High Velocity Ratio Research Articles

Pressure Effects on Geometry and Structure of Gas Jet Flames in Crossflow

Flame structure and geometry of natural gas andpropanediffusion  ames in cross ow are presented to delineate the effects of buoyancyand ambientpressure. The fuel was injected horizontally into a verticallymovingairstream. The buoyancy acted along the direction of the cross ow. The combustion-chamber pressure was varied from 1 to 1.45 bar and the cross ow to jet velocity ratio from 0.1 to 1.45. Quantitative rainbow schlieren de ectometry was used to visualize the  ame and to measure the geometrical parameters. The centerline  ame trajectory showed three distinct regions, and the dimensionless coordinate of the jet centerline in the jet direction varied with 0.45, 0.25, 0 power of the coordinate in the cross ow direction and i 0.5 power of the Froude number based on the jet velocity in these regions. The  ame trajectories did not change signiŽ cantly with pressure. Flame chord length varied with 0.45 power of the cross ow/jet velocity ratio. Flame length and soot formation characteristics changed notably with pressure. Propane  ames were more susceptible than natural gas  ames to the ambient pressure. The  ame luminosity caused by soot in the propane  ame changed only slightly with velocity ratio. However, the natural gas  ame became nonsooty at high velocity ratios.

Application of particle image velocimetry and proper orthogonal decomposition to the study of a jet in a counterflow

Particle image velocimetry (PIV) experiments were carried out on a round jet in a uniform counterflow. The complex dynamics of this flow has so far hindered its understanding, and PIV appears to be a promising investigation method to help fill this gap. In fact PIV allows the dynamics of single vorticity structures to be followed, at least within the limits of its spatial and temporal resolution. In particular, the combination of PIV and proper orthogonal decomposition (POD) analysis showed that it is possible to isolate a few typical patterns out of the apparently chaotic fluctuations of the jet. A POD analysis at high velocity ratios was performed to investigate the fluctuations typical of the far field of the jet, while one at the critical velocity ratio of 1.3 delivered further information on the transition between the stable and the unstable flow condition.

Aspects of Vane Film Cooling With High Turbulence: Part II—Adiabatic Effectiveness

A four-vane subsonic cascade was used to investigate the influence of turbulence on vane film cooling distributions. The influence of film injection on vane heat transfer distributions in the presence of high turbulence was examined in part I of this paper. Vane effectiveness distributions were documented in the presence of a low level of turbulence (1 percent) and were used to contrast results taken at a high level (12 percent) of large-scale turbulence. All data were taken at a density ratio of about 1. The three geometries chosen to study included one row and two staggered rows of downstream film cooling on both the suction and pressure surfaces as well as a showerhead array. Turbulence was found to have a moderate influence on pressure surface film cooling, particularly at the lower velocity ratios. The strong pressure gradients on the pressure surface of the vane were also found to alter film cooling distributions substantially. At lower velocity ratios, effectiveness distributions for two staggered rows of holes could be predicted well using data from one row superposed. At higher velocity ratios the two staggered rows produced significantly higher levels of effectiveness than values estimated from single row data superposed. Turbulence was also found to reduce effectiveness levels produced by showerhead film cooling substantially.

Effects of velocity ratio on mixing layer three-dimensionality

Abstract Three-dimensionality in transitioning mixing layers, in the form of streamwise vortical structures, is now well established and understood. In the present investigation, the effects of velocity ratio, or more precisely of velocity difference across the layer, on the near-field generation and development of three-dimensionality in two-stream mixing layers have been investigated for the first time. Detailed time-averaged velocity measurements were obtained using a single rotatable cross-wire probe on fine cross-plane grids at four streamwise locations in the near-field region. The effects of five velocity ratios, ranging from r =0.5 to 0.9, were investigated by keeping the velocity of one stream constant while varying that of the other. The results indicate that the mixing layer three-dimensionality is strongest for the mixing layer with the lowest velocity ratio. The peak mean streamwise vorticity levels decrease with increasing velocity ratio at all the streamwise locations investigated. However, the rate of decrease is highest at the most upstream station and it decreases with increasing downstream distance. The mean streamwise vorticity contours at the first station show that their distribution is quite similar at the different velocity ratios, implying that the generating mechanism and initial disturbance fields remain unchanged with velocity ratio. However, it is conceivable that the amount of stretching in the braid regions due to the spanwise vortical structures is affected by velocity ratio. As the velocity ratio decreases (and the velocity difference across the layer increases), stronger spanwise rollers are generated which increase the amount of stretching in the braid regions and hence the streamwise vorticity is amplified. The splitter plate wake has a lasting effect on the three-dimensional structure of the mixing layers at the higher velocity ratios. The presence and effects of the wake are clearly seen in the mean velocity, mean streamwise vorticity and Reynolds stress contours.

Scalar mixing in turbulent concentric round jets

AbstractThe scalar mixing field of a free, turbulent concentric round jet has been examined using marker nephelometry. The flow conditions included velocity ratios between the centre and annular jet of 0.188, 0.519 and 0.911. The correlation function between the concentration fluctuations in the two jet streams increased from –1.0 near the nozzle to + 1.0 further downstream indicating a tendency to complete mixing between the jets. The initial mixing behaviour between the jets was better for the lower velocity ratio between the jets (Ui/Uo = 0.188) although further downstream there was better transverse mixing between the jets with the higher velocity ratio (Ui/Uo = 0.911).

Poisson's ratio and crustal seismology

New measurements of compressional and shear wave velocities to hydrostatic pressures of 1 GPa are summarized for 678 rocks. Emphasis was placed on obtaining high‐accuracy velocity measurements, which are shown to be critical in calculating Poisson's ratios from velocities. The rocks have been divided into 29 major groups for which velocities, velocity ratios, and Poisson's ratios are presented at several pressures. Observed Poisson's ratios for the monomineralic rocks compare favorably with theoretical Poisson's ratios calculated from single‐crystal elastic constants. Plagioclase feldspar composition is important in understanding rock Poisson's ratios, since Poisson's ratio of albite increases from 0.28 to a predicted value of 0.31 for anorthite. Fe substitution for Mg in pyroxene and olivine also increases Poisson's ratio. Plotting rock compressional wave velocities versus Poisson's ratios reveals a triangular distribution bounded by quartzite with low compressional wave velocity and low Poisson's ratio, dunite with high compressional wave velocity and intermediate Poisson's ratio, and serpentinite with low compressional wave velocity and high Poisson's ratio. For common plutonic igneous rocks, there is a clear trend relating Poisson's ratio to composition, in which Poisson's ratio for granitic rocks increases from 0.24 to 0.29 as composition changes to gabbro and then decreases with decreasing plagioclase and increasing olivine contents to 0.25 in dunite. Changes in Poisson's ratio with progressive metamorphism of mafic and pelitic rocks correlate reasonably well with mineral reactions. There is no simple correlation between Poisson's ratio and felsic and mafic rock compositions; however, a linear correlation of increasing Poisson's ratio with decreasing SiO2 content is observed for rocks with 55 to 75 wt % SiO2. Average Poisson's ratios for continental and oceanic crusts are estimated to be 0.265 and 0.30, respectively.

Some flow characteristics of lobed forced mixers at higher velocity ratios

The flow characteristics of two types of lobed forced mixers, the unscalloped and the scalloped mixers, have been examined at velocity ratios higher than unity, in relation to the variation of mass flux uniformity, the decay of the streamwise vorticity, the variation of turbulent kinetic energy and the growth of the shear layer with distance from the trailing edge. Three trailing edge configurations have also been considered for each type of mixer, namely a square wave, a semi-circular wave and a triangular wave. The analysis showed that the strength of the streamwise vorticity shed at the trailing edge and the subsequent decaying rate with downstream distance are found to be very important in studying the mixing effectiveness of the lobed mixers.

Co- and contrarotating streamwise vortices in a turbulent boundary layer

A study was carried out on streamwise vortices in a turbulent boundary layer using computational fluid dynamics. The vortices were generated by either a single jet or an array of jets of coor contrarotating arrangement exhausting into the boundary layer. The effects of jet angle, velocity ratio, and spacing were studied. Results confirmed previous experimental observations of single vortex formation at a sufficient distance downstream of the jet exit, from the initial multiple vortices. The study found that jet skew angle variation from 60 to 90 deg did not cause significant changes in the overall flow features. The results also suggested that a high jet velocity ratio might not necessarily be effective for flow control. For the contrarotating jets, it was found that 1) they produced stronger vortices, 2) the circulation level was reduced with the jet spacing, and 3) the maximum vorticity level was not affected by the jet spacing. For the corotating jets, it was found that 1) the circulation level was not affected by the jet spacing and 2) the vortices decayed much faster than those of the contrarotating arrangement. Good comparison was obtained between the calculated circulation levels and previous measurements.

An experimental study on the two-dimensional opposed wall jet in a turbulent boundary layer: Change in the flow pattern with velocity ratio

Results of the measurement of flow properties in a two-dimensional turbulent wall jet which is injected into the turbulent boundary layer in the direction opposite to that of the boundary layer flow are presented by varying the ratio of the jet issuing velocity to the mainstream velocity λ. This flow includes the flow separation and the recirculating flow, and so it requires the magnitude and direction of instantaneous velocity be measured. In the present work, a tandem hot-wire probe is manufactured and its characteristics are examined experimentally. With the use of this probe the change in the penetration length of the jet with the velocity ratio is investigated. It is clarified that two regimes of flow patterns exist: in the low velocity ratio the penetration length of the jet changes little with λ, and in the high velocity ratio it goes far from the nozzle with increasing λ. Streamlines, turbulence intensity contours and static pressure contours are presented in the two typical velocity ratios corresponding to each of two flow patterns, and they are compared.

Influence of sideband oscillations on gyrotron efficiency

We report the observation of sideband mode effects on the efficiency of overmoded gyrotron operation. Two cavities were designed and operated which differed in the presence of sideband modes. In one version of the cavity, parasitic backward waves modes were observed and efficiencies were approximately 22% at 40 A beam current. With the use of a multi-mode self-consistent nonlinear code, a modified design was generated which eliminated the sideband modes. Experiments were conducted with this new cavity which produced efficiencies of approximately 33% at 30 A and 27% at 40 A beam current, but with a slightly higher velocity ratio than seen with the earlier cavity. An additional cavity, also with no sideband modes but with a longer cavity length and therefore higher Q obtained powers up to 1.3 MW with an efficiency of 39% at a 40 A beam current. >

Crustal structure of the southeastern Grenville Province, northern New York State and eastern Ontario

The Grenville province exposes an oblique cross section through mid‐lower crustal lithologies that were pervasively deformed and subjected to regional thermal overprinting during the Grenvillian orogeny (1.1 Ga). The southeastern Grenville province is divided into two subterranes by the Carthage‐Colton mylonite zone, a 110‐km‐long lineament characterized by intense ductile shear and igneous intrusion, which separates the amphibolite facies metasediments of the Central Metasedimentary Belt to the west from the granulite facies metaplutonics of the Central Granulite Terrane to the east. The recognition of distinct lithotectonic domains separated by zones of intense ductile shear in the Grenville province raises questions concerning the deep structure of these subterranes and, in particular, the means by which the mid‐lower crustal rocks exposed in the Grenville province were emplaced. Seismic refraction/wide‐angle reflection data were acquired to investigate the deep structural interrelationships within the southeastern Grenville province. A travel time inversion for velocity and interface depth was applied to the seismic data, together with constraints from amplitude modeling to produce a seismic velocity model of the crust in the southeastern Grenville province. In the Central Metasedimentary Belt the upper crust is characterized by velocities in the range 6.3–6.4 km/s and a Poisson's ratio of 0.26 ± 0.01 which are attributed to quartzofeldspathic rocks. Farther east in the Central Granulite Terrane, upper crustal velocities of 6.55 km/s and a Poisson's ratio of 0.28 ± 0.01 are associated with the Marcy Anorthosite. The seismic homogeneity of the upper crust in the region of the Carthage‐Colton mylonite zone suggests that this boundary is a shallow feature, limited to the upper 2–3 km of the crust. The deep crustal structure of the southeastern Grenville province is characterized by two discrete and laterally discontinuous seismic interfaces. In the Central Metasedimentary Belt the top of the lower crust is delineated by an eastward dipping interface at 24–28 km depth. In the Central Granulite Terrane, prominent en echelon reflections, referred to as the Tahawus complex, form a gently arched dome at 17–22 km depth. Interpretation of the Tahawus complex as a zone of layered mafic cumulates is supported by its high velocity (7.1 km/s) and Poisson's ratio (0.27 ± 0.02). The lower crust is characterized by a velocity of 7.0–7.2 km/s and an anomalously high Poisson's ratio of 0.30 ± 0.02, which are representative of pyroxene‐garnet granulites. In contrast, velocities of 6.8–7.0 km/s are modeled beneath the Central Granulite Terrane and appear to signify a lateral change in composition. The Moho lies at 44–45 km depth and is characterized by pronounced en echelon reflection segments, suggesting compositional interlayering around the crust‐mantle boundary. The velocity of the upper mantle is 8.0–8.2 km/s. An anomalous upper mantle layer with a reversed velocity of 8.6 km/s dips eastward from 50 to 60 km depth beneath the southeastern Grenville province. Our results indicate that remnants of magmatic intrusions that mobilized and thickened the crust during the Grenvillian orogeny are preserved in the mid‐lower crust as a layered cumulate body (Tahawus complex) and in the upper mantle as an eclogitic lens, possibly delaminated from the overthickened crust during uplift of the southeastern Grenville province.

Modeling and Analysis of a Manipulator Joint Driven Through a Worm Gear Transmission

Worm gear transmissions are capable of high velocity ratios as well as redirection of rotation. Both of these features are desirable for some robot geometries. A problem has been encountered in several robot designs; however, where a self-excited vibration occurs for some configurations of the manipulator in the joint containing the worm gear. In this work, a system which exhibits this type of undesirable motion is examined. The system consists of a DC servo motor which is used to position a flexible cantilever arm through a worm gear transmission. A nonlinear model is developed to describe the motion of the system. The model is then validated by comparing the predicted response to the observed response of an experimental system. It is demonstrated that the model accurately predicts the onset of the unstable vibration. The model is then linearized and it is shown that the linear model will predict the occurrence of the instability as well.

Evaluation of the peripheral arteries with duplex US after angioplasty.

Duplex ultrasound (US) was performed in 22 patients before and immediately after percutaneous transluminal balloon angioplasty (PTA) for peripheral artery stenoses or occlusions. Two patients underwent PTA on two occasions, and one patient underwent PTA of each lower extremity, resulting in 25 duplex US imaging pairs at a total of 40 PTA sites. The criterion for significant stenosis on duplex US studies was an increase in peak systolic velocity of at least 100% compared with the velocity in the arterial segment proximal to the lesion (velocity ratio, greater than or equal to 2.0). For 22 paired duplex US studies, pulse volume recordings or ankle-brachial indexes were obtained before and after PTA. After PTA, eight patients had residual high velocity ratios at 12 PTA sites. Only two of these patients had a residual hemodynamic stenosis as determined with post-PTA arteriography, pulse volume recordings, or ankle-brachial indexes. In this study, duplex US that was performed immediately after PTA for evaluation of residual stenosis was frequently misleading.

プランジ研削の最適化に関する研究

In this paper, a new method is proposed to minimize the grinding cycle time of cylindrical plunge grinding operations. The proposed method is based on the changing of the velocity ratio (the peripheral speed of workpiece/the peripheral speed of grinding wheel) in a grinding cycle although the conventional plunge grinding has been done with a constant velocity ratio in one cycle. The proposed plunge grinding cycle consists of three stages ; that is, (1) the rough grinding with high velocity ratio, (2) the fine grinding with low velocity ratio and (3) the spark-out grinding with low velocity ratio. At the first stage (the rough grinding), the reduction in grinding time is planed by high stock removal rate based on high velocity ratio. On the other hand, the main role at the second stage (the fine grinding) and the third stage (the spark-out grinding) is improving the surface quality of the workpiece, especially the decrease of the surface roughness and the damaged surface layer by relatively low velocity ratio. The validity of this method has been examined by computer simulations and some experiments. As a result of this, it has been cleared that the cylindrical plunge grinding with a high efficiency can be realized without the deterioration of the workpiece surface quality by using the proposed grinding method.

A Noninvasive Technique for the Evaluation of Diversion Cross Flow at the Inlet of a Simulated Fuel Rod Bundle

Diversion cross flow was characterized from a two-subchannel simulation of a nuclear fuel assembly using a gamma camera. The gamma camera alllowed external monitoring over the length of the test assembly, thereby eliminating experimental problems associated with flow partitioning and an isokinetic withdrawal system, allowing the possibility of noninvasive measurement. The experiment was performed by providing fixed but different flow rates to each subchannel. The higher mass flow rate stream was traced with a gamma-emitting radionuclide, /sup 99m/Tc pertechnetate. Activity in each subchannel was measured by the camera. Diversion length was found to be relatively small and strongly dependent on gap spacing. Effective lateral velocity through the gap was also evaluated. With some exceptions, the results were in good agreement with the predictions of the subchannel analysis computer code COBRA IIIC. At a high inlet axial mass velocity ratio of 4, however, the agreement with the prediction was poor.

19 高速度比で混合する凝縮気液二相流の可視化について

For investigation of two phase flow characteristics, it is important to measure their void fraction, and bubble population and sizes. Although X-Ray, Gamma-Ray and electrical condutivity probe have been used to estimate these values, the former two methods may be so complicate and more expensive, the latter distubs flow condition.In this paper, a simple measuring technique by using laser beam is treated with direct contact condensation processes of mixing streams at high velocity ratio, which is observed within such a condesing ejector and ECCS of reactor etc. It may be possible to visualize two dimensional pattern of bubble distribution along the flow direction by using this method, which is based on the detection of laser beam acrossa chanel. The relationship between the numbers of bubble and the intensity of laser beam and effectiveness of this technique are discussed.

Particle segregation in slurry flow through vertical tees

An experimental study has been conducted of particle segregation in slurry flow through vertical tees. Water-sand slurries with solids concentrations to 25% by volume were used with tees of various sizes and angles. The experiments showed that the branch concentration is less than the upstream value for all the branches studied at velocity ratios less than unity. The separation ratio was found to be a function of upstream conditions. velocity ratio. branch size and angle. For lateral branches. the inertia effect is dominant at low velocity ratios. whereas the gravity effect becomes important at high velocity ratios. A two-dimensional model explains the results qualitatively.

Pivot Contact Behavior in Low-Inertia Snap-Action Rocker Switches

A study has been made of snap-action rocker switches to valuate some of the principal parameters contributing to the mechanics of operation. These are identified as the actuator and pivot radii and the distance of the actuator center of rotation above the rocking pivot. Equations are developed for the actuator/contact-blade angular velocity ratio as a function of blade angle. Graphs show that a knife edge pivot will produce a high velocity ratio for a low-mass blade. Further equations are resented showing the distribution of forces in the mechanism after the main contacts have met. The equations indicate that a make up configuration may have advantages in increasing pivot force and reducing pivot bounce in practical cases. This is borne out in tests on switches which show negligible bounce and reduced erosion for the make up arrange- ment.

Measurements in a Jet-Pipe Flow Issuing Perpendicularly Into a Cross Stream

Measurements are presented of velocity fluctuation statistics in the jet-pipe of a jet in a cross-flow situation for various values of the jet-pipe to cross-flow velocity ratio. The nonuniformities of the velocity profiles inside the pipe extend as far as 3 pipe-diameters upstream of the exit plane for small velocity ratios and to 2.5 diameters for higher velocity ratios. Longitudinal flow acceleration and strong streamline curvature affect turbulence activities at the exit plane for small velocity ratios. The horseshoe vortex which is formed in front of the exit plane results in a streamline curvature with a stabilizing effect on turbulence in the nearby flow field while the streamlines are unstably curved everywhere else. At high velocity ratios the pipe flow is very weakly affected by the cross-flow.

Pressure distribution in bubbly flow through venturis

The pressure distribution in vertical air-water mixture flows through venturis was investigated using area contraction ratios of 3.16 and 7.11 with variations in angles of convergence and divergence. The flow conditions were predominantly of the bubbly type and covered a range of gas volume fractions at the throat between 0.2 and 0.6. The one-dimensional momentum equation assuming isothermal flow with interphase relative motion was solved for the necessary relationship between pressure and area. An analysis was also developed to predict the pressure rise across a shock wave. Static pressure measurements obtained in eight venturi assemblies were compared with theoretical prediction and the results showed that the momentum equation assuming constant velocity ratio with properties normalized about the sonic throat pressure could account with fair accuracy for pressure in the converging passage of the venturis whilst downstream of the venturi throat the presence of a two-phase shock gave a good overall description of the steep pressure rise in supersonic flows. Departures from theory are accounted for in venturis with sharp contractions where three-dimensional flow effects gave rise to an appreciable transverse pressure gradient, a high velocity ratio and in some cases a vena contracta effect.