Vertex Angle Research Articles

Characteristics of hollow bluff body-stabilized natural gas-air premixed flames with heat recirculation

The combined effects of flow recirculation and preheating on the premixed flame stability limits were employed via two flow configurations. In the first configuration, the natural gas-air mixture was set to flow around a bluff body whose orientation, number of vertices and vertex angle were varied. In the second configuration, an innovative design was developed where the fuel–air mixture was set to flow inside the bluff body as two opposing jets whose resultant flow is redirected to pass around the bluff body. The peak turbulent kinetic energy (T. K. E.) decreased from 7.24 to 4.94 m2/s2 with the star shape of 4 vertices as its orientation changed from 45 to 0° and such decrease was limited to 5.27 m2/s2 upon having a smaller vertex angle. A smaller drop from 7.24 to 6.0 m2/s2 was experienced when the 4 vertices were replaced by 5 vertices at 0° angle of orientation, while the drop continued to 4.3 m2/s2 upon having 6 vertices due to the reduction in the space available for eddies. A smaller peak T. K. E. of 2.33 m2/s2 was found with the star shape of 3 vertices because the sites for turbulence development were limited. With the star cross-section of 4 vertices at 45° angle of orientation, a maximum blow-off velocity as high as 51.5 m/s and a minimum lean limit as low as 0.40 were obtained. A further extension in the flame stability limits was provided via the second flow configuration due to the favorable effects of impingement and prolonged path of preheating. As the distance between the bluff body and the combustor separating wall decreased to 1.7 times the jet diameter, the blow-off velocity increased to 79.1 m/s; while the lean limit decreased to 0.31 with the star shape of 4 vertices at 45° angle of orientation.

Control of shock wave/boundary layer interaction induced by the microjet configuration

Shock wave/boundary layer interaction (SBLWI) is a common coupling phenomenon that occurs in hypersonic vehicles, and it adversely affects the flow fields inside and outside the vehicle. Currently, the microjet active flow control approach has been extensively investigated experimentally. Herein, the influence of the microjet hole type on SBLWI control is investigated and the flow field structures of the microjet in the near field are obtained. Additionally, the control effects of isosceles triangular microjet holes with different vertex angles are compared with those of circular and square microjet holes. The numerical results show that the control effect of the microjet on SBLWI gradually improves with increasing triangular vertex angle, and the control effect of the triangular microjet hole with a large vertex angle is better than that of circular and square microjet holes. In all working conditions, the triangular microjet hole with a 90° vertex angle that is placed along the flow direction affords the best control effect, and it can reduce the volume of the separation zone at the corner by 74.96%. Simultaneously, the addition of the microjet causes some loss of the total pressure, but the value is small.

Thermal transport in porous graphene with coupling effect of nanopore shape and defect concentration

Thermal conductivity of porous graphene can be affected by defect concentration, nanopore shape and distribution, and it is hard to clarify the effects due to the correlation of those factors. In this work, molecular dynamics simulation is used to compare the thermal conductivity of graphene with three shapes of regularly arranged nanopores. The results prove the dominant role of defect concentration under certain circumstances in reducing thermal conductivity, while the coupling effect of nanopore shape should be noticed. When the atoms at the local phonon scattering area around each nanopore are properly removed, the abnormal increment of thermal conductivity can be detected with the increase of defect concentration. Heat flux vector angles can effectively characterize the local phonon scattering area, which can be used to describe the effect of nanopore shape. The coupling effect of defect concentration and pore shape with similar heat flux path is clarified according to this process. By adjusting vertex angle of triangle defect, there is a balanced state of the effect factors between the variation of defect concentration and the same phonon scattering area. It provides a possible way to describe the weighing factors of the coupling effect. The results suggest a feasible approach to optimize and regulate thermal properties of porous graphene in nanodevice.

Shear horizontal wave propagation in inhomogeneous wedge space

In this paper, a closed-form analytical solution is presented for SH wave propagation in density radial inhomogeneous wedge space. The material parameter of this inhomogeneous wedge space with arbitrary vertex angle is given in functional form. Based on complex function method, an appropriate mapping function is introduced to transform the governing Helmholtz equation with variable coefficients into a standard one. The wave field expression satisfying zero-stress boundary condition in wedge space is derived. Finally, numerical examples are presented to analysis the influence of different parameters on displacement amplitudes.

Metallic Scaffold with Micron-Scale Geometrical Cues Promotes Osteogenesis and Angiogenesis via the ROCK/Myosin/YAP Pathway.

The advent of precision manufacturing has enabled the creation of pores in metallic scaffolds with feature size in the range of single microns. In orthopedic implants, pore geometries at the micron scale could regulate bone formation by stimulating osteogenic differentiation and the coupling of osteogenesis and angiogenesis. However, the biological response to pore geometry at the cellular level is not clear. As cells are sensitive to curvature of the pore boundary, this study aimed to investigate osteogenesis in high- vs low-curvature environments by utilizing computer numerical control laser cutting to generate triangular and circular precision manufactured micropores (PMpores). We fabricated PMpores on 100 μm-thick stainless-steel discs. Triangular PMpores had a 30° vertex angle and a 300 μm base, and circular PMpores had a 300 μm diameter. We found triangular PMpores significantly enhanced the elastic modulus, proliferation, migration, and osteogenic differentiation of MC3T3-E1 preosteoblasts through Yes-associated protein (YAP) nuclear translocation. Inhibition of Rho-associated kinase (ROCK) and Myosin II abolished YAP translocation in all pore types and controls. Inhibition of YAP transcriptional activity reduced the proliferation, pore closure, collagen secretion, alkaline phosphatase (ALP), and Alizarin Red staining in MC3T3-E1 cultures. In C166 vascular endothelial cells, PMpores increased the VEGFA mRNA expression even without an angiogenic differentiation medium and induced tubule formation and maintenance. In terms of osteogenesis-angiogenesis coupling, a conditioned medium from MC3T3-E1 cells in PMpores promoted the expression of angiogenic genes in C166 cells. A coculture with MC3T3-E1 induced tubule formation and maintenance in C166 cells and tubule alignment along the edges of pores. Together, curvature cues in micropores are important stimuli to regulate osteogenic differentiation and osteogenesis-angiogenesis coupling. This study uncovered key mechanotransduction signaling components activated by curvature differences in a metallic scaffold and contributed to the understanding of the interaction between orthopedic implants and cells.

INFLUENCE OF EDGE REINFORCING RING ROTATION ON LOAD CARRYING CAPACITY OF CONICAL SHELLS LOADED BY EXTERNAL PRESSURE

The aim of the article is to present a part of the problem of calculating the load carrying capacity of conical shells, which by their dimensions and selected boundary conditions do not comes under within the scope the standards. The investigated conical shells have a semi vertex angle in the range of 75 ° - 85 ° and are provided with a reinforcing ring at the lower edge. When the conical shells are loaded by external pressure, not only does the edge ring move in the radial direction, but also its rotation (the moment has the direction of the tangent to the edge of the cone). This paper addresses the question of how this rotation affects the overall load capacity of a conical shell. Due to the fact that the investigated shell structures cannot be solved using standard methods and procedures, this problem is solved by means of numerical analyzes and experiments. Based on the results of numerical analyzes of the load carrying capacity of conical shells with different boundary conditions, the suitability of using simplified numerical models and samples for performing experiments was verified.

Pressure-sensitive paint measurements for microscale supersonic flow with wedge models

The pressure distribution around wedge models inside a submillimeter supersonic wind tunnel was experimentally investigated using pressure-sensitive paint (PSP) at a flow speed of Mach 1.6. The throat of the submillimeter supersonic wind tunnel was 500 μm. The two wedge models were isosceles triangles with a width of 50 μm and vertex angles of 20° and 30°, respectively. The pressure profiles and pressure distributions along the centerline inside the submillimeter supersonic wind tunnel with the wedge models agreed with the results of numerical simulation performed using ANSYS Fluent. The pressure distributions around the wedge models were examined, and a strong pressure rise at the front end of the wedge models was observed. A low-pressure region in the wake region downstream of the wedge models was identified. However, these results differed from the simulation data for the middle layer of the wind tunnel, which revealed bow shock and a shock wave interaction. This difference occurred because the PSP coating was located at the bottom of the wind tunnel, which was embedded inside a viscous layer. The pressure data measured with PSP were smeared, and it was consistent with the simulation data for the bottom layer. The PSP results reveal the overall pressure variation around the wedge models, and they will be useful for future designs of micro propulsion systems with supersonic nozzles.

Edge spin wave transmission through a vertex domain wall in triangular dots

Spin waves (SWs), being usually reflected by domain walls (DWs), could also be channeled along them. Edge SWs yield the interesting, and potentially applicable to real devices property of broadband spin wave confinement to the edges of the structure. Here, we investigate through numerical simulations the propagation of quasi one-dimensional spin waves in triangle-shaped amorphous YIG (Y3Fe5O12) micron sized ferromagnets as a function of the angle aperture. The edge spin waves (ESWs) have been propagated over the corner in triangles of 2 microns side with a fixed thickness of 85 nm. Parameters such as superior vertex angle (in the range of 40^circ –75^circ ) and applied magnetic field have been optimized in order to obtain a higher transmission coefficient of the ESWs over the triangle vertex. We observed that for a certain aperture angle for which dominated ESW frequency coincides with one of the localized DW modes, the transmission is maximized near one and the phase shift drops to pi /2 indicating resonant transmission of ESWs through the upper corner. We compare the obtained results with existing theoretical models. These results could contribute to the development of novel basic elements for spin wave computing.

Experimental Study on Flow over Triangular Labyrinth Weirs

Recently, many research studies have focused on labyrinth weirs' hydraulic performance, especially as dependent on engineering features. In the current study, the hydraulic properties of flow over labyrinth triangular weirs models (from the upper perspective) with sharp crest have been experimentally studied and compare their efficiency with suppressed rectangular weirs (conventional weirs). Twelve fiberglass models are developed for this reason and tested in a 6m in length, 30cm in width, and 40cm height in laboratory flume, nine models were constructed for triangular labyrinth weirs and three models were constructed for suppressed rectangular weirs, Three alternative heights (p=15, 20, and 25cm) were employed in this research, for each height, the vertex angle (θ) changed three times (60օ, 90օ, 120օ), and for each one of these weirs was used, seven different discharge were approved. The overall tests in this study were 84. The dimensionless parameters on which the discharge coefficient (Cd) is dependent were obtained using dimensional analysis. parameters were plotted. According to this experimental present study, as compared to linear weirs, labyrinth triangular weirs shown to be more hydraulically efficient. Also, the height of the weir (P) has effects on the discharge coefficient, where (Cd) increased with decreasing (P). Also, the vertex angle of triangular labyrinth weirs(θ) has a major influence on discharge coefficient and on weir performance, where the discharge coefficient raises when decreases the value of angle(θ), in another means, when the angle decreases gave an increase in the path of the flow, where it gave the triangular labyrinth weir with an angle of 60o the discharge coefficient reached its greatest value (2.55), followed by the weir with an angle of 90o and 120o respectively. In other words (a small vertex angle gives more length effective (Le) to the weir) and this leads to an increase in flow capacity or performance for the weir.

The kinetics of crack propagation in CVD graphene film

The preparation of graphene by chemical vapor deposition (CVD) is often accompanied by the growth of some structural defects, one of which is crack. The understanding of crack formation is key to the preparation of high-quality graphene films. In this work, the crack defects of graphene grown on liquid copper substrates by chemical vapor deposition (CVD) were examined. Then, the effects of growth temperature, growth time and total pressure on kinetics of cracks were analyzed, respectively. It is found that (I) The crack appeared during the period of graphene growth, not the cooling process of graphene; (II) the crack preferred to propagate at the vertex angle of etched hexagonal holes; (III) the crack tended to orient along the same direction—the zigzag direction. Finally, a dynamic mechanism of crack growth was proposed. Our study provides significant insights into the tearing mechanism of defective graphene.

Analysis of process efficiency: Role of flow and thermal characteristics on entropy production and heat transfer rates for thermal convection in porous beds confined within triangular configurations with hot slanted walls

Flow and heating characteristics associated with heat transfer rates vis-a-vis entropy generation based on flow and thermal irreversibilities are numerically studied for thermal convection in the porous bed confined within various configurations of triangular enclosures. The triangular configurations involve various vertex angles ( and ) with three tilt positions (configurations 1–3) subjected to a linear heating pattern of the slanted walls. Numerical studies are carried out for various dimensionless parameters (Prm and Dam ) at fixed Ram . Simulation results infer that the triangular configuration 3 [configuration 3: triangle is tilted perpendicularly from horizontal position (configuration 1 or 2)] involving is the optimal configuration based on the larger rate of heat transfer and moderate entropy production at larger porosities () for buoyancy dominant scenarios () irrespective of Prm .

Thermal Stress Analysis of the Adhesive Layer in Composite Laminates

This paper presents a thermal stress analysis of the adhesive structure to study the effect of temperature change on the performance of the resin layer. The adhesive structure’s finite element model (FEM) is established, and the verified test is conducted in an environmental chamber. The simulated predictions are in good agreement with the experimental data. Subsequently, the effect of thickness of the resin layer, the elastic modulus of sheet materials, and vertex angle on the thermal behavior of the adhesive structure are discussed. The results show that the stiffness of sheet materials and vertex angle have a limited influence on the thermal stress of the resin layer. It is beneficial to reduce its thermal stress by increasing the height of the resin layer. In addition, the difference in thermal expansion coefficients between the upper and bottom sheets is the major cause of thermal stress in the resin layer.

Study of aerodynamic parameters of the sail blade

This article studies the aerodynamic characteristics of a triangular sail blade of various parameters. For this purpose, we made a triangular sail blade with a dynamically changing surface shape. The airflow velocity varied from 3 to 12 m/s. The dependences of the aerodynamic forces of the sail blade on the flow velocity were investigated at various angles of the apex of the triangular blade. The experiments were carried out at different vertices of the angles: 00; 300; 600; 900. As a result of the experiment, it was revealed that at the vertex angle γ = 900, the triangular sail blade has optimal aerodynamic parameters. The dependences of the aerodynamic coefficients on the dimensionless angle of attack are obtained. It is found that the optimal number oftriangular blades for a wind power plant with sailing blades is 6. It is established that at the angle of attack α= 00, the maximum value of the middle section of the wind wheel to the streamlined airflow will introduce a decrease in the value of the drag coefficient with an increase in attack α. The analysis of the experiment results on the change in α from the speed of the airflow of the sail blade is carried out. When the blade position changes, drag changes relatively to the airflow. The wind wheel will change its position relative to the stream with an increase in the attack angle. With an angular position change, the area of the middle section of the wind wheel begins to decrease relative to the incoming flow. With a decrease in the middle section of the wind wheel, the drag force decreases, and the drag coefficient decreases accordingly. Thus, the total result of pressure changes on the leeward and windward surfaces of the sail can be represented as one resultant aerodynamic force directed at an angle to the line perpendicular to the wind direction.

Performance enhancement of latent energy storage system using effective designs of tubes and shell

This study aims to numerically investigate the effects of geometric designs of tubes and shell on thermal performance enhancement of latent thermal energy storage system (LTESS). Stearic acid is used as a phase change material (PCM) while water acts as heat transfer fluid (HTF). Starting with a base case consisting of three circular HTF tubes within a circular shell, the tube and shell geometries are modified systematically. First, the effect of tube shapes and their orientations are investigated in detail. The circular exteriors of HTF tubes are modified with hexagonal, pentagonal, square and triangular shapes. The performance of triangular tubes with the vertex pointing downward exceeds all the other tube configurations. It augments the melting rate of the PCM by 27.2% and the energy storage capacity of the LTESS by 3.72%, as compared to the base case. The bottom vertex angle of the best HTF tube design is then varied yielding 45∘ as the optimum triangular tube configuration. It improves the energy storage capability of the LTESS by 7.61% and the melting rate of the PCM by 41.4%. Following the optimum HTF tube design, the triangulated shell designs with various bottom vertex angles are explored. The 75∘ bottom vertex angle of the shell offers maximum improvement. It accelerates the melting rate of the PCM by 66.9% while enhancing the energy storage capacity of the LTESS by 23.7% in comparison to the base case. Lastly, two new correlations of melting Fourier number and average Nusselt number are proposed for the optimum LTESS design configuration.

Application of AI Approaches to Estimate Discharge Coefficient of Novel Kind of Sharp-Crested V-Notch Weirs

In this study, the hydraulic features of the SCVW (a novel type of sharp-crested V-notch weirs) were scrutinized in the popular vertex angles θ, i.e., 30°, 45°, 60°, 90°, 120°, 128°, and 150°, under aerated, steady and free overflow conditions in an open channel for large physical models. To assess the changes of the discharge coefficient of the SCVW (i.e., CdSCVW) versus weir height and θ, widespread laboratory works were performed by measuring the water head over the crest of the weir and the discharge. Special formulas for the CdSCVW in the θ=60° were checked, and an appropriate empirical equation was recommended. The calculated CdSCVW by the proposed equation was within 0%–10% of the measured values. Three types of nonparametric artificial intelligence (AI) methods, namely, support vector regression (SVR), gene expression programming (GEP), and a robust hybrid model entitled hybrid (SVR-ACO) were developed to estimate the CdSCVW. For the sake of modeling, 196 experimental datasets were applied in the mentioned methods to evaluate the CdSCVW by taking into consideration the dimensionless variables which impact the determining procedure of the CdSCVW. In this modeling, by varying the architecture and core factors of the aforementioned methods, several scenarios were defined. The generated mathematical equation of CdSCVW by the best scenario of the GEP was compared with the corresponding measured values in which the results were in 0%–10%. According to the attained statistical indices, scatter plots, and the values of the total grade (TG) technique, the hybrid SVR(RBF)-ACO model was determined as the superior and optimal method to estimate the CdSCVW with high performance and accuracy.

A Numerical Investigation of the Mixing Performance in a Y-Junction Microchannel Induced by Acoustic Streaming.

In this study, the mixing performance in a Y-junction microchannel with acoustic streaming was investigated through numerical simulation. The acoustic streaming is created by inducing triangular structures at the junction and sidewalls regions. The numerical model utilizes Navier–Stokes equations in conjunction with the convection–diffusion equations. The parameters investigated were inlet velocities ranging from 4.46 to 55.6 µm/s, triangular structure’s vertex angles ranging from 22° to 90° oscillation amplitude ranging from 3 to 6 µm, and an oscillation frequency set to 13 kHz. The results show that at the junction region, a pair of counter-rotating streaming vortices were formed, and unsymmetrical or one-sided vortices were formed when additional triangles were added along the sidewalls. These streaming flows significantly increase the vorticity compared with the case without the acoustic stream. Mixing performances were found to have improved with the generation of the acoustic stream. The mixing performance was evaluated at various inlet velocities, the vertex angles of the triangular structure, and oscillation amplitudes. The numerical results show that adding the triangular structure at the junction region considerably improved the mixing efficiency due to the generation of acoustic streaming, and further improvements can be achieved at lower inlet velocity, sharper vertex angle, and higher oscillation amplitude. Integrating with more triangular structures at the sidewall regions also improves the mixing performance within the laminar flow regime in the Y-microchannel. At Y = 2.30 mm, oscillation amplitude of 6 µm, and flow inlet velocity of 55.6 µm/s, with all three triangles integrated and the triangles’ vertex angles fixed to , the mixing index can achieve the best results of 0.9981, which is better than 0.8355 in the case of using only the triangle at the junction, and 0.6642 in the case without acoustic streaming. This is equal to an improvement of 50.27% in the case of using both the junction and the two sidewall triangles, and 25.79% in the case of simply using a junction triangle.

Stagnation Zone Near A Corner In Viscoplastic Fluid Flow

Abstract The shape, size and location of the stagnation zone between flat non-parallel walls that make up the corner of a tube with non-circular cross section through which a phase change material of the Bingham plastic type flows is investigated. We show that the stagnant area is bounded by a convex meniscus whose size depends on the degree of plasticity and the vertex angle. The maximum and minimum energy dissipation occurs at the wall and at the bisectrix, respectively. The stagnant zone can be altogether avoided by modifying the shape of the wall in the corner area. A new design of the cross section of the tube that allows reducing or eliminating this area to optimize the mass transport is developed. Two optimal solutions, a vertex with a straight cut and a concavely curved vertex, are proposed.

Generalized formulation for resonance frequency of even polygonal microstrip antennas

ABSTRACT A generalized expression has been derived for resonance frequency of polygonal microstrip antennas with even number of edges using modified magnetic wall method. Nature of polygonal resonators is analyzed with their equivalence to corresponding circumcircle resonators. Magnetic wall has been transformed into a dynamic function of vertex angle of polygons. The transformed magnetic wall includes the effect of non-uniform fringing around vertices and edges. A scheme to achieve the complete response of circular antennas from square and other polygonal antennas has also been presented. The proposed general expression accurately gives resonance frequency of even polygonal antennas at the fundamental frequency as well as higher harmonics. The proposed expression and theory agree with simulation and measured results of different polygonal antennas.

Hydraulics of combined triangular sharp crested weir with inverted V-shaped gate

The current research investigates experimentally the flow passing through combined hydraulic structure consists of V-notch sharp crested weir and inverted V-shaped sharp gate installed in straight channel as a control structure. Nine structure models were used considering three different vertex angles simultaneously used for the weir and the gate (θ = 60°, 90° and 120°). Eighty-one experimental runs were executed to explore the influence of the combined structure geometry, the upstream head, and the tailwater depth on the conveyed flow, the discharge coefficient and the downstream flow pattern with special emphasize on the hydraulic jump characteristics. The outcomes were analyzed and graphically presented. The results proved that the simultaneous flow through the combined structure regardless the vertex angles conveyed more discharge with less downstream water disturbance on account the classical V-notch weir and the inverted V-shaped gate. The flow discharge increased up to 10 times, and the discharge coefficient increased by around 26% for combined structure of 120° vertex angle under similar hydraulic conditions. The conveyed discharge was influenced by the gate angle than the weir angle. The downstream flow characteristics were more sensitive to the weir angle than the gate angle under similar hydraulic conditions. The measured hydraulic jump lengths were compared to other formulas and showed good agreement. Also, the weir and gate vertex angles effectively influenced the hydraulic jump characteristics. The outcomes were used to develop empirical equations for predicting the discharge coefficient and dimensionless jump length associated to the combined structure. The results and analysis in this research are limited to tested data range.

Numerical study of droplet thermocapillary migration behavior on wettability-confined tracks using a three-dimensional color-gradient lattice Boltzmann model

Thermocapillary migration describes the phenomenon whereby liquid droplets move from warm to cold regions on a nonuniformly heated hydrophilic surface. Surface modifications can be applied to manipulate this migration process. In the present study, a three-dimensional color-gradient lattice Boltzmann model is used to investigate the droplet migration behavior on a series of wettability-confined tracks subject to a uniform temperature gradient. The model is validated by simulating the thermocapillary-driven flow with two superimposed planar fluids in a heated microchannel and the capillary penetration of a wetting fluid in a capillary tube. An in-depth study of the wettability-confined tracks confirms the capacity to manipulate the droplet migration process, that is, the wettability-confined tracks can accelerate thermocapillary migration compared with a smooth surface. The effects of changes in the viscosity ratio and interfacial tension are investigated, and it is found that a lower viscosity ratio and larger interfacial tension cause the droplet to migrate faster. Moreover, a systematic study of the track vertex angle is conducted, and the mechanism through which this parameter influences the droplet migration is analyzed. Then the effect of the track wettability on droplet migration is explored and analyzed. Finally, a serial wettability-confined track is designed to realize long-distance droplet migration, and the narrow side width of the connection region is found to play a key role in determining whether the droplets can migrate over long distances. The results provide some guidance for designing tracks that enable precise droplet migration control.