Vortex interaction in patches of randomly placed emergent cylinders

The flow field of multiple-cylinder configurations exhibits complex interactions between shear layers, vortexes and wakes. For high stem-Reynolds numbers, the flow is turbulent and, low and intermediate areal number-densities of cylinders, and turbulence is produced mostly by the work of Reynolds shear stresses in the horizontal plane (uv component) against the time-averaged shear rate characteristic of vertical-axis vortex shedding in the wake of cylinders. The spatial pattern of turbulent production and of other terms of the equation of conservation of Turbulent Kinetic Energy (TKE) is thus mostly determined by the interaction of vortexes shed by individual cylinders and by the distance between cylinders. The main objective of this paper is to advance on the understanding of vortex interaction in patches of randomly placed emergent and rigid cylinders. In particular, the relation between cylinder Strouhal numbers, vortex decay and vortex path statistics is investigated for isolated cylinder and for a cylinder within an array of randomly placed cylinders with a areal-number density of 980 cylinders/m2. Results are compared to shed light on the influence of neighbouring cylinders. An experimental database acquired with 2D Particle Image Velocimetry (PIV) was explored. A methodology to detect vortexes in 2D flow fields is proposed. It features a point-based criterion and a global search to detect all the possible vortex core locations, combined with a curve-based criterion, to decide whether the detected point corresponds to a vortex, depending on the geometry of streamlines. The results show a decrease on the amount of vortexes and a shorter vortex life for the cylinder within the array when compared with the isolated cylinder. The averaged vortex path is also affected by the presence of neighbouring cylinders. Concerning the Strouhal number, the normalized shedding frequency is approximately the same for both studied cases

Flow-structure-seabed interactions in coastal and marine environments

Flow–structure–seabed interaction in coastal and marine environments is a rapidly growing area of research and applications. In this vision paper, this area is discussed with a view of identifying its state of the art and current research challenges. The discussion draws attention to key issues related to structures such as marine pipelines, offshore windfarms, and multiuse offshore platforms. Tsunamis, which received considerable attention after two recent extreme events (2004 Indonesia tsunami and 2011 Japan tsunami) are also included in the discussion. Marine hydro-geomechanics is highlighted, among other areas, as an emerging branch of Marine Civil Engineering. Predictions of the field development for the forthcoming years are also briefly outlined."b

Base Pressure Measurements on a Circular Cylinder in Subsonic Cross Flow

A circular cylinder was tested in cross flow over the subsonic speed range. Timeresolved pressure distributions give information on surface pressure fluctuations and the corresponding drag and base drag coefficients are provided. The Strouhal number variation is compared with the measurements of other authors. Flow changes at higher subsonic velocities and into the transonic range are described. At Mach numbers above 0.6 the changing strength of the vortices reduces the base drag coefficient up to a Mach number of 0.9, where the onset of sonic flow increases the drag. Time-resolved base pressure fluctuations at low Mach numbers are in agreement with the findings of other researchers with regard to the relative time spent in vortex formation and shedding. As the Mach number increases the time spent in vortex formation becomes equal to that spent in shedding. The paper concentrates on providing detailed base pressure data rather than attempting to produce universal correlations. Physical explanations have been given, where possible, to assist toward a more general modeling of the problem.Peer reviewed: YesNRC publication: Ye