Transverse Velocity Profiles Research Articles

A SEARCH FOR CONSISTENT JET AND DISK ROTATION SIGNATURES IN RY TAU

We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks, and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape which appears near jet shock positions, and a flat profile which appears between shocks. We do not detect a rotation signature above 3 sigma uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km/s, implying a launch radius of < 0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.

Hall Effects on Mhd Flow Past an Accelerated Plate with Heat Transfer

Hall current and rotation on an MHD flow past an accelerated horizontal plate relative to a rotating fluid, in the presence of heat transfer has been analyzed. The effects of the Hall parameter, Hartmann number, rotation parameter (non-dimensional angular velocity), Grashof’s number and Prandtl number on axial and transverse velocity profiles are presented graphically. It is found that with the increase in the Hartmann number, the axial and transverse velocity components increase in a direction opposite to that of obtained by increasing the Hall parameter and rotation parameter. Also, when Ω=M&lt;sup&gt;2&lt;/sup&gt;m /(1 + m&lt;sup&gt;2&lt;/sup&gt; ) , it is observed that the transverse velocity component vanishes and axial velocity attains a maximum value.

Magnetohydrodynamic Viscous Oscillatory Stratified Flow in a Vertical Narrow Channel with a Porous Wall

In this paper we consider Magnetohydrodynamic viscous oscillatory fully developed flow of stratified fluid in a long vertical narrow rectangular channel with one side being pervious and the other side being impervious. By applying Lubrication approximation and similarity transformation, closed form solutions are obtained. The graphical interpretations of the effects of various parameters related to the problem on transverse and axial velocity profiles are illustrated in detail. The outcome of the investigation reveals that the stratification effects reverse the flow near the center of the channel while magnetohydrodynamic effects make the flow linear closer to the plates. The results obtained give a significant measure to control the flow with the effects of various parameters involved.

Experimental study of the mean wake of a tidal stream rotor in a shallow turbulent flow

The mean wake of a three-bladed horizontal axis tidal stream turbine operating at maximum power coefficient has been investigated experimentally in a wide flume with width 11 times the depth, providing minimal restriction to transverse wake development and behaviour of large-scale horizontal turbulence structures. This is an important first stage for understanding wake interaction in turbine arrays and hence large-scale power generation. The rotor diameter has a typical value of 60% of the depth and the thrust coefficient is representative of a full-scale turbine. The shear layers originating from the rotor tip circumference show classic linear expansion downstream, with the rate of a plane shear layer vertically and 1.5 times that horizontally. These shear layers merge by around 2.5 diameters downstream forming a self-similar two-dimensional wake beyond eight diameters downstream with a virtual origin at two diameters downstream of the rotor plane. The spreading rate is somewhat less than that for solid bodies. The detailed velocity measurements made in the near wake show rotation and vorticity similar to that measured previously for wind and marine turbines although with asymmetry associated with bed and surface proximity. The longitudinal circulation in a transverse plane is conserved at about 1% of the swept circulation from the blade tip within two diameters downstream, the extent of detailed measurement. Turbines are usually designed using blade element momentum theory in which velocities at the rotor plane are characterised by axial and tangential induction factors and it is now possible to see how this idealisation relates to actual velocities. The axial induction factor corresponds to velocity deficits at 0.4–0.8 radii from the rotor axis across the near wake while the tangential induction factor at the rotor plane corresponds to velocities at 0.4–0.6 radii between 1–2 diameters downstream, indicating some general correspondence. For the two-dimensional self-similar far wake the two parameters defining the centreline velocity deficit and the transverse velocity profiles are likely to be insensitive to Reynolds number in turbulent conditions.

Experimental Investigations on Condensation in the Framework of ENhanced COndensers in Microgravity (ENCOM-2) Project

We report preliminary results on experimental investigations on condensation in the framework of the European Space Agency funded programme Enhanced Condensers in Microgravity (ENCOM-2) which aims at better understanding underlying phenomena during condensation. The first experiment is a study on condensation of HFE on external curvilinear surface of 15 mm height during reduced gravity experiments. It is found that the local minimum of the film thickness exists at the conjugation area of condensed film and the meniscus at the bottom of the fin; this leads to the local maximum of the heat transfer coefficient, which we also found moves towards the fin tip. The second experiment is a study of falling films hydrodynamics inside a vertical long pipe. In particular, characteristics of wavy falling films produced employing intermittent liquid feed are examined in order to assess wave effects on film condensation. Preliminary results suggest that intermittent feed simply divides the film in two autonomous regions with the wave feature of each one depending only on its flow rate. The processing of registered film thickness data can lead to the estimation of the transverse velocity profile in the film, which is mainly responsible for heat transfer during condensation. The third experiment looks at in-tube convective condensation at low mass fluxes (typical of Loop Heat Pipes and Capillary Pumped Loops) of n-pentane inside a 0.56 mm diameter channel. The results show that the mean heat transfer in the annular zone when it is elongated may be less than the mean heat transfer when it is shorter, due to the interface deformation involved by surface tension effect. When the length of this annular zone reaches a critical value, the interface becomes unstable, and a liquid bridge forms, involving the release of a bubble. The heat transfer due to the phase-change in this isolated bubble zone appears to be very small compared to the sensible heat transfer: the bubbles evolve and collapse in a highly subcooled liquid. The last experiment concerns in-tube condensation of R134a inside a square channel of 1.23 mm hydraulic diameter at mass fluxes of 135 kg m−2 s−1 and 390 kg m−2 s−1 for three different configurations: horizontal, vertical downflow and vertical upflow. For the calculated heat transfer coefficient it is found that gravity has no effect on condensation in downflow configurations at 390 kg m−2 s−1 and in upflow conditions at both values of mass velocity. The effect of gravity on the condensation heat transfer coefficient becomes noteworthy in downflow at mass velocity G = 135 kg m−2 s−1 and vapour quality lower than 0.6.

Numerical analysis of oscillating flow around a cylinder

This paper presents the numerical model of the measuring stand - the wind tunnel, in which there is fixed a cylinder with a turbulent inlet oscillating stream. The aim of this work is the juxtaposition and comparison of characteristic values concerning the oscillating turbulent flow around the cylinder, obtained from the experiment conducted in the wind tunnel at the Institute of Thermal Machinery with the data obtained as a result of numerical modelling of unsteady phenomena. The model discussed in this paper was created using a commercial program ANSYS FLUENT that is used for mathematical modelling of flow and heat transfer processes. The expected outcome of this study is possibility of the numerical modelling of the stand concerning the analogous unsteady flows without significant invest- ment of time. Comparison of longitudinal and transverse velocity profiles in aerodynamic wake and the pressure coefficient distributions on the cylinder surface show similarities between experimental and numerical studies.

On the nonlinear development of shear layers in partially vegetated channels

A predictive theory is developed to investigate the nonlinear instability regime of perturbed shear layers in open-channel flows with lateral vegetation. The turbulence is characterized by two distinct scales: a sub-depth turbulence which is associated with the bed shear stress and a large-scale turbulence associated with the large horizontal eddies which develop in the shear layer. The sub-depth turbulence is modeled by assuming a logarithmic vertical distribution of the velocity. Meanwhile, an analogous model for the large-scale turbulence requires the estimation of the transverse velocity profile in the nonlinear state because the growth of the large-scale disturbances expands the shear layer and modifies the velocity distribution across the channel. The nonlinear growth of the disturbances is limited, however, because solid boundaries in the channel play stabilizing mechanisms which lock the amplitude of the large-scale disturbances into a finite-equilibrium state, for which a corresponding transverse velocity profile is determined. A weakly nonlinear stability analysis is performed and the results are validated using experimental data from previous works.

A Preliminary Study of Effects of Wave and Crossflow on Side Discharge of Wastewater

Transverse and longitudinal velocity profiles on the xoy plane at z=0 and 5cm of side discharge jet under the action of crossflow and wave, velocity vectors on the xoy plane at z=0 and 5cm of side discharge jet under the action of wave and crossflow were measured by Micro ADV in this paper, respectively. Effects of wave and crossflow on velocity profiles and velocity vectors of side discharge jet were analyzed. The preliminary experimental results showed that transverse velocity profiles of side discharge jet centerline was less affected by crossflow and wave, however, effects on transverse and longitudinal velocities over the jet centerline were significant. Also, velocity vectors over of side discharge jet centerline were remarkably affected by wave and crossflow though velocity vectors on the jet centerline was less affected.

산지하천의 전자파 표면유속 측정에 기반한 유량 및 유속 관측 오차 분석

Abstract Fixed Electromagnetic Wave Surface Velocimetry (Fixed EWSV) has been started to be used to measure flood discharge in the mountain stream, since it has various advantages such that it works well to continuously measure stream discharge even in the night time as well as very strong weather. On the contrary, the Fixed EWSV only measures single point surface velocity, thus it does not consider varying feature of the transverse velocity profile in the given stream cross-section. In addition, a conventional value of 0.85 was generally used as the ratio for converting the measured surface velocity into the depth-averaged velocity. These aspects could bring in error for accurately measuring the stream discharge. The capacity of the EWSV for capturing rapid flow velocity was also not properly validated. This study aims at conducting error analysis of using the EWSV by: 1) measuring transverse velocity at multiple points along the cross-section to assess an error driven by the single point measurement; 2) figuring out ratio between surface velocity and the depth-averaged velocity based on the concurrent ADCP measurements; 3) validating the capacity of the EWSV for capturing rapid flow velocity. As results, the velocity measured near the center by the fixed EWSV overestimated about 15% of the cross-sectional mean velocity. The converting ratio from the surface velocity to the depth-averaged velocity was 0.8 rather than 0.85 of a conventional ratio. Finally, the EWSV revealed unstable velocity output when the flow velocity was higher than 2 m/s.

On the Flow of a Visco-Elastic Fluid between Two Rotating Non-Concentric Cylinders for Small Eccentricity

The motion of a visco elastic fluid contained between two rotating circular cylinders whose axes are set slightly apart is considered. An approximate solution of the Navier Stokes equations is obtained by a perturbation method for the case of small eccentricity. The expansions contain a perturbation parameter Epsional related to the eccentricity e which is assumed to be small. The method entails the employment of asymptotic expansions of Bessel functions and the results thus obtained are valid for finite gap between the two cylinders. The leading terms of the expansions are the exact solution to the Couette flow of Newtonian Fluid between concentric rotating cylinders. The Transverse velocity profiles are presented for small eccentricity and gap, when both the cylinders are rotating with the same angular velocities in the same direction and compared with the corresponding transverse velocity profile in Newtonian flow.

Transient free convection flow past an accelerated vertical cylinder in a rotating fluid

The flow of a viscous incompressible fluid past an accelerated vertical circular cylinder in a rotating fluid is analyzed in this study. The cylinder starts impulsively from rest with uniform acceleration in its own plane relative to the rotating fluid. The closed form solutions of the governing boundary layer equations in non-dimensional form are obtained in terms of Bessel functions and modified Bessel functions by Laplace transform technique. Numerical values of the axial velocity, transverse velocity and temperature profiles are obtained for various physical parameters and presented in graphs. Skin friction and Nusselt number are also discussed graphically.

Quantification of Ultrasound Correlation‐Based Flow Velocity Mapping and Edge Velocity Gradient Measurement

This study investigated the use of ultrasound speckle decorrelation- and correlation-based lateral speckle-tracking methods for transverse and longitudinal blood velocity profile measurement, respectively. By studying the blood velocity gradient at the vessel wall, vascular wall shear stress, which is important in vascular physiology as well as the pathophysiologic mechanisms of vascular diseases, can be obtained. Decorrelation-based blood velocity profile measurement transverse to the flow direction is a novel approach, which provides advantages for vascular wall shear stress measurement over longitudinal blood velocity measurement methods. Blood flow velocity profiles are obtained from measurements of frame-to-frame decorrelation. In this research, both decorrelation and lateral speckle-tracking flow estimation methods were compared with Poiseuille theory over physiologic flows ranging from 50 to 1000 mm/s. The decorrelation flow velocity measurement method demonstrated more accurate prediction of the flow velocity gradient at the wall edge than the correlation-based lateral speckle-tracking method. The novelty of this study is that speckle decorrelation-based flow velocity measurements determine the blood velocity across a vessel. In addition, speckle decorrelation-based flow velocity measurements have higher axial spatial resolution than Doppler ultrasound measurements to enable more accurate measurement of blood velocity near a vessel wall and determine the physiologically important wall shear.

A semi-analytical model of the 3D boundary layer over the streamlined nose of a train

The boundary layer concept is applied to the flow around the nose of a streamlined train. In general, that flow is not axisymmetric due to the shape of the nose and the crosswind component of the relative incoming velocity. This departure from axisymmetry produces a transverse pressure gradient that is responsible for skewing an otherwise plane boundary layer. An empirical correlation, dependent on the longitudinal velocity and one unknown parameter, is used to represent the transverse velocity profile. The value of that unknown parameter is obtained from the momentum equations integrated streamwise inside the boundary layer. A visual comparison was carried out between the numerical simulations and the skin shear pattern of a scale model in a wind tunnel. The qualitative results compare well, the numerical model being able to locate the position of the main longitudinal vortices on the lee side of the train.

The 2008/09 surge of central Yulinchuan glacier, northern Tibetan Plateau, as monitored by remote sensing

AbstractThe 2008/09 surge of central Yulinchuan glacier (CYG) on the northwestern slope of Muztag mountain, Tibetan Plateau, is studied based on satellite remote sensing. The widely used cross-correlation feature-tracking method was used to collect satellite image control points and validate their geometric accuracies, as well as to derive glacier surface velocity. Changes in glacier length and area were also retrieved. Results show that the surge of CYG initiated in May 2008 and terminated in July 2009. Two diffluent glacier termini advanced 590 ± 26 m (5.1 ± 0.2% of the 2004 length) and 182 ± 26m (1.8 ± 0.3%), respectively, and glacier area increased by ∼1.41 ± 0.11 km2 (4.6 ± 0.4% of the 2004 area) during this period. The most significant surge period was October 2008 to March 2009, when most of the terminus advances and area increases occurred. The glacier surface drastically crevassed during this time, as much as 1657 ± 297 m of horizontal surface displacements were produced by surge ice, and maximum surface speed reached 13 ± 1.5 m d-1. Results of transverse and longitudinal velocity profiles revealed two surge waves during this surge of CYG.

河岸植生域境界における水平せん断層の空間発達過程に関する数値計算

Quasi-3D model and SDS (sub-depth scale) turbulence model are combined to simulate the horizontal shear layer development along the interface of bank vegetation. Turbulence productions caused by bottom friction and vegetation drag are formulated based on previous experiments on turbulence intensity in flows in an open channel and through model vegetation (cylinder arrays). Computations are made for two flow conditions of flume experiment with vegetation model published in literatures. Good agreements are obtained for transverse and streamwise velocity profiles in the developing shear layer containing horizontal coherent vortices. The characteristics of turbulence components are also predicted well. Furthermore, simulation results suggest that strong SDS turbulence is generated near vegetation boundary and transported to vegetation zone and main channel by horizontal coherent vortices.

Secondary Current and Classification of River Channels

In this research, the secondary current theory is used in investigating the role of phase shift angle between the secondary current and the channel axis displacement in stability analysis of a river channel. To achieve this, a small-perturbation stability analysis is developed for investigation of the role of the secondary current accompanying channel curvature in the initiation and early development of meanders in open channels. The secondary currents are generating in planes perpendicular to the primary direction of motion. The secondary currents form a helical motion in which the water in the upper part of the river is driven outward, whereas the water near the bottom is driven inward in a bend. Force-momentum equations for longitudinal and transverse direction in open channel bends were utilized. Assuming that the transverse force contributed by the bed is negligible, the pressure force associated with the transverse surface inclination is balanced by the centripetal force. Existing equations of the transverse velocity profile were analyzed. Since the magnitude of the vertical velocity is negligible compared to the transverse velocity in secondary currents, this study concentrates on the transverse velocity which is the radial component of the secondary current. This formulation leads to a linear differential equation which is solved for its orthogonal components which give the rates of meander growth and downstream migration. It is shown that instability increases with decrease in phase shift angle. Transition from straight to meandering and then from meandering to braiding occurs when phase shift angle is reduced.

Using P-I Diagram Method to Assess the Failure Modes of Rigid-Plastic Beams Subjected to Triangular Impulsive Loads

This paper puts forward a simplified method for assessing the failure modes of rigid-plastic beams by solving the governing partial differential equation with defined initial conditions based on five previously developed transverse velocity profiles. It is found that there are twelve different response patterns possible for a rigid-plastic beam subjected to a triangular pulse shape impulsive load. As developed in this paper, the P-I diagram is based on the derived deformation pattern such that selected failure criteria can be used to identify and differentiate various failure patterns. The shear-to-bending ratio, the boundary conditions, and the load pulse shape, all influence the response of the rigid-plastic beams, and are discussed in detail. Although the peak pressure and the shear-to-bending ratio together determine the response pattern, it is also found that the combination of peak pressure, impulse, and shear-to-bending ratio define the failure type and sequence. Fully clamped beams are relatively resistant to bending failure; however, they are more vulnerable to shear failure at the supports than simply supported beams. Compared with the triangular-shape impulsive load, the rectangular-shape impulsive load is more vulnerable in the pressure and impulse combination-controlled zone. The explicit solutions are compared with results obtained by using the Single-Degree-of-Freedom (SDOF) approach and are found to be exactly the same whether the beams have a small shear-to-bending ratio (υ ≤ 1) or a large such ratio (υ ≥ 1.5). But for beams with medium shear-to-bending ratio (1 ≤ υ ≤ 1.5), only the presented approach derived solutions.

Flow structures of Jupiter's Great Red Spot extracted by using optical flow method

The flow structures of Jupiter's Great Red Spot (GRS) are studied based on a high-resolution velocity field extracted from the Galileo 1996 cloud images of the GRS by using the physics-based optical flow method. The mean transverse velocity profile across the anti-cyclonic near-elliptical collar of the GRS is obtained. The flow structures in the relatively quiescent inner region enclosed by the high-speed collar are revealed at a coarse-grained level. The cyclonic source node in the inner region is identified that is directly associated with the observed cyclonic rotation near the center of the GRS, and its significance in the maintenance of the GRS is explored by using a topological constraint.

High-speed granular chute flows

AbstractThis paper reports experimental findings on the flow of sand down a steep chute. Nearly all granular flow models have a maximum value for the friction and therefore predict that flows on steep slopes will accelerate at a constant rate until the interaction with the ambient fluid becomes important. This prediction has not been tested by previous work, which has focused on relatively low slope angles where steady, fully developed flows occur after short distances. We test this by investigating flows over a much greater range of slope angles (30–50${}^{\ensuremath{\circ} } $) and flow depths (4–130 particle diameters). We examine flows with two basal conditions, one flat and frictional, the other bumpy. The latter imposes a no-slip condition for slow, deep flows, but permits some degree of slip for high flow velocities. The data suggests that friction can be much larger than theories such as the $\ensuremath{\mu} (I)$ rheology proposed by Jop, Forterre &amp; Pouliquen (Nature, vol. 441, 2006) suggest and that there may be constant velocity states above the angle of vanishing ${h}_{\mathit{stop}} $. Although these flows do not vary in time, all but the flows on the bumpy base at low inclinations accelerate down the slope. A recirculation mechanism sustains flows with a maximum mass flux of $20~\mathrm{kg} ~{\mathrm{s} }^{\ensuremath{-} 1} $, allowing observations to be made at multiple points for each flow for an indefinite period. Flows with Froude number in the range 0.1–25 and bulk inertial number 0.1–2.7 were observed in the dense regime, with surface velocities in the range 0.2–5.6 $\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $. Previous studies have focused on $I\lessapprox 0. 5$. We show that a numerical implementation of the $\ensuremath{\mu} (I)$ rheology does not fully capture the accelerating dynamics or the transverse velocity profile on the bumpy base. We also observe the transverse separation of the flow into a dense core flanked by dilute regions and the formation of longitudinal vortices.

Steady Laminar Axisymmetrical Nozzle Flow at Moderate Reynolds Numbers: Modeling and Experiment

Flow through an axisymmetrical parameterized contraction nozzle of limited size with area contraction ratio 21.8 and total length 6 cm is studied for moderate Reynolds numbers 300 &lt; Re &lt; 20,200. The transverse flow profiles at the nozzle exit are characterized by hot film anemometry for two different spatial step sizes. The flow at the exit is laminar and uniform in its core. Boundary layer characteristics at the nozzle exit are estimated from the transverse velocity profiles. Flow throughout the nozzle is modeled by implementing Thwaites laminar axisymmetrical boundary layer solutions in an iterative algorithm for which both universal functions, describing the shape factor and skin friction parameters respectively, are altered by adding a constant. The value of the constants is determined by fitting the modified universal functions to tabulated values reported in Blevins (Blevins, R., 1992, Applied Fluid Dynamics Handbook. Krieger, Malabar, FL.). The model is validated on the measured data. Adding nonzero constants to the universal functions improves the prediction of boundary layer characteristics so that the range of Reynolds numbers for which the discrepancy with experimental findings is less than 4% is extended from Re &gt; 3000 to Re &gt; 1000. Therefore, the studied contraction nozzle is of use for applications requiring a small nozzle with known low turbulence flow at the exit such as moderate Reynolds number free jet studies or bio fluid mechanics (respiration, speech production,…) and the flow at the exit of the nozzle can be accurately described by a simple boundary layer algorithm for Re &gt; 1000.