A study of the aerodynamics of a generic container freight wagon using Large-Eddy Simulation

Equilibrium concepts are widespread in aeolian geomorphology The main objective of this chapter is to reflect critically on whether a new paradigm based on coherent flow structures (CFS) is beginning to emerge as an alternative to our current understanding of aeolian processes, which is predicated on time-averaged flow and transport assessments A survey of recent research addressing the existence and nature of CFS in aeolian systems indicates that: (1) there is as yet no convincing evidence in support of the classic bursting process or of any discrete flow structure with a characteristic topology (eg, hairpin vortex) for the case of near-surface boundary layer flow over flat sandy surfaces (with or without saltation); (2) there are instances when near-surface vortices of varying geometry are found in association with small obstacles (eg, logs, pebbles, vegetation clumps) on sandy surfaces, but it is not always apparent what the pattern of erosion or deposition in the vicinity of the obstacle will be given that there are additional controls that involve surface hardness and sediment delivery from upwind; (3) flow over aeolian dunes is generally well understood and very similar to flow over fluvial dunes with characteristic zonation, including flow acceleration and streamline compression on the stoss slope and a recirculation eddy and wake region in the lee; and (4) the importance of these dune-related flow zones to sediment transport response is more reliably understood through examination of a range of turbulence parameters (eg, Reynolds stress, turbulent kinetic energy) rather than mean flow quantities alone In order to advance our understanding of CFS in aeolian geomorphology, it will be essential to develop better technologies for high-frequency monitoring of wind and sediment flux, to focus attention on sediment transport events with specific topologies (eg, streamers) rather than attempt to capture flow events and hope that there is an accompanying transport signal, to move beyond simple quadrant analysis and adopt analytical methods that elucidate the time-history of event signatures, and to reformulate existing time-averaged parameterizations of sediment flux to incorporate event-based information in ways that are not immediately apparent

Critical Reflections on the Coherent Flow Structures Paradigm in Aeolian Geomorphology

Effects of leading edge geometry on the vortex shedding frequency of an elongated bluff body at high Reynolds numbers

Serviceability and running safety of the high-speed train on/through a bridge are of major concern in China. Due to the uncertainty chain of the train dynamic analysis in crosswinds originating mainly from the aerodynamic assessment, this paper primarily reviews five meaningful progresses on the aerodynamics of the train-bridge system done by Wind Tunnel Laboratory of Central South University in the past several years. Firstly, the flow around the train and the uncertainty origin of the aerodynamic assessment are described from the fluid mechanism point of view. After a brief introduction of the current aerodynamic assessment methods with their strengths and weaknesses, a new-developed TRAIN-INFRASTRUCTURE rig with the maximum launch speed of 35 m/s is introduced. Then, several benchmark studies are presented, including the statistic results of the characterized geometry parameters of the currently utilized bridge-decks, the aerodynamics of the train, and the aerodynamics of the flat box/truss bridge-decks. Upon compared with the foregoing mentioned benchmarks, this paper highlights the aerodynamic interference of the train-bridge system associated with its physical natures. Finally, a porosity- and orientation-adjustable novel wind barrier with its effects on the aerodynamics of the train-bridge system is discussed.

Review of aerodynamics of high-speed train-bridge system in crosswinds

POD analysis of momentumless trailing edge wake using synthetic jet actuation

Features of the turbulent flow around symmetric elongated bluff bodies

Computing power has increased substantially over the last several years. Along with developments in processing speed, the reliability of commercially available computational fluid dynamics (CFD) packages has also increased. The wind engineering community has long recognized the importance and difficulties of using CFD as a design tool [1]. The need has also been recognized to validate the results of these numerical simulations with both full scale and wind tunnel test data [2]. One of the simplest forms of a bluff body is the rectangular cylinder. Although the geometry is simple, the flow around such a body proves to be quite complicated and difficult to predict because of the separation at the leading edge, subsequent reattachment, and separation again at the trailing edge. Compounding this difficulty are possible interactions between vortices shed from the leading edge interacting with vortices shed from the trailing edge. Thus, this flow has many of the characteristics which make computation difficult in bluff body aerodynamics. There has been some work done to understand this flow [3,4]; however, there remains a need for research in order to develop algorithms for the numerical prediction of long-span bridge aerodynamics. In the current study an elongated rectangular cylinder with a chord to thickness (c:t) ratio of 7:1 in a flow of Re = 3x10 has been evaluated with a commercial CFD code. Experiments were also performed on the cylinder using Particle Image Velocimetry (PIV) and surface pressure measurements. The data presented reveals that there are important differences between the results of the CFD simulations and the experimental data.

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Comparisons of CFD and PIV data for the flow around a rectangular cylinder

Using Particle Image Velocimetry (PIV) we investigate the influence of leading and trailing edge geometry on the wake flows of various elongated cylinders in smooth uniform flow The results present a comparison between the mean wake flows, as well as the vortex shedding activity found to occur in each case Pressure measurements were recorded on the surface of the cylinders to examine the corresponding fluctuating and mean forces exhibited by each model tested Significant variations in the wake topology and aerodynamic behaviour of the four cylinder geometries tested were observedCopyright © 2006 by ASME

Particle Image Velocimetry Measurements of Wake Flows of Various Bridge Sections

Using Particle Image Velocimetry (PIV) we investigate the influence of leading and trailing edge geometry on the wake flows of various elongated cylinders in smooth uniform flow. The results present a comparison between the mean wake flows, as well as the vortex shedding activity found to occur in each case. Pressure measurements were recorded on the surface of the cylinders to examine the corresponding fluctuating and mean forces exhibited by each model tested. Significant variations in the wake topology and aerodynamic behaviour of the four cylinder geometries tested were observed.Copyright © 2006 by ASME

Emanuela Palombi

Papers

Features of the turbulent flow around symmetric elongated bluff bodies

Comparisons of CFD and PIV data for the flow around a rectangular cylinder

Particle Image Velocimetry Measurements of Wake Flows of Various Bridge Sections

Particle Image Velocimetry Measurements of Wake Flows of Various Bridge Sections