Experimental Study of Wake Shielding Effects of Three Cylinders in Currents

2004 ◽  
Author(s):  
Shan Huang ◽  
Jarle Bolstad ◽  
Adolfo Maro´n
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Experimental Work ◽  
Critical Reynolds Number ◽  
Flow Direction ◽  
Towing Tank ◽  
The Past ◽  
Number Of Publications ◽  
Shielding Effects

A large amount of experimental work has been carried out in the past to understand forces on a single cylinder in cross flows. In comparison substantially less work can be found on the interference between multiple cylinders and the number of publications available becomes drastically smaller as the number of cylinders involved increases. The current experimental work systematically examines the wake shielding effects of three cylinders by testing in a towing tank. Though staggered, the three cylinders are arranged mainly along the flow direction. The tests are carried out in the subcritical and critical Reynolds number regimes. Significant drag reduction on downstream cylinders is identified.

Spar VIM Model Tests at Supercritical Reynolds Numbers

2007 ◽  
Author(s):  
Tim Finnigan ◽  
Dominique Roddier
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Model Tests ◽  
Energy Technology ◽  
Testing Procedures ◽  
The Past ◽  
Critical Reynolds Numbers ◽  
Truss Spar ◽  
Number Of Publications

There have been a number of publications on spar Vortex-Induced-Motions (VIM) model testing procedures and results over the past few years. All tests allowing full 6 DOF response to date have been done under sub-critical Reynolds Number conditions. Tests under super-Critical Reynolds Number conditions have only been done with a fully submerged 1 DOF rig. Early in 2006, Chevron Energy Technology Company (CETC) completed a series of model tests to investigate the effect of Reynolds Number and hull appurtenances on spar vortex induced motions (VIM) for a vertically moored 6DOF truss spar hull model with strakes. Tests were done at both sub- and super-critical Reynolds Numbers, with matching Froude Numbers. In order to assess the importance of appurtenances (chains, pipes and anodes) and current heading on strake effectiveness, tests were done with several sets of appurtenances, and at various headings and reduced velocities. This paper addresses the challenges of performing spar VIM model tests at Super Critical Reynolds Numbers, and how they were resolved without the restrictions noted in earlier publications. Certain aspects of the effect of appurtenances and current heading on strake effectiveness and VIM response are discussed.

Primary instability of a shear-thinning film flow down an incline: experimental study

2017 ◽  
Vol 821 ◽  
Author(s):  
M. H. Allouche ◽  
V. Botton ◽  
S. Millet ◽  
D. Henry ◽  
S. Dagois-Bohy ◽  
...  
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Primary Stability ◽  
Shear Thinning ◽  
Driving Frequency ◽  
Neutral Curves ◽  
Theoretical Predictions ◽  
Sommerfeld Equation ◽  
Primary Instability

The main objective of this work is to study experimentally the primary instability of non-Newtonian film flows down an inclined plane. We focus on low-concentration shear-thinning aqueous solutions obeying the Carreau law. The experimental study essentially consists of measuring wavelengths in marginal conditions, which yields the primary stability threshold for a given slope. The experimental results for neutral curves presented in the $(Re,f_{c})$ and $(Re,k)$ planes (where $f_{c}$ is the driving frequency, $k$ is the wavenumber and $Re$ is the Reynolds number) are in good agreement with the numerical results obtained by a resolution of the generalized Orr–Sommerfeld equation. The long-wave asymptotic extension of our results is consistent with former theoretical predictions of the critical Reynolds number. This is the first experimental evidence of the destabilizing effect of the shear-thinning behaviour in comparison with the Newtonian case: the critical Reynolds number is smaller, and the ratio between the critical wave celerity and the flow velocity at the free surface is larger.

VIV Suppression and Drag Reduction With Pivoted Control Plates on a Circular Cylinder

2008 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Flow Direction ◽  
Cross Flow ◽  
Two Dimensional ◽  
Dimensional Control ◽  
Helical Strakes ◽  
Low Mass ◽  
Viv Suppression

Experiments have been carried out on two-dimensional devices fitted to a rigid length of circular cylinder to investigate the efficiency of pivoting control plates as VIV suppressors. Measurements are presented for a circular cylinder with low mass and damping which is free to respond in the cross-flow direction. It is shown how vortex-induced vibration can be practically eliminated by using free to rotate, two-dimensional control plates. Unlike helical strakes, the devices achieve VIV suppression with drag reduction. The device producing the largest drag reduction was found to have a drag coefficient equal to about 70% of that for a plain cylinder at the same Reynolds number.

scholarly journals Drag Reduction of a Turbulent Boundary Layer over an Oscillating Wall and Its Variation with Reynolds Number

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Martin Skote ◽  
Maneesh Mishra ◽  
Yanhua Wu
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Downstream Distance ◽  
The Past ◽  
Layer Flow ◽  
Reynolds Number Dependency ◽  
Downstream Development

Spanwise oscillation applied on the wall under a spatially developing turbulent boundary layer flow is investigated using direct numerical simulation. The temporal wall forcing produces a considerable drag reduction over the region where oscillation occurs. Downstream development of drag reduction is investigated from Reynolds number dependency perspective. An alternative to the previously suggested power-law relation between Reynolds number and peak drag reduction values, which is valid for channel flow as well, is proposed. Considerable deviation in the variation of drag reduction with Reynolds number between different previous investigations of channel flow is found. The shift in velocity profile, which has been used in the past for explaining the diminishing drag reduction at higher Reynolds number for riblets, is investigated. A new predictive formula is derived, replacing the ones found in the literature. Furthermore, unlike for the case of riblets, the shift is varying downstream in the case of wall oscillations, which is a manifestation of the fact that the boundary layer has not reached a new equilibrium over the limited downstream distance in the simulations. Taking this into account, the predictive model agrees well with DNS data. On the other hand, the growth of the boundary layer does not influence the drag reduction prediction.

Drag reduction on grooved cylinders in the critical Reynolds number regime

2013 ◽  
Vol 48 ◽  
pp. 15-18 ◽  
Author(s):  
Steven J. Quintavalla ◽  
Alexander J. Angilella ◽  
Alexander J. Smits
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Critical Reynolds Number

Influence of the Reynolds Number on Spar Vortex Induced Motions (VIM): Multiple Scale Model Test Comparisons

2009 ◽  
Author(s):  
Dominique Roddier ◽  
Tim Finnigan ◽  
Stergios Liapis
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Multiple Scale ◽  
Scale Model ◽  
Taylor Model ◽  
Testing Procedures ◽  
Critical Reynolds Numbers ◽  
Number Of Publications ◽  
Six Degree Of Freedom ◽  
First Time

There have been a number of publications on spar Vortex-Induced-Motions (VIM) model testing procedures and results over the past few years. All tests allowing full 6 DOF response to date have been done under sub-critical Reynolds Number conditions. Prior to 2006 tests under super-Critical Reynolds Number conditions had only been done with a fully submerged 1 DOF rig. Early in 2006, a series of Spar VIM experiments was undertaken in three different facilities: Force Technology in Denmark, the David Taylor Model Basin in Bethesda Maryland and UC Berkeley in California. The motivation of this work was to investigate the effect of Reynolds Number and hull appurtenances on spar vortex induced motions (VIM) for a vertically moored 6DOF truss spar hull model with strakes. The three series of tests were done at both sub and super-critical Reynolds Numbers, with matching Froude Numbers. In order to assess the importance of appurtenances (chains, pipes and anodes) and current heading on strake effectiveness, tests were done with several sets of appurtenances, and at various headings and reduced velocities. These experiments were unique and groundbreaking in many ways: • For the first time the issue of scalability of Spar VIM experiments has been addressed and tested in a systematic way. • For the first time the effect of appurtenances (pipes, chains and anodes) was systematically tested. • The model tested at the David Taylor Model Basin (DTMB) had a diameter of 5.8′ and a weight of 15,600 lbs. It is the largest spar model ever tested. Furthermore the DTMB tests series is the only supercritical spar VIM performed with a six degree of freedom (6DOF) rig. This paper describes the three model tests campaigns, focusing on the efforts made to ensure three complete geo-similar programs, and on the significant findings of these tests, effectively that the influence of Re is to add some conservativeness in the results as the testing scale is smaller.

Improvement on Aerodynamic Characteristics and Drag Reduction for Supermileage Cars with Wide View Field

2016 ◽  
Vol 366 ◽  
pp. 47-62
Author(s):  
Pey Shey Wu ◽  
Min Jho Young ◽  
Jun Yun Wu ◽  
Chia Chian Wang ◽  
Hao Yu Hu ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Flow Direction ◽  
Aerodynamic Characteristics ◽  
Total Drag ◽  
Design Concepts ◽  
The Past ◽  
Traditional Design ◽  
New Concepts ◽  
Analytical Verification

Aerodynamic characteristics of three supermileage car chassis with new design concepts for improving the driver’s view field and driving comfort is investigated and compared with that of one with traditional low-height design. New car shapes with shorter axle distance and higher center of gravity are created. Feasibility of the new design is verified from the aspects of rollover safety, due to the maximum crosswind speed of 40 km/h, and the drag coefficient at straight driving up to 40 km/h. The analytical verification is conducted with a commercial CFD software. Comparing to the traditional design, the analysis shows that it is possible to obtain a lower drag coefficient and lower total drag, while rollover safety is still guaranteed, for a supermileage car with wider view field and taller appearance. Reduction of the form drag is intimately related to the decrease of velocity curl in the flow direction and the size of the vortices in the wake. Results of this study can provide new concepts that are different from those used in the past for the development of supermileage cars.

scholarly journals Toward design of the antiturbulence surface exhibiting maximum drag reduction effect

2018 ◽  
Vol 850 ◽  
pp. 262-303 ◽  
Author(s):  
V. Krieger ◽  
R. Perić ◽  
J. Jovanović ◽  
H. Lienhart ◽  
A. Delgado
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Stokes Equations ◽  
Flow Direction ◽  
Friction Reduction ◽  
Navier Stokes ◽  
Channel Height ◽  
Initial Flow ◽  
Flat Wall ◽  
Flow Development

The flow development in a groove-modified channel consisting of flat and grooved walls was investigated by direct numerical simulations based on the Navier–Stokes equations at a Reynolds number of $5\times 10^{3}$ based on the full channel height and the bulk velocity. Simulations were performed for highly disturbed initial flow conditions leading to the almost instantaneous appearance of turbulence in channels with flat walls. The surface morphology was designed in the form of profiled grooves aligned with the flow direction and embedded in the wall. Such grooves are presumed to allow development of only the statistically axisymmetric disturbances. In contrast to the rapid production of turbulence along a flat wall, it was found that such development was suppressed over a grooved wall for a remarkably long period of time. Owing to the difference in the flow structure, friction drag over the grooved wall was more than 60 % lower than that over the flat wall. Anisotropy-invariant mapping supports the conclusion, emerging from analytic considerations, that persistence of the laminar regime is due to statistical axisymmetry in the velocity fluctuations. Complementary investigations of turbulent drag reduction in grooved channels demonstrated that promotion of such a state across the entire wetted surface is required to stabilize flow and prevent transition and breakdown to turbulence. To support the results of numerical investigations, measurements in groove-modified channel flow were performed. Comparisons of the pressure differentials measured along flat and groove-modified channels reveal a skin-friction reduction as large as $\text{DR}\approx 50\,\%$ owing to the extended persistence of the laminar flow compared with flow development in a flat channel. These experiments demonstrate that early stabilization of the laminar boundary layer development with a grooved surface promotes drag reduction in a fully turbulent flow with a preserving magnitude as the Reynolds number increases.

scholarly journals An experimental study of the motion of a light sphere in a rotating viscous fluid

2018 ◽  
Vol 847 ◽  
pp. 119-133 ◽  
Author(s):  
T. Sauma-Pérez ◽  
C. G. Johnson ◽  
L. Yang ◽  
T. Mullin
Keyword(s):  
Experimental Study ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Viscous Fluid ◽  
Fixed Points ◽  
Critical Reynolds Number ◽  
Solid Sphere ◽  
Rotating Cylinder ◽  
Quantitative Agreement ◽  
Rotation Rates

We present the results of an experimental investigation of the motion of a light, solid sphere in a horizontal rotating cylinder filled with viscous fluid. At high rotation rates, the sphere sits near the axis of the cylinder. At lower rotation rates, a set of off-axis fixed points are observed for a range of sphere radii. The locations of these fixed points are in quantitative agreement with the predictions of a model based on available theory. The fixed points are observed to become unstable to periodic orbits below a critical Reynolds number $Re_{c}$. The radius of the observed orbits increases with Reynolds number more slowly than a typical Hopf bifurcation, in this case, growing as $1/Re^{2}$.

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