Brief Reviews of Some Time-Dependent Flows

1992 ◽  
Vol 114 (3) ◽  
pp. 283-298 ◽  
Author(s):  
T. Sarpkaya
Keyword(s):  
Three Dimensional ◽  
Separated Flows ◽  
Time Dependent ◽  
Circular Cylinders ◽  
Vortical Structures ◽  
Unsteady Separation ◽  
Flow Phenomena ◽  
Fundamental Research ◽  
The Subject ◽  
New Research

Separated flows in general and time-dependent flows in particular provide fertile territory for fundamental research in fluid dynamics and account for much of the subject matter. Thus, it is thought appropriate to review some of these unsteady flows with special emphasis on hydrodynamic applications which are, admittedly, of special interest to this writer: unsteady separation; characteristics of impulsively and nonimpulsively-started flow about cylinders; excursion of separation points on circular cylinders in oscillating flow; separation and other flow phenomena governing the unsteady maneuvers of large submerged bodies, and, finally, the three-dimensional footprints of subsurface vortical structures rising toward the free surface. It is hoped that these concise reviews will enhance communication between various groups of researchers, draw attention to many exciting phenomena in naval hydrodynamics, and inspire new research topics.

Large Eddy Simulation of a Vortex Ring Impacting a Bump

2014 ◽  
Vol 6 (3) ◽  
pp. 261-280
Author(s):  
Heng Ren ◽  
Ning Zhao ◽  
Xi-Yun Lu
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Ring ◽  
Three Dimensional ◽  
Vortical Flow ◽  
Flow State ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Phenomena ◽  
Flow Evolution

AbstractA vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial diameter and translational speed of the vortex ring. The effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are investigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump surface. The circulation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Further, the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent state. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

Three-Dimensional Flow Pattern Upstream of a Surface-Mounted Rectangular Obstruction

1989 ◽  
Vol 111 (4) ◽  
pp. 449-456 ◽  
Author(s):  
K. Y. M. Lai ◽  
A. H. Makomaski
Keyword(s):  
Saddle Point ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Computer Code ◽  
Experimental Results ◽  
Circular Cylinders ◽  
Vortex Model ◽  
Flow Phenomena ◽  
The One ◽  
Corner Vortex

A three-dimensional TEACH-like computer code is developed and employed to study the flow phenomena upstream of a rectangular obstruction placed in a two-dimensional turbulent boundary layer. Satisfactory comparison is obtained with the experimental results of Blair (1984, 1987). The general trends, regarding the dependence of vortex dimensions, wall static pressure distributions and saddle point positions on Re = U∞δ*/ν and on D* = D/δ*, are similar to the experimental results for circular cylinders (Eckerle and Langston, 1986 and Baker, 1980). The position of the saddle point depends on the turbulence intensity in the primary vortex. The pressure coefficient at the foot of the obstruction depends solely on D* if no corner vortex exists. This coefficient is reduced when a corner vortex is present. All the computed flow patterns are similar to the one-vortex model of Eckerle and Langston (1986). The four-vortex model reported by Baker (1980) and Hunt et al. (1978) cannot be found in any of the calculations.

scholarly journals Aerodynamic coefficients and pressure distribution on two circular cylinders with free end immersed in experimentally produced downburst-like outflows

2020 ◽  
pp. 136943322095876
Author(s):  
Djordje Romanic ◽  
Andrea Ballestracci ◽  
Federico Canepa ◽  
Giovanni Solari ◽  
Horia Hangan
Keyword(s):  
Pressure Distribution ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Wind Loading ◽  
Dominant Factor ◽  
Aerodynamic Coefficients ◽  
Transient Phenomena ◽  
Fundamental Research ◽  
Drag And Lift ◽  
Different Diameters

Thunderstorms winds are localized and transient phenomena characterized by three-dimensional non-stationary velocity fields. While numerous studies investigated the wind loading on cantilevered structures under thunderstorm downburst winds, there is a lack of fundamental research on the behavior of simple circular cylinders subjected to downburst-like outflows. This paper investigates the pressure distribution and aerodynamic coefficients of two cylinders with different diameters immersed in three different types of wind: (1) isolated downburst (DB); (2) downburst embedded in an atmospheric boundary layer (ABL) wind (DBABL); and (3) steady ABL wind. The focus of this study is to provide a comparative analysis between aerodynamic coefficients (drag and lift) and surface pressures that result from these three different wind systems. The ABL winds caused a higher drag on the thinner cylinder than the two DB-like outflows. The lift coefficients during the primary vortex passage in the DB-like outflows were negative at the base of the cylinders and approached zero or to slightly positive values close to the cylinders’ top. The location of the cylinders in DB-like outflows is the dominant factor for their aerodynamics.

Nonlinear flow phenomena in a symmetric sudden expansion

1990 ◽  
Vol 211 ◽  
pp. 595-608 ◽  
Author(s):  
R. M. Fearn ◽  
T. Mullin ◽  
K. A. Cliffe
Keyword(s):  
Symmetry Breaking ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Time Dependent ◽  
Nonlinear Flow ◽  
Sudden Expansion ◽  
Numerical Techniques ◽  
Flow Phenomena ◽  
Asymmetric Flows ◽  
Good Agreement

The origin of steady asymmetric flows in a symmetric sudden expansion is studied using experimental and numerical techniques. We show that the asymmetry arises at a symmetry-breaking bifurcation and good agreement between the experiments and numerical calculations is obtained. At higher Reynolds numbers the flow becomes time-dependent and there is experimental evidence that this is associated with three-dimensional effects.

A summary of measurements of steady and oscillatory pressures on a rectangular wing

1988 ◽  
Vol 92 (911) ◽  
pp. 10-28 ◽  
Author(s):  
D. G. Mabey ◽  
B. L. Welsh ◽  
C. R. Pyne
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Wind Tunnel ◽  
Perturbation Methods ◽  
Three Dimensional ◽  
Separated Flows ◽  
Time Dependent ◽  
Angle Of Incidence ◽  
Pressure Measurements ◽  
Three Dimensional Configuration

Summary This paper describes a series of steady and time-dependent pressure measurements on a half-model of a rectangular wing of aspect ratio 4. The wing was mounted on a half-body attached to a sidewall of the RAE 8 x 8 ft wind tunnel and the tests were made at Mach numbers of 0·20, 0·42, 0·70, 0·80 and 0·85 with fixed transition and a Reynolds number of about 2·5 x 106 at the highest Mach number. The wing was oscillated about its mid-chord axis at four frequencies giving frequency parameters up to 1·15 at M = 0·20 and 0·25 at M = 0·85. The static angle of incidence was varied from –10° to + 10°. Selected mean and oscillatory measurements are offered as a challenge to computational fluid dynamicists for this simple three-dimensional configuration. Comparisons are made with calculations by means of subsonic linearised theory and recent transonic small perturbation methods. The measurements are of particular interest at transonic speeds, where both attached and incipient separated flows are considered.

Velocity Perturbations Induced by the Longitudinal Vortices in a Cylinder Wake

1996 ◽  
Vol 118 (3) ◽  
pp. 531-536 ◽  
Author(s):  
J. Wu ◽  
J. Sheridan ◽  
M. C. Welsh
Keyword(s):  
Three Dimensional ◽  
Vortex Pair ◽  
Circular Cylinders ◽  
Cylinder Wake ◽  
Wake Region ◽  
Near Wake ◽  
Vortical Structures ◽  
Longitudinal Vortices ◽  
Piv Technique ◽  
Image Velocimetry

This paper presents data showing the three-dimensional vortical structures in the near wake region of circular cylinders. The in-plane velocity field was measured using a digital Particle Image Velocimetry (PIV) technique. The vortical structures are found to include inclined counter-rotating longitudinal vortices in the braids joining consecutive Ka´rma´n vortices. A simple vortex-pair model is proposed to estimate velocity perturbation induced by the longitudinal vortices in the near wake region. The perturbation resulting from the longitudinal vortices is shown to induce spanwise velocity modulation and a velocity spike of a nominally two-dimensional vortex street.

Performance Management Transformation

2020 ◽  
Keyword(s):  
Organizational Performance ◽  
Performance Management ◽  
High Performance ◽  
Best Practice ◽  
Call To Action ◽  
Daily Work ◽  
The Past ◽  
Great Debate ◽  
The Subject ◽  
New Research

No other talent process has been the subject of such great debate and emotion as performance management (PM). For decades, different strategies have been tried to improve PM processes, yielding an endless cycle of reform to capture the next “flavor-of-the-day” PM trend. The past 5 years, however, have brought novel thinking that is different from past trends. Companies are reducing their formal processes, driving performance-based cultures, and embedding effective PM behavior into daily work rather than relying on annual reviews to drive these. Through case studies provided from leading organizations, this book illustrates the range of PM processes that companies are using today. These show a shift away from adopting someone else’s best practice; instead, companies are designing bespoke PM processes that fit their specific strategy, climate, and needs. Leading PM thought leaders offer their views about the state of PM today, what we have learned and where we need to focus future efforts, including provocative new research that shows what matters most in driving high performance. This book is a call to action for talent management professionals to go beyond traditional best practice and provide thought leadership in designing PM processes and systems that will enhance both individual and organizational performance.

Thermodynamics of Flowing Systems: with Internal Microstructure

1994 ◽  
Author(s):  
Antony N. Beris ◽  
Brian J. Edwards
Keyword(s):  
Free Energy ◽  
Theoretical Study ◽  
Flow Behavior ◽  
Irreversible Thermodynamics ◽  
Hamiltonian Mechanics ◽  
Complex Interplay ◽  
Microscopic Models ◽  
Flow Phenomena ◽  
The Subject ◽  
The Continuum

This much-needed monograph presents a systematic, step-by-step approach to the continuum modeling of flow phenomena exhibited within materials endowed with a complex internal microstructure, such as polymers and liquid crystals. By combining the principles of Hamiltonian mechanics with those of irreversible thermodynamics, Antony N. Beris and Brian J. Edwards, renowned authorities on the subject, expertly describe the complex interplay between conservative and dissipative processes. Throughout the book, the authors emphasize the evaluation of the free energy--largely based on ideas from statistical mechanics--and how to fit the values of the phenomenological parameters against those of microscopic models. With Thermodynamics of Flowing Systems in hand, mathematicians, engineers, and physicists involved with the theoretical study of flow behavior in structurally complex media now have a superb, self-contained theoretical framework on which to base their modeling efforts.

Geological Field Sketches and Illustrations

2019 ◽  
Author(s):  
Matthew J. Genge
Keyword(s):  
Cross Sections ◽  
Earth Science ◽  
Three Dimensional ◽  
Worked Examples ◽  
Scientific Publications ◽  
Thin Sections ◽  
Geological Features ◽  
Different Types ◽  
The Subject

Drawings, illustrations, and field sketches play an important role in Earth Science since they are used to record field observations, develop interpretations, and communicate results in reports and scientific publications. Drawing geology in the field furthermore facilitates observation and maximizes the value of fieldwork. Every geologist, whether a student, academic, professional, or amateur enthusiast, will benefit from the ability to draw geological features accurately. This book describes how and what to draw in geology. Essential drawing techniques, together with practical advice in creating high quality diagrams, are described the opening chapters. How to draw different types of geology, including faults, folds, metamorphic rocks, sedimentary rocks, igneous rocks, and fossils, are the subjects of separate chapters, and include descriptions of what are the important features to draw and describe. Different types of sketch, such as drawings of three-dimensional outcrops, landscapes, thin-sections, and hand-specimens of rocks, crystals, and minerals, are discussed. The methods used to create technical diagrams such as geological maps and cross-sections are also covered. Finally, modern techniques in the acquisition and recording of field data, including photogrammetry and aerial surveys, and digital methods of illustration, are the subject of the final chapter of the book. Throughout, worked examples of field sketches and illustrations are provided as well as descriptions of the common mistakes to be avoided.

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