Simulation of flow across a row of transversely oscillating square cylinders

2011 ◽  
Vol 680 ◽  
pp. 361-397 ◽  
Author(s):  
C. M. SEWATKAR ◽  
ATUL SHARMA ◽  
AMIT AGRAWAL
Keyword(s):  
Reynolds Number ◽  
Oscillation Frequency ◽  
Amplitude Ratio ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Oscillation Amplitude ◽  
Flow Regimes ◽  
Flow Parameters ◽  
Square Cylinders ◽  
Wake Interaction

A numerical study of flow across a row of transversely oscillating square cylinders (of diameter d) has been undertaken using the lattice Boltzmann method, for a better understanding of fluid–structure interaction problems. The effects of cylinder oscillation frequency ratio (fe/fo, where fe is the cylinder oscillation frequency and fo is the corresponding vortex shedding frequency for stationary row of cylinders), amplitude ratio (A/d), non-dimensional spacing between the cylinders (s/d) and Reynolds number (Re) on ensuing flow regimes and flow parameters have been studied to understand the flow physics. Six different flow regimes observed in this study are the quasi-periodic non-lock-on-I, synchronous lock-on, quasi-periodic lock-on, quasi-periodic non-lock-on-II, synchronous non-lock-on and chaotic non-lock-on. It is observed that the range of the lock-on regime depends upon the relative dominance of incoming flow and cylinder motion. Although the lock-on regime in the case of Re = 80, s/d = 4 and A/d = 0.2 is substantially larger as compared to that for a single oscillating cylinder, the range of the lock-on regime shrinks with a reduction in the cylinder spacing, increase in the Reynolds number or decrease in the oscillation amplitude. It is also observed that the wake interaction behind the cylinders weakens with an increase in fe/fo, Re, A/d or s/d, leading to the formation of independent wakes and synchronous nature of the flow. For fe/fo ≥ 1.2, independent and intact oscillating wakes are noted and an additional frequency (wake oscillation frequency) is obtained in the time series of the lift coefficient. Although it was expected that the complexity in the wake interaction would increase with cylinder oscillation or amplitude ratio, an opposite effect (that is, formation of independent wakes) is noted from the results.

Flow around six in-line square cylinders

2012 ◽  
Vol 710 ◽  
pp. 195-233 ◽  
Author(s):  
C. M. Sewatkar ◽  
Rahul Patel ◽  
Atul Sharma ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Flow Regime ◽  
Lift Coefficient ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Square Cylinders ◽  
Chaotic Nature ◽  
Regime Map ◽  
Flow Regime Map

AbstractThe flow around six in-line square cylinders has been studied numerically and experimentally for $0. 5\leq s/ d\leq 10. 0$ and $80\leq \mathit{Re}\leq 320$, where $s$ is the surface-to-surface distance between two cylinders, $d$ is the size of the cylinder and $\mathit{Re}$ is the Reynolds number. The effect of spacing on the flow regimes is initially studied numerically at $\mathit{Re}= 100$ for which a synchronous flow regime is observed for $0. 5\leq s/ d\leq 1. 1$, while quasi-periodic-I, quasi-periodic-II and chaotic regimes occur between $1. 2\leq s/ d\leq 1. 3$, $1. 4\leq s/ d\leq 5. 0$ and $6. 0\leq s/ d\leq 10. 0$, respectively. These regimes have been confirmed via particle-image-velocimetry-based experiments. A flow regime map is proposed as a function of spacing and Reynolds number. The flow is predominantly quasi-periodic-II or chaotic at higher Reynolds numbers. The quasi-periodic and chaotic nature of the flow is due to the wake interference effect of the upstream cylinders which becomes more severe at higher Reynolds numbers. The appearance of flow regimes is opposite to that for a row of cylinders. The Strouhal number for vortex shedding is the same for all the cylinders, especially for synchronous and quasi-periodic-I flow regimes. The mean drag (${C}_{Dmean} $) experienced by the cylinders is less than that for an isolated cylinder, irrespective of the spacing. The first cylinder is relatively insensitive to the presence of downstream cylinders and the ${C}_{Dmean} $ is almost constant at 1.2. The ${C}_{Dmean} $ for the second and third cylinders may be negative, with the value of ${C}_{Dmean} $ increasing monotonically with spacing. The changes in root mean square lift coefficient are consistent with changes in ${C}_{Dmean} $. Interestingly, the instantaneous lift force can be larger than the instantaneous drag force on the cylinders. These results should help improve understanding of flow around multiple bluff bodies.

Simulation of Low-Reynolds Number Flow Around a Circular Cylinder Following a Slender Elliptical Path

2013 ◽  
Author(s):  
László Baranyi
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Oscillation Amplitude ◽  
Base Pressure ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Lock In

Two-dimensional flow around a circular cylinder forced to follow an elliptical path at low Reynolds numbers is investigated numerically using a thoroughly tested in-house code based on the finite difference method. Time-mean (TM) and rms values of lift, drag and base pressure coefficients are investigated within the lock-in region against the transverse oscillation amplitude for Reynolds number Re = 150 at frequency ratios of 0.8, 0.9 and 1.0 while the ratio of in-line and transverse cylinder oscillation amplitudes is kept at six different values yielding slender elliptical cylinder paths. The objective of the paper is to investigate the effect of the shape of the path, or amplitude ratio, on force coefficients. Findings show that for the cases investigated the rms of lift and TM of drag and base pressure are hardly affected by the amplitude ratio, while its effects are pronounced on the TM of lift and rms of drag and base pressure.

Prototype Reynolds Number Vortex-Induced Vibration Tests on a Full-Scale Rigid Riser

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Decao Yin ◽  
Halvor Lie ◽  
Rolf J. Baarholm
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Flow Regime ◽  
Amplitude Ratio ◽  
Flow Regimes ◽  
Offshore Structures ◽  
Full Scale ◽  
Displacement Amplitude ◽  
Small Scale ◽  
Supercritical Flow

Slender offshore structures in deep water subjected to currents may experience vortex-induced vibrations (VIV), which can cause significant fatigue damage. Extensive experimental researches have been conducted to study the VIV in the past several decades. However, most of the experimental works have small-scale models and relatively low Reynolds number (Re)—“subcritical” or even lower Reynolds number regime. There is a lack of full understanding of the VIV in prototype Re flow regime. Applying the results with low Re to a full-scale riser with prototype Re might have uncertainties due to the scaling effects. In addition, the surface roughness of the riser is also an important parameter, especially in critical Re regime, which is the case for prototype risers. In the present study, two full-scale rigid riser models with different surface roughness ratios were tested in the towing tank of MARINTEK in 2014. Stationary tests, pure crossflow (CF) free oscillation tests, and forced/controlled motion tests were carried out. Several conclusions could be made: The drag coefficient is dependent on the Re number and surface roughness ratio. At critical and supercritical flow regimes, the displacement amplitude ratio is less sensitive to Re than that at lower Re. The displacement amplitude ratio in subcritical flow regime is significantly larger than that in critical and supercritical flow regimes. Two excitation regions for the ‘smooth riser’ and one excitation region for the “rough riser” are identified.

Prototype Reynolds Number VIV Tests on a Full-Scale Rigid Riser

2017 ◽  
Author(s):  
Decao Yin ◽  
Halvor Lie ◽  
Rolf J. Baarholm
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Flow Regime ◽  
Amplitude Ratio ◽  
Flow Regimes ◽  
Offshore Structures ◽  
Full Scale ◽  
Displacement Amplitude ◽  
Small Scale ◽  
Supercritical Flow

Slender offshore structures in deep water subjected to currents may experience vortex-induced vibrations (VIV), which can cause significant fatigue damage. Extensive experimental researches have been conducted to study the VIV in the past several decades. However, most of the experimental works have small-scale models and relatively low Reynolds number (Re) - ‘subcritical’ or even lower Reynolds number regime. There is a lack of full understanding the VIV in prototype Re flow regime. Applying the results with low Re to a full scale riser with prototype Re might have uncertainties due to the scaling effects. In addition, the surface roughness of the riser is also an important parameter, especially in prototype Re regime. In present study, two full-scale rigid riser models with different surface roughness ratios were tested in the towing tank of MARINTEK in 2014. Stationary tests, pure cross-flow (CF) free oscillation tests and forced/controlled motion tests were carried out. Several conclusions could be made: • The drag coefficient is dependent on the Re number and surface roughness ratio. • At critical and supercritical flow regimes, the displacement amplitude ratio is less sensitive to Re than that at lower Re. The displacement amplitude ratio in subcritical flow regime is significantly larger than that in critical and supercritical flow regimes. • Two excitation regions for the ‘smooth riser’ and one excitation region for the ‘rough riser’ are identified.

Numerical Study of Winglet Cant Angle Effect on Wing Performance at Low Reynolds Number

2013 ◽  
Vol 393 ◽  
pp. 366-371
Author(s):  
C.F. Mat Taib ◽  
Abdul Aziz Jaafar ◽  
Salmiah Kasolang
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Lift Coefficient ◽  
Wing Model ◽  
Low Reynolds ◽  
Wing Performance ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The study on the effect of winglet shape in wing design has been a focus of many researchers. Nevertheless, the effect of cant angle on the wing performances at low Reynolds number has not been fully explored. This paper describes the effect of a single semi-circular shaped winglet attached with a rectangular wing model to lower the drag without increasing the span of the wing. Aerodynamic characteristics for the rectangular wing (NACA 65-3-218) with and without semi-circular winglets have been studied using STAR CCM+ 4.0. This numerical analysis is based on Finite Volume Approach. Simulations were carried out on the rectangular wing model with and without winglet at aspect ratio of 2.73 and Reynolds number of 0.16 x 10 6 for various angles of attack. From the numerical analysis, wing performance characteristics in terms of lift coefficient CL, drag coefficient CD, and lift-to-drag ratio, CL/CD were obtained. It was found that the addition of a semi-circular winglet has resulted in a larger lift curve slope and higher Lift-to-Drag ratio in comparison with the case of a wing without winglet. Further investigation has revealed that a wing with semi-circular winglet with cant angle of 45 degree has produced the best Lift-to-Drag ratio, CL/CD.

Static Pressure Distributions Over 2D Mast/Sail Geometries

1989 ◽  
Vol 26 (04) ◽  
pp. 333-337
Author(s):  
Stuart Wilkinson
Keyword(s):  
Reynolds Number ◽  
Static Pressure ◽  
Incidence Angle ◽  
Flow Regimes ◽  
Two Dimensional ◽  
Test Program ◽  
Flow Parameters ◽  
Pressure Distributions

A variable-camber aerofoil with integral pressure tappings has been built to investigate the nature of the flows around two-dimensional, highly cambered, sail-like aerofoil sections with circular masts. Data have been obtained in the form of static pressure distributions over representative ranges of Reynolds number, camber ratio, incidence angle, mast diameter/chord ratio and mast angle. Two sail shapes—based on the NACA a = 0.8 and NACA 63 mean-line camber distributions—were involved in the test program. All flow regimes present have been identified and related to the salient model and flow parameters.

scholarly journals Vortex dynamics and elliptical structure wake interaction in the proximity of wall using 2-D RANS simulation

2018 ◽  
Vol 144 ◽  
pp. 04018
Author(s):  
H. S. Arunkumar ◽  
Chidanand Mangrulkar ◽  
Trushar Gohil
Keyword(s):  
Reynolds Number ◽  
Flow Characteristic ◽  
Numerical Study ◽  
Wall Effect ◽  
Suitable Model ◽  
Computational Domain ◽  
Turbulent Model ◽  
Area Of Interest ◽  
Gap Ratio ◽  
Wake Interaction

The 2-D numerical study is performed to analyses the flow characteristic behind the elliptical structure placed near the wall for three different gap ratios as 0.25, 0.5, and 1.0. Computational domain and model is initially validated with the unbounded flow over a cylinder without considering wall effect for Reynolds number of 3900. For flow over the cylinder with near wall, computational domain is modelled as Blasius profile is the input to the area of interest. At different gap ratios the effect of boundary layer on vortex shedding is studied with Reynolds number of 1440. By applying different turbulent model for analysis, study the variation in the results and suggest the suitable model for the present type of study. It has been observed that the wall effect is predominant in case of the gap ratio of 0.25 as compared to other gap ratios.

Numerical study on flow over a confined oscillating cylinder with a splitter plate

2019 ◽  
Vol 29 (5) ◽  
pp. 1629-1646 ◽  
Author(s):  
Arya Ghiasi ◽  
Seyed Esmaeil Razavi ◽  
Abel Rouboa ◽  
Omid Mahian
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Oscillation Frequency ◽  
Stokes Equations ◽  
Numerical Study ◽  
Splitter Plate ◽  
Content Type ◽  
Plate Length ◽  
Parametric Studies

Purpose This study aims to investigate the effect of the simultaneous usage of active and passive methods (which in this case are rotational oscillation and attached splitter plate, respectively) on the flow and temperature fields to find an optimum situation which this combination results in heat transfer increment and drag reduction. Design/methodology/approach The method of the solution was based on finite volume discretization of Navier–Stokes equations. A dynamic grid is coupled with the solver by the arbitrary Lagrangian–Eulerian (ALE) formulation for modeling cylinder oscillation. Parametric studies were performed by altering oscillation frequency, splitter plate length and Reynolds number. Findings Oscillation in different frequencies was found to be complicated. Higher frequencies provide more heat transfer, but in the lock-on region, they bring remarkable increment to the drag coefficient. It was observed that simultaneous usage of oscillation and splitter plate may have both positive and negative effects on drag reduction and heat transfer increment. Finally F = 2 and L = 0.5 were chosen as an optimum combination. Originality/value In this study, the laminar incompressible flow and heat transfer from a confined rotationally oscillating circular cylinder with an attached splitter plate are investigated. Parametric studies are performed by changing oscillation frequency, splitter plate length and Reynolds number.

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