Orifice Aspect Ratio Research Articles

Radiant Heat Flux Profile of Horizontally Oriented Rectangular Source Fuel Jet Fires

A series of numerical simulations were performed to investigate the flame radiant heat flux of horizontally oriented jet fires by rectangular source fuel with the same orifice area (400 mm2) but different aspect ratios (1, 2, 4). The natural gas was carried out as fuel, of which the jet velocity varied from 27.5 to 205.8 m/s. The nondimensional radiant heat flux was defined to reveal the effect of fuel jet velocity and orifice aspect ratio on radiant heat flux. Results show that the flame size increases with the increasing fuel jet velocity and the larger orifice aspect ratio results in shorter flame length. The radiant heat flux is affected by the orifice aspect ratio as the different soot particle distribution. The predicted model to characterize the radiant heat flux is proposed by taking the orifice aspect ratio into account. The prediction results of proposed model agree well with the simulated data and previous experimental results.

3D Experimental and Computational Analysis of Eccentric Mitral Regurgitant Jets in a Mock Imaging Heart Chamber.

Mitral valve regurgitation (MR) is a disorder of the heart in which the mitral valve does not close properly. This causes an abnormal leaking of blood backwards from the left ventricle into the left atrium during the systolic contractions of the left ventricle. Noninvasive assessment of MR using echocardiography is an ongoing challenge. In particular, a major problem are eccentric or Coanda regurgitant jets which hug the walls of the left atrium and appear smaller in the color Doppler image of regurgitant flow. This manuscript presents a comprehensive investigation of Coanda regurgitant jets and the associated intracardiac flows by using a combination of experimental and computational approaches. An anatomically correct mock heart chamber connected to a pulsatile flow loop is used to generate the physiologically relevant flow conditions, and the influence of two clinically relevant parameters (orifice aspect ratio and regurgitant volume) on the onset of Coanda effect is studied. A two parameter bifurcation diagram showing transition to Coanda jets is obtained, indicating that: (1) strong wall hugging jets occur in long and narrow orifices with moderate to large regurgitant volumes, and (2) short orifices with moderate to large regurgitant volumes produce strong 3D flow features such as vortex rolls, giving rise to the velocities that are orthogonal to the 2D plane associated with the apical color Doppler views, making them "invisible" to the single plane color Doppler assessment of MR. This is the first work in which the presence of vortex rolls in the left atrium during regurgitation is reported and identified as one of the reasons for under-estimation of regurgitant volume. The results of this work can be used for better design of imaging strategies in noninvasive assessment of MR, and for better understanding of LA remodeling that may be associated with the presence of maladapted vortex dynamics. This introduces a new concept in clinical imaging, which emphasizes that the quality and not only the quantity of regurgitant flow matters in the assessment of severity of mitral valve regurgitation.

Predicting the main geometrical features of horizontal rectangular source fuel jet fires

The main geometrical features of horizontal jet fire with rectangular source fuel have seldom been revealed in the past, especially the rectangular orifice with same area but different aspect ratios. In order to better understand the rectangular jet fire, a set of numerical simulations were carried out by rectangular source fuel with same rectangular orifice area S (4 cm2) but different aspect ratios (orifice length to orifice width: L/W = 1, 2, 4) to investigate the flame shape, flame length and flame width. The simulated flame lengths and flame widths were compared with previous experimental data and calculated values using the Thornton model. The non-dimensional flame length and flame width were defined, in which the flame geometrical features were found in relation to the orifice aspect ratio and fuel jet velocity. Results show that the flame length and flame width increases with fuel jet velocity, while the flame length decreases with aspect ratio n for same orifice area, but the flame width increases simultaneously. The simulated data agree well with previous experimental data, but the predictions by Thornton model are larger than simulated and previous experimental values. The modified Thornton model is proposed considering both orifice shape and aspect ratio to apply to rectangular jet fire.

Boundary layer suction through rectangular orifices: effects of aspect ratio and orientation

The flow field generated by suction through a rectangular orifice within a laminar boundary layer is investigated using stereoscopic particle image velocimetry. For orifice aspect ratios of 6, 12, and 18, the impact of suction on the surrounding flow field appears to be self-similar, scaling with aspect ratio and suction velocity. Changing the orifice pitch angle had almost no impact on the surrounding boundary layer, but, as expected, changing the skew angle significantly altered the extent of the suction impact on the flow field.

Three-dimensional interaction of a finite-span synthetic jet in a crossflow

The formation and evolution of flow structures due to the interaction of a finite-span synthetic jet with a zero-pressure gradient laminar boundary layer were experimentally investigated using stereoscopic particle image velocimetry. A synthetic jet with three orifice aspect ratios of AR = 6, 12, and 18 was issued into a free-stream velocity of U∞ = 10 m/s (Reδ = 2000) at blowing ratios of Cb = 0.5–1.5. The interaction was found to be associated with two sets of flow structures: (1) a recirculation region downstream of the orifice due to virtual blockage, and (2) a steady streamwise vortex pair farther downstream. These two flow structures were characterized in detail. Tube-like velocity deficits in the free-stream were evident, as well as regions of increased velocity within the boundary layer. Reducing the aspect ratio of the orifice decreased the spacing of the edgewise vortices (generated due to the finite span of the orifice) as well as reducing the virtual blockage of the jet. A control volume analysis of the fluid streamwise momentum indicates that there is a momentum deficit just downstream of the jet orifice and the change in streamwise momentum is proportionally similar for all cases.

Acoustic and heat transfer characteristics of an impinging elliptical synthetic jet generated by acoustic actuator

Abstract The acoustic aspects and average heat transfer characteristics of an elliptic synthetic jet impinging on a heated flat plate were experimentally investigated and compared with circular, rectangular and square orifices having same equivalent diameter. The aim of the study is to investigate the effect of orifice shape, aspect ratio and operating parameters of the synthetic jet at which optimum acoustic and heat transfer performance is obtained. It is found that irrespective of the shape of the orifice, the synthetic jet generates the minimum sound pressure level when operated at its resonance frequency, which is equal to the diaphragm frequency in the present case. The maximum heat transfer enhancement is obtained at the resonance frequency for elliptical orifice of aspect ratio 1.4 at the jet to plate spacing (z/de) of 3, where z is the axial distance and de is the equivalent diameter of the orifice. The aspect ratio of an orifice is a sensitive parameter as with increase in the aspect ratio, reduction in the Nusselt number is observed. For low jet to plate spacing ratios (z/de

Parametric Study of Synthetic-Jet-Based Control for Performance Enhancement of a Vertical Tail

Application of aerodynamic flow control to the vertical tail of an aircraft could enable significant decrease in its size, with corresponding reductions in drag, weight, and fuel costs. Wind-tunnel experiments at a Reynolds number of 350,000 were conducted on a sweptback tapered vertical tail capable of sideslip rotation. The model used in the present work was approximately th scale with a NACA 0012 airfoil section. It was instrumented with an array of finite-span synthetic jet actuators distributed along the span, just upstream of the rudder hingeline. When the synthetic jets were activated, the side force coefficient was increased by a maximum of 0.17 (34%) over the baseline vertical tail. A primary objective of this work was to explore the effect of the orientation, location, and geometry of the synthetic jet orifices on control effectiveness. The parameters under investigation were orifice aspect ratio, spacing between adjacent orifice edges, the chordwise jet location, spanwise location, skew angle, and spanwise actuator density. This set of experiments suggested that the actuators’ spanwise spacing can be too dense (that is, maintaining constant individual jet strength and reducing the spanwise density of active actuators such that the total area-based momentum decreased, did not have a detrimental effect on side force enhancement for some conditions). The relative importance of other parameters that are typically used to quantify synthetic jet strength was also analyzed; the area-based momentum coefficient was determined to be a much more dominant factor than the blowing ratio and chord-based momentum coefficient.

Vortex formation of a finite-span synthetic jet: effect of rectangular orifice geometry

AbstractThe formation and evolution of flow structures of a finite-span synthetic jet issuing into a quiescent flow were investigated experimentally using stereoscopic particle image velocimetry (SPIV). The effect of two geometrical parameters, the orifice aspect ratio and the neck length, were explored at a Strouhal number of 0.115 and a Reynolds number of 615. Normalized orifice neck lengths of 2, 4 and 6 and aspect ratios of 6, 12, and 18 were examined. It was found that the effect of the aspect ratio is much larger than the effect of the neck length, and as the aspect ratio increases the size of the edge vortices decreases and the presence of secondary structures is more evident. Moreover, axis switching was observed and its streamwise location increases as the aspect ratio increases. The effect of the neck length on the flow structures and the evolution of the synthetic jet was found to be secondary, where the effect was only in the very near field (i.e. close to the jet’s orifice).

노즐 오리피스 형상에 따른 Discharge Coefficient와 Cavitation에 관한 실험적 연구

본 연구는 타원형 노즐과 원형 노즐 내부에서 발생되는 cavitation의 발생 및 성장을 실험적으로 관찰하였다. 원형 노즐과 타원형 노즐의 cavitation 특성을 가시화 하기위해 투명한 아크릴로 노즐을 제작하였다. 실험에 사용된 노즐들은 같은 단면적으로 제작되었으며, 타원형 노즐의 경우 형상비(a/b)를 다르게 하였다. 분사압력의 증가에 따라 노즐내부 유동은 no cavitation, cavitation, hydraulic flip 영역으로 나뉘어졌다. 노즐의 형상에 상관없이 no cavitation과 cavitation 영역에서는 분사압력의 증가에 따라 유량은 증가하며, 유출계수는 감소하는 경향을 나타냈다. 그러나 hydraulic flip 영역에서의 유량계수는 일정한 값을 나타냈다. 타원형 노즐은 원형 노즐에 비해 높은 cavitation number에서 cavitation이 성장, 발달하였다. 특히 타원형 노즐에서는 장축의 cavitation length가 단축보다 길게 나타났다.

Micronization and characterization of drug substances by RESS with supercritical CO2

A RESS (rapid expansion of supercritical solution) process for the preparation of ultra-fine drug particles with no organic solvent has been developed with supercritical CO2. Three drug substances with different solubility in supercritical CO2 were used, and orifice disks and capillary tubes were adapted as an expansion device. The solubilities of drug substances in supercritical CO2 and the effects of various operating parameters on the characteristics of the particles prepared by RESS process were experimentally investigated. The solubility of the drug substance in supercritical CO2 had a major effect on the average diameter of the particle prepared by RESS process, and the particle diameter decreased with the solubility for all the drugs and operating conditions. The particle diameter also decreased with preexpansion temperature and increased with the hole diameter of the orifice nozzle and aspect ratio (L/D) of the capillary tube.

EFFECT OF NOZZLE GEOMETRY ON THE ATOMIZATION AND SPRAY CHARACTERISTICS OF GELLED-PROPELLANT SIMULANTS FORMED BY TWO IMPINGING JETS

Near- and far-field atomization processes of impinging doublets are experimentally characterized using nongelled and gelled water as working fluids. The main emphasis of the study is on the effect of nozzle geometry, such as orifice inlet shape and aspect ratio, on jet stream surface dynamics and break-up processes before and after jet impingement, respectively. Gelled water jets (non-Newtonian), due to increased viscosity, display fewer surface disturbances than nongelled water jets (Newtonian). As a result, for a given flow rate the sheet formed by impinging jets is much more stable, and the corresponding break-up length is much greater for gelled water than for nongelled water jets. The nozzle aspect ratio has a more significant effect on the near-field jet stream characteristics for both fluids than the orifice inlet shape. Longer nozzles (l /d = 20) form more stable jet streams and delay the breakup of sheets, leading to greater breakup length than that attained with shorter nozzles (l /d = 5). For similar Reynolds numbers and hence, much higher respective flow rates, the droplet size for gelled water is much smaller than that for nongelled water. Also, impinging jets employing gelled water produce sprays with greater spatial distributions and wider ranges of droplet size than jets with nongelled water.

Flow and breakup characteristics of elliptical liquid jets

This paper presents the results of an experimental study on liquid jets discharging from elliptical orifices into still ambient air. The experiments were conducted with a set of elliptical orifices of approximately same area of cross section but varying orifice aspect ratio using water and water–glycerol mixture as experimental fluids. The flow behavior of liquid jets was analyzed using their photographs captured by an imaging system. The measurements obtained for the elliptical liquid jets were compared with the circular liquid jets discharging from a circular orifice of the same area of cross section. Elliptical geometry of the orifice results in a flow process by which the emanating liquid jet periodically switches its major and minor axes as it flows downstream of the orifice. In this paper, we attempt to characterize the axis-switching process through its wavelength and amplitude. For a given elliptical orifice, the axis-switching process is dominantly seen in a particular range of flow conditions. The effects of the orifice aspect ratio and liquid viscosity on the axis-switching process are revealed through this study. The experimental results on jet breakup show that axis-switching process has a destabilizing effect on elliptical liquid jets within a particular range of flow conditions and it results in shorter breakup lengths compared to the circular jet. The extent to which axis-switching destabilizes the jet is dictated by the viscosity of liquid. An increase in orifice aspect ratio destabilizes elliptical liquid jets with low viscosity like water; however, this behavior seems to get obscured in water–glycerol mixture elliptical jets due to high viscosity.

BREAKUP OF LIQUID JETS EMANATING FROM ELLIPTICAL ORIFICES AT LOW FLOW CONDITIONS

This article presents experimental results on the breakup behavior of liquid jets emanating from elliptical orifices with different orifice aspect ratios. The experiments were carried out in the range of mean jet velocity 0−5 m/s, using water as the working fluid; the liquid jets were injected vertically downward in still, ambient air. Photographic methods were employed to analyze the breakup characteristics of the liquid jets. The breakup curves of the elliptical orifice jets are compared with those of circular orifices with the same exit area as the elliptical orifices. The comparison shows that the liquid jets emanating from the elliptical orifice are less stable than jets from the circular orifice in a particular range of flow conditions corresponding to a √We range of 2−20. We attribute this enhanced instability of the elliptical jet to the axis-switching process occurring in this √We regime, a phenomenon by which the elliptical jet interchanges major and minor axes periodically as the jet flows downstream. The breakup process of the elliptical jet resembles that of the circular jet below this range of flow conditions, and their breakup curves coincide. Above this range, the elliptical liquid jets exhibit different flow behavior from the circular jet, although their breakup curves coincide again.

Flashing liquid jets and two-phase droplet dispersion: I. Experiments for derivation of droplet atomisation correlations

The large-scale release of a liquid contained at upstream conditions above its local atmospheric boiling point is a scenario often given consideration in process industry risk analysis. Current-hazard quantification software often employs simplistic equilibrium two-phase approaches. Scaled water experiments have been carried out measuring droplet velocity and droplet size distributions for a range of exit orifice aspect ratios ( L/ d) and conditions representing low to high superheat. 2D Phase-Doppler Anemometry has been utilised to characterise droplet kinematics and spray quality. Droplet size correlations have been developed for non-flashing, the transition between non-flashing and flashing, and fully flashing jets. Using high-speed shadowography, transition between regimes is defined in terms of criteria identified in the external flow structure. An overview companion paper provides a wider overview of the problem and reports implementation of these correlations into consequence models and subsequent validation. The fluid utilised throughout is water, hence droplet correlations are developed in non-dimensional form to allow extrapolation to other fluids through similarity scaling, although verification of model performance for other fluids is required in future studies. Data is reduced via non-dimensionalisation in terms of the Weber number and Jakob number, essentially representing the fluid mechanics and thermodynamics of the system, respectively. A droplet-size distribution correlation has also been developed, conveniently presented as a volume undersize distribution based on the Rosin–Rammler distribution. Separate correlations are provided for sub-cooled mechanical break-up and fully flashing jets. This form of correlation facilitates rapid estimates of likely mass rainout quantities, as well as full distribution information for more rigorous two-phase thermodynamic modelling in the future.

Evolution of finite span synthetic jets

The streamwise and spanwise evolutions of finite span synthetic (zero net mass flux) jets were investigated experimentally using particle image velocimetry. The synthetic jet was produced over a broad range of length and time scales at Reynolds numbers from 85 to 364, stroke lengths from 16 to 50 times the slit width, and two formation frequencies, f=300 and 917Hz. The velocity and vorticity fields were measured in two planes, across the slit (i.e., along the short axis of the orifice) and along the slit (i.e., along the long axis). The paper presents the effect of the slit aspect ratio on the development of the synthetic jet, and the spatial evolution of secondary three-dimensional vortical structures in the flow field. The measurements in the plane along the slit revealed a unique flow pattern, where near the orifice the flow is two-dimensional, while farther downstream the vortex pair lines develop secondary counter-rotating structures. The streamwise and spanwise spacing between these structures vary with stroke length and formation frequency. As the orifice aspect ratio increases the effect of the slit edges decreases, thus the secondary structures are less pronounced.

Low-Current, Xenon Orificed Hollow Cathode Performance for In-Space Applications

An experimental investigation of the operating characteristics of 3.2-mm diameter orificed hollow cathodes was conducted to examine low current and low flow rate operation. Cathode power was minimized with an orifice aspect ratio of approximately one and the use of an enclosed keeper. Cathode flow rate requirements were proportional to orifice diameter and the inverse of the orifice length. The minimum power consumption in diode mode was 10-W, and the minimum mass flow rate required for spot-mode emission was approximately 0.08-mg/s. Cathode temperature profiles were obtained using an imaging radiometer and conduction was found to be the dominant heat transfer mechanism from the cathode tube. Orifice plate temperatures were found to be weakly dependent upon the flow rate and strongly dependent upon the current.

Color Doppler velocity accuracy proximal to regurgitant orifices: influence of orifice aspect ratio

Many noninvasive methodologies used for the accurate evaluation of valvular regurgitation require precise velocity measurements from ultrasound instruments. Previous studies have indicated that velocity measurements from color Doppler (CD) instruments are susceptible to errors due to the interaction of the ultrasound beam and the proximal orifice flow field. This study examined the influence of high aspect ratio (AR) orifices on the CD velocity error. Center line velocity error distributions for orifices ranging from 7.07 to 78.5 mm 2, varying in shape from circular to an AR = 8 ellipse, were evaluated using a numerical model of the ultrasound beam and the simulated regurgitant flow field. An in vitro study was also performed and confirmed the findings of the numerical model. The study showed that increasing AR does not significantly change the error characteristics. The study confirmed that orifice size is the dominant factor in the error distribution, and that corrections speculated for circular orifices can be extended to elliptical orifices without significant errors.

An improved flow evaluation scheme in orifices of different aspect ratios

An accurate and reliable method of regurgitant flow calculation is currently unavailable. The goal of this study was to define a new general method of flow calculation for orifices of different aspect ratios. The success of the method relies on matching the imaged flow field distribution obtained by color flow mapping (CFM) to a three-dimensional (3D) numerical flow field distribution of known geometry. The flow field in three orifices of identical cross-sectional area with aspect ratios of 1 (circular), 2 and 4 (elliptical) was evaluated by: (a) CFM, (b) 3D echocardiographic imaging, and (c) 3D finite element modeling (FEM). The orifice shape and size were accurately estimated by 3D echocardiographic imaging. FEM showed that the normalized centerline velocity profile of the flow field depends on the orifice aspect ratio. CFM provided a good description of the centerline profile for each case. For a given distance from the orifice center, the equivelocity contour surface area increases with increasing aspect ratio. A simple flow calculation scheme was developed to calculate regurgitant flow independent of orifice shape. This improved method showed better results than previous studies and may prove to be advantageous when analyzing in vivo flow fields with complex geometries.

Mixing of gases due to injection of a low-pressure jet into a cross-flow

A gas jet injected into a channel is simulated numerically. The dependence of the mixing efficiency on the injection orifice aspect ratio, jet “screening”, and the ratio of the injected and channel gas densities is established. The mixing efficiency is estimated in terms of the mean concentration across the jet.

Tungsten etching using an electron cyclotron resonance plasma

Electron cyclotron resonance (ECR) plasma etching is one of the most suitable methods to realize a highly selective and highly anisotropic etching because the ECR is able to generate a high density plasma at low pressure. We applied this technique to W etching using sulfur hexafluoride (SF6) and octafluoro cyclobutane (C4F8) mixture gases at the etching chemistry. The characteristics of the W etching using ECR plasma were investigated. Consequently, high selectivity to photoresist is obtained without biasing rf power. Furthermore, it is clear that the addition of C4F8 to the plasma decreases the reactive ion etching lag effect in W etching. Both our simulations and mass spectral analysis with changing orifice aspect ratios show the surface reaction coefficients of the precursors to increase with increasing molecular weight. For example, the surface reaction coefficient of the parent species of the C4F+9 fragment is estimated to be about 0.12. Furthermore, in our simulation, the flux of these parent species is lowered below 60% in the 2.5-aspect-ratio trench pattern.