Rectangular Orifice Research Articles

358 長方形オリフィスから流出する超音速自由噴流のDSMC解析(OS5-5 乱流現象の実験と数値シミュレーション5(せん断流2),OS5 乱流現象の実験と数値シミュレーション)

358 長方形オリフィスから流出する超音速自由噴流のDSMC解析(OS5-5 乱流現象の実験と数値シミュレーション5(せん断流2),OS5 乱流現象の実験と数値シミュレーション)

노즐 오리피스 형상 및 형상비가 디젤과 바이오디젤 연료의 노즐 내부 및 외부 유동특성에 미치는 영향

The aim of this study is to investigate the effects of nozzle orifice shapes and the nozzle length-to-diameter ratio(L/D) on the nozzle cavitation formation inside the orifice and the external flow pattern. The nozzle used in this work was tested the taper orifice nozzle and the rectangular orifice nozzle which was made from the transparent acrylic acid resin. For studying the effect of the nozzle L/D ratio, it was used to three L/D ratios of 3.33, 10, and 20. The cavitation flow of nozzle was visualized by using the ICCD camera and optical system. This work revealed that the flow rate and discharge coefficient() of the taper orifice nozzle was larger than those of the rectangular orifice nozzle at the same injection pressure. The cavitation flow was observed in the nozzle orifice at the low injection pressure and the breakup of liquid jet was promoted as the L/D ratio is decreased. The cavitation of biodiesel fuel was formed at the lower injection pressure than that of diesel fuel because of higher viscosity and density.

115 長方形断面オリフィスからの脈動噴流の可視化(GS1-1 自然対流,噴流,一般セッション:GS1 流体工学)

115 長方形断面オリフィスからの脈動噴流の可視化(GS1-1 自然対流,噴流,一般セッション:GS1 流体工学)

An investigation into feasibility of impingement heat transfer and acoustic abatement of meso scale synthetic jets

While synthetic jets have found more applications in controlling fluid flow especially in aerospace applications, more recently they captured a lot of attention for the thermal management of electronics. While the jet sizes vary and may be large for microfluidic applications, it is preferred that they should be in the meso scale range for removing heat from electronics components. Current study focuses on the heat transfer and acoustic aspects of the small-scale synthetic jets. Synthetic jets designed and developed at the General Electric Global Research Center can provide peak air velocities in excess of 90 m/s from a 1 mm hydraulic diameter rectangular orifice. The jets are driven by a sine wave with an operating frequency of between 3 and 4.5 kHz, providing the highest thermal performance for the current jets. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. Two heater sizes have been studied in the current study to understand the effect of the characteristic length. Several parameters are varied to find the change in the heat transfer rates with the jet location, driving voltage, driving frequency, and heater power. Heat transfer enhancements over the specific heater sizes are presented for the same jet. It is found that the enhancement can be between 4 and 10 times depends on the heater size showing that smaller sizes provide the best jet effectiveness. It is also noted that jet noise can be as large at 73 dB, but possible abatement techniques can decrease this noise level as low as to 30 dB.

4037 縦渦発生ジェットによる流れ場変化に適合したはく離の能動制御(G05-8 境界層・はく離,G05 流体工学)

Flow separation is mostly an undesirable phenomenon and boundary layer control is an important technique for flow separation problems on airfoils and in diffusers. The vortex generator jet method is one of the boundary layer control technique and an active control technique which provides a time-varying control action to optimize performance under a wide range of flow conditions because the strength of longitudinal vortices can be adjusted by varying the jet speed. In this study, an adaptive separation control system using vortex generator jets with rectangular orifices has been developed. The separation control system can be practically applied to the flow separation control of a two-dimensional diffuser. It was confirmed that our separation control system could adaptively suppress flow separation for the flow fields caused by some changes in freestream velocity and the divergence angle of the diffuser. Furthermore, we developed the system which starts the jet blowing just before the onset of separation.

The Flow Behaviors of MR Fluids Flowing Through an Orifice for Damper Designing

The flow behavior of magnetorheologic fluids (MRFs) flowing through variable orifices were experimented and the properties of the magnetic field around the orifice were analyzed by the finite element method in this article. The results show that the magnetic effects of MRF differ according to: the material, the position, and the thickness of the rectangular orifice. In this article, the relationship between orifice shapes and flow behavior of MRF is described. The results are valuable for MRF device design.

Meso Scale Pulsating Jets for Electronics Cooling

Microfluid devices are conventionally used for boundary layer control in many aerospace applications. Synthetic jets are intense small-scale turbulent jets formed from periodic entrainment and expulsion of the fluid in which they are embedded. The jets can be made to impinge upon electronic components thereby providing forced convection impingement cooling. The small size of these devices accompanied by the high exit air velocity provides an exciting opportunity to significantly reduce the size of thermal management hardware in electronics. A proprietary meso scale synthetic jet designed at GE Global Research is able to provide a maximum air velocity of 90m∕s from a 0.85 mm hydraulic diameter rectangular orifice. An experimental study for determining the cooling performance of synthetic jets was carried out by using a single jet to cool a thin foil heater. The heat transfer augmentation caused by the jets depends on several parameters, such as, driving frequency, driving voltage, jet axial distance, heater size, and heat flux. During the experiments, the operating frequency for the jets was varied between 3.4 and 5.4 kHz, while the driving voltage was varied between 50 and 90VRMS. Two different heater powers, corresponding to approximately 50 and 80 °C, were tested. A square heater with a surface area of 156mm2 was used to mimic the hot component and detailed temperature measurements were obtained with a microscopic infrared thermal imaging technique. A maximum heat transfer enhancement of approximately 10 times over natural convection was measured. The maximum measured coefficient of performance was approximately 3.25 due to the low power consumption of the synthetic jets.

Effect of Vortex Generator Jets with Different Aspect Ratios on Boundary Layer Control

The vortex generator jets can achieve the adaptive control by adjusting properly the jet speed in response to flow situations. The vortex generator jet method may accomplish separation control only when it is necessary, and therefore it is useful for both design and off-design conditions. In this study, the effect of vortex generator jets on separation control is investigated for three types of rectangular orifices with aspect ratios AR=0.16, 1 (square) and 6.4. The rectangular orifice with AR=0.16 set the long side of the orifice in the streamwise direction and the long side turned to the spanwise direction for AR=6.4. For the rectangular orifices with AR=6.4, the vortices become stronger and exist at lower vertical positions in comparison with those for the other orifice types. Therefore, the rectangular orifices with AR=6.4 promote the boundary layer mixing and make effective the separation control.

C304 位相平均変動静圧測定による噴流中の三次元渦構造の抽出

Measurements of fluctuating static-pressure in a rectangular jet were conducted to educe three-dimensional vortical structure with phase-averaging technique. The experiments were performed for the air issuing from a sharp-edged rectangular orifice. The jet was excited at the interaction mode, where the stable interaction of vortices was generated. For phase-averaging processing, the reference signals were detected by a single normal hot-wire probe fixed at a downstream station whose distance from the jet exit corresponded to an equivalent diameter of the exit, and fluctuating static-pressure were measured over the flow field by a static pressure probe. Phase-average incoherent fluctuating static-pressure, which is related to jittering motions of vortices and is defined in phase-averaging, and adequacy of Taylor hypothesis to obtain three-dimensional structure were discussed. The results suggested that interaction and stretching of vortices contributes to generation of the incoherent vortex motions, and the use of a constant convection velocity in the hypothesis is acceptable for qualitative consideration.

Flow and Heat Transfer Characteristics of Confined Noncircular Turbulent Impinging Jets

A three dimensional computational fluid dynamic investigation is carried out to predict the turbulent flow and surface heat transfer under an impinging air jet issuing normally from a single noncircular orifice in a plate held parallel to the target surface. Static pressure distributions, velocity fields and local as well as average Nusselt number on the impinged surface are presented for square, elliptic, and rectangular orifices and compared with those for a circular orifice. Effects of jet Reynolds number as well as spacing between the nozzle plate and the impinged surface are examined using a two-layer κ–η turbulence model. Results show flow structure similarities between the characteristics of rectangular and elliptic jets of equal aspect ratio. Further, it is observed that noncircular impinging jets can provide higher average heat transfer rates than corresponding circular jets for certain geometric parameters viz. nozzle-to-plate spacing and the size of the averaging area used to compute the average Nusselt number.

A study of synthetic jets from rectangular and dual-circular orifices

AbstractThe results of an investigation into the effect of both the number of orifices and the geometry of these orifices on the fluid structures exiting from a synthetic jet actuator are presented. The experiments have used smoke and laser visualisation and single hotwire measurement techniques to establish the flow field exiting the various orifices and the fluid velocities in the exit plane of the orifice. The results indicate that the use of two small orifices can perhaps produce two coherent vortex rings with a total circulation greater than that found in the ring produced by a large, single orifice of equivalent area. However, they have also shown that there are three different types of interaction between two adjacent orifices, related to the spacing between them and the level of excitation applied to the diaphragm. In addition, these interactions may affect the overall level of circulation in different ways. Finally the results have shown that a rectangular orifice of a given exit plane area is more likely to produce a turbulent ring than the equivalent circular orifice due to a ‘smoothing’ process which endeavours to create an axisymmetric ring from a non-axisymmetric slug of fluid. This work has shown that when using synthetic jet actuators in flow control applications, care should be taken in selecting the spacing and geometry of the orifices used, as certain set-ups may be more suited to certain applications than others.

Spray Characteristics of Slit Nozzle for DI Gasoline Engines.

Direct injection gasoline engines have been developed for the improvement of fuel economy and exhaust emissions. Recently, a new concept of stratified charge combustion has been proposed. A slit nozzle was adopted to realize the new concept. The nozzle has a rectangular orifice and forms a thin fan-shaped spray. This paper describes the spray characteristics of the slit nozzle. The following results were obtained. (1) The spray penetration increases with increasing the slit thickness. (2) The effect of the slit thickness on spray drop size is small. (3) The features of the slit nozzle are high spray penetration, widely diffuse spray and fine atomization compared with the swirl nozzle.

Influence of the Metering Chamber Volume and Actuator Design on the Aerodynamic Particle Size of a Metered Dose Inhaler

Presented in this work are the results of a study designed to investigate the impact of the valve metering chamber volume and actuator design on the aerodynamic particle size distribution (PSD) of a suspension metered dose inhaler (MDI) containing propellant HFA-227. It was hypothesized that the valve metering volume and the actuator design in the MDI could influence the PSD of the emitted dose since it would affect the aerosol spray dynamics. The PSD results from this study, measured using cascade impaction, revealed that samples containing an actuator intended for oral delivery (rectangular mouthpiece and orifice diameter of ≈0.5 mm) produced a higher fine particle dose (FPD) than those containing an actuator intended for nasal delivery (circular nosetip and orifice diameter of ≈1 mm). In addition, the drug PSD profile was shown to be more sensitive to differences in the particle size of the suspended material when the oral actuator was used compared to when the nasal actuator was used. The valve metering chamber (25 vs. 63 μL volume) did not appear to have a major effect on the product aerodynamic PSD or the droplet size. These results demonstrate the importance of actuator design and orifice size in determining the aerodynamic PSD of an MDI.

704 異なるアスペクト比の四角形ジェット孔による渦発生ジェットを用いたはく離制御

704 異なるアスペクト比の四角形ジェット孔による渦発生ジェットを用いたはく離制御

Unsteady two-dimensional orifice flow: a large-size experimental investigation

Orifice flows were used as water clocks since the Antiquity up to the 16-th century. Today orifices and nozzles are used for measuring discharges. Most works were conducted with steady flow conditions and there is little information on the unsteady flow pattern. In this study, the writers describe an experimental investigation of an unsteady orifice flow discharging vertically. The study was conducted in a large-size facility with a rectangular orifice (0.75-m by 0.07-m) discharging up to 1.2 m3in about 10 seconds. The study presents new information on the unsteady flow patterns, the discharge capacity and the velocity field in the reservoir. The results are compared with “classical” orifice flow results.

A Study on the Flow Field around a Circular Cylinder Placed in a Rectangular Orifice Jet.

A long circular cylinder with the diameter of 20 mm was placed in an air jet, issuing from a rectangular orifice with the short side, h, of 3 mm and the aspect ratio of 10. The cylinder was settled on the symmetrical plane of the jet flow along the long side of the exit. The impinging distances between the jet exit and the front surface of the cylinder, xi, were varied within fifty times of the short side length. The jet exit velocity was kept constant at 24 m/s and the Reynolds number, based on the short side length, was about 4 900. It was found that the mean and fluctuating(rms) pressure profiles around the circular cylinder showed remarkable changes with the impinging distance and the position along the cylinder axis, z. The value of fluctuating pressure at the stagnation, being different from that of fluctuating velocity of the free jet, was large even at the vicinity of the jet exit. The negative pressure region, formed on the front surface of the cylinder, alone diminished clearly at a position of z over the impinging distance of xi/h<5. The saddle-backed velocity profiles for the orifice jet as well as the diminshment of the negative pressure region along z-axis might result in the off-axis distributions of the drag per unit width. The drag per unit width at z/h=3.3 of xi/h=5 was increased up to 2.4 times of the drag at z/h=0. The coefficient of total drag on the cylinder was estimated 1.16 at the jet exit and 0.76 at xi/h=50.

Effect of Grazing Flow on the Acoustic Impedance of an Orifice

A linearized potential flow model is developed to study the effect of grazing flow on the acoustic behavior of an orifice. In accordance with the previous flow visualization and measurements, this model uses the particle velocity continuity boundary condition rather than the widely used displacement to match the flow-fields separated by the shear layer over the orifice. An experiment is also carried out to validate the present theory in the case of circular or rectangular orifices. The theory agrees well with the experiment. In addition, further comparison is made between the present and two existing impedance models. One major objective of the present investigation is to make a tentative judgement on the two boundary conditions for a sound wave transmitting through a turbulent boundary layer over an orifice. It is found that, compared to the particle displacement continuity boundary condition, the use of the particle velocity continuity boundary condition results in a much better agreement between the theoretical predictions and the experimental data. Finally, there is a discussion on the influence of plate thickness on orifice impedance in the presence of grazing flow.

A Versatile Flat-Deposit Impactor-Type Aerosol Collector Part 1: Design and Qualitative Study

Cascade impactors provide an efficient method for sampling aerosols according to their size, grossly between 0.1 mu m and a few tens of microns in diameter. We have designed such an apparatus, with rotatable substrate plates and radially aligned rectangular orifices. The nominal cutpoint diameters are, respec tively, for stages 1-7 of the collector: 10, 5, 2, 1, 0.5, 0.25, and 0.1 mu m aed for an airflow of 10/L min. The sampler has an auxiliary set of orifice plates for operation at 20/L min giving the same cutpoint characteristics. Annular deposits are obtained following complete rotation of the collecting substrates. The airflow is controlled with a critical orifice at the last stage. A calculation program was written for a rectangular orifice impactor in order to determine the cutpoints in different conditions. The constant exit pressure mode of operation appears to be the best way to minimize fluctuations of the effective cutpoints against the varying conditions of ambient temperature and pressure. T...

Spreading characteristics of compressible jets from nozzles of various geometries

The spreading characteristics of jets from several asymmetric nozzles, and a set of rectangular orifices are compared, covering a jet Mach number range of 0.3–2.0. The effect of ‘tabs’ for a rectangular and a round nozzle is also included in the comparison. Compared to a round jet, the jets from the asymmetric nozzles spread only slightly more at subsonic conditions whereas at supersonic conditions, when ‘screech’ occurs, they spread much more. The dynamics of the azimuthal vortical structures of the jet, organized and intensified under the screeching condition, are thought to be responsible for the observed effect at supersonic conditions. Curiously, the jet from a ‘lobed’ nozzle spreads much less at supersonic condition compared to all other cases; this is due to the absence of screech with this nozzle. Screech stages inducing flapping, rather than varicose or helical, flow oscillation cause a more pronounced jet spreading. At subsonic conditions, only a slight increase in jet spreading with the asymmetric nozzles contrasts previous observations by others. The present results show that the spreading of most asymmetric jets is not much different from that of a round jet. This inference is further supported by data from the rectangular orifices. In fact, jets from the orifices with small aspect ratio (AR) exhibit virtually no increase in the spreading. A noticeable increase commences only when AR is larger than about 10. Thus, ‘shear layer perimeter stretching’, achieved with a larger AR for a given cross-sectional area of the orifice, by itself, proves to be a relatively inefficient mechanism for increasing jet spreading. In contrast, the presence of streamwise vortices or ‘natural excitation’ can cause a significant increase – effects that might explain the observations in the previous investigations. Thus far, the biggest increase in jet spreading is observed with the tabs. This is true in the subsonic regime, as well as in the supersonic regime, in spite of the fact that screech is eliminated by the tabs. The characteristic spreading of the tabbed jets is explained by the induced motion of the tab-generated streamwise vortex pairs. The tabs, however, incur thrust loss; the flow blockage and loss in thrust coefficient, vis-à-vis the spreading increase, are evaluated for various configurations.

Effect of cut-outs on underexpanded rectangular jets

AbstractThe flowfield characteristics of jets from plain and rectangular orifices with semi-circular cut-outs have been experimentally investigated for both sonic and underexpanded conditions. Detailed pitot pressure measurements revealed that the cut-outs had a strong influence on the emerging flowfield. The rectangular orifice with cut-outs at the minor axis ends showed more effective mixing with shorter core lengths and faster near field jet decay when compared with the plain rectangular and the rectangular orifice with cut-outs at the major axis ends. The general trend of variation of shock cell length with fully expanded Mach number was consistent with Tam's theory, but the shock cell length of orifice jets were less than that predicted by Tam.