Détermination du Champ de Vitesse du Sillage d'une Sphère Hypersonique à l'Aide de Peignes de Sondes Ioniques

1972 ◽  
Vol 50 (16) ◽  
pp. 1842-1855 ◽  
Author(s):  
L. Sévigny ◽  
D. Heckman ◽  
A. Emond
Keyword(s):  
Velocity Field ◽  
Velocity Distribution ◽  
Large Scale ◽  
Ambient Ionization ◽  
Convection Velocity ◽  
Near Wake ◽  
Air Atmosphere ◽  
Ion Probe ◽  
Other Information ◽  
Hypersonic Wake

The technique of measuring convection velocity in the hypersonic wake with a pair of in-line probes has been applied on a large scale to the mapping of the velocity field in the hypersonic wake through the use of a transverse survey array containing up to 8 ion-probe pairs. Measurements are reported of the velocity field in the wakes of 2.7 in. diameter spheres flown at 14 500 f/s in ballistic range atmospheres at 7.6 Torr and at 20 Torr of nitrogen. The array technique leads to convection velocity results which are in excellent agreement with the mean wake velocity data obtained by the sequential spark technique in an air atmosphere. In addition, the technique has permitted an extension of the mapping of the velocity field of 15 000 f/s spheres to considerably smaller axial distances than was possible with the spark method because of the difficulty of forming distinct sparks at the higher levels of ambient ionization encountered in the near wake.A comparison of the data obtained at 7.6 Torr and at 20 Torr shows that the amplitude of the velocity distribution in the wake, as defined by the velocity on the wake axis, is higher at higher pressure. Considering the wake width, however, it is found that the width of the velocity distribution is larger at the lower pressure of 7.6 Torr than is the case at 20 Torr, at least in the near wake. However, at axial distances greater than 300 or 400 diameters, the data for the two pressures tend to overlap. These observations appear to be related to other information indicating that for 2.7 in. diameter spheres launched at 7.6 Torr, the wake is not fully turbulent until about 300 or 400 diameters.

scholarly journals On the numerical solution of diabatic quasi-geostrophic Omega equation

MAUSAM ◽  
2021 ◽  
Vol 22 (1) ◽  
pp. 35-46
Author(s):  
J. SHUKLA
Keyword(s):  
Velocity Field ◽  
Velocity Distribution ◽  
Vertical Velocity ◽  
Large Scale ◽  
Middle Latitude ◽  
Sensible Heat ◽  
Layer Model ◽  
Large Scale Disturbance ◽  
Omega Equation ◽  
Good Agreement

The quasi-geostrophic omega equation has been numerically solved to get the vertical velocity distribution in a typical westerly disturbance. The effects of sensible heat and latent heat of condensation are also for a 4-layer model. The computations were performed on HITAC 5020. The numerically obtained vertical velocity field is in good agreement with the observed weather pattern associated with the middle latitude large-scale disturbance, i.e., ascending motion in front of the trough and downward motion in the rear of the trough.

The entrainment interface

1972 ◽  
Vol 51 (1) ◽  
pp. 97-118 ◽  
Author(s):  
O. M. Phillips
Keyword(s):  
Velocity Field ◽  
Turbulent Flow ◽  
Surface Area ◽  
Large Scale ◽  
Positive Curvature ◽  
Lagrangian Description ◽  
Eulerian Description ◽  
Entrainment Process ◽  
Necessary And Sufficient ◽  
Small Disturbances

A theory is developed to describe the evolution of the entrainment interface in turbulent flow, in which the surface is convoluted by the large-scale eddies of the motion and at the same time advances relative to the fluid as a result of the micro-scale entrainment process. A pseudo-Lagrangian description of the process indicates that the interface is characterized by the appearance of ‘billows’ of negative curvature, over which surface area is, on average, being generated, separated by re-entrant wedges (lines of very large positive curvature) where surface area is consumed. An alternative Eulerian description allows calculation of the development of the interfacial configuration when the velocity field is prescribed. Several examples are considered in which the prescribed velocity field in the z direction is of the general form w = Wf(x – Ut), where the maximum value of the function f is unity. These indicate the importance of leading points on the surface which are such that small disturbances in the vicinity will move away from the point in all directions. The necessary and sufficient condition for the existence of one or more leading points on the surface is that U [les ] V, the speed of advance of an element of the surface relative to the fluid element at the same point. The existence of leading points is accompanied by the appearance of line discontinuities in the surface slope re-entrant wedges, In these circumstances, the overall speed of advance of the convoluted surface is found to be W + (V2 – U2)½, where W is the maximum outwards velocity in the region; this result is independent of the distribution f.When the speed U with which an ‘eddy’ moves relative to the outside fluid is greater than the speed of advance V of an element of the front, the interface develops neither leading points nor discontinuities in slope; the amplitude of the surface convolutions and the overall entrainment speed are both reduced greatly. In a turbulent flow, therefore, the large-scale motions influencing entrainment are primarily those that move slowly relative to the outside fluid (with relative speed less than V). The experimental results of Kovasznay, Kibens & Blackwelder (1970) are reviewed in the light of these conclusions. It appears that in their experiments the entrainment speed V is of the order fifteen times the Kolmogorov velocity, the large constant of proportionality being apparently the result of augmentation by micro-convolutions of the interface associated with small and meso-scale eddies of the turbulence.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

Buoyancy effects on large-scale motions in convective atmospheric boundary layers: implications for modulation of near-wall processes

2018 ◽  
Vol 856 ◽  
pp. 135-168 ◽  
Author(s):  
S. T. Salesky ◽  
W. Anderson
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Boundary Layers ◽  
Vertical Velocity ◽  
Amplitude Modulation ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Small Scale ◽  
Convective Conditions ◽  
Wide Range

A number of recent studies have demonstrated the existence of so-called large- and very-large-scale motions (LSM, VLSM) that occur in the logarithmic region of inertia-dominated wall-bounded turbulent flows. These regions exhibit significant streamwise coherence, and have been shown to modulate the amplitude and frequency of small-scale inner-layer fluctuations in smooth-wall turbulent boundary layers. In contrast, the extent to which analogous modulation occurs in inertia-dominated flows subjected to convective thermal stratification (low Richardson number) and Coriolis forcing (low Rossby number), has not been considered. And yet, these parameter values encompass a wide range of important environmental flows. In this article, we present evidence of amplitude modulation (AM) phenomena in the unstably stratified (i.e. convective) atmospheric boundary layer, and link changes in AM to changes in the topology of coherent structures with increasing instability. We perform a suite of large eddy simulations spanning weakly ($-z_{i}/L=3.1$) to highly convective ($-z_{i}/L=1082$) conditions (where$-z_{i}/L$is the bulk stability parameter formed from the boundary-layer depth$z_{i}$and the Obukhov length $L$) to investigate how AM is affected by buoyancy. Results demonstrate that as unstable stratification increases, the inclination angle of surface layer structures (as determined from the two-point correlation of streamwise velocity) increases from$\unicode[STIX]{x1D6FE}\approx 15^{\circ }$for weakly convective conditions to nearly vertical for highly convective conditions. As$-z_{i}/L$increases, LSMs in the streamwise velocity field transition from long, linear updrafts (or horizontal convective rolls) to open cellular patterns, analogous to turbulent Rayleigh–Bénard convection. These changes in the instantaneous velocity field are accompanied by a shift in the outer peak in the streamwise and vertical velocity spectra to smaller dimensionless wavelengths until the energy is concentrated at a single peak. The decoupling procedure proposed by Mathiset al.(J. Fluid Mech., vol. 628, 2009a, pp. 311–337) is used to investigate the extent to which amplitude modulation of small-scale turbulence occurs due to large-scale streamwise and vertical velocity fluctuations. As the spatial attributes of flow structures change from streamwise to vertically dominated, modulation by the large-scale streamwise velocity decreases monotonically. However, the modulating influence of the large-scale vertical velocity remains significant across the stability range considered. We report, finally, that amplitude modulation correlations are insensitive to the computational mesh resolution for flows forced by shear, buoyancy and Coriolis accelerations.

Non-uniqueness in wakes and boundary layers

1984 ◽  
Vol 391 (1800) ◽  
pp. 1-26 ◽  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Algebraic Decay ◽  
Scale Separation ◽  
Boundary Layer Equations ◽  
Classical Boundary ◽  
Streamlined Flow ◽  
High Reynolds

In streamlined flow past a flat plate aligned with a uniform stream, it is shown that ( a ) the Goldstein near-wake and ( b ) the Blasius boundary layer are non-unique solutions locally for the classical boundary layer equations, whereas ( c ) the Rott-Hakkinen very-near-wake appears to be unique. In each of ( a ) and ( b ) an alternative solution exists, which has reversed flow and which apparently cannot be discounted on immediate grounds. So, depending mainly on how the alternatives for ( a ), ( b ) develop downstream, the symmetric flow at high Reynolds numbers could have two, four or more steady forms. Concerning non-streamlined flow, for example past a bluff obstacle, new similarity forms are described for the pressure-free viscous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include non-uniqueness, singularities and algebraic behaviour, consistent with non-entraining shear layers with algebraic decay. Non-uniqueness also seems possible in reattachment onto a solid surface and for non-symmetric or pressure-controlled flows including the wake of a symmetric cascade.

Large-Scale Sustainable Information Systems Development in a Developing Country

2008 ◽  
pp. 788-803
Author(s):  
Adekunle Okunoye
Keyword(s):  
Information System ◽  
Developing Countries ◽  
Large Scale ◽  
Business Environment ◽  
Systems Development ◽  
Islamic Bank ◽  
Long Duration ◽  
Rapid Changes ◽  
Other Information ◽  
Outsourcing Decision

Information technology (IT) transfer to developing countries is often affected by various problems. Most available application packages are too expensive and were originally designed to work in a developed economy. The international features of the application packages reduced the problems associated with long duration and huge cost of customization. Nevertheless, there are still some processes that require many peculiar requirements that customization of the off-the-shelf applications cannot meet. With the rapid changes in IT and the business environment, it is becoming essential to rely on information system that can be sustained and upgraded without much cost in order to meet those changes. This case describes a project for the development of such a system. We present the background of the IT company and an Islamic bank as the customer. We highlight the circumstances that led to their decision to develop the systems locally. We discuss the facts that surround the development of the system: the outsourcing decision made by the African Arab Islamic Bank (AFAIB), the project management and systems development at Technology Associates Ltd. (TA), and other information system issues related to developing countries and their effect on the project’s success.

Spiral Galaxies, Elliptical Galaxies and the Large-Scale Velocity Field Within 3500 Km/s of the Local Group

1988 ◽  
pp. 177-180 ◽  
Author(s):  
David Burstein ◽  
Roger L. Davies ◽  
Alan Dressler ◽  
S. M. Faber ◽  
Donald Lynden-Bell ◽  
...  
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Local Group ◽  
Spiral Galaxies ◽  
Elliptical Galaxies

scholarly journals Origins of Wilson’s Warblers migrating through southwest Canada: Adding value to banding data by using stable isotopes and genetic markers

2018 ◽  
Vol 5 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Kevin J. Kardynal ◽  
Douglas M. Collister ◽  
Keith A. Hobson
Keyword(s):  
Pacific Northwest ◽  
Large Scale ◽  
Rocky Mountain ◽  
Population Changes ◽  
Stopover Site ◽  
Future Studies ◽  
The Pacific ◽  
Catchment Areas ◽  
Other Information ◽  
Northwestern North America

Abstract Stopovers used by birds during migration concentrate individuals from broad geographic areas potentially providing important information on catchment areas of birds moving through these sites. We combined stable isotope (δ2H), genetic fingerprinting and band recovery data to delineate the molt origins of Wilson’s Warblers (Cardellina pusilla) migrating through a stopover site in southwestern Canada in the fall. We assessed changes in δ2Hf indicating latitudinal origins with ordinal date to show this species likely underwent leapfrog migration through this site. Using the combined approach to determine origins, Wilson’s Warblers migrating through southwestern Alberta in 2015 were mostly from the western boreal population (n = 155, 96%) with some individuals from the Pacific Northwest (n = 1, 0.6%), Rocky Mountain (n = 2, 1.2%) and eastern boreal (n = 3, 1.8%) populations. Our results suggest that individuals migrating through our study site come from a broad catchment area potentially from a large part of northwestern North America. Future studies should link population changes at banding stations with other information to determine associations with large-scale landscape-level drivers (e.g. climate, land use).

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