Influence of surface roughness on the wake structure of a circular cylinder at Reynolds number 5 × 10 to 12 × 10
Introduction
Circular cylinders often find applications in the form of cables, rods, etc. as parts of structural or mechanical engineering structures. These cylinders as so-called substructures are subjected to fluid and air loading, and their response to this loading can have in the worst cases destructive effects. The cables or rods are often assumed to have perfect circular cross-sections. However, in many cases the circular cross-section is disturbed by various influences, e.g. manufacturing processes. Either way, the perfect circularity disappears and some kind of surface roughness is created. In particular, climatic conditions (ice accretion) define the so-called climatic roughness, and geometrical deviations, corrosion and other surface changes define the so-called technological roughness.
Flow around circular cylinders with various surface changes has been studied by many authors. Zdravkovich [1] made an overview of flow past smooth and rough cylinders by means of Strouhal number and drag analysis. Adachi [2] measured Strouhal numbers on eight cylinders with various surface roughness over a wide range of Reynolds numbers. Buresti [3] studied the influence of surface roughness on transition between subcritical up to postcritical flow regimes around circular cylinders. Various surface roughness profiles of cylinders were tested by Fuss [4], and significant changes in drag were observed in the critical Reynolds number range. Many researchers have tried to increase the cylinder surface roughness with grooves, fabric covering or other methods in order to shift the drag crisis into lower Reynolds numbers and therefore reduce the drag. Skeide et al. [5] reduced the drag of the cylinder with the use of hydrophobised sand. Sooraj et al. [6] studied the flow over a superhydrophobic and smooth cylinder using particle image velocimetry (PIV). They found that superhydrophobicity substantially affects the flow in terms of drag reduction and changes in near-wake coherent structures.
Besides experimental work, a growing number of numerical simulations are also being done. Rodrigues et al. [7], [8] employed large-eddy simulation (LES) of the roughness effects on the wake of a circular cylinder. Michalcova and Lausova [9] numerically determined the aerodynamic roughness of industrial chimneys. Flow over rough cylinders is also applicable in ocean engineering, as underwater surfaces are often covered with aquatic organisms which change the flow regime around the structure. Zeinoddini et al. [10] investigated the effects of vortex-induced vibrations (VIV) on circular cylinders with regular pyramidal roughness. They found that VIV amplitude, drag coefficient and other parameters were decreased by the roughness. Gao et al. [11] studied the effects of surface roughness on the VIV of a flexible cylinder with the finding that rough cylinders have a smaller displacement response and a higher vortex shedding frequency than smooth cylinders. Drag reduction was also studied for the purpose of sports aerodynamics. Terra et al. [12] measured the drag of the surfaces of cylinders roughened with fabric used in sports clothing. Khashehchi et al. [13] investigated the wake behind finned and foamed cylinders and incorporated the POD method. The climatic roughness caused mainly by ice accretion was in focus as well, e.g. with Gorski et al. [14] and Pospisil et al. [15], who studied ice accretion on bridge cables and its influence on Strouhal number and wind-induced vibrations. They concluded that ice accreted on the circular bridge cables has a significant impact on the dependence of Strouhal number on Reynolds number throughout the entire studied Reynolds number range. Xu et al. [16] conducted pressure and force measurements on a large diameter circular cylinder with accreted ice to determine its aerodynamic characteristics. They observed that the mean aerodynamic coefficients of the ice-accreted cylinders exhibited significant Reynolds number effects closely related to the shape of the ice. Zhou et al. [17] demonstrated that grooved and dimpled cylinders produce lower mean drag than smooth cylinders. Aiman and Samion [18] found that grooved cylinders produce lower drag the smooth ones.
The aim of this paper was to investigate the effect of surface roughness on flow around and in the wake of roughened circular cylinders and evaluate its drag and Strouhal numbers as well as the occurrence of coherent structures in the flow. These measurements were carried out in the subcritical Reynolds number range 5.14 × 103–1.18 × 104, and the research was concentrated upon the analysis of the flow around roughened circular cylinders using Proper Orthogonal Decomposition, which is still less common even today, as can be also seen from selected references in Table 1, where a summary of most relevant literature is presented. There, following abbreviations were used: AR — aspect ratio of the cylinder (AR l/D, where l is cylinder length and D is cylinder diameter), NA — information is not available, TH — thermocouple(s), PT — pressure taps, HWA — hot wire anemometry, FB — force balance technique, LC — load cells and Vis. – visualization technique.
Section snippets
Experiment instrumentation and setup
The measurements were carried out at the Laboratory of Turbulent Shear Flows of the Institute of Thermomechanics of The Czech Academy of Sciences (IT CAS). A blow-down wind tunnel with a test section 250 250 mm2 in cross section was used. The inlet velocities at the test sections were .2 m/s and . The flow in the facility contraction outlet was measured using the hot-wire anemometry technique. The flow apart from the boundary layers on the walls (thickness about 2–3 mm) was
Proper Orthogonal Decomposition (POD)
The POD method is an important tool in the study of dynamical systems. It was first introduced in 1967 by J. L. Lumley [20], and its principle was described, e.g., by Uruba [21]. The POD method provides a tool for identification of deterministic structures from a random turbulent flow. It is a systematic way to localize organized motions, so-called coherent structures in a stochastic signal. Uruba and Prochazka [22] analysed the POD spectrum of the wake behind a smooth circular cylinder. Other
Mean flow field
The resulting mean flow field images for the flow perpendicular to the cylinder axis are presented in the following figures. The figures depict the mean flow velocity of the streamwise velocity component U and its standard deviation. The values in the colour bars are dimensionless [–]. Fig. 3a and b present mean streamwise velocity U of the case SC (smooth cylinder) and its standard deviation for the reference velocity . Fig. 3c and d present the mean streamwise velocity of the case
Conclusions
The aim of this work was an investigation of the effect of cylinder surface roughness on the flow both around and in the wake of a circular cylinder. These measurements were carried out in the subcritical Reynolds numbers range 5.14 × 103 – 1.18 × 104, and the research concentrated on the analysis of the flow around roughened circular cylinders using Proper Orthogonal Decomposition, which is currently still less common. The study was conducted in a wind tunnel using the PIV method. The Strouhal
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This research was supported by the Czech Academy of Sciences , institutional support RVO:68378297 and RVO:61388998.
References (29)
Conceptual overview of laminar and turbulent flows past smooth and rough circular cylinders
J. Wind Eng. Ind. Aerodyn.
(1990)Effects of surface roughness on the universal Strouhal number over the wide Reynolds number range
J. Wind Eng. Ind. Aerodyn.
(1997)The effect of surface skewness on the super/postcritical coefficient of drag of roughened cylinders
Proc. Eng.
(2011)- et al.
Numerical approach to determination of equivalent aerodynamic roughness of industrial chimneys
Comput. Struct.
(2018) - et al.
Towards an understanding of the marine fouling effects on VIV of circular cylinders: Response of cylinders with regular pyramidal roughness
Appl. Ocean Res.
(2016) - et al.
Experimental study of the effects of surface roughness on the vortex-induced vibration response of a flexible cylinder
Ocean Eng.
(2015) - et al.
Drag analysis from PIV data in speed sports
Proc. Eng.
(2016) - et al.
A comparison between the wake behind finned and foamed circular cylinders in crosss-flow
Exp. Therm. Fluid Sci.
(2014) - et al.
Experimental study on aerodynamic characteristics of a large-diameter ice-accreted cylinder without icicles
J. Wind Eng. Ind. Aerodyn.
(2021) - et al.
Experimental study on flow past a circular cylinder with rough surface
Ocean Eng.
(2015)
Detached-eddy simulations of the flow over a cylinder at Re=3900 using OpenFOAM
Comput. & Fluids
The effect of surface roughness on the flow regime around circular cylinders
J. Wind Eng. Ind. Aerodyn.
The significant impact of ribs and small-scale roughness on cylinder drag crisis
J. Wind Eng. Ind. Aerodyn.
Effect of superhydrophobicity on the flow past a circular cylinder in various flow regimes
J. Fluid Mech.
Cited by (9)
Effect of the angle of attack on the flow around two non-identical-height square buildings in tandem arrangement
2024, Building and EnvironmentMachine Learning Approach for Flow Fields Over a Circular Cylinder Based on Particle Image Velocimetry Measurements
2023, Measurement: Journal of the International Measurement ConfederationThe Effect of the Surface Roughness of the Circular Cylinder on Drag Coefficient
2023, AIP Conference Proceedings