Flow Characteristics of a Three Dimensional Bluff Body With a Single Rotating Cylinder

2012 ◽  
Author(s):  
James R. Bell ◽  
David Burton ◽  
Damien McArthur ◽  
John Sheridan
Keyword(s):  
Bluff Body ◽  
Aerodynamic Drag ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
The Body ◽  
Surface Velocity ◽  
Cylinder Surface ◽  
Low Velocity ◽  
Freestream Velocity

This work investigated the application of a rotating cylinder to the upper leeward edge of a three dimensional bluff body in ground proximity. Aerodynamic drag measurements, base pressure contours and wake velocity profiles were obtained in a closed jet wind tunnel for Reynolds Numbers in the range of approximately 220,000 to 660,000. The cylinder of diameter 0.1H was mounted on the upper edge of the leeward face of the body. The ratio of cylinder surface velocity to freestream velocity was varied from 0 to 2.0. A computational model of the geometry was developed and results are presented for various velocity ratios and cylinder diameters. The results of this work demonstrated that, even at low velocity ratios, the cylinder rotation has a large effect on the flow structures in the body wake region. A large downwash is observed that creates two large counter-rotating vortices and a resultant significant increase in drag. The aerodynamic drag changes are presented as a function of velocity ratio and are shown to be Reynolds Number insensitive over the range tested. Aerodynamic drag was shown to increase with increasing velocity ratio over the velocity ratio range 0.25 to 2.0.

scholarly journals In-line flow-induced vibrations of a rotating cylinder

2015 ◽  
Vol 781 ◽  
pp. 127-165 ◽  
Author(s):  
Rémi Bourguet ◽  
David Lo Jacono
Keyword(s):  
Rotation Rate ◽  
Vibration Amplitude ◽  
Three Dimensional ◽  
Low Frequency ◽  
Rotating Cylinder ◽  
The Body ◽  
Cylinder Surface ◽  
Force Frequency ◽  
Direction Parallel ◽  
Flow Induced Vibrations

The flow-induced vibrations of an elastically mounted circular cylinder, free to oscillate in the direction parallel to the current and subjected to a forced rotation about its axis, are investigated by means of two- and three-dimensional numerical simulations, at a Reynolds number equal to 100 based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to 2 (first vibration region), then the body and the flow are steady until a rotation rate close to 2.7 where a second vibration region begins. Each vibration region is characterized by a specific regime of response. In the first region, the vibration amplitude follows a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency). The maximum vibration amplitudes, even though considerably augmented by the rotation relative to the non-rotating body case, remain lower than 0.1 cylinder diameters. Due to their trends as functions of the reduced velocity and to the fact that they develop under a condition of wake-body synchronization or lock-in, the responses of the rotating cylinder in this region are comparable to the vortex-induced vibrations previously described in the absence of rotation. The symmetry breaking due to the rotation is shown to directly impact the structure displacement and fluid force frequency contents. In the second region, the vibration amplitude tends to increase unboundedly with the reduced velocity. It may become very large, higher than 2.5 diameters in the parameter space under study. Such structural oscillations resemble the galloping responses reported for non-axisymmetric bodies. They are accompanied by a dramatic amplification of the fluid forces compared to the non-vibrating cylinder case. It is shown that body oscillation and flow unsteadiness remain synchronized and that a variety of wake topologies may be encountered in this vibration region. The low-frequency, large-amplitude responses are associated with novel asymmetric multi-vortex patterns, combining a pair and a triplet or a quartet of vortices per cycle. The flow is found to undergo three-dimensional transition in the second vibration region, with a limited influence on the system behaviour. It appears that the transition occurs for a substantially lower rotation rate than for a rigidly mounted cylinder.

scholarly journals Flow-induced vibrations of a rotating cylinder in an arbitrary direction

2018 ◽  
Vol 860 ◽  
pp. 739-766 ◽  
Author(s):  
Rémi Bourguet
Keyword(s):  
Three Dimensional ◽  
Rotating Cylinder ◽  
The Body ◽  
Arbitrary Direction ◽  
Fast Rotation ◽  
Flow Past ◽  
Symmetrical Configuration ◽  
Wide Range ◽  
Flow Induced Vibrations ◽  
The Impact

The flow-induced vibrations of an elastically mounted circular cylinder, free to oscillate in an arbitrary direction and forced to rotate about its axis, are examined via two- and three-dimensional simulations, at a Reynolds number equal to 100, based on the body diameter and inflow velocity. The behaviour of the flow–structure system is investigated over the entire range of vibration directions, defined by the angle $\unicode[STIX]{x1D703}$ between the direction of the current and the direction of motion, a wide range of values of the reduced velocity $U^{\star }$ (inverse of the oscillator natural frequency) and three values of the rotation rate (ratio between the cylinder surface and inflow velocities), $\unicode[STIX]{x1D6FC}\in \{0,1,3\}$, in order to cover the reference non-rotating cylinder case, as well as typical slow and fast rotation cases. The oscillations of the non-rotating cylinder ($\unicode[STIX]{x1D6FC}=0$) develop under wake-body synchronization or lock-in, and their amplitude exhibits a bell-shaped evolution, typical of vortex-induced vibrations (VIV), as a function of $U^{\star }$. When $\unicode[STIX]{x1D703}$ is increased from $0^{\circ }$ to $90^{\circ }$ (or decreased from $180^{\circ }$ to $90^{\circ }$), the bell-shaped curve tends to monotonically increase in width and magnitude. For all angles, the flow past the non-rotating body is two-dimensional with formation of two counter-rotating spanwise vortices per cycle. The behaviour of the system remains globally the same for $\unicode[STIX]{x1D6FC}=1$. The principal effects of the slow rotation are a slight amplification of the VIV-like responses and widening of the vibration windows, as well as a limited asymmetry of the responses and forces about the symmetrical configuration $\unicode[STIX]{x1D703}=90^{\circ }$. The impact of the fast rotation ($\unicode[STIX]{x1D6FC}=3$) is more pronounced: VIV-like responses persist over a range of $\unicode[STIX]{x1D703}$ but, outside this range, the system is found to undergo a transition towards galloping-like oscillations characterised by amplitudes growing unboundedly with $U^{\star }$. A quasi-steady modelling of fluid forcing predicts the emergence of galloping-like responses as $\unicode[STIX]{x1D703}$ is varied, which suggests that they could be mainly driven by the mean flow. It, however, appears that flow unsteadiness and body motion remain synchronised in this vibration regime where a variety of multi-vortex wake patterns are uncovered. The interaction with flow dynamics results in deviations from the quasi-steady prediction. The successive steps in the evolution of the vibration amplitude versus $U^{\star }$, linked to wake pattern switch, are not captured by the quasi-steady approach. The flow past the rapidly-rotating, vibrating cylinder becomes three-dimensional over an interval of $\unicode[STIX]{x1D703}$ including the in-line oscillation configuration, with only a minor effect on the system behaviour.

scholarly journals Effects of Jet Induced by String-type Plasma Actuator on Flow Around Three-Dimensional Bluff Body and Drag Force

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 872 ◽  
Author(s):  
Takatoshi Matsubara ◽  
Yoshiki Shima ◽  
Hikaru Aono ◽  
Hitoshi Ishikawa ◽  
Takehiko Segawa
Keyword(s):  
Flow Control ◽  
Bluff Body ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Plasma Actuator ◽  
Recirculation Region ◽  
Back Surface ◽  
Burst Frequency ◽  
Freestream Velocity ◽  
String Type

An experimental investigation of active flow control on a three-dimensional (3D) curved surface bluff body was conducted by using a string-type plasma actuator. The 3D bluff body model tested in this study was composed of a quarter sphere and a half cylinder, and the Reynolds number based on the diameter of half cylinder was set at 1.3 × 104. The modulation drive was adopted for flow control, and the control effects of variations in dimensionless burst frequency (fm+) normalized by the width of the model and freestream velocity were studied. Velocity distributions analyzed by particle image velocimetry showed that the recirculation region behind the model shrank due to the flow control. The static pressure distributions on the back surface of the model tended to decrease under any fm+ set in this study, especially in the ranges of 0.40 ≤ fm+ ≤ 0.64. The drag coefficient reached its maximum value under the similar ranges of fm+. Although the aerodynamic wake sharpening was observed due to the flow control, the entrainment of separated flow into the back surface of the model was enhanced. This scenario of wake manipulation was considered to be responsible for increasing drag acting on the model.

scholarly journals Influence of the hydrofoil inclination angle at free surface flow around junctions

2020 ◽  
Vol 43 ◽  
pp. 103-108
Author(s):  
Costel Ungureanu ◽  
Costel Iulian Mocanu
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Bluff Body ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Breaking Waves ◽  
Surface Flow ◽  
Vortex Structures ◽  
The Body ◽  
Flow Topology

"Free surface flow is a hydrodynamic problem with a seemingly simple geometric configuration but with a flow topology complicated by the pressure gradient due to the presence of the obstacle, the interaction between the boundary layer and the free surface, turbulence, breaking waves, surface tension effects between water and air. As the ship appendages become more and more used and larger in size, the general understanding of the flow field around the appendages and the junction between them and the hull is a topical issue for naval hydrodynamics. When flowing with a boundary layer, when the streamlines meet a bluff body mounted on a solid flat or curved surface, detachments appear in front of it due to the blocking effect. As a result, vortex structures develop in the fluid, also called horseshoe vortices, the current being one with a completely three-dimensional character, complicated by the interactions between the boundary layer and the vortex structures thus generated. Despite the importance of the topic, the literature records the lack of coherent methods for investigating free surface flow around junctions, the lack of consistent studies on the influence of the inclination of the profile mounted on the body. As a result, this paper aims to systematically study the influence of profile inclination in respect to the support plate."

Three-dimensionality in the wake of a rapidly rotating cylinder in uniform flow

2013 ◽  
Vol 730 ◽  
pp. 379-391 ◽  
Author(s):  
A. Rao ◽  
J. S. Leontini ◽  
M. C. Thompson ◽  
K. Hourigan
Keyword(s):  
Steady State ◽  
Rotation Rate ◽  
Free Stream ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
Marginal Stability ◽  
Cylinder Surface ◽  
Rotation Rates ◽  
Centrifugal Instability ◽  
The Stability

AbstractThe flow around an isolated cylinder spinning at high rotation rates in free stream is investigated. The existence of two steady two-dimensional states is confirmed, as is the existence of a secondary mode of vortex shedding. The stability of the two steady states to three-dimensional perturbations is established using linear stability analysis. At lower rotation rates on the first steady state, two three-dimensional modes are confirmed, and their structure and curves of marginal stability as a function of rotation rate and Reynolds number are determined. One mode (named mode $E$) appears consistent with a hyperbolic instability in the wake, while the second (named mode $F$) appears to be a centrifugal instability of the flow very close to the cylinder surface. At higher rotation rates on the second steady state, a single three-dimensional mode due to centrifugal instability (named mode ${F}^{\prime } $) is found. This mode becomes increasingly difficult to excite as the rotation rate is increased.

Experimental evidence of new three-dimensional modes in the wake of a rotating cylinder

2013 ◽  
Vol 734 ◽  
pp. 567-594 ◽  
Author(s):  
A. Radi ◽  
M. C. Thompson ◽  
A. Rao ◽  
K. Hourigan ◽  
J. Sheridan
Keyword(s):  
Rotation Rate ◽  
Numerical Study ◽  
Water Channel ◽  
Three Dimensional ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Travelling Wave ◽  
Cylinder Surface ◽  
Rotation Rates

AbstractA recent numerical study by Rao et al. (J. Fluid Mech., vol. 717, 2013, pp. 1–29) predicted the existence of several previously unobserved linearly unstable three-dimensional modes in the wake of a spinning cylinder in cross-flow. While linear stability analysis suggests that some of these modes exist for relatively limited ranges of Reynolds numbers and rotation rates, this may not be true for fully developed nonlinear wakes. In the current paper, we present the results of water channel experiments on a rotating cylinder in cross-flow, for Reynolds numbers $200\leqslant \mathit{Re}\leqslant 275$ and non-dimensional rotation rates $0\leqslant \alpha \leqslant 2. 5$. Using particle image velocimetry and digitally post-processed hydrogen bubble flow visualizations, we confirm the existence of the predicted modes for the first time experimentally. For instance, for $\mathit{Re}= 275$ and a rotation rate of $\alpha = 1. 7$, we observe a subharmonic mode, mode C, with a spanwise wavelength of ${\lambda }_{z} / d\approx 1. 1$. On increasing the rotation rate, two modes with a wavelength of ${\lambda }_{z} / d\approx 2$ become unstable in rapid succession, termed modes D and E. Mode D grows on a shedding wake, whereas mode E consists of streamwise vortices on an otherwise steady wake. For $\alpha \gt 2. 2$, a short-wavelength mode F appears localized close to the cylinder surface with ${\lambda }_{z} / d\approx 0. 5$, which is presumably a manifestation of centrifugal instability. Unlike the other modes, mode F is a travelling wave with a spanwise frequency of ${\mathit{St}}_{3D} \approx 0. 1$. In addition to these new modes, observations on the one-sided shedding process, known as the ‘second shedding’, are reported for $\alpha = 5. 1$. Despite suggestions from the literature, this process seems to be intrinsically three-dimensional. In summary, our experiments confirm the linear predictions by Rao et al., with very good agreement of wavelengths, symmetries and the phase velocity for the travelling mode. Apart from this, these experiments examine the nonlinear saturated state of these modes and explore how the existence of multiple unstable modes can affect the selected final state. Finally, our results establish that several distinct three-dimensional instabilities exist in a relatively confined area on the $\mathit{Re}$–$\alpha $ parameter map, which could account for their non-detection previously.

scholarly journals Aerodynamically Interacting Vertical-Axis Wind Turbines: Performance Enhancement and Three-Dimensional Flow

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2724 ◽  
Author(s):  
Ian D. Brownstein ◽  
Nathaniel J. Wei ◽  
John O. Dabiri
Keyword(s):  
Wind Direction ◽  
Wind Farm ◽  
Bluff Body ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Wind Farms ◽  
Vertical Axis ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Turbine Performance

This study examined three-dimensional, volumetric mean velocity fields and corresponding performance measurements for an isolated vertical-axis wind turbine (VAWT) and for co- and counter-rotating pairs of VAWTs with varying incident wind direction and turbine spacings. The purpose was to identify turbine configurations and flow mechanisms that can improve the power densities of VAWT arrays in wind farms. All experiments were conducted at a Reynolds number of R e D = 7.3 × 10 4 . In the paired arrays, performance enhancement was observed for both the upstream and downstream turbines. Increases in downstream turbine performance correlate with bluff–body accelerations around the upstream turbine, which increase the incident freestream velocity on the downstream turbine in certain positions. Decreases in downstream turbine performance are determined by its position in the upstream turbine’s wake. Changes in upstream turbine performance are related to variations in the surrounding flow field due to the presence of the downstream rotor. For the most robust array configuration studied, an average 14% increase in array performance over approximately a 50° range of wind direction was observed. Additionally, three-dimensional vortex interactions behind pairs of VAWT were observed that can replenish momentum in the wake by advection rather than turbulent diffusion. These effects and their implications for wind-farm design are discussed.

Effect of Upstream Shear on Flow and Heat (Mass) Transfer Over a Flat Plate

2008 ◽  
Author(s):  
Kalyanjit Ghosh ◽  
R. J. Goldstein
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Velocity Ratio ◽  
Leading Edge ◽  
Surface Velocity ◽  
Freestream Velocity ◽  
Inner Region

A parametric study is conducted to investigate the effect of wall shear on a two-dimensional turbulent boundary layer. The shear is imparted by a moving belt, flush with the wall, translating in the flow direction. Velocity and mass transfer experiments have been performed for four surface-to-freestream velocity ratios (0, 0.38, 0.52, 0.65) with a Reynolds number based on the momentum thickness between 770 and 1776. The velocity data indicate that the location of the ‘virtual origin’ of the turbulent boundary layer ‘moves’ downstream towards the trailing edge of the belt with increasing surface velocity. The highest velocity ratio represents a case which is responsible for the removal of the inner region of the boundary layer. Mass transfer measurements downstream of the belt show the presence of a local minimum in the variation of the Stanton vs. Reynolds number for the highest velocity ratio. Downstream of this minimum, approximately 1 cm from the leading edge of the mass transfer plate, the characteristics of the turbulent boundary layer are restored and the data fall back on the empirical variation of the Stanton number with Reynolds number.

Experimental Studies of External Hygrocysts

1980 ◽  
Vol 102 (2) ◽  
pp. 226-230 ◽  
Author(s):  
J. P. Kovac ◽  
R. T. Balmer
Keyword(s):  
Steady State ◽  
Velocity Field ◽  
Film Thickness ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
Surface Velocity ◽  
Data Sets ◽  
Centrifugal Acceleration ◽  
Average Film Thickness

The three-dimensional banding phenomenon that occurs on the outside of single horizontal rotating cylinders covered with a liquid film was experimentally studied. Over 400 data sets from a variety of cylinders and liquids produced an emperical correlation between the number of bands formed and the rotational Reynolds, Weber, and Froude numbers. The average film thickness on the top of the rotating cylinder was found to be independent of the physical properties of the liquid and the centrifugal acceleration of the cylinder. The surface velocity measured in the crown of the bands was found to be nearly the same as that predicted by the steady state unbanded velocity field solution of Moffatt.

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