The laminar wake behind a 6:1 prolate spheroid at 45° incidence angle

Fengjian Jiang; José P. Gallardo; Helge I. Andersson

doi:10.1063/1.4902015

The flow structure in the lee of an inclined 6:1 prolate spheroid

Journal of Fluid Mechanics ◽

10.1017/s0022112094001497 ◽

1994 ◽

Vol 269 ◽

pp. 79-106 ◽

Cited By ~ 15

Author(s):

T. C. Fu ◽

A. Shekarriz ◽

J. Katz ◽

T. T. Huang

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Flow Structure ◽

Incidence Angle ◽

Prolate Spheroid ◽

The Body ◽

Boundary Layer Transition ◽

Primary Vortex ◽

Vortex Sheets ◽

Vorticity Distribution

Particle displacement velocimetry is used to measure the velocity and vorticity distributions around an inclined 6: 1 prolate spheroid. The objective is to determine the effects of boundary-layer tripping, incidence angle, and Reynolds number on the flow structure. The vorticity distributions are also used for computing the lateral forces and rolling moments that occur when the flow is asymmetric. The computed forces agree with results of direct measurements. It is shown that when the flow is not tripped, separation causes the formation of a pair of vortex sheets. The size of these sheets increases with increasing incidence angle and axial location. Their orientation and internal vorticity distribution also depend on incidence. Rollup into distinct vortices occurs in some cases, and the primary vortex contains between 20 % and 50 % of the overall circulation. The entire flow is unsteady and there are considerable variations in the instantaneous vorticity distributions. The remainder of the lee side, excluding these vortex sheets, remains almost vorticity free, providing clear evidence that the flow can be characterized as open separation. Boundary-layer tripping causes earlier separation on part of the model, brings the primary vortex closer to the body, and spreads the vorticity over a larger region. The increased variability in the vorticity distribution causes considerable force fluctuations, but the mean loads remain unchanged. Trends with increasing Reynolds number are conflicting, probably because of boundary-layer transition. The separation point moves towards the leeward meridian and the normal force decreases when the Reynolds number is increased from 0.42 × 106 to 1.3 × 106. Further increase in the Reynolds number to 2.1 × 106 and tripping cause an increase in forces and earlier separation.

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Large Eddy Simulation of the Wake Behind an Ellipsoid at 45° Incidence Angle

Volume 7B: Ocean Engineering ◽

10.1115/omae2017-61678 ◽

2017 ◽

Author(s):

Zongxin Yu ◽

Hao Liu ◽

Xianzhou Wang ◽

Zhiguo Zhang ◽

Fanchen Zhang

Keyword(s):

Incidence Angle ◽

Near Field ◽

Axial Flow ◽

Flow Simulation ◽

Prolate Spheroid ◽

Wake Flow ◽

Leeward Side ◽

Stream Velocity ◽

Incline Angle ◽

The Asymmetry

For the well-defined bodies of revolution, the viscous flow past Prolate spheroids has fascinated scientists in fluid mechanics, marine hydrodynamics and aero-dynamical communities for decades. Previous experiment in different yaw and pitch angles of a prolate-spheroid like submarine mode suggests that the asymmetry is a feature of the high Reynolds wake of the symmetric body of revolution with incline angle. The objective of this paper is to examine the similar phenomenon — the asymmetric wake flow — in the relatively low Reynolds number. The present paper focuses on flow field with LES model for a 45° inclined 6:1 prolate spheroid. LESs of the flow and wake have been conducted at Reynolds numbers ReD = 3000, and 10000 (ReD based on the free-stream velocity U0 and the minor axes length D). The maximum grid points reaches 30 million. Results from simulation show the dominant structure of the wake to be a pair of counter-rotating vortices. Detailed observations and analyses show strong leeward side axial flow. Simulation results from LES were compared with the DNS results for ReD = 3000. The wake at ReD = 3000 and 10000 shown was complex with numerous disordered vortical structures. Strong asymmetric wake and large side-force were surprisingly observed and the asymmetry in near field and far field were analyzed and compared.

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Electron Channeling Patterns

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077700 ◽

1977 ◽

Vol 35 ◽

pp. 12-13

Author(s):

David C. Joy

Keyword(s):

Electron Diffraction ◽

Incidence Angle ◽

Photographic Plate ◽

Diffraction Effect ◽

Angle Of Incidence ◽

Bulk Single Crystal ◽

Time Resolved ◽

Electron Channeling ◽

Spatially Resolved ◽

Large Bulk

Electron channeling patterns (ECP) were first found by Coates (1967) while observing a large bulk, single crystal of silicon in a scanning electron microscope. The geometric pattern visible was shown to be produced as a result of the changes in the angle of incidence, between the beam and the specimen surface normal, which occur when the sample is examined at low magnification (Booker, Shaw, Whelan and Hirsch 1967).A conventional electron diffraction pattern consists of an angularly resolved intensity distribution in space which may be directly viewed on a fluorescent screen or recorded on a photographic plate. An ECP, on the other hand, is produced as the result of changes in the signal collected by a suitable electron detector as the incidence angle is varied. If an integrating detector is used, or if the beam traverses the surface at a fixed angle, then no channeling contrast will be observed. The ECP is thus a time resolved electron diffraction effect. It can therefore be related to spatially resolved diffraction phenomena by an application of the concepts of reciprocity (Cowley 1969).

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Atomic force microscopy (AFM) of the topography of silicon surfaces exposed to ion beams

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130298 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1132-1133

Author(s):

Mark Denker ◽

Jennifer Wall ◽

Mark Ray ◽

Richard Linton

Keyword(s):

Secondary Ion Mass Spectrometry ◽

Incidence Angle ◽

Ion Beam ◽

Depth Profiling ◽

Depth Resolution ◽

Ion Beams ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Trace Impurities ◽

Energy Dose

Reactive ion beams such as O2+ and Cs+ are used in Secondary Ion Mass Spectrometry (SIMS) to analyze solids for trace impurities. Primary beam properties such as energy, dose, and incidence angle can be systematically varied to optimize depth resolution versus sensitivity tradeoffs for a given SIMS depth profiling application. However, it is generally observed that the sputtering process causes surface roughening, typically represented by nanometer-sized features such as cones, pits, pyramids, and ripples. A roughened surface will degrade the depth resolution of the SIMS data. The purpose of this study is to examine the relationship of the roughness of the surface to the primary ion beam energy, dose, and incidence angle. AFM offers the ability to quantitatively probe this surface roughness. For the initial investigations, the sample chosen was <100> silicon, and the ion beam was O2+.Work to date by other researchers typically employed Scanning Tunneling Microscopy (STM) to probe the surface topography.

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Principle and practice of high-resolution imaging with a field-emission TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121090 ◽

1992 ◽

Vol 50 (1) ◽

pp. 138-139

Author(s):

Max T. Otten ◽

Wim M.J. Coene

Keyword(s):

High Resolution ◽

Field Emission ◽

Incidence Angle ◽

Temporal Coherence ◽

Energy Spread ◽

High Resolution Imaging ◽

Major Improvement ◽

High Resolution Images ◽

Resolution Imaging

High-resolution imaging with a LaB6 instrument is limited by the spatial and temporal coherence, with little contrast remaining beyond the point resolution. A Field Emission Gun (FEG) reduces the incidence angle by a factor 5 to 10 and the energy spread by 2 to 3. Since the incidence angle is the dominant limitation for LaB6 the FEG provides a major improvement in contrast transfer, reducing the information limit to roughly one half of the point resolution. The strong improvement, predicted from high-resolution theory, can be seen readily in diffractograms (Fig. 1) and high-resolution images (Fig. 2). Even if the information in the image is limited deliberately to the point resolution by using an objective aperture, the improved contrast transfer close to the point resolution (Fig. 1) is already worthwhile.

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Calculating the aerodynamics of vertical axis wind turbines

Vietnam Journal of Mechanics ◽

10.15625/0866-7136/34/3/2358 ◽

2012 ◽

Vol 34 (3) ◽

pp. 169-184 ◽

Cited By ~ 1

Author(s):

Hoang Thi Bich Ngoc

Keyword(s):

Wind Turbine ◽

Incidence Angle ◽

Vertical Axis ◽

Rotor Blades ◽

Vertical Axis Wind Turbine ◽

Horizontal Axis Wind Turbine ◽

Velocity Triangle ◽

Relationship Of ◽

The Relationship

Vertical axis wind turbine technology has been applied last years, very long after horizontal axis wind turbine technology. Aerodynamic problems of vertical axis wind machines are discussible. An important problem is the determination of the incidence law in the interaction between wind and rotor blades. The focus of the work is to establish equations of the incidence depending on the blade azimuth, and to solve them. From these results, aerodynamic torques and power can be calculated. The incidence angle is a parameter of velocity triangle, and both the factors depend not only on the blade azimuth but also on the ratio of rotational speed and horizontal speed. The built computational program allows theoretically selecting the relationship of geometric parameters of wind turbine in accordance with requirements on power, wind speed and installation conditions.

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