139,292 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
Parapalicus clinodentatus Castro 2000
No full text<i>Parapalicus clinodentatus</i> Castro, 2000 <p> <i>Parapalicus clinodentatus</i> Castro, 2000: 495, 587, 588, figs 18, 19c, 57.</p> <p> MATERIAL EXAMINED. — <b>Tonga.</b> BORDAU 2, stn CP 1511, 21°08’S, 175°22’W, 384-402 m, 31. V.2000, 1 ♂ (MNHN-B 31951). — Stn CP 1541, 21°15’S, 175°14’W, 319-333 m, 5. VI.2000, 2 ovig. ♀♀ (MNHN-B 31952). — Stn CP 1641, 21°09’S, 175°22’W, 395 m, 21. VI.2000, 8 ♂♂, 1 ♀ (MNHN-B 31953).</p> <p>DISTRIBUTION. — Vanuatu (type locality), New Caledonia, Fiji (Castro 2000: table 6, fig. 57) and now Tonga. Depth: 282-950 m (Castro 2000: table 5).</p>Published as part of <i>Castro, Peter, 2010, A new species and new records of palicoid crabs (Crustacea, Decapoda, Brachyura, Palicoidea, Palicidae, Crossotonotidae) from the Indo-West Pacific region, pp. 73-86 in Zoosystema 32 (1)</i> on page 82, DOI: 10.5252/z2010n1a3, <a href="http://zenodo.org/record/4520863">http://zenodo.org/record/4520863</a>
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
Recommended from our members
A letter from Mrs. Lesley Castro to Dr. Hector P. Garcia.
No full textA handwritten letter from Mrs. Lesley Castro to Dr. Hector P. Garcia, asking for his help in locating information on her husband's father
Thyraplax truncata Castro 2007
No full text<i>Thyraplax truncata</i> Castro, 2007 (Fig. 3) <p> <i>Thyraplax truncata</i> Castro, 2007: 683, figs 25, 26. — Ahyong 2009: 66, fig. 1A-C.</p> <p> MATERIAL EXAMINED. — <b>New Caledonia.</b> EBISCO, stn CP 2498, 24°45.0’S, 159°43.0’E, 367-536 m, 6.X.2005, 1 ♀, 7.2 mm, cw 9.7 mm (MNHN-B30794).</p> <p>REMARKS</p> <p> <i>Thyraplax truncata</i>, was described from five specimens, all males, which were collected from depths of 430- 500 m in New Caledonia and Fiji. Ahyong (2009) subsequently recorded a female from the Kermadec Is., New Zealand. A second female specimen from New Caledonia now permits the description of the female. All characters related to the morphology of the carapace and pereopods (Fig. 3A) agree with those described for the males (Castro 2007: 683, figs 25A, 26). One exception is the dark-brown tip of the cheliped fingers, which extended slightly less in the female than in the five males previously studied.</p> <p>DESCRIPTION OF THE FEMALE</p> <p>Abdomen wide.Telson triangular,slightly wider than long. Somite 3 covers space between P5 coxae and episternites 7, somite 2 only slightly narrower than somite 3, thoracic sternite8not visible.Vulva (Fig.3B) crescent-shaped, extending from edge of anteriorly deflected suture 5/6 to middle portion of thoracic sternite 6; small, triangular sternal vulvar cover on posterior margin of vulva, covering about third of aperture, soft membrane covering rest of aperture.</p>Published as part of <i>Castro, Peter, 2009, Two new species of Carcinoplax H. Milne Edwards, 1852, and Pycnoplax Castro, 2007, from the western Pacific, and a description of the female of Thyraplax truncata Castro, 2007 (Crustacea, Decapoda, Brachyura, Goneplacidae), pp. 949-957 in Zoosystema 31 (4)</i> on pages 956-957, DOI: 10.5252/z2009n4a9, <a href="http://zenodo.org/record/4520584">http://zenodo.org/record/4520584</a>
Recommended from our members
A letter from Gilbert Anthony Castro to Dr. Hector P. Garcia.
No full textA letter from Gilbert Anthony Castro to Dr. Hector P. Garcia, requesting information on Felix Longoria
Recommended from our members
A letter from Mary Lou Castro to Dr. Hector P. Garcia.
No full textA handwritten letter from Mary Lou Castro to Dr. Hector P. Garcia, wishing him health, and informing him that she received the Distinguished Service Award from the National Association of Women Veterans of Illinois
Recommended from our members
A letter from Genaro Castro Garcia to Dr. Hector P. Garcia, asking for help for his family and himself.
No full textA letter from Genaro Castro Garcia to Dr. Hector P. Garcia, asking for help for his family and himself
- …
