Exit Orifice Research Articles

Impact of Orifice Length/Diameter Ratio on 90 deg Sharp-Edge Orifice Flow With Manifold Passage Cross Flow

The available information describing the various stages of flow conditions that occur as the flow transitions from noncavitation to cavitation (turbulent flow), supercavitation, and finally separation in sharp-edge 90 deg orifices is extensive. However, although sharp-edge orifices in cross flow represent a significant number of injection schemes inherent in many applications, data for this configuration are sparse or nonexistent. This study is intended to increase the database and understanding of the driving variables affecting the flow in all of these conditions. Tests were carried out in a unique test facility capable of achieving large variations in back pressure, flowrate, and operating upstream pressure. The configuration and test ranges of this study includes orifice length/diameter ratios from 2 to 10, upstream pressures from 7.03 kg/cm2 to 105.1 kg/cm2, orifice/manifold area ratio of 0.028 to 0.082, and manifold cross flow velocity of from 410 cm/s to 1830 cm/s. The results for these small area ratio configurations support two different first order models, one for cavitation and the other noncavitation both in turbulent flow. Under cavitation conditions the discharge coefficient is related to the contraction coefficient and the cavitation parameter to the 1/2 power. In the noncavitation flow regime the head loss is related to the loss coefficient and the dynamic pressure at the orifice exit. Both the head loss and contraction coefficient were found to be a strong function of the ratio of manifold/orifice exit velocity. Equations are provided defining the relationships that allow determination of the contraction coefficient, discharge coefficient, and head loss between the contraction coefficient, as well as the loss coefficient and operating conditions. Cavitation parameter values for cavitation inception, cavitation, and supercavitation are also provided. The potential flow theory was shown to predict the contraction coefficient when upstream (manifold to vena-contracta) losses are minimal.

Lumped element modelling of synthetic jet actuators

In this paper, a lumped element model of synthetic jet actuator is presented and used to predict the temporal variation of the jet velocity. Unlike the previous model reported in the literature, in this model the mechanical movement of the diaphragm is decoupled from the fluid phenomenon in the actuator cavity to allow the modelling of fluid mechanics aspect of the actuator to be investigated and validated separately. Furthermore, the “minor losses” occurring at the orifice exit is included and linked to the jet exit velocity profile. The results from this model are validated using the existing experimental data and CFD simulations. It is found that this model is capable of predicting the temporal variation of synthetic jets both in phase and magnitude when the actuator is operating away from the Helmholtz resonance frequency. Although the model fails to predict the correct phase information at the Helmholtz resonance frequency, it can still produce the jet peak velocity that is in good agreement with the experimental data. The lumped element model presented in this paper can be used to provide a reliable prediction of the jet peak velocity needed in the initial design of synthetic jet actuators for practical applications.

Effects of trapped air bubbles on frequency responses of the piezo-driven inkjet printheads and visualization of the bubbles using synchrotron X-ray

The reliability of drop formation is one of the key factors for the successful commercialization of inkjet printing applications. However, when the air bubble is entrapped from the nozzle exit, it leads to stop jetting of the droplets immediately. It has been known that the trapped air bubbles inside the chamber prevent a printhead from stable jetting. In this study the synchrotron X-ray has been used to visualize the air bubbles in the flow field inside of the printhead undergoing the standard jetting with the firing frequency of 1–20 kHz. An air pocket of bubble was formed repeatedly and reproduced well through the tested printheads at a certain jetting condition. To see the effects of the bubbles on the dynamic characteristics of the piezoelectric printheads, the piezoelectric velocity on the top of the pressure chamber was measured with a laser vibrometer. When the bubble was trapped at the nozzle exit orifice, the piezo velocity signals showed significantly different frequency peaks appearing in the spectrum and the high frequency components were identified with the frequency response measurements.

Propagation of orifice- and nozzle-generated vortex rings in air

The effect of the exit geometry of a vortex ring generator was studied experimentally. Two types of exit geometries were chosen: an orifice and a nozzle. Vortex rings were generated by pushing a solenoid-valve-controlled, pressurized-air jet through the circular opening of the orifice or nozzle. Experiments were performed over a wide range of initial Reynolds number (450 l Re l 4580) and length-to-diameter ratio (0.7 l L / D l 7.0) of the air jet. The exit geometry was found to significantly influence the entire course of propagation of the vortex ring. The orifice-generated vortex ring had superior characteristics to that produced by the nozzle under the same conditions. The vorticity generated along the wall in the orifice exit plane had a negligible effect on the circulation of the vortex ring within the specified range of Reynolds number. Compared to the nozzle-generated vortex ring, the orifice-generated ring showed reduced initial vorticity losses and less diffusive entrainment of ambient fluid. The vortex rings produced by the orifice attained more circulation, less entrainment of ambient fluid and hence rapidly propagated through longer distances in comparison to the nozzle-generated rings.

Experimental Evaluation of a Low Pressure-Swirl Atomizer Applied Engineering Design Procedure

In a pressure-swirl atomizer a swirling motion is imparted to the fuel leading it, under the action of centrifugal forces, to spread out in the shape of a hollow cone as soon as it leaves the exit orifice. This kind of atomizer is used in gas turbines and liquid-propellant rockets. The need to minimize the combustor length usually leads to spray angles around 90 deg. The present work presents a procedure to design and verify the experimental behavior for low pressure-swirl atomizers. This atomization condition is especially important, for example, in the case of gas turbine operation under idle regime. The Sauter mean diameter and the spray-cone angle are evaluated and made to fit the calculated atomizer dimensions. The Sauter mean diameter is obtained through the use of a model originally developed for fan-spray atomizers and extended for pressure-swirl atomizers. A pressure-swirl atomizer was manufactured following this design procedure. The discharge coefficient, the spray-cone angle, and the Sauter mean diameter were evaluated experimentally and compared with the theory used to design the atomizer displaying a good matching. The spray Sauter mean diameter was measured with a laser scattering system.

シンセティックジェットにより誘起される渦の挙動(流体工学,流体機械)

This paper describes a detailed study of a synthetic jet governing flow field. The synthetic jet, known as a zero net mass-flux jet, is generated by a vibrating diaphragm to oscillate flow through a small orifice. The synthetic actuator consists of the orifice and cavity installed the PZT disk of 31.2mm diameter. The test is conducted in variable input voltages and frequencies to PZT disk. The time-mean velocity and phase-locked velocity is measured by Laser Doppler Velocimeter. In the test condition of the input voltage of AC 30.0V at the actuation frequency of 990Hz, the time-mean data show the entrainment from vortexes increases the mass flow with the high blowing velocity away the orifice exit. Phase-locked velocity vector and vorticity fields reveal the periodic vortexes behavior, ejecting from the orifice, extending itself with loosing the coherent structures, and diminishing in the ambient air.

Jet fires: An experimental study of the main geometrical features of the flame in subsonic and sonic regimes

AbstractAlthough jet fires are usually smaller than other fires, they may lead to a destructive chain of events that can increase the scale of an accident. Therefore, their size should be predicted for accurate risk assessment. In the literature, most of the proposals for estimating jet fire size concern small jet fires (up to 2.5 m in length) or subsonic flames. In this study, experiments on relatively large propane jet fires in still air were performed. Vertical turbulent diffusion flames up to 10 m in length, with sonic and subsonic mass flow rates, were obtained using six different orifice exit diameters. The experiments were filmed with video and thermographic cameras and the resulting visible and infrared images were used to determine flame length and lift‐off distance. Expressions for estimating jet length as a function of several variables (mass flow rate, orifice exit diameter, Froude and Reynolds numbers) are also proposed. © 2008 American Institute of Chemical Engineers AIChE J, 2009

A Study of the Twisted Strength of the Whirled Airflow in Murata Vortex Spinning

In Murata vortex spinning, the highspeed whirled airflow twists the open-end trailing fibers converged at the inlet of the hollow spindle into a yarn. The twisted strength acting on the vortex spun yarn by the whirled airflow was investigated by an analytical model based on simulating the flow field inside the nozzle block. The results showed that the twisted strength acting on the vortex spun yarn by the vortex could be regarded as the following functions: (1) the number of jet orifices, the jet angle, the inner diameter of the jet orifice and the nozzle block; (2) the distance from the inlet of the nozzle block to the inlet of the hollow spindle; (3) the projecting height of open-trail-end fibers twined over the top exterior of the hollow spindle; (4) the vortex spun yarn diameter; and (5) the velocity at exit of the jet orifice (i.e. corresponding to nozzle pressure). Increasing the velocity at exit of the jet orifice increased the strength twisted by the whirled airflow. The strength twisted by the whirled airflow increased with decreasing inlet diameter of the nozzle block, and was enhanced with increasing outer diameter of the hollow spindle. The strength twisted by the whirled airflow was weaker when the distance from the inlet of the nozzle block to the inlet of the hollow spindle was bigger. The numerical results validated the effectiveness of the analytical model.

Flow of power-law fluids in simplex atomizers

This paper presents a computational analysis of flow of time-independent, purely-viscous, power-law fluids in simplex atomizers using the volume-of-fluid (VOF) method. Flow of shear-thinning (0.4 < n < 1), Newtonian ( n = 1) and shear thickening fluids (1 < n < 1.2) has been considered. The effect of power-law index and atomizer geometry on the flow and atomizer performance has been investigated. Three geometry parameters have been considered, viz., the atomizer constant which is the ratio of inlet area to the product of swirl chamber diameter and the exit diameter, the ratio of swirl chamber diameter to exit orifice diameter, and the length-to-diameter ratio of the exit orifice. The dimensionless film thickness at exit, spray cone angle, and the discharge coefficient for different values power-law index as well as those with varying atomizer geometry are reported. The pressure drop across the atomizer has been kept constant in all simulations. A change in the power-law index significantly alters the flow field in the in the swirl chamber of the atomizer. The velocity magnitudes and liquid film thickness at the orifice exit change with the power-law index. With fixed atomizer geometry, the pseudoplastic fluids tend to produce thinner liquid sheet, larger spray cone angle, and have lower discharge coefficient compared to dilatant fluids. Changes in the atomizer geometry have a significant impact on the flow for all values of power-law index. The spray cone angle decreases and the discharge coefficient and the film thickness increase with increasing atomizer constant. With increasing D s/ d o, the dimensionless film thickness at exit increases whereas the dimensional film thickness decreases monotonically. The discharge coefficient increases and the spray cone angle decreases with increasing D s/ d o. The discharge coefficient, the spray cone angle, and the film thickness decrease with increasing l o/ d o. A significant finding is that the variations of film thickness, spray cone angle, and discharge coefficient with a change in atomizer geometry are similar for different values of fluid power-law index, although the numerical values depend on the power-law index. This has important implications for atomizer design and industrial applications as most atomizers are designed for, and characterized with, Newtonian fluids.

Non-Equilibrium Molecular Dynamics Simulation of Nanojet Injection with Adaptive-Spatial Decomposition Parallel Algorithm

An Adaptive-Spatial Decomposition parallel algorithm was developed to increase computation efficiency for molecular dynamics simulations of nano-fluids. Injection of a liquid argon jet with a scale of 17.6 molecular diameters was investigated. A solid annular platinum injector was also solved simultaneously with the liquid injectant by adopting a solid modeling technique which incorporates phantom atoms. The viscous heat was naturally discharged through the solids so the liquid boiling problem was avoided with no separate use of temperature controlling methods. Parametric investigations of injection speed, wall temperature, and injector length were made. A sudden pressure drop at the orifice exit causes flash boiling of the liquid departing the nozzle exit with strong evaporation on the surface of the liquids, while rendering a slender jet. The elevation of the injection speed and the wall temperature causes an activation of the surface evaporation concurrent with reduction in the jet breakup length and the drop size.

CICLO DE VIDA DE Dasineura gigantea ANGELO &amp; MAIA, 1.999 (DIPTERA, CECIDOMYIIDAE)

Dasineura gigantea induz a galha dos botões em araçazeiro (Psidium cattleianum, Myrtaceae), planta nativa do Brasil que foi introduzida em algumas áreas tropicais do mundo. As galhas são histióides, prosoplasmáticas e multiloculares (3,45 ± 2,33 câmaras por galha, n = 260), com crescimento iniciado em duas épocas: fevereiro/abril e agosto/outubro. As fêmeas depositam ovos sobre os tecidos da planta e a alimentação das larvas induz a formação de galhas (período larval: 152,27 ± 9,35 dias, n = 86). As larvas possuem uma espátula protorácica que é usada para abrir o orifício de saída do adulto. Após a construção desse orifício, a larva abriga-se no interior da galha e empupa (período pupal: 35,67 ± 1,62 dia, n = 27). Com o desenvolvimento do adulto, o inseto contorce-se e força sua saída através do orifício de emergência, deixando o tegumento pupal preso a esse orifício. Os adultos não se alimentam e tem um período de vida curto (um dia, n = 45), apenas o tempo necessário para o acasalamento e oviposição.

Experimental investigations on separation control and flow structure around a circular cylinder with synthetic jet

Circular cylinder separation control and flow structure influenced by the synthetic jet have been experimentally investigated in a water channel. The synthetic jet issues from a slot and ejects toward upstream from the front stagnation point of the cylinder. It has been found that, similar to the traditional synthetic jet which is positioned near the separation point or inside the separation region, the present synthetic jet arrangement constitutes an efficient way to control flow separation of the circular cylinder, but with a different control mechanism. The present synthetic jet leads to an upstream displacement of the front stagnation point and the formation of a vortex pair near both sides of the exit orifice. When Re u based on the synthetic jet average exit orifice velocity is about lower than 43, a closed envelope forms in front of the windward side of the cylinder during the blowing cycle of synthetic jet, which acts as an apparent modification for the cylinder configuration. When Re u is high enough, an open envelope forms upstream of the cylinder, and the flow around the cylinder becomes much energetic. Thus, regardless of Re u, the present synthetic jet can improve separation for flow around a circular cylinder. With regard to the leeward side, as Re u increases, the flow separation region behind the cylinder gradually disappears. The flow over cylinder may be fully attached when the open envelope forms upstream of the cylinder and Re u is greater than 344. Then, the flow past the cylinder will converge near the back stagnation point of the cylinder, where a new vortex pair shedding periodically is generated due to the high shear layer.

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.

Optimization of Mass Bleed for Base-Drag Reduction

Efficient mass-bleed conditions to minimize base drag are examined in consideration of various base-to-orifice-exit area ratios for a body of revolution in the Mach 2.47 freestream. Axisymmetric, compressible, mass-averaged Navier-Stokes equations are solved using the standard k-w turbulence model, a fully implicit finite volume scheme, and a second-order upwind scheme. Base flow characteristics are explained regarding the base configuration as well as the injection parameter, which is defined as the mass flow rate of the bleed jet nondimensionalized by the product of the base area and freestream mass flux. The results obtained through the present study show that for a smaller base area, the optimum mass-bleed condition leading to minimum base drag occurs at relatively larger mass bleed, and a larger orifice exit can offer better drag control.

A static compressible flow model of synthetic jet actuators

AbstractIn this paper, a simple static compressible flow model for circular synthetic jet actuators is described. It is used to undertake a systematic computational investigation of the effect of changing actuator geometrical and operating parameters on the magnitude of peak jet velocity at the orifice exit of an actuator whose diaphragm displacement and frequency are allowed to vary independently. It is found that, depending on the flow conditions inside the orifice duct, the actuator may operate in two distinct regimes, i.e. the Helmholtz resonance regime and the viscous flow regime. In the Helmholtz resonance regime, the resultant synthetic jet is generated by the mass physically displaced by the oscillating diaphragm coupled with the Helmholtz resonance in the actuator. In the viscous flow regime, the Helmholtz resonance is completely damped by viscous effect such that the jet is produced by the diaphragm oscillation alone. The relationship between actuator geometrical and operating parameters at the optimum condition which yields the maximum peak jet velocity at a given diaphragm displacement is also established for these two regimes. Finally, a preliminary procedure for designing synthetic jet actuators for flow separation control on an aircraft wing is proposed.

Aerodynamically assisted bio-jets: the development of a novel and direct non-electric field-driven methodology for engineering living organisms

We recently demonstrated the ability to use electrified jets under stable conditions for the generation of cell-bearing droplets to the formation of composite threads which are biologically active. Our studies established that processed cells were viable over several generations post-jetting and -threading. These harmless and successful techniques for jet-based cell handling to deployment for precision deposition have great potential and widespread applications in bioengineering and biotechnology. Nonetheless, our investigations into ‘bio-electrosprays’ and ‘cell electrospinning’ have elucidated these jets having direct applicability in regenerative and therapeutic medicine to studies in developmental biology. For these very reasons, jet methodologies having the capability to safely handle living organisms for drop and placing are increasingly gaining the interests of life scientists. We now demonstrate yet another technique (a non-electric field-driven approach, previously never explored with jetting living cells), possessing the ability to directly handle the processing of primary living organisms by means of the flow of a cell suspension within a needle placed in a pressure chamber in the presence of an applied pressure difference. The technique we introduce here is referred to as ‘aerodynamically assisted bio-jets/-jetting’ which is driven completely by aerodynamic forces applied over an exit orifice by way of a differential pressure. Our investigations present an operational window in which stable jetting conditions are achieved for the formation of a near-monodispersed distribution of cell-bearing droplets and droplet residues. Finally, the aerodynamically bio-jetted living primary organisms are assessed (over both short and long time points) for cellular viability by means of FACScan, a flow cytometry technology which quantifies the percentage of living and dead cells. These advanced biophysical and bioengineering studies elucidate the emergence of a non-electric field-driven bio-jetting technology which now joins the cell jetting race.

Initiation of detonation in flows of fuel-air mixtures

Regimes of self-ignition of the fuel mixture obtained by controlled separate injection of hydrogen and air into a plane-radial vortex chamber with a rapid (0.2 msec) transition to detonation have been realized for the first time. Self-ignition occurs in the stoichiometric region with a slightly higher (up to 6–30%) content of hydrogen and, normally, in a subsonic flow. The energy of guaranteed detonation initiation is determined for combustors of different geometries and different ratios of fuel components by using a thermal pulse produced by blasting a wire by electric current. Detonation initiation is ensured by using energy of 0.1 J. It is found that the main contribution of energy into the flow of the mixture occurs at the stage of evaporation (ionization) of copper of the blasted wire. The continuous spin detonation regime is found to decay as the exit cross section of the combustor is reduced. In the regime of combustion, both detonation and conventional turbulent combustion, the pressure at the periphery of the plane-radial vortex chamber is lower and the pressure at the edge of the exit orifice is higher than that in the case of exhaustion of cold fuel components.

Experimental study on flow and heat transfer characteristics of synthetic jet driven by piezoelectric actuator

To investigate the flow and heat transfer characteristics of a synthetic jet driven by piezoelectric actuator, experimental investigation utilizing particle image velocimetry, hot-wire anemometer and infrared camera was carried out. The results show that: (1) At the jet orifice exit, pairs of vortexes ar

Is Helmholtz Resonance a Problem for Micro-jet Actuators?

A theoretical analysis is described that determines the conditions for Helmholtz resonance for a popular class of self-contained microjet actuator used in both synthetic- and pressure-jump (pulse-jet) mode. It was previously shown that the conditions for Helmholtz resonance are identical to those for optimizing actuator performance for maximum mass flux. The methodology is described for numerical-simulation studies on how Helmholtz resonance affects the interaction of active and nominally inactive micro-jet actuators with a laminar boundary layer. Two sets of numerical simulations were carried out. The first set models the interaction of an active actuator with the boundary layer. These simulations confirm that our criterion for Helmholtz resonance is broadly correct. When it is satisfied we find that the actuator cannot be treated as a predetermined wall boundary condition because the interaction with the boundary layer changes the pressure difference across the exit orifice thereby affecting the outflow from the actuator. We further show that strong inflow cannot be avoided even when the actuator is used in pressure-jump mode. In the second set of simulations two-dimensional Tollmien–Schlichting waves, with frequency comparable with, but not particularly close to, the Helmholtz resonant frequency, are incident on a nominally inactive micro-jet actuator. The simulations show that under these circumstances the actuators act as strong sources of 3D Tollmien–Schlichting waves. It is surmised that in the real-life aeronautical applications with turbulent boundary layers broadband disturbances of the pressure field, including acoustic waves, would cause nominally inactive actuators, possibly including pulsed jets, to act as strong disturbance sources. Should this be true it would probably be disastrous for engineering applications of such massless microjet actuators for flow control.

Experimental investigations on a two-phase jet pump used in desalination systems

With an ever-increasing population and rapid growth of industrialization, there is a great demand for fresh water, especially for drinking. In view of this, different desalination technologies have evolved with a thrust for utilization of renewable energy sources such as solar energy, ocean thermal energy, geothermal energy, and waste heat. Flash desalination is a technology in which fresh water is produced from seawater by evaporation and subsequent condensation. One such desalination technique involves different processes like pressurization of seawater using a pump, creation and maintenance of vacuum using jet pump in a flash chamber, evaporation of seawater at reduced pressure using warm water from the sea surface and condensation of water vapour using cold water from the deep sea. A two-phase variable geometry jet pump was designed, developed and tested for the flash desalination system to create a vacuum inside the flash chamber. The area ratio of the jet pump used for the investigation was 0.25. Experimental results are reported from tests on the jet pump with a view to assessing the optimum distance between orifice exit and mixing tube entrance. Overall performance of the jet pump was assessed by plotting its characteristics. Performance of the jet pump was analyzed by plotting iso-efficiency curves on characteristics curves drawn for various primary water flow rates. The optimum orifice to mixing tube distance of the jet pump was found and corresponding maximum efficiency was reported. Maximum vacuum created by the jet pump at an optimum condition, i.e., at maximum jet pump efficiency, with respect to time was determined.