110,962 research outputs found
Vortex shedding from tapered, triangular plates: taper and aspect ratio effects
No full textFurther experiments on features of the vortex shedding from tapered flat plates normal to an airstream are described. The work extends that of Castro and Rogers (2002) and concentrates on the study of the effects of varying the spanwise aspect ratio for a fixed shape plate, by appropriate adjustment of end-plates, and of the nature of the shedding as the degree of taper becomes very large, so that the body is more like a triangular plate—e.g. an isosceles triangle—than a slightly tapered plate. With the taper ratio TR defined as the ratio of plate length to average cross-stream width, the paper concentrates on the range 0.58<TR<60. Reynolds numbers, based on the average plate width, exceed 104. It is confirmed that for a small enough taper ratio the geometrical three-dimensionality is sufficiently strong that all signs of periodic vortex shedding cease. For all other cases, however, the flow at different locations along the span can vary substantially, depending on taper. There appear to be at least four different regimes, each appropriate for a different range of taper ratio. These various regimes are described
Weakly stratified laminar flow past normal flat plates
No full textNumerical computations of the steady, two-dimensional, incompressible, uniform velocity but stably stratified flow past a normal flat plate (of unit half-width) in a channel are presented. Attention is restricted to cases in which the stratification is weak enough to avoid occurrence of the gravity wave motions familiar in more strongly stratified flows over obstacles. The nature of the flow is explored for channel half-widths, H, in the range 5 [less-than-or-eq, slant] H [less-than-or-eq, slant] 100, for Reynolds numbers, Re, (based on body half-width and the upstream velocity, U) up to 600 and for stratification levels between zero (i.e. neutral flow) and the limit set by the first appearance of waves. The fourth parameter governing the flow is the Schmidt number, Sc, the ratio of the molecular diffusion of the agent providing the stratification to the molecular viscosity. For cases of very large (in the limit, infinite) Sc a novel technique is used, which avoids solving the density equation explicitly. Results are compared with the implications of the asymptotic theory of Chernyshenko & Castro (1996) and with earlier computations of neutral flows over both flat plates and circular cylinders. The qualitative behaviour in the various flow regimes identified by the theory is demonstrated, but it is also shown that in some cases a flow zone additional to those identified by the theory appears and that, in any case, precise agreement would, for most regimes, require very much higher Re and/or H. Some examples of multiple (i.e. non-unique) solutions are shown and we discuss the likelihood of these being genuine, rather than an artefact of the numerical scheme.<br/
The stability of laminar symmetric separated wakes
No full textTime-dependent computations of the two-dimensional incompressible uniform-velocity laminar flow past a normal flat plate (of unit half-width) in a channel are presented. Attention is restricted to cases in which the well-known anti-symmetric (von Kármán-type) vortex shedding is suppressed by the imposition of a symmetry plane on the downstream plate centreline. With a further symmetry plane at the channel's upper boundary, the only two governing parameters in the problem are the channel half-width, H, and the Reynolds number, Re (based on the body half-width and the upstream velocity, U). The former is restricted to the range 3?H?30 and the interest lies in determining the nature of the initial instability which occurs in the separated wake as Re is gradually increased. It is found that for sufficiently large H and at a critical Re, a long-time-scale global (supercritical) instability is initiated, which in its saturated (limit) state takes the form of ‘lumps’ of vorticity being periodically shed from the tail end of the separated bubble. Stability calculations of corresponding mean flow profiles (typical of those found in the separated wake) are undertaken by examining the impulse response of particular profiles via appropriate solution of the Orr–Sommerfeld equation. The results of this analysis extend those available from related published work and are consistent with the behaviour found from the numerical computations. Taken together, all the results suggest that this type of global instability may be generic to many kinds of separated wakes and, indeed, may provide the fundamental explanation for the very low-frequency oscillations often noticed in fully turbulent wake bubbles
Channel flow over large cube roughness: a direct numerical simulation study
No full textComputations of channel flow with rough walls comprising staggered arrays of cubes having various plan area densities are presented and discussed. The cube height h is12.5% of the channel half-depth and Reynolds numbers (u? h/?) are typically around 700 – well into the fully rough regime. A direct numerical simulation technique, usingan immersed boundary method for the obstacles, was employed with typically 35 million cells. It is shown that the surface drag is predominantly form drag, which is greatest at an area coverage around 15%. The height variation of the axial pressure force across the obstacles weakens significantly as the area coverage decreases, but is always largest near the top of the obstacles. Mean flow velocity and pressure data allow precise determination of the zero-plane displacement (defined as the height at which the axial surface drag force acts) and this leads to noticeably better fits to the log-law region than can be obtained by using the zero-plane displacementmerely as a fitting parameter. There are consequent implications for the value ofvon K´arm´ an’s constant. As the effective roughness of the surface increases, it is also shown that there are significant changes to the structure of the turbulencefield around the bottom boundary of the inertial sublayer. In distinct contrast to twodimensional roughness (longitudinal or transverse bars), increasing the area density of this three-dimensional roughness leads to a monotonic decrease in normalized vertical stress around the top of the roughness elements. Normalized turbulence stresses in the outer part of the flows are nonetheless very similar to those in smooth-wallflows
[Papeles del escultor Felipe de Castro] [Manuscrito]
No full textMss. apuntes sobre materias moi diversas e de distintas mans, en castelánClaude Bédat atribúe ó escultor Felipe de Castro a autoría das follas 9 a 33 nas que se describen algunhas cidades de España e os seus monumentosEncadernado en pergameo. Na etiqueta da enc.: Papeles Varios. Tomo VIIIContén ademais o seguinte impreso: Oración gratulatoria / que dixo don Joseph de Mascareñas Pacheco y Pereyra quando fue admitido en la Rl. Academia de la Historia ; respuestas del señor don Agustín de Montiano y Luyando.-- Madrid : Gabriel Ramírez, 1754 (18 páginas)Foliación antiga a tinta nunha parte dos manuscritosA la muerte de Luis primero, Rey de España / por el Rmo.P.M. Feijoo y Montenegro - Al muy insigne gallego Dn. Felipe de Castro estatuario del Rey nuestro Señor / Diego Antonio Cernadas de Castro - Descripción de algunas ciudades y sus monumentos / Felipe de Castro - Apuntes sobre algunos Papas y Reyes - El Gran Mogol - La pesca de las perlas - Valor del Real Herario de España y sus gastos - Noticias y coplas satíricas sobre el tumulto de Madrid - Respuesta a la carta que escrivio la Junta de Agricultura del Reyno de Galicia al Rmo. Pe. Fray Martin Sarmiento / Fr. Martín Sarmiento - Actos de fe que un gallego rancio haze a los pies del Santisimo Apostol Patron Santiago el Zebedeo / Diego Antonio Cernadas de Castro? - El tumulto de Madrid en tiempo de Carlos 3º - Copia de la carta que el Rey escrivio a su Santidad sobre la causa de la beatificación del Obispo Dn. Juan de Palafox - Memorial al Rey de Dn. Melchor de Macanaz - Coplas y otros escritos satiricos - Escritos sobre la expulsión de la Compañía de Jesú
Large-eddy simulation for flow and dispersion in urban streets
No full textLarge-eddy simulations (LES) with our recently developed inflow approach (Xie &Castro, 2008a) have been used for flow and dispersion within a genuine city area -the DAPPLE site, located at the intersection of Marylebone Rd and Gloucester Plin Central London. Numerical results up to second-order statistics are reported fora computational domain of 1.2km (streamwise) x 0.8km (lateral) x 0.2km (in fullscale), with a resolution down to approximately one meter in space and one secondin time. They are in reasonable agreement with the experimental data. Such a comprehensiveurban geometry is often, as here, composed of staggered, aligned, squarearrays of blocks with non-uniform height and non-uniform base, street canyons andintersections. Both the integrative and local effect of flow and dispersion to thesegeometrical patterns were investigated. For example, it was found that the peaksof spatially averaged urms, vrms, wrms and < u0w0 > occurred neither at the meanheight nor at the maximum height, but at the height of large and tall buildings. Itwas also found that the mean and fluctuating concentrations in the near-source fieldis highly dependent on the source location and the local geometry pattern, whereasin the far field (e.g. >0.1km) they are not. In summary, it is demonstrated thatfull-scale resolution of around one meter is sufficient to yield accurate prediction ofthe flow and mean dispersion characteristics and to provide reasonable estimationof concentration fluctuation
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Bluff bodies in deep turbulent boundary layers: Reynolds-number issues
No full textIt is generally assumed that flows around wall-mounted sharp-edged bluff bodies
submerged in thick turbulent boundary layers are essentially independent of the
Reynolds number Re, provided that this exceeds some (2–3) × 104. (Re is based on
the body height and upstream velocity at that height.) This is a particularization of
the general principle of Reynolds-number similarity and it has important implications,
most notably that it allows model scale testing in wind tunnels of, for example,
atmospheric flows around buildings. A significant part of the literature on wind
engineering thus describes work which implicitly rests on the validity of this
assumption. This paper presents new wind-tunnel data obtained in the ‘classical’ case
of thick fully turbulent boundary-layer flow over a surface-mounted cube, covering an
Re range of well over an order of magnitude (that is, a factor of 22). The results are
also compared with new field data, providing a further order of magnitude increase in
Re. It is demonstrated that if on the one hand the flow around the obstacle does not
contain strong concentrated-vortex motions (like the delta-wing-type motions present
for a cube oriented at 45? to the oncoming flow), Re effects only appear on fluctuating
quantities such as the r.m.s. fluctuating surface pressures. If, on the other hand, the
flow is characterized by the presence of such vortex motions, Re effects are significant
even on mean-flow quantities such as the mean surface pressures or the mean velocities
near the surfaces. It is thus concluded that although, in certain circumstances and for
some quantities, the Reynolds-number-independency assumption is valid, there are
other important quantities and circumstances for which it is not
<p class="HeadingRunIn"><strong><em>Cattleya</em> × <em>itabapoanaensis</em> (Orchidaceae), a new natural hybrid from Rio Janeiro State (Brazil)</strong></p>
No full textP., CASTRO NETO, V., D., MOTTE, Y., DUBUISSON J. (2012): <p class="HeadingRunIn"><strong><em>Cattleya</em> × <em>itabapoanaensis</em> (Orchidaceae), a new natural hybrid from Rio Janeiro State (Brazil)</strong></p>. Phytotaxa 56 (1): 9, DOI: 10.11646/PHYTOTAXA.56.1.2, URL: http://dx.doi.org/10.11646/phytotaxa.56.1.
Extracting Boer-Mulders functions from p+D Drell-Yan processes
No full textWe extract the Boer- Mulders functions of valence and sea quarks in the proton from unpolarized p + D Drell- Yan data measured by the FNAL E866 Collaboration. Using these Boer- Mulders functions, we calculate the cos2 phi asymmetries in unpolarized pp Drell- Yan processes, both for the FNAL E866/ NuSea and the BNL Relativistic Heavy Ion Collider experiments. We also estimate the cos2 phi asymmetries in the unpolarized p (P) over bar Drell- Yan processes at GSI.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)37ARTICLE5null7
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