High Tangential Velocity Research Articles

Investigation of the Flow Characteristics in a Sink-Swirl Flow within Two Disks

Flow characteristics in a sink-swirl flow within two disks are examined experimentally and numerically. The experiments and the predictions have been carried out for three bulk Reynolds numbers and four contraction ratios. Results show that as the contraction ratio and the Reynolds number increase, the pressure coefficient increases. Stronger vortices will be produced resulting in a higher tangential velocity and hence a higher pressure drop. The radial pressure decreases slowly from the inlet periphery up to halfway along the disk and then decreases sharply as the flow approach the exit hole. Air enters through the peripheral gap between the two disks and converges to the center where it discharges axially through the exit hole. This indicates that the flow moved towards a more favorable pressure gradient, hence the vortex flow accelerated according to the angular momentum conservation. It can be seen that the Reynolds stress model gives good agreement with the present experimental data and the percentage difference error between the predicted and experiments is less than 10%.

Role of air core in particle separation in cyclones

Detailed studies were carried out to study the effect of air core formation in cyclones on separation of particles using statistical techniques. The design and operating variables of a 100 mm perspex hydrocyclone, both flat bottom and conical, were varied and their effect on different types of air core was studied. The results were analysed using analysis of variance. The % underflow split was the most important variable affecting the air core formation. Studies were also carried out with density tracers under different air core conditions. The studies showed that the lighter particles separated better in the absence of the air core. Particle separation tests were then carried out after suppressing the air core with a metal rod. The separation of lighter particles with specific gravity close to the separating fluid was improved when the air core was suppressed. Numerical simulation studies showed that a higher tangential velocity and a lower radial velocity is the reason for better separation efficiency in the absence of the air core.

THE COLDEST BROWN DWARF (OR FREE-FLOATING PLANET)?: THE Y DWARF WISE 1828+2650

We have monitored the position of the cool Y dwarf WISEPA J182831.08+265037.8 using a combination of ground- and space-based telescopes and have determined its distance to be 11.2$_{-1.0}^{+1.3}$ pc. Its absolute H magnitude, M$_H=22.21^{+0.25}_{-0.22}$ mag, suggests a mass in the range 0.5-20 M$_{Jup}$ for ages of 0.1-10 Gyr with an effective temperature in the range 250-400 K. The broad range in mass is due primarily to the unknown age of the object. Since the high tangential velocity of the object, 51$\pm5$ km s$^{-1}$, is characteristic of an old disk population, a plausible age range of 2-4 Gyr leads to a mass range of 3-6 M$_{Jup}$ based on fits to the (highly uncertain) COND evolutionary models. The range in temperature is due to the fact that no single model adequately represents the 1-5 $\mu$m spectral energy distribution (SED) of the source, failing by factors of up to 5 at either the short or long wavelength portions of the spectral energy distribution. The appearance of this very cold object may be affected by non-equilibrium chemistry or low temperature condensates forming clouds, two atmospheric processes that are known to be important in brown dwarf atmospheres but have proven difficult to model. Finally, we argue that there would have to be a very steep upturn in the number density of late type Y-dwarfs to account for the putative population of objects suggested by by recent microlensing observations. Whether WISE 1828+2650 sits at the low mass end of the brown dwarf population or is the first example of a large number of "free-floating" planets is not yet known.

Three-dimensional flow visualization in the wake of a miniature axial-flow hydrokinetic turbine

Three-dimensional 3-component velocity measurements were made in the near wake region of a miniature 3-blade axial-flow turbine within a turbulent boundary layer. The model turbine was placed in an open channel flow and operated under subcritical conditions (Fr = 0.13). The spatial distribution of the basic flow statistics was obtained at various locations to render insights into the spatial features of the wake. Instantaneous and phase-averaged vortical structures were analyzed to get insights about their dynamics. The results showed a wake expansion proportional to the one-third power of the streamwise distance, within the first rotor diameter. Wake rotation was clearly identified up to a distance of roughly three rotor diameters. In particular, relatively high tangential velocity was observed near the wake core, but it was found to be nearly negligible at the turbine tip radius. In contrast, the radial velocity showed the opposite distribution, with higher radial velocity near the turbine tip and, due to symmetry, negligible at the rotor axis. Larger turbulence intensity was found above the hub height and near the turbine tip. Strong coherent tip vortices, visualized in terms of the instantaneous vorticity and the λ2 criterion, were observed within the first rotor diameter downstream of the turbine. These structures, influenced by the velocity gradient in the boundary layer, appeared to loose their stability at distances greater than two rotor diameters. Hub vortices were also identified. Measurements did not exhibit significant tip–hub vortex interaction within the first rotor diameter.

The effect of diameter and height of the inserted rod in a dense medium cyclone to suppress air core

Studies were carried out by suppressing the air core in a 100mm DMC using a metal rod inserted through the spigot. The effect of the diameter of the inserted rod and its height of insertion on the Ep of the cyclone was studied. A spigot blocking ratio of 0.4 with 60% of free VF clearance gave the best separation efficiency. Multiphase CFD studies showed that the improved performance of the cyclone was because of (i) higher tangential velocity and hence higher centrifugal force acting on the particles (ii) lower radial and axial velocities at the VF reducing misplacement.

Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools

Aims: With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities. Methods: From an all-sky cross-match between the optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions >50mas/yr and very red V-Ks colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures Teff~2900-3400K. From our time-series analysis, we discovered a long secondary period in Ruber 4 and an extremely long primary period in Ruber 6. With the CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of which seems to be one of the brightest metal-poor M giants ever identified.

Development of a Tabletop Guidance System for Educational Robots

The guidance of a vehicle in an outdoor setting is typically implemented using a Real Time Kinematic Global Positioning System (RTK-GPS) potentially enhanced by auxiliary sensors such as electronic compasses, rotation encoders, gyroscopes, and vision systems. Since GPS does not function in an indoor setting where educational competitions are often held, an alternative guidance system was developed. This article describes a guidance method that contains a laser-based localization system, which uses a robot-borne single laser transmitter spinning in a horizontal plane at an angular velocity up to 81 radians per second. Sensor arrays positioned in the corners of a flat rectangular table with dimensions of 1.22 m × 1.83 m detected the laser beam passages. The relative time differences among the detections of the laser passages gave an indication of the angles of the sensors with respect to the laser beam transmitter on the robot. These angles were translated into Cartesian coordinates. The guidance of the robot was implemented using a uni-directional wireless serial connection and position feedback from the localization system. Three experiments were conducted to test the system: 1) the accuracy of the static localization system was determined while the robot stood still. In this test the average error among valid measurements was smaller than 0.3 %. However, a maximum of 3.7 % of the measurements were invalid due to several causes. 2) The accuracy of the guidance system was assessed while the robot followed a straight line. The average deviation from this straight line was 3.6 mm while the robot followed a path with a length of approximately 0.9 m. 3) The overall performance of the guidance system was studied while the robot followed a complex path consisting of 33 sub-paths. The conclusion was that the system worked reasonably accurate, unless the robot came in close proximity (<0.2 m) to one of the sensor arrays where errors occurred due to a high angle of incidence of the laser beam onto the sensor arrays and due to a high tangential velocity of the laser beam at the opposite sensor array. Hence, this article presents a low-cost guidance system which is simple, reliable, and reasonably accurate.

Lagrangian characterization of multi-phase turbulent flow in a solar reactor for particle deposition prediction

Solar cracking of methane is a promising technology for emission free hydrogen production. One of the major problems affecting methane cracking solar reactors' performance is the carbon particle deposition on the window, walls, and at the exit. In present study, a Lagrangian particle dispersion model has been implemented for predicting the particle deposition on the window of a seeded solar thermal reactor. A three-dimensional Computational Fluid Dynamics (CFD) analysis using Discrete Phase Model (DPM) has been done for qualitative validation of the experimental observations. In order to evaluate the turbulent quantities in the solar reactor; RNG k– ɛ model has been applied. Species transport has been solved by taking the gas for window screening as different from that used in the main flow. In addition, this paper presents a thorough parametric study predicting the particle deposition on reactor window for various flow configurations and flow conditions, which can be summarized as; (1) when the inlet flow angle is smaller, higher tangential velocities or swirl strength is obtained, (2) higher tangential velocities help in maintaining a stronger swirl, which keeps the screening flow close to the reactor window, (3) by increasing the main flow and the screening flow rates, the particle deposition on window is reduced, (4) when a lower density fluid is used as window screening gas, the particle deposition is reduced because the Taylor instabilities are avoided. The CFD work and the findings presented in this paper would be used as a guide in designing a solar reactor or improving the configuration of existing reactor.

THE BROWN DWARF KINEMATICS PROJECT I. PROPER MOTIONS AND TANGENTIAL VELOCITIES FOR A LARGE SAMPLE OF LATE-TYPE M, L, AND T DWARFS

We report proper motion measurements for 427 late-type M, L and T dwarfs, 332 of which have been measured for the first time. Combining these new proper motions with previously published measurements yields a sample of 841 M7-T8 dwarfs. We combined parallax measurements or calculated spectrophotometric distances and computed tangential velocities for the entire sample. We find that kinematics for the full and volume-limited 20 pc samples are consistent with those expected for the Galactic thin disk, with no significant differences between late-type M, L, and T dwarfs. Applying an age-velocity relation we conclude that the average kinematic age of the 20 pc sample of ultracool dwarfs is older than recent kinematic estimates and more consistent with age results calculated with population synthesis models. There is a statistically distinct population of high tangential velocity sources whose kinematics suggest an even older population of ultracool dwarfs belonging to either the Galactic thick disk or halo. We isolate subsets of the entire sample, including low surface-gravity dwarfs, unusually blue L dwarfs, and photometric outliers in J-Ks color and investigate their kinematics. We find that the spectroscopically distinct class of unusually blue L dwarfs has kinematics clearly consistent with old age, implying that high surface-gravity and/or low metallicity may be relevant to their spectral properties. The low surface-gravity dwarfs are kinematically younger than the overall population, and the kinematics of the red and blue ultracool dwarfs suggest ages that are younger and older than the full sample, respectively. We also present a reduced proper motion diagram at 2MASS Ks for the entire population and find that a limit of H_Ks > 18 excludes M dwarfs from the L and T dwarf population regardless of near-infrared color.

Discovery of Two Nearby Peculiar L Dwarfs from the 2MASS Proper‐Motion Survey: Young or Metal‐Rich?

We present the discovery of two nearby L dwarfs from our 2MASS proper motion search, which uses multi-epoch 2MASS observations covering ~4700 square degrees of sky. 2MASS J18212815+1414010 and 2MASS J21481628+4003593 were overlooked by earlier surveys due to their faint optical magnitudes and their proximity to the Galactic Plane (10 degrees < |b| < 15 degrees). Assuming that both dwarfs are single, we derive spectrophotometric distances of ~10 pc, thus increasing the number of known L dwarfs within 10 pc to 10. In the near-infrared, 2MASS J21481628+4003593 shows a triangular-shaped H-band spectrum, strong CO absorption, and a markedly red J-Ks color (2.38+/-0.06) for its L6 optical spectral type. 2MASS J18212815+1414010 also shows a triangular-shaped H-band spectrum and a slightly red J-Ks color (1.78+/-0.05) for its L4.5 optical spectral type. Both objects show strong silicate absorption at 9-11 microns. Cumulatively, these features imply an unusually dusty photosphere for both of these objects. We examine several scenarios to explain the underlying cause for their enhanced dust content and find that a metal-rich atmosphere or a low-surface gravity are consistent with these results. 2MASS J18212815+1414010 may be young (and therefore have a low-surface gravity) based on its low tangential velocity of 10 km/s. On the other hand, 2MASS J21481628+4003593 has a high tangential velocity of 62 km/s and is therefore likely old. Hence, high metallicity and low-surface gravity may lead to similar effects.

Fluid mechanics of liquid–solid fluidization in the centrifugal field

AbstractThe flow pattern in the bed and in the freeboard of a liquid–solid fluidized bed operated in the centrifugal field was investigated. Centrifugal accelerations between 20 and 500 times the gravity were acting on the particles. Both the radius‐dependent centrifugal acceleration and the Coriolis force were found to strongly influence the fluid dynamics. A CFD simulation of the liquid flow in absence of particles showed high tangential velocities which were two orders of magnitude higher than the radially oriented fluidizing velocity. Measurements with a 1 m diameter rotor confirmed the calculations and revealed that also the liquid–solid fluidized bed is moving in the tangential direction although with lower speed than the pure liquid. The bed expansion under these conditions can be described by a Richardson–Zaki type correlation.

Craniocervical feeding dynamics of Tyrannosaurus rex

Tyrannosaurus rex and other tyrannosaurid theropods exerted high bite forces, and large muscle attachments suggest that the tyrannosaurid neck was a concomitantly powerful component of the feeding apparatus. We examine accelerative and work-generating capacity (WGC) of neck muscles in adult Tyrannosaurus rex, using a 3-D vector-based method that incorporates aspects of muscle force generation, reconstruction of muscle morphology and moment arms, and rotational inertias of the head and neck. Under conservative assumptions, radial accelerations of the head by large superficial muscles (M. transversospinalis capitis, M. complexus, and M. longissimus capitis superficialis) enabled rapid gaze shifts and imparted high tangential velocities to food sufficient for inertial feeding. High WGC by these and deeper muscles under eccentric contraction indicate high efficacy for tearing flesh, especially with the head and neck in an extended posture. Sensitivity analyses suggest that assigned density of the antorbital region has substantial effects on calculated rotational inertia, and hence on the accuracy of results. However, even with high latitude for estimation errors, the results indicate that adult T. rex could strike rapidly at prey and engage in complexly modulated inertial feeding, as seen in extant archosaurs.

Gridless simulations of splashing processes and near-shore bore propagation

The generation and evolution of two-dimensional bores in water of uniform depth and on sloping beaches are simulated through numerical solution of the Euler equations using the smoothed particle hydrodynamics (SPH) method, wherein particles are followed in Lagrangian fashion, avoiding the need for computational grids. In water of uniform depth, a piston wavemaker produces cyclically breaking bores in the Froude number range 1.37–1.82, which were shown to move at time-averaged speeds in very good agreement with the requirements of global mass and momentum conservation. A single Strouhal number for the breaking period was discovered. Complex repetitive splashing patterns are observed and described, involving forward jet formation growth, impact and ricochet, and similarly, backward jet formation and impact. Observed consequences were the creation of vortical regions of both signs, dipole creation through pairing, large-scale transport of surface water downward and high tangential scouring velocities on the bed, which are quantified. These bores are further allowed to rise on linear slopes to the shoreline, where they are seen to collapse into a tongue-like flow resembling dam-break evolution.This essentially inviscid calculation is able to reproduce the development of a highly vortical flow in excellent agreement with experimental observations and theoretical concepts. The turbulent flow behaviour is partially described by the numerical solution.

The White Dwarf Luminosity Function from Sloan Digital Sky Survey Imaging Data

A sample of white dwarfs is selected from SDSS DR3 imaging data using their reduced proper motions, based on improved proper motions from SDSS plus USNO-B combined data. Numerous SDSS and followup spectra (Kilic et al. 2005) are used to quantify completeness and contamination of the sample; kinematic models are used to understand and correct for velocity-dependent selection biases. A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth, and rises nearly monotonically to Mbol = 15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars are identified that may have high tangential velocities, and a preliminary luminosity function is constructed for them.

Improvement and modelling of a batch polyelectrolyte enhanced ultrafiltration process for the recovery of copper

A batch Polyelectrolyte Enhanced Ultrafiltration (PEUF) process with Poly(acrylic acid) sodium salt (PAASS) for the recovery of Cu(II) from industrial wastewaters has been studied. In contrast to previous researches, insertion of an internal steel rod inside tubular ceramic membrane, which implies a decrease of hydraulic diameter, enables to minimize pumping energy (lower feed flow rates are required) and provides high tangential velocities in order to avoid concentration polarization and to lessen fouling. Simultaneously, working at higher temperature improves turbulence conditions over the membrane and makes possible to increase operating polyelectrolyte concentration (maintaining high permeate fluxes) and, subsequently, metal ion concentration in waste stream to treat. Temporal decrease of permeate fluxes has been reproduced with an in-series resistance model. Evolution of metal rejection coefficients is estimated with a model taking into account chemical equilibriums in solution and mass conservation equations. Furthermore, replacement of a polyelectrolyte of analytical grade by an analogous polymer of industrial grade reduces significantly raw material costs.

Mixed convection turbulent film condensation on a sphere

The present paper reports a research on condensation heat transfer of an isothermal sphere with an external flow of vapor. The high tangential velocity of the vapor flow is determined from potential flow theory. The transition criterion of the onset turbulence has been given in the local film Reynolds number ( Re Γ ). An eddy diffusivity model along with an expression by [H. Kato, N.N. Shiwaki, M. Hirota, On the turbulent heat transfer by free convection from a vertical plate, Int. J. Heat Mass Transfer, 11(1968) 1117–1125] is used to model turbulence. And the local liquid–vapor interfacial shear which occurs for high velocity vapor flow across a sphere surface is defined by the Colburn analogy. The paper then presents analytical analysis for the local dimensionless film thickness and heat transfer characteristics for the film condensation. And a comparison with those generated by previous theoretical of laminar condensation is discussed. The comparison shows the heat transfer coefficient of turbulent film condensation is higher than laminar film condensation under the high vapor velocity.

526 大気圧下で回転する超音速フライホイール

The Drag Coefficient of a rotating article in the fluid is reduced drastically by effect of the newly developed an aerodynamic system that has Floating Shrouds, up to Supersonic Velocity. Details of the system are disclosed as a theoretical study on the fluid dynamics and experimental observations are described in this paper. We produced some rotors for experiment as flywheels they rotate extremely great angular velocity and high tangential velocity under the atmospheric pressure, and vacuum containers to reduce the friction loss of rotors rotating on high speed are in no use. And we make analogical reasoning on electric circuits.

Turbulent Film Condensation on an Isothermal Sphere

An investigation is presented of turbulent film condensation on a sphere. It begins by considering the case of vapor flow past an isothermal sphere. The high tangential velocity of the vapor flow at the boundary layer is determined from potential flow theory. The Colburn analogy is used to define the local liquid‐vapor interfacial shear that occurs for high-velocity vapor flow across the spherical surface. The results generated for the local dimensionless film thickness and heat transfer characteristics are discussed. Finally, the results developed in the current study are compared with those generated by previous theoretical and experimental results for laminar flow. It is found that the correlation between the two sets of data is quite satisfactory for low-vapor velocity. However, at the higher vapor velocities, the rate of increase of the coefficient with velocity is greater than that associated with laminar theory. It other words, for high-vapor velocity, the onset of turbulence in the condensate causes discrepancies between the two sets of data. Note that the results of the present study may be used to estimate the heat transfer coefficient more accurately than the result of previous laminar studies.

Numerical study of flow field in cyclones of different height

This paper presents the results of numerical simulation of flow pattern in cyclones of different height, which have recently been tested for separation efficiency without any information about flow field. Results show that the difference between tangential velocity in the upper cylinder and in the lower cone of a certain cyclone is not significant, suggesting that reduced cross-section in the cone does not lead to tangential velocity acceleration. Tangential velocity in cyclones of different height is quite different. Tangential velocity decreases with increasing cyclone height, and this should be responsible for the lower separation efficiency observed in long cyclones. However, if there exists considerable shortcut flow at the entrance of the gas exit tube, the higher tangential velocity will not give rise to the higher separation efficiency, for example, in the case of the shortest cyclone covered in this study, whose gas exit tube protrudes into the conical part.

Turbulent film condensation on a horizontal elliptical tube

An investigation has been made of turbulent film condensation on a horizontal elliptical tube. The present study is based on Colburn analogy [1] and potential flow theory to determine the high tangential velocity of vapor flow at the boundary layer and to define the local interfacial shear owing to high velocity vapor flow across the tube surface. The condensate film flow and local/or mean heat transfer characteristics from a horizontal elliptical tube with variable ellipticities, e, under the influence of Froude number, sub-cooling parameter and system pressure have been performed. The present result for dimensionless mean heat transfer coefficient reduces to the same result obtained by Sarma et al.’s [2] e=0 (circular tube). Compared with laminar model by Yang and Hsu [3], the present turbulent model shows in better agreement with Michael’s experimental data [4] (for e=0). The dependence of mean Nusselt coefficient on the effect of n (power of Reynolds) [1] is also discussed.