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The flow around tapered cylinders can act as basic models for numerous bluff body flows with a spanwise variation of either the body shape or the inflow conditions. The well-known vortex street is influenced by strong three-dimensional effects from the spanwise variation of the shedding frequency, namely oblique vortex shedding and vortex dislocations. Stereo-PIV was chosen to study these phenomena, since it allows analyzing planes with the full three-component, instantaneous velocity fields and local, time-dependent variations in the same setting. Hence, detailed aspects of the vortex dislocation phenomenon are presented. Single vortex dislocation events are presented through the local variation of the three measured velocity components u, v and w. Longer time-series reveal both period and location of these dislocation events, as well as quantity and sizes of the cells of constant shedding velocity in between them. The influence of the Reynolds number and the cylinder aspect ratio on the vortex cells could be shown. The analysis of the vortex shedding behavior shows good agreement with previously published results. At the same time, the applied PIV technique provides more spatial information than point-based measurements and offers insight into a Reynolds number range that is currently out of reach of Direct Numerical Simulations.

This paper present results from numerical simulations and laboratory experiments investigating the flow around a riser with fairings at Reynolds number of 5000. We present fully resolved direct numerical simulations (DNS), large eddy simulations (LES) and compare the results with flowfields obtained from particle image velocimetry (PIV) experiments in a circulating water tunnel. The DNS and LES results do agree very well on surface integral quantities such as drag and lift force, but there are discrepancies in first order statistical flow parameters such as recirculation length. This indicate that a comparison of force coefficients is not sufficient to validate this type of bluff body wake flows. Comparing the simulation data with the experimental PIV data, also reveals significant discrepancies in the mean flow field, although the Strouhal number agrees between DNS and PIV results.Copyright © 2015 by ASME

This paper reports calculations of three dimensional (3D) unsteady cross flow over two ship sections in close proximity and compares the results with measurements. The ship sections have different breadth and draft, and represent typical situations in a ship-to-ship marine operation in a cross current. The behavior of the vortex-shedding around the two different ship hull sections is investigated numerically by CFD methods and experiments. For the two sections, simulations are done for several Reynolds numbers by using the dynamic Smagorinsky Large Eddy Simulation (LES) turbulence model. Finally the cross flow past the ship sections in side-by-side position is simulated and vortex interaction between the sections is found by using the software (Ansys) FLUENT. The numerical predictions are compared with PIV results taken in a circulating water tunnel.Copyright © 2014 by ASME

In hydrodynamic model testing, the choice of the scaling factor is often a compromise between the size of the facility and close matching of the characteristic numbers such as Reynolds and Froude. When combining the two aspects into model testing of offshore floating wind turbines, limitations on the size of the model test facilities apply and it is not possible to use both Froude and Reynolds number scaling effects at the same time. To investigate Reynolds number similarity, two wing geometries, a NACA 0012 and a NREL S825 were manufactured in several sizes and tested at identical Reynolds numbers. The wakes behind the airfoils were measured using Particle Image Velocimetry. One would expect to obtain similar results, but differences in the wake profiles were observed. Understanding the mechanisms involved are important as it then enables model building techniques to be improved, and thus make model testing more effective.Copyright © 2013 by ASME

The present experimental investigation focuses on the flow structure around short free end cylinders with an aspect ratio of L/D = 3 at a Reynolds number of Re = 5000. Cylinders with varying degrees of inclination and porosity were tested in a towing tank, acting as models for fish farm cages. According to studies of fish cages at commercial Norwegian fish farms, the inclination angle of the structure change up to 25 degrees from the vertical when exposed to a current. Cylinders with porosities of 0% and 75% were tested, the latter representing fish cage netting with fouling. To visualize the flow around the cylinders, 2- and 3-Component (2C and 3C) Particle Image Velocimetry (PIV) was used. The effects of inclination and porosity on the three-dimensional flow field will be described and discussed.Copyright © 2008 by ASME

Measurements of instantaneous velocity fields in the separated flow downstream of a backward-facing step in a rotating channel are presented for the first time. Particle image velocimetry (PIV) measurements were made for 13 different rotation numbers Ro at a bulk flow Reynolds number of about 5600. The expansion ratio 2:1 was the same as in the flow visualization study by Rothe and Johnston [ASME J. Fluids Eng. 101, 117 (1979)] which covered about the same range of Ro. The measured mean flow pattern exhibited substantial variations with the rate of system rotation. In particular, the length of the primary separation bubble decreased monotonically with increasing anti-cyclonic rotation and increased with increasing rate of cyclonic rotation, in keeping with the earlier observations. At the highest anti-cyclonic rotation rate, the flow field also separated from the planar wall where the shear layer flow was subjected to cyclonic rotation. The PIV data for the in-plane components of the Reynolds stress tenso...