate the local hemodynamics in the Left Coronary Artery (LCA) bifurcation, a methodology combining numerical (CFD) and experimental methods (μPIV and streak photography) was designed. A whole volume μPIV experimental method was developed and applied to a simplified 3D phantom of the LCA bifurcation. The experimental and numerical results prove to be in a good agreement. Implications of a deviation from Murray’s law and the effect of different Reynolds numbers in flow behavior were also explored. A streak line photography method was used to complement the methodology and analyze the flow patterns. When the deviation from Murray’s law is significant, secondary flows are observed and they intensify as the Reynolds number increases. The secondary flows are visible in regions of low wall shear stresses (WSS). The present work reinforces, with numerical and experimental support, the importance of flow patterns that are relevant for prevention and treatment of atherosclerosis.

Numerical study of surface radiation and combined natural convection heat transfer in a solar cavity receiver

PurposeThe purpose of this paper is to present the numerical solutions of surface radiation and combined natural convection heat transfer in a solar cavity receiver. The paper aims to discuss sundry issues that take place in the said model.Design/methodology/approachThe numerical solutions are developed by means of second-order upwind scheme using the SIMPLE algorithm.FindingsThe effects of physical factors such as Rayleigh number (104 ≤ Ra ≤ 106), inclination angels of insulated walls (0º ≤ θ ≤ 10º) and the wall surface emissivity (0 ≤ ε ≤ 1) on natural convection-surface radiation heat transfer rate are analyzed. Impact of sundry parameters on flow quantities are discussed and displayed via graphs and tables. Stream lines and isothermal lines have also been drawn in the region of cavity. The numerical results reveal that increasing the Rayleigh number, wall surface emissivity and inclination angels of insulated walls in an open cavity enhances the mean total Nusselt number. The variations of the surface radiation and natural convection heat transfer mean Nusselt numbers are very small to the inclination angle of θ, while a significant change is noted for the case of Rayleigh number and emissivity.Originality/valueTo the best of authors’ knowledge, this model is reported for the first time.