Circular Exit Research Articles

Note: Electrohydrodynamic atomization of liquid sheet

Novel electrohydrodynamic atomization via liquid sheet is presented herein to produce monodisperse. Instead of multiple capillaries/holes used in previous publication, the spray heads with a circular slit exit, shaping the spray liquid into a thin sheet, were utilized. A number of notches were machined along the outer edge of an annular slit to bifurcate the liquid sheet into multiple jets and anchor them to establish the stable multijet operation. The liquid-sheet electrospray heads with 6, 12, and 20 notches were investigated in this study. It is observed that, for spraying liquids of low electrical conductivity, the maximal liquid flowrate of a 20-notched head is 166 times higher than that of single capillary with an inner diameter the same as the slit spacing of studied heads. The above observation evidences that the liquid-sheet electrospray technique and heads have excellent potential for high mass throughput while keeping the spray head cost low.

Surface properties for rarefied circular jet impingement on a flat plate

In this paper, we investigate rarefied jet gas flows out of a circular exit impinging on a vertical flat plate. We employ a constraint relation about the velocity components of gas particles leaving a nozzle exit point and arriving at a given spatial point outside the nozzle. This relation leads to several analytical expressions for collisionless flow property distributions on the plate surface, including density, slip-velocity, temperature, pressure, shear stress, and heat flux. Numerical simulation results obtained with the direct simulation Monte Carlo method validate the analytical collisionless flow solutions. The impingement properties on the plate surface are accurate when the Knudsen number is large.

원형노즐 출구 유동장의 수치해석

The programs of grid generation and flow analysis for the 3-D flow field. were developed. The finer results from numerical analysis could be obtained by using developed programs than those of the experimental data in the flow field of the circular nozzle exit region. Especially A virtual-origin of 3.2 times of nozzle diameter within three percent error inside from nozzle exit plane could be obtained.

The impact force acting on a flat plate exposed normally to a rarefied plasma plume issuing from an annular or circular nozzle

With the indirect thrust measurement of electric thrusters working at a low vacuum chamber pressure as the research background, this paper analyses the impact force acting on a flat plate exposed normally to a rarefied plasma plume issuing from a thruster with an annular or circular exit section for the free-molecule flow regime (at large Knudsen numbers). The constraint relation proposed by Cai and Boyd (2007 J. Spacecr. Rockets 44 619, 1326) about the velocity components of gas particles leaving a location on the nozzle exit section and arriving at a given spatial point outside the nozzle has been employed here to derive the analytical expressions for calculating the impact force. Sample calculation results show that if the flat plate is sufficiently large, the impact force acting on the flat plate calculated for the case without accounting for gas particle reflection at the plate surface agrees well with the axial momentum flux calculated at the thruster exit or the theoretical thrust force of the studied thruster, while accounting for the contribution of gas particles reflected from the plate surface to the impact force production may significantly increase the calculated impact force acting on the flat plate. For a Hall-effect thruster in which the thrust force is dominantly produced by the ions with high directional kinetic energy and the ions are not directly reflected from the plate surface, the contribution to the impact force production of atom species and of gas particles reflected from the plate surface is negligibly small and thus the measured axial impact force acting on a sufficiently large plate can well represent the thrust force of the thruster. On the other hand, if the contribution of the gas particles reflected from the plate surface to the impact force production cannot be neglected (e.g. for the electric thrusters with comparatively low thruster exit temperatures), appreciable error would appear in the indirect thrust measurement.

Volumetric velocity measurements of vortex rings from inclined exits

Vortex rings were generated by driving pistons within circular cylinders of inner diameter D = 72.8 mm at a constant velocity U0 over a distance L = D. The Reynolds number, U0L/(2ν), was 2500. The flow downstream of circular and inclined exits was examined using volumetric 3-component velocimetry (V3V). The circular exit yields a standard primary vortex ring that propagates downstream at a constant velocity and a lingering trailing ring of opposite sign associated with the stopping of the piston. By contrast, the inclined nozzle yields a much more complicated structure. The data suggest that a tilted primary vortex ring interacts with two trailing rings; one associated with the stopping of the piston, and the other associated with the asymmetry of the cylinder exit. The two trailing ring structures, which initially have circulation of opposite sign, intertwine and are distorted and drawn through the center of the primary ring. This behavior was observed for two inclination angles. Increased inclination was associated with stronger interactions between the primary and trailing vortices as well as earlier breakdown.

A Study on Flow Transition and Development in Circular and Rectangular Ducts

The present paper reports observations on some aspects regarding the dependence of the transition Reynolds number and flow development on the inlet flow conditions and the entrance length in circular and rectangular ducts for Rem≤106×103, where Rem is the Reynolds number based on the bulk flow velocity (U¯b) and the duct integral length scale (D). The hot-wire anemometer was used to carry out measurements close to the circular duct exit; however, the laser-Doppler anemometry was utilized for the rectangular duct measurements. Particular considerations were given to the bulk flow velocity, the mean-velocity profile, the centerline-average-velocity, and the centerline turbulence statistics to the fourth order. Transition criteria in both ducts were discussed, reflecting effects of flow geometry, entrance flow conditions, and entrance length on the transition Reynolds number. A laminar behavior was maintained up to Rem≈15.4×103 and Rem≈2×103 in the circular and rectangular ducts, respectively, and the transition was observed to take place at different downstream positions as the inlet flow velocity varied.

Performance and Flow Characteristics of Double-Offset Y-Shaped Aircraft Intake Ducts

A Y-shaped intake duct is a critical component of a single-engine modern combat aircraft. The present study is an attempt to establish the flow behavior of a double-offset Y duct with uniform wall roughness with a semi-elliptical ' inlet and a circular exit. These studies are carried out using the commercial computational fluid dynamics code FLUENT with a renormalized-group k-e turbulence model. An attempt was made to establish the effect of Reynolds number and vertical offset on the flow characteristics of a double-offset Y duct for a fixed horizontal offset. It is seen that performance and flow characteristics of the duct are independent of Reynolds number for Re > 105. In the presence of a vertical offset, the core of the flow moves along the diagonal plane, which is inclined to the vertical axis at an angle determined by the magnitude of the vertical offset (a 15/15-deg offset gives an angle of 30 deg).

Effect of corner rounding on the performance of the double offset Y-shaped aircraft intake duct

A Y-shaped intake duct is a crucial component of a modern combat aircraft having a single engine. The flow analyses in these ducts have been done using renormalization group k- turbulence model. The present study attempts to demonstrate the effect of corner rounding on the performance and the flow characteristics of a double offset Y-shaped aircraft intake duct having a semi-elliptical inlet and a circular exit with an area ratio of 2, and uniform wall roughness. It is seen that the performance and the flow characteristics of the Y-shaped intake duct improve significantly with rounding of the sharp corners up to an arc radius ( r/ Dh) of 0.14.

INFLUENCE OF THE INLET SHAPE ON THE PERFORMANCE OF DOUBLE OFFSET TRANSITION S-DUCT WITH DIFFUSION

Transition S-shaped intake duct is a crucial component of dual engine used in modern combat aircrafts. Present flow investigation demonstrates the flow behavior of double offset transition S-duct for different inlet geometries having circular exit (ϕ = 72.5 mm) and uniform roughness. The inlet geometries namely rectangular, square, elliptical, oval, and semicircular have been analyzed for double offset transition S-duct having 300 mm centerline length and an area ratio of 2.0. Incompressible flow analysis carried out for free stream velocity at 30 m/s with RNG k–ε turbulence model has shown that the elliptical inlet shape gives the best performance whereas square inlet gives the worst performance in terms of longitudinal and cross-flow velocity distribution, pressure recovery, total pressure loss, distortion coefficient, and swirl coefficient at the exit of the duct.

Vortex ring head-on collision with a heated vertical plate

We report experimental results of the normal impact of a vortex ring in air on a vertical heated plate at constant temperature. We address the case in which the natural convection boundary layer is laminar and the vortex ring is stable. Vortex rings are created by pushing air through a circular exit orifice of a cavity, using a piston-cylinder system. The impinging vortex ring perturbs both the thermal and dynamical boundary layers where we measure the total heat flux exchanged by the heated plate and visualize the vortex motion during the impact. This unsteady impingement process is investigated for different vortex sizes and self-induced velocities, characterized by the Reynolds number of the ring. As a result, a localized heat transfer enhancement is originated by the ring impingement, which increases with the Reynolds number.

Computational Analysis on Flow Through Transition s-Diffusers: Effect of Inlet Shape

DOI: 10.2514/1.22828 Diffusing transition S-ducts are often used in dual engine fighter aircrafts as intake ducts. The cross section shape at the inlet of the intake duct affects the performance of the duct. The present paper establishes computational fluid dynamics as a design tool for intake design. Various cross section shapes of the inlet, namely, elliptic, semicircular, oval, rectangular, and square, have been analyzed using the standard and the renormalized group k– turbulence model. For all the ducts, the angle of turn (22:5=22:5 deg), the centerline length (300 mm) and the circular exit diameter(100mm)havebeenkeptconstant.Incompressible flowanalysishasbeendoneat0.17Machnumberatthe entry of the duct which corresponds to the throat of intakes. The elliptic-shaped inlet duct shows the best performance in terms of pressure recovery, loss coefficient, and flow distortion at the compressor face, whereas square duct produces the worst flow characteristics. It is also established that the renormalized group k– model predicts better than the standard k– turbulence model.

Tecia solanivora

<i>Tecia solanivora</i>

Tecia solanivora

<i>Tecia solanivora</i>

Measurement and analysis of noise from a ventilation fan

A window‐type ventilation fan of 150 mm in diameter with a flow rate of 170 cfm is studied. The fan has four rotor blades and the downstream motor is held by two metal struts. Acoustic measurement in an anechoic chamber reveals an asymmetric pattern of sound intensity at the blade passing frequency with a major beam in the front and a minor beam at the back of the fan. The beams are basically aligned with the rotational axis, implying a thrust‐noise mechanism, but there is irregularity in the distribution. Analysis shows that such irregularity may be caused by the interference between the leading order thrust noise and the higher order noise mechanisms. Modifications of the front and back geometries reveal that the dominant tone noise mechanism lies in the vortex shedding from the four rims of the short circular exit passage which is housed in a square outer frame. Correction of the exit duct geometry reduces the tone noise power by about 5 dB, and the pattern of the residual sound intensity is changed drastically. Comparison is also made between the directivity of the ventilation fan with that of a computer cooling fan with similar features.

Shear-thinning drop formation

A volume-of-fluid numerical method is used to predict the dynamics of drop formation from a nozzle with a circular exit, directed vertically downwards in air, when the drop fluid is shear-thinning. The validity of the numerical calculation is first confirmed for a Newtonian fluid by comparison with experimental measurements. For the cases considered, predictions for a shear-thinning drop fluid result in more rapid pinch-off and a smaller final neck length consistent with a related study of liquid bridges.

高速鉄道トンネル出口から発生する微気圧波のパッシブコントロール

When a high-speed train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. This wave subsequently emerges from the exit portal of the tunnel as a micro pressure wave which may cause an impulsive noise problems in the surrounding area. The objective of this paper is to show the optimum silencer to reduce an impulsive noise. The effects of the exit boxes at the circular tube exit on the impulsive noise were investigated numerically. As a result, the optimum location of an exit box are found and the noise alleviative rate have been clarified.

Probing radial and axial secular frequencies in a quadrupole ion trap

We simulate an operating mode in which the ions are introduced inside a quadrupole trap and slowed down to be confined; after a given confinement time, they are ejected out of the trap towards the detector through the upper end-cap. This elementary experiment is repeated for a set of increasing confinement times. The temporal ion signal obtained is an image of the confined ions' motion. This signal, which is periodical, contains the radial and/or axial secular frequencies of all the confined ionic species depending on the mode of detection. In previous papers, we have shown that with a large circular exit hole centred on the z axis of the trap and with a numerical treatment of the ion time-of-flight (TOF) histogram recorded for each confinement time, we obtain only the z secular frequency. In this paper, we show that the exit position of an ion in the radial plane depends principally on its radial position at the end of the confinement. For this, simply by reducing the dimension of the centred exit hole or by decentring it and counting only the number of ions passing through the hole, we can obtain evidence on the radial secular frequencies. Also, this simulation work allows one to clarify the best operating conditions to measure the x-secular frequencies, that is a decentred exit hole tangential to the oz axis and an ion cloud the excursion of which along the ox axis is limited to the radial position of the exterior edge of the hole and with an ox dimension about three times lower than the hole diameter. In this case, the amplitude calibration is possible as the frequency peak amplitude is proportional to the square value of the mean number of created ions. Moreover, we give the signal over noise ratio under usual values of the operating parameters. This operating mode and its two associated modes of detection could be an useful tool to measure ion motion secular frequencies along the oz axis and along any radial directions. Besides mass spectrometry, the determination of the frequencies shifts and couplings related to the ion motion can lead to other important applications.

Jet flames from noncircular burners

Gas jets from noncircular exits entrain more air from surroundings than jets from circular exits of equivalent area. Because the mixing rate of fuel and air governs the combustion and pollutant emission of diffusion flames and partially premixed flames, noncircular geometries offer a passive control of the flame characteristics. In this paper, the literature on nonburning, noncircular jets is reviewed and recent studies on noncircular jet flames are discussed with focus on the work conducted in the author’s laboratory.

The influence of spatially random wavefronts on coherent diffraction imagery

The averaged diffraction image of a coherently illuminated object viewed through an optical system with a circular exit pupil in the presence of a spatially random wavefront is derived. The final expression for the averaged diffraction image is given by a fourfold integral which contains the covariance function of the random wavefront. It is shown that when the covariance function is very narrow compared with the radius of the exit pupil, the averaged diffraction image decomposes into the sum of a slowly varying background term and the diffraction image of the object (in the absence of the random wavefront) modulated by the exponential of the variance of the random wavefront. The special, but important, case of line objects is considered in detail along with representative numerical calculations.

Flow Patterns in Three-Dimensional Laryngeal Models

A three-dimensional model of the larynx was created based on morphometric measurements of replica human casts. The larynx is simulated as a 6-cm-long cylinder with circular entrance and exit cross sections of 1.8 cm diameter. The ventricular folds are 2.5 cm from the entrance, and the vocal folds are 2.1 cm further down-stream. The ventricular folds cross section is modeled as an ellipse with axes of 1.8 and 1.0 cm. The vocal folds cross section is also assumed to be an ellipse where one axis is fixed at 1.6 cm and the length of the other axis is dependent on the inspiratory flow rate. For flow rates representing sedentary, light, and heavy breathing activities (15, 30, and 60 liters/min) these lengths are 0.70, 1.11, and 1.93 cm, respectively. The major axis of the ventricular and the fixed axis of the vocal folds are perpendicular. Preliminary flow studies have been performed using a finite element analysis. Velocity vector plots have been produced using a turbulence model of the flow field for the case of heavy breathing activity. They reveal a swirling circumferential flow that is caused by the alternating major axes of the ventricular and vocal folds.