A Comparative Study Between DNS, LES and PIV for a Marine Riser With Fairings

2015 ◽  
Author(s):  
Håkon Strandenes ◽  
José Patricio Gallardo Canabes ◽  
Jan Visscher ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Bluff Body ◽  
Mean Flow ◽  
Surface Integral ◽  
Circulating Water ◽  
Flow Parameters ◽  
Image Velocimetry ◽  
Drag And Lift ◽  
Recirculation Length ◽  
Bluff Body Wake

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.

INVESTIGATION ON FLOW STRUCTURE BEHIND A RING BY IMPLEMENTING OPTICAL PARTICLE CHARACTERIZATIONS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4511-4516
Author(s):  
CHEOL WOO PARK
Keyword(s):  
Flow Structure ◽  
Bluff Body ◽  
Water Channel ◽  
Cross Flow ◽  
Circular Ring ◽  
Outer Side ◽  
Mean Velocity ◽  
Circulating Water ◽  
Image Velocimetry ◽  
Bluff Body Wake

The flow structure behind circular and elliptical type rings embedded in a cross-flow was investigated experimentally using a particle image velocimetry (PIV), implementing optical particle characterizations. The experiments were performed in a circulating water channel with a test section of 0.2m height × 0.3m width × 1.2m length. The Reynolds number based on the ring hoop cord length is about Re =1200. The velocity fields near the ring hoop were measured using the two-frame cross-correlation PIV method. As a result, the flow near the sharp-edged end of ring hoop ascends fast and showed a conventional vortical structure appeared in a bluff body wake. In the mean velocity field behind a circular ring, there were two large vortices rotating in different directions from each other in the near wake regime caused by the interaction between the central jet flow and the entrained ambient fluids from outer side of ring hoop.

Investigation of Mean and Turbulent Flow Behaviour Over an Escarpment

2016 ◽  
Author(s):  
R. Kilpatrick ◽  
K. Siddiqui ◽  
H. Hangan ◽  
D. Parvu
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Behaviour ◽  
Scale Model ◽  
Mean Flow ◽  
Scaled Model ◽  
Energy And Environment ◽  
Flow Parameters ◽  
Image Velocimetry ◽  
Bolund Hill

Mean and turbulent flow behaviour over a 1:25 scale model of Bolund hill was investigated at Western University’s Wind Engineering, Energy, and Environment Research Institute (WindEEE) using Particle Image Velocimetry (PIV). A range of upstream flow and surface conditions were considered. Results showed almost no Reynolds dependency on the mean flow and weak dependency of Reynolds number on the upstream surface roughness conditions. However, a strong Reynolds number and upstream surface rough dependency is observed on the turbulent flow particularly in the shear layer formed in the immediate downstream region of the escarpment. It is concluded that the consideration of Reynolds number independency must be cautiously used when extrapolating the flow parameters from scaled model testing to full scale in the field.

scholarly journals Moving Surface Actuation, Effects of Frequency-based Shear Layer Excitation on the Response of a Bluff Body Wake

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Matthew Singbeil ◽  
Calin Ghiroaga ◽  
Chris Morton ◽  
Robert Martinuzzi
Keyword(s):  
Velocity Field ◽  
Bluff Body ◽  
Sensor Data ◽  
Reynolds Stresses ◽  
Actuation Frequency ◽  
Nsga Ii ◽  
Moving Surface ◽  
Image Velocimetry ◽  
Pod Analysis ◽  
Bluff Body Wake

The effect of actuation frequency, using moving surface actuation, is investigated for a square cylinder bluff body wake. Pressure sensor data are used to optimize actuation characteristics through the implementation of an NSGA-II evolutionary algorithm. Velocity field data are obtained using Particle Image Velocimetry (PIV) for baseline and optimized actuation cases. A Proper Orthogonal Decomposition (POD) analysis shows that the vortex shedding frequency shifts between frequencies associated with the actuation, moving between regions of lock-on and quasi-periodicity. Additionally, the POD shows that the energy contained in the coherent shedding motion is reduced through actuation, while the total energy in the velocity field stays relatively constant. A reconstruction of the first 10 POD modes indicates that the coherent contribution to the Reynolds stresses significantly decreases compared to the non-actuated case. The mechanism for drag reduction is investigated using the shed circulation flux and Kochin’s drag formulation model. The drag obtained using PIV measurements and Kochin’s formulation is consistent with trends observed for the base pressure as a function of actuation frequency.

scholarly journals Unravelling turbulence near walls

2009 ◽  
Vol 630 ◽  
pp. 1-4 ◽  
Author(s):  
IVAN MARUSIC
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Turbulent Flows ◽  
Direct Numerical Simulations ◽  
Aircraft Wing ◽  
Physical Mechanisms ◽  
Drag And Lift

Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for example. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct numerical simulations have contributed significantly towards this understanding.

Aerodynamic Characteristics of Asymmetric Bluff Bodies

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
J. C. Hu ◽  
Y. Zhou
Keyword(s):  
Bluff Body ◽  
Laser Doppler Anemometry ◽  
Vortex Formation ◽  
Aerodynamic Characteristics ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Freestream Velocity ◽  
Drag And Lift ◽  
Particle Imaging ◽  
Visualization Techniques

The wake of asymmetric bluff bodies was experimentally measured using particle imaging velocimetry, laser Doppler anemometry, load cell, hotwire, and flow visualization techniques at Re=2600–8500 based on the freestream velocity and the characteristic height of the bluff bodies. Asymmetry is produced by rounding some corners of a square cylinder and leaving others unrounded. It is found that, with increasing corner radius, the flow reversal region is expanded, and the vortex formation length is prolonged. Accordingly, the vortex shedding frequency increases and the base pressure rises, resulting in a reduction in the mean drag as well as the fluctuating drag and lift. It is further found that, while the asymmetric cross section of the cylinder causes the wake centerline to shift toward the sharp corner side of the bluff body, the wake remains globally symmetric about the shifted centerline. The near wake of asymmetric bluff bodies is characterized in detail, including the Reynolds stresses, characteristic velocity, and length scale, and is further compared with that of the symmetric ones.

Scale-to-scale anisotropy in homogeneous turbulence

2017 ◽  
Vol 827 ◽  
pp. 250-284 ◽  
Author(s):  
Douglas W. Carter ◽  
Filippo Coletti
Keyword(s):  
Large Scale ◽  
Velocity Structure ◽  
Longitudinal Velocity ◽  
Reynolds Numbers ◽  
Homogeneous Turbulence ◽  
Mean Flow ◽  
Spatially Correlated ◽  
Air Jets ◽  
Image Velocimetry ◽  
Definition Of

We experimentally investigate scale-to-scale anisotropy from the integral to the dissipative scales in homogeneous turbulence. We employ an apparatus in which two facing arrays of randomly actuated air jets generate turbulence with negligible mean flow and shear, over a volume several times larger than the energy-containing eddy size. The Reynolds number based on the Taylor microscale is varied in the range$Re_{\unicode[STIX]{x1D706}}\approx 300{-}500$, while the axial-to-radial ratio of the root mean square velocity fluctuations ranges between 1.38 and 1.72. Two velocity components are measured by particle image velocimetry at varying resolutions, capturing from the integral to the Kolmogorov scales and yielding statistics up to sixth order. Over the inertial range, the scaling exponents of the velocity structure functions are found to differ not only between the longitudinal and transverse components, but also between the axial and radial directions of separation. At the dissipative scales, the moments of the velocity gradients indicate that departure from isotropy is, at the present Reynolds numbers, significant and more pronounced for stronger large-scale anisotropy. The generalized flatness factors of the longitudinal velocity differences tend towards isotropy as the separation is reduced from the inertial to the near-dissipative scales (down to about$10\unicode[STIX]{x1D702}$,$\unicode[STIX]{x1D702}$being the Kolmogorov length), but become more anisotropic for even smaller scales which are characterized by high intermittency. At the large scales, the direction of turbulence forcing is associated with a larger integral length, defined as the distance over which the velocity component in a given direction is spatially correlated. Because of anisotropy, the definition of the integral length is not trivial and may lead to dissimilar conclusions on the qualitative behaviour of the large scales and on the quantitative values of the normalized dissipation. Alternative definitions of these quantities are proposed to account for the anisotropy. Overall, these results highlight the importance of evaluating both the different velocity components and the different spatial directions across all scales of the flow.

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