Conventional Circular Nozzle Research Articles

Effects of blades inside a nozzle on the fiber orientation and distribution in fiber-reinforced cement-based materials

This study developed a nozzle with blades inside called the B-nozzle to improve the fiber orientation and distribution in fiber-reinforced cement-based materials. Numerical simulations were conducted to determine the shape parameters of the B-nozzle while considering the physical interactions between the flow of the cementitious material, the boundaries of the nozzle, and the movement and rotation of the fiber. Based on the shape parameters of the B-nozzle designed from the numerical simulations, experiments were conducted for two sizes of B-nozzles with diameters of 80 and 100 mm to evaluate the influence of the blades on the fiber orientation and distribution. Pouring equipment was also fabricated to maintain the flow direction and initial pressure condition during the tests. The dimensions of the specimen are defined as 130 mm × 130 mm × 260 mm in consideration of the sizes of the fiber and nozzle. A specimen was cut into six pieces to measure the fiber orientation and distribution on the cutting surfaces using image acquisition and processing techniques. Compared to conventional circular nozzles, the B-nozzles increased the mean fiber orientation coefficients by approximately 31–39% and the fiber distribution coefficients by 3–23%.

Effect of Nozzle Geometry on Flowfield for High Subsonic Jets

The present Paper aims to present a comparative study of the external and internal flow characteristics through an axisymmetric circular convergent nozzle, a nonserpentine convergent nozzle with an elliptic exit, and a shallow single serpentine convergent nozzle with an elliptic exit under the fully expanded condition at a nozzle pressure ratio of 1.6. The static wall pressure measurements reveal that, due to the axisymmetric shape, the conventional circular nozzle shows symmetric jet development. However, the flow through the serpentine nozzle follows its curvature, making the flow through it asymmetric. The upper and the lower walls have different flow expansion due to the secondary flow created by the wall curvature and transition. This asymmetric nature of the flow through the serpentine nozzle also vectors the external jet toward the lower wall. The saddle-shaped velocity profile is observed along the major axis plane of serpentine nozzle. The nozzles with elliptic exits show higher mass entrainment and faster velocity decay as compared to the conventional circular nozzle. The nonserpentine elliptic nozzle shows the maximum velocity decay with the fastest decay rate among the three nozzles considered. This nozzle also shows the maximum mass entrainment across its major as well as minor axes and thus reduces the length of the external jet more effectively.

On the flow organization of a chevron synthetic jet

In the present study, the flow fields generated by two synthetic jets with a chevron and a conventional circular nozzle exits are studied and compared. For both configurations, the devices are operated at the same input electrical power, thus leading to Reynolds and Strouhal numbers equal to 5600 and 0.115 (for the circular exit) and 6000 and 0.106 (for the chevron exit). Phase-locked stereoscopic particle image velocimetry measurements are used to reconstruct the three-dimensional coherent vortex structures. Time-averaged and phase-averaged mean and turbulent statistics are analysed and discussed. The flow field strongly depends on the exit geometry. In presence of the chevron exit, the conventional vortex ring issued through the circular nozzle exit, is replaced by a non-circular vortex ring with additional streamwise vortices. The mutual interaction between these structures prevents the axis-switching of the non-circular vortex ring during its convection. These streamwise vortices disappear convecting downstream and the vortex ring assumes a circular shape. Comparing the two configurations, the chevron exit generates a larger time-averaged streamwise velocity along the centreline but with lower turbulent kinetic energy intensity. Differences are also present between the notch and the apex planes of the chevron exit. In the notch plane, both the time-averaged axial velocity component profile in the spanwise direction and the shearlayer width are wider than in the apex plane. Furthermore, the presence of the streamwise vortices causes a flow motion towards the jet axis in the apex plane and an opposite motion in the notch plane.

초음속 사각노즐을 이용하는 레이저 가공 보조가스의 특성에 관한 실험적 연구

An experimental study to improve the impingement characteristics of the assist gas in laser cutting was carried out. For various assist-gas pressures, and locations and installation angles of the nozzle, the characteristics of the impingement of the jet from a supersonic rectangular nozzle were compared to those previously observed for typical circular nozzles. Schlieren flow visualizations and Pitot pressure measurements downstream of the kerf surface were utilized for this purpose. The present rectangular supersonic nozzle decreased the strength of the Mach disc occurring at the corner of the kerf surface, and thus, could weaken the separation of the assist gas on the kerf surface and increase the Pitot pressures downstream compared to conventional circular nozzles.

Axis-switching and breakup of low-speed elliptic liquid jets

Theoretical and experimental investigations are conducted to analyze the instability of a low-speed liquid jet emerging from an elliptic nozzle. The complexity of viscous free surface flow analysis for an asymmetric geometry is simplified using an approach based on the Cosserat theory (also called director theory) which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. This work is mainly focused on the spatial instability analysis to examine the key characteristics of an elliptic jet such as jet profile, axis-switching and breakup length. In the experimental part, both natural (free) and excited (forced) breakup behaviors are studied. In the natural breakup, the effects of nozzle’s ellipticity and length to diameter ratio are examined. In the forced breakup case, disturbances are applied to the jet, by modulating the jet exit velocity using a piezoelectric actuator with given sinusoidal perturbations. The spatial evolution of the jet shape is captured with a high speed camera. Liquid jet instability is studied for various nozzle geometries over a specific range of jet velocities and excitation frequencies. Results are compared with conventional circular nozzles which can be considered as a special case of an elliptic jet.

A Digital Particle Image Velocimetry Study on Jets Issuing from Hybrid Inclined Nozzles

Digital particle image velocimetry was used to study hybrid inclined nozzles formed by combining flat- and inclined-sections, where the latter are designed based on the aspect-ratios (AR = 2 and 4) of half-ellipses. Results show that AR2 nozzle exhibits flow behaviour largely similar to inclined nozzles with inclined vortex roll-ups moving away from the nozzle centerline. In contrast, AR4 nozzle leads to significantly more intense near-field flow behaviour caused by the sharper junctions, which prevent similar movement of the vortex roll-ups. Streamwise vortices are also observed to form off the peaks of inclined-sections which produce wider jets-spreads along the inclined-sections due to associated lateral jet fluid ejection, though there is a limit to the jet-spread increment. Lastly, both nozzles produce higher turbulent stress levels over those of the conventional circular nozzle, and vortex roll-up vectoring leads to higher turbulent stresses for the AR2 nozzle along certain measurement planes.

Effect of Fuel Nozzle Geometry on the Stability of a Turbulent Jet Methane Flame

The effect of asymmetric fuel nozzles on the stability of turbulent jet methane flame discharging into still air is investigated experimentally. The emphasis of this study is however, more on the flame liftoff height and velocity, as well as reattachment and blowout velocities. Five nozzles; a pipe, a contracted circular, a triangular, a rectangular and a square, which all have an equivalent diameter of approximately 4.50 mm, are tested. The experimental results reveal that asymmetric nozzles reduces the jet flame liftoff height, and hence stabilizes the flame base closer to the nozzle compared with conventional circular nozzles. This finding correlates well with the entrainment rate of the corresponding non-reacting jets. That is, the flame liftoff height decreases as the jet entrainment increases. Furthermore, the asymmetric nozzles are found to significantly influence the blowout, liftoff and reattachment velocities. The blowout is believed to be primarily governed by the far-field local mixing rate.

Gas-Particle Two-Phase Jet Flow from Slot Nozzle and Micro-Blasting Process

Recently, the micro-blasting process has been widely used to process brittle material, and a conventional circular nozzle has been commonly used. But the cutting performance of a circular nozzle does not process a large area well, so the use of a slot nozzle is considered. In this study, in order to improve the cutting performance of the micro-blasting nozzle, a new slot nozzle with a large aspect ratio is proposed and the flow characteristics and cutting performance are examined precisely by experimental and numerical analyses. The main results show that (1) setting the circular vane in the slot nozzle perpendicular to the stream can diffuse particle flow uniformly at the nozzle exit, making the particle velocity distribution uniform, (2) expanding the nozzle outlet at an angle, uniform air and particle velocity distributions at the nozzle exit can be obtained, (3) in spite of setting obstacles at the nozzle, a fine cutting efficiency is obtained compared to the conventional micro-blasting circular nozzle.

Particle Laden Impinging Jet Flow from Rectangular Nozzle and Abrasive Jet Machining(Multiphase Flow 2)

Recently, abrasive jet machining is used widely to process brittle materials, and at that time a conventional nozzle, circular one is used commonly. But, the cutting performance of circular nozzle is not sq good to process a large area and then the use of a rectangular nozzle, slot nozzle, is considered. In this study, in order to improve the cutting performance of abrasive jet machining nozzle a new rectangular nozzle with a large aspect ratio is proposed and the flow characteristics and cutting performance are examined precisely by experimental and numerical analyses. Main results show that (1) setting circular vane in the rectangular nozzle perpendicular to the stream can diffuse particle-flow uniformly at the nozzle exit and then particle velocity distribution becomes uniform, (2) expanding the nozzle outlet at an angle uniform air and particle velocity distributions at the nozzle exit can be obtained, (3) in spite of setting obstacles in the nozzle a fine cutting efficiency can be obtained comparing with the conventional circular abrasive jet machining nozzle. It will be shown that the new rectangular nozzle has a high cutting performance comparing with a conventional circular nozzle.

Gas-Particle Two-Phase Jet Flow from Slot Nozzle and Micro-Blasting Process

Recently micro-blasting process has been widely used to process brittle material, and at that time a conventional circular nozzle was commonly used. But, the cutting performance of the circular nozzle does not process a large area well so the use of a slot nozzle is considered. In this study, in order to improve the cutting performance of the micro-blasting nozzle, a new slot nozzle with a large aspect ratio is proposed and the flow characteristics and cutting performance are examined precisely by experimental and numerical analysis. Main results show that (1) setting the circular vane in the slot nozzle perpendicular to the stream can diffuse particle flow uniformly at the nozzle exit and then particle velocity distribution becomes uniform, (2) expanding the nozzle outlet at an angle, uniform air and particle velocity distributions at the nozzle exit can be obtained, (3) in spite of setting. obstacles in the nozzle, a fine cutting efficiency is obtained compared to the conventional micro-blasting circular nozzle.

A study on a lobed jet mixing flow by using stereoscopic particle image velocimetry technique

In a continuing effort to study the mixing enhancement by large-scale streamwise vortices generated by a lobed nozzle, a high-resolution stereoscopic particle image velocimetry (PIV) system was used in the present study to conduct three-dimensional measurements of air jet flows exhausted from a lobed nozzle and a conventional circular nozzle. The three-dimensional instantaneous and ensemble-averaged velocity fields, instantaneous and ensemble-averaged streamwise vorticity distributions and turbulent kinetic energy distributions were used to analyze the characteristics of the mixing process in the lobed jet flow compared with conventional circular jet flow. The existence of large-scale streamwise vortices in the lobed jet mixing flow is revealed clearly from the stereoscopic PIV measurement results. The instantaneous streamwise vorticity distributions revealed that the large-scale streamwise vortices generated by the corrugated trailing edge of the lobed nozzle break into smaller, but not weaker streamwise vortices gradually as they travel downstream. This is the proposed reason why a lobed nozzle would enhance both large-scale mixing and small-scale mixing reported by other researchers. The overall effect of the lobed nozzle on the mixing process in the lobed jet mixing flow was evaluated by analyzing the ensemble-averaged streamwise vorticity distributions. It was found that ensemble-averaged streamwise vortices in the lobed jet mixing flow grew up and expanded radially over the first diameter of the test nozzle, then began to break down into smaller and weaker vortices further downstream. The averaged turbulent kinetic energy profile indicated that most of the intensive mixing between the core jet flow and ambient flow, due to the special geometry of the lobed nozzle, occurred within the first two diameters of the lobed nozzle, which corresponds to the upstream region where the ensemble-averaged streamwise vortices break down.

Particle image velocimetry and planar laser-induced fluorescence measurements on lobed jet mixing flows

An experimental investigation of the vortical and turbulent structures in lobed jet mixing flows was conducted. The techniques of planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) were used to accomplish flow visualisation and velocity filed measurements of the lobed jet mixing flows. Compared with a conventional circular jet flow, the lobed jet mixing flows were found to have a shorter laminar region, a smaller scale of spanwise Kelvin–Helmholtz vortices, quicker transition to turbulence and earlier appearance of small-scale vortical and turbulent structures. The intensive mixing of the core jet flow with ambient flow was found to concentrate within the first two nozzle diameters in the lobed jet mixing flow. More rapid growth of the shear layer at the near field and quicker decay of the central line velocity were also found in the lobed jet mixing flow. All these indicated a better mixing enhancement performance of the lobed nozzle compared with the conventional circular nozzle in the near-field region.

Studies on freejets from nozzles for high-speed mixing applications

In this study four different supersonic nozzles – circular, elliptical, tabbed, and radially lobed nozzles are compared experimentally for their freejet mixing performance. With the background of studies by various groups conducted on elliptical, tabbed, and radially lobed nozzles, the present paper aims at a comparative experimental study to compare their mixing performance with that of a conventional circular nozzle under identical operating conditions. The investigation is performed non-intrusively, using digital image processing of the planar Mie scattering images of the flow field. The results of these investigations reveal the superiority of the mixing performance of the lobed nozzles over conventional circular and other non-conventional nozzles.

Research on the vortical and turbulent structures in the lobed jet flowusing laser induced fluorescence and particle image velocimetrytechniques

The changes in vortical and turbulent structure in the near field(X / D < 3.0) of jet mixing flow caused by a lobed nozzle were investigatedexperimentally in the present study. The techniques of planar laser inducedfluorescence and particle image velocimetry were used to accomplishflow visualization and velocity field measurements. The experimental resultsshowed that, compared with a circular jet flow, lobed jet mixing flow wasfound to have a shorter laminar region, a smaller scale of the spanwiseKelvin-Helmholtz vortices, earlier appearance of small scale turbulentstructures and a larger region of intensive mixing in the near field of the jetmixing flow. The central line velocity decay of the lobed jet mixing flow wasalso found to be much faster than that in a conventional circular jet. Allthese indicated that the lobed nozzle provides better mixing performance thandoes a conventional circular nozzle.

Structure and properties of thin, slit-shaped carbon fibers prepared from mesophase pitch

A mesophase pitch of 100% anisotropy prepared from methylnaphthalene using HF/BF 3 was spun through the slit-shaped nozzle in a temperature range of 260–275°C. Very thin fibers were obtained, about 2–5 μm in thickness and 10–18 μm in width, according to spinning temperature. The slit-shaped transversal section of tape was observed under optical microscope, scanning and transmission electron microscopes. The symmetric Double Layer is proposed as a model of the cross-sectional texture, which carried radial orientation at the semicircular edges, onion-skin at the flat edges, alignments perpendicular to the flat edges in the intermediate parts and alignments parallel to the major axis at the central part of the ellipse fiber. Present carbon fibers exhibited better mechanical properties, as compared to those of round fibers spun through conventional circular nozzles. The fibers after graphitization at 2500°C showed excellent tensile strength and modulus as high as 340–395 Kg/mm 2 and 84–92 ton/mm 2, respectively. The particular shape and texture of transversal section appears principally responsible for such tensile properties.

High-temperature pulsed slit nozzle for supersonic jet spectrometry

An interface converting a cone flow into a rectangular flow is attached to a conventional nozzle with a circular orifice. This assembly can be heated to 300 °C, due to a metal-to-metal contact between an orifice and a plunger and to a Teflon-insulated copper wire of an electromagnet. At the top of the interface, two razor blades are attached to convert the rectangular flow into a slit flow. The enhancement factor (long axis/short axis) is 6 in fluorescence measurements. The signal intensity obtained by the slit nozzle is four times larger than the best value obtained by the conventional circular nozzle.

Acoustical-Attenuation Qualities of Plug Nozzles

A theoretical investigation is presented describing the acoustic-attenuation qualities of plug nozzles over circular nozzles for the case of supersonic flows. The acoustic characteristics of a given nozzle are related to the constant shock-wave structure and, hence, they are a function of the effective shock-wave surface and shape. Thus, knowing the acoustic qualities of a conventional circular nozzle of a given diameter, an estimate of the attenuation properties of a plug nozzle is obtained as a function of the plug diameter and Mach number. Specifically, if C is the plug radius and r is the radius of the conventional nozzle, the attenuation qualities of the plug nozzle as functions of the dimensionless ratio ρ = C/r and Mach number M are obtainable. The final expression is of the form D = log[(1 + ρ2)][1 +k2(1 + ρ−2)]3/2{[1 +k2(1 + ρ2)]3/2−1}[(1 + k2)3/2−1], with D representing the acoustic attenuation in decibels. k is a function of the Mach number and is determined from the properties of the original nozzle.