Profiles Of Velocity Components Research Articles

A constant-beam-width transducer for 3D acoustic Doppler profile measurements in open-channel flows

An ultrasonic constant-beam-width transducer system which is capable of generating an extended focal zone by electronically focusing the beam over the desired water-depth range is described. Beam directivity measurements show that the higher beam directivity and the reduction in side-lobe level lead to an increase of the signal-to-noise ratio by up to 15 dB compared with that of a plane disc transducer. It also allows one to attain a significant reduction of undesirable spectral broadening effects which in the case of plane disc transducers lower the final resolution and interfere with the correct interpretation of data. Using the focalized transducer, simultaneous 3D velocity component profile measurements over the whole water depth are carried out in uniform, open-channel flow and reveal the presence of coherent structures. In the transversal direction, a stationary secondary current composed of two stationary vortices is observed. Compared with a plane disc transducer system, the focalized system increases the resolution by up to 50%.

Thermohydrodynamic Analysis of Tilting-Pad Journal Bearings Operating in Turbulent Flow Regime

Abstract A thermohydrodynamic analysis of tilting-pad bearing in turbulent flow regime is presented. Two tilting-pad journal bearings are studied. A local analysis of thermal turbulent phenomena is shown. The theoretical prediction of the maximum temperature decreases when the flow regime becomes nonlaminar and the decrease corresponding to higher power losses is explained using the velocity component profiles and the local heat flux in the film.

Comparison of Different Bin-mapping Methods for a Bottom-mounted Acoustic Profiler

Abstract Acouste Doppler current profilers (ADCPS) can measure profiles of velocity components and some other properties of bodies of water. If the profiler is firmly mounted, the profiles can be recorded without immediate coordinate transform. This gives more flexibility to the instrument settings and increases the capabilities of the instrument. If the instrument tilts, some data cell positioning—bin mapping—is usually needed in the post-processing of the data. The errors during that procedure depend on the degree of the tilt and the method used. If there are high gradients in the profiles, maximum errors can easily be greater than the statistical accuracy of the ADCP, If the tilts are fixed, these errors occur systematically at equal distances. In this study it is shown that the errors can be made smaller by slicing the beam profiles or by taking weighted averages instead of straight nearest bin selections. The disadvantage of these methods is that all sharp changes will be smoothed.

Distribution of volume-averaged parameters of vortex flow over the energy separation chamber of a vortex tube with supplemented flow

The profiles of averaged circular and axial velocity components, temperature, and pressure are measured in the axisymmetric channel of the energy separation chamber of a vortex tube with the introduction of additional flow in the near-axis zone on the side cross section where throttle is located.

Transient hydromagnetic free-convection flow past an impulsively started vertical plate

The effect of rotation on unsteady free-convective started vertical plate is considered. It is assumed that the induced magnetic field is negligible compared to the applied magnetic field, which is fixed with the moving plate. Mathematical expressions for velocity and skin-friction are obtained by the Laplace transform technique. The profiles for velocity components are shown graphically with the effects of the rotation parameter, magnetic parameter and Grashof number. The numerical values of skin-friction components are given in tabalar form for different values of the parameters.

On the flow in the unobstructed space between shrouded corotating disks

A model of a computer hard disk drive was constructed and measurements of the air flow in the unobstructed space between a pair of disks were obtained. The disks were centrally clamped to a common hub, and rotated within an axisymmetric (cylindrical) enclosure or shroud. Measurements of the circumferential velocity component were made at five radial locations and three rotation rates (Ω=300, 1200, and 3600 rpm) using a laser-Doppler velocimeter. The resulting mean and rms circumferential velocity profiles are presented and discussed. The data show that the circumferential velocity component profiles are fairly uniform in the axial direction in the space between the disks, except near the shroud where the flow is strongly sheared. The circumferential velocity peaks at a critical radius. Between the hub and the critical radius location the flow is in solid body rotation. Between the critical radius and the shroud the circumferential velocity decreases to zero, gradually at first and then very quickly as the shroud is approached. Analysis based on simplified force balance considerations facilitates the interpretation of the experimental observations and leads to improved understanding of the complex flow phenomena. Numerical calculations of the present configuration assuming axisymmetric steady flow were performed by Chang et al. (submitted to Int. J. Heat Mass Transfer). These calculations show reasonable agreement with the averaged velocity data but, for the reasons discussed, fail to reproduce features of the rms distribution associated with nonturbulent flow unsteadiness.

Velocity profiles, the resistance law and the dissipation rate of mean flow kinetic energy in a neutrally and stably stratified planetary boundary layer

The logarithmic + polynomial approximation is suggested for vertical profiles of velocity components in a planetary boundary layer (PBL) at neutral and stable stratification. The resistance law functions A and B are determined on the basis of this approximation, using integral relations derived from the momentum equations, the Monin-Obukhov asymptotic formula for the wind profile in a stably stratified near-surface layer and the known expressions for the PBL depth. This result gives a realistic and convenient method for calculating the surface friction velocity and direction and the total dissipation rate of mean flow kinetic energy in terms of geostrophic velocity, buoyancy flux at the surface, the roughness parameter and the Coriolis parameter. In the course of these derivations a review is given of current views on the main problems of the neutral and stable PBL.

Application of a Flow Model to the Ice-divide Region of Devon Island Ice Cap, Canada

AbstractThe steady-state flow model of Reeh (1988) is applied to a flow line that starts at the highest point of the Devon Island ice cap, follows the surface crest for 7.6 km, and then runs down the slope for a further 3.7 km. The effects of bedrock undulations, divergence of the flow lines, the variation of temperature with depth, and a basal layer of “soft” ice-age ice are taken into account. A flow law with n = 3 and a value of A close to that of Paterson (1981) is used. Longitudinal stress variations are neglected so that shear stress is calculated by the usual formula. It is estimated that these calculated values may be in error by at most 30%. Depth profiles of effective shear stress, and of the components of velocity and normal strain-rate, are presented at selected points along the flow line. These illustrate the large variations that occur near an ice divide and over bedrock undulations of amplitude comparable with the mean ice thickness. The model gives good predictions of the surface profile and of longitudinal and transverse surface strain-rates measured at ten points along the flow line. Predicted depth profiles of horizontal and vertical velocity components are compared with those measured in a bore hole. Comparison is limited by the fact that the model works in ice equivalent, whereas about 20% of the ice column consists of firn with different rheological properties from ice. The vertical velocity prediction is good. However, the model does not reproduce well the shape of the horizontal velocity profile, although measured and calculated fluxes differ only slightly. Predicted annual-layer thicknesses are within 15% of the measured ones in the upper half of the ice column, which consists of ice deposited in the last 1000 years. Predicted thicknesses in older ice are too small and the discrepancy increases with depth. This might indicate increased precipitation or, more likely, a thinner ice cap in the climatic optimum. However, it could also result from the fact that the layer of “soft” ice has been thinning continuously since the end of the ice age, so that the ice cap has never been in a steady state.

Application of a Flow Model to the Ice-divide Region of Devon Island Ice Cap, Canada

AbstractThe steady-state flow model of Reeh (1988) is applied to a flow line that starts at the highest point of the Devon Island ice cap, follows the surface crest for 7.6 km, and then runs down the slope for a further 3.7 km. The effects of bedrock undulations, divergence of the flow lines, the variation of temperature with depth, and a basal layer of “soft” ice-age ice are taken into account. A flow law withn= 3 and a value ofAclose to that of Paterson (1981) is used. Longitudinal stress variations are neglected so that shear stress is calculated by the usual formula. It is estimated that these calculated values may be in error by at most 30%. Depth profiles of effective shear stress, and of the components of velocity and normal strain-rate, are presented at selected points along the flow line. These illustrate the large variations that occur near an ice divide and over bedrock undulations of amplitude comparable with the mean ice thickness. The model gives good predictions of the surface profile and of longitudinal and transverse surface strain-rates measured at ten points along the flow line. Predicted depth profiles of horizontal and vertical velocity components are compared with those measured in a bore hole. Comparison is limited by the fact that the model works in ice equivalent, whereas about 20% of the ice column consists of firn with different rheological properties from ice. The vertical velocity prediction is good. However, the model does not reproduce well the shape of the horizontal velocity profile, although measured and calculated fluxes differ only slightly. Predicted annual-layer thicknesses are within 15% of the measured ones in the upper half of the ice column, which consists of ice deposited in the last 1000 years. Predicted thicknesses in older ice are too small and the discrepancy increases with depth. This might indicate increased precipitation or, more likely, a thinner ice cap in the climatic optimum. However, it could also result from the fact that the layer of “soft” ice has been thinning continuously since the end of the ice age, so that the ice cap has never been in a steady state.

Axisymmetric inviscid swirling flows produced by bellmouth and centerbody

The effect of large deformation in the flow between the bellmouth and centerbody is considered analytically for application to studies of vortex breakdown in a pipe. Basic equations are defined for axisymmetric inviscid swirling flows at the inflow and outflow sections. Axial and circumferential velocity component profiles are presented, and comparisons are made with trials involving vane angles of 42 deg and Re of 2300. Axial components of the prediction matched well in the inner half of the pipe radius and not well with the outer, while circumferential predictions were good only at the axis. A lack of viscosity was concluded to result in the inaccuracies near the wall.

A parameterization of the boundary layer of a tropical cyclone

In an earlier paper by one of the authors (Smith, 1968), a momentum integral method was developed to parameterize the gross constraint imposed by the surface boundary layer of a steady, axisymmetric, tropical cyclone on the meridional circulation within the vortex itself. Specifically, the method provides an effective means of estimating the radial variation of mean upflow/downflow induced by the boundary layer, compatible with a prescribed radial variation of azimuthal velocity just above the boundary layer,V gr. However, it relies on a judicious choice of vertical profiles of radial and azimuthal velocity components within the boundary layer. An especially suitable set of profiles is discussed herein; these are Ekman-like profiles in which turbulent mixing is characterized by a vertically constant eddy diffusivityK M , matched to a constant stress sublayer just above the sea surface. An attractive feature of the formulation is that a suitable value forK M as a function of radius, which is extremely difficult to extract from observational data, can be calculated when the state of the sea surface, described by a roughness lengthZ 0, is prescribed. Although observations ofZ 0 at high wind speeds are not yet available, the effect of radial variations in sea surface roughness can be assessed and it is shown that these affect the upflow to a significant degree.

Nearly spherical constant-power detonation waves as driven by focused radiation

An analysis is made of the flow within a three-dimensional explosion, or spark, created in a gas absorbing energy from a steady conical beam of radiation with nearly spherical symmetry. The radiation, typically from an array of lasers with a common focus, is assumed to be very intense, and absorbed immediately behind an outwardly advancing strong shock. The resulting self-similar flow has previously been studied for spherical symmetry; somewhat improved calculations for that case are presented here.Departures of the laser power from spherical uniformity, which would result from practical problems of arrangement, are conveniently represented by an ascending series of Legendre polynomials in the polar angle. For non-uniformities of small amplitude, first-order perturbations of the flow field are analysed in detail. Self-similarity is shown to be retained, for zero counter-pressure and power constant with time.For the first five harmonics in power distortion, the resulting fourth-order system of equations is solved numerically for profiles of velocity components, density and pressure, and for shock shape. Results are presented graphically. These solutions are singular near the focus, but are nevertheless fully determined. In the limit of large wavenumber, the core of the flow has vanishing tangential velocity and pressure perturbations, and hence the governing equations are only of second order, except presumably in a boundary layer appearing near the shock.Study of the nonlinear case of large wavenumber along the axis of symmetry shows that the singularity at the focus reflects the existence of a ‘forbidden zone’ whose extent depends on the degree of asymmetry. It is argued that this zone is one within which diffusional processes must dominate.