Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000 < Re < 120,000

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations (VIV) of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. Two identical rigid cylinders suspended by springs with their axes perpendicular to the flow are allowed one degree of freedom motion transverse to the flow direction. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth cylinder is similar to that of an isolated smooth cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. Galloping is suppressed in both cylinders. In addition, the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000

2013 ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. The two identical cylinders are rigid, suspended by springs, and allowed to move transversely to the flow direction and their own axis. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth-cylinder is similar to that of the isolated smooth-cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. In addition the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

scholarly journals Computational and Experimental Assessment of Turbulence Stimulation on Flow Induced Motion of a Circular Cylinder

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Ethan Fassezke ◽  
Michael M. Bernitsas
Keyword(s):  
University Of Michigan ◽  
Amplitude Response ◽  
Turbulence Control ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Highly Nonlinear ◽  
Invaluable Tool ◽  
Induced Motion ◽  
The University ◽  
Passive Turbulence Control

Vortex-induced vibrations (VIVs) are highly nonlinear and it is hard to approach the problem analytically or computationally. Experimental investigation is therefore essential to address the problem and reveal some physical aspects of VIV. Although computational fluid dynamics (CFDs) offers powerful methods to generate solutions, it cannot replace experiments as yet. When used as a supplement to experiments, however, CFD can be an invaluable tool to explore some underlying issues associated with such complicated flows that could otherwise be impossible or very expensive to visualize or measure experimentally. In this paper, VIVs and galloping of a cylinder with selectively distributed surface roughness—termed passive turbulence control (PTC)—are investigated experimentally and computationally. The computational approach is first validated with benchmark experiments on smooth cylinders available in the literature. Then, experiments conducted in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan are replicated computationally to visualize the flow and understand the effects of thickness and width of roughness strips placed selectively on the cylinder. The major outcomes of this work are: (a) Thicker PTC initiates earlier galloping but wider PTC does not have a major impact on the response of the cylinder and (b) The amplitude response is restricted in VIV due to the dead fluid zone attached to the cylinder, which is not observed in galloping.

The Numerical Research of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinders

2012 ◽  
Vol 204-208 ◽  
pp. 4598-4601
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Degrees Of Freedom ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Line Frequency ◽  
Ansys Cfx ◽  
Vortex Induced Vibrations ◽  
Lock In

The two-degrees-of-freedom of vortex-induced vibration of circular cylinders is numerically simulated with the software ANSYS/CFX. The VIV characteristic, in the two different conditions (A/D=0.07 and A/D=1.0), is analyzed. When A/D is around 0.07, the amplitude ratio of the cylinder’s VIV between in-line and cross-flow direction in the lock-in is lower than that in the lock-out. The in-line frequency is twice of that in cross-flow direction in the lock-out, but in the lock-in, it is the same as that in cross-flow direction and the same as that of lift force. When A/D is around 1.0, the amplitude ratio of the VIV between in-line and cross-flow in the lock-in is obviously larger than that in the lock-out. Both in the lock-in and in the lock-out, the in-line frequency is twice of that in cross-flow direction.

scholarly journals Virtual Spring–Damping System for Flow-Induced Motion Experiments

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hai Sun ◽  
Eun Soo Kim ◽  
Marinos P. Bernitsas ◽  
Michael M. Bernitsas
Keyword(s):  
First Generation ◽  
Closed Loop ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Data Generation ◽  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Vortex Induced Vibrations ◽  
Induced Motion ◽  
The University

Flow-induced motion (FIM) experiments of a single circular cylinder or multiple cylinders in an array involve several configuration and hydrodynamic parameters, such as diameter, mass, damping, stiffness, spacing, Reynolds number, and flow regime, and deviation from circular cross section. Due to the importance of the FIM both in suppression for structural robustness and in enhancement for hydrokinetic energy conversion, systematic experiments are being conducted since the early 1960s and several more decades of experimentation are required. Change of springs and dampers is time consuming and requires frequent recalibration. Emulating springs and dampers with a controller makes parameter change efficient and accurate. There are two approaches to this problem: The first involves the hydrodynamic force in the closed-loop and is easier to implement. The second called virtual damping and spring (Vck) does not involve the hydrodynamic force in the closed-loop but requires an elaborate system identification (SI) process. Vck was developed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan for the first time in 2009 and resulted in extensive data generation. In this paper, the second generation of Vck is developed and validated by comparison of the FIM experiments between a Vck emulated oscillator and an oscillator with physical springs and dampers. The main findings are: (a) the Vck system developed keeps the hydrodynamic force out of the control-loop and, thus, does not bias the FIM, (b) The controller-induced lag is minimal and significantly reduced compared to the first generation of Vck built in the MRELab due to use of an Arduino embedded board to control a servomotor instead of Labview, (c) The SI process revealed a static, third-order, nonlinear viscous model but no need for dynamic terms with memory, and (d) The agreement between real and virtual springs and dampers is excellent in FIM including vortex-induced vibrations (VIVs) and galloping measurements over the entire range of spring constants and velocities tested (16,000 < Re < 140,000).

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Map of Passive Turbulence Control to Flow-Induced Motions for a Circular Cylinder at 30,000

2013 ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Che-Chun Chang
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Damping Ratio ◽  
Water Channel ◽  
University Of Michigan ◽  
Strong Suppression ◽  
Variable Parameters ◽  
Turbulence Control ◽  
The University ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of two straight roughness strips with variable width, and thickness about equal to the boundary layer thickness, is used to modify the flow-induced motions (FIM) of a rigid circular cylinder. The cylinder is supported by two end-springs and the flow is in the TrSL3, high-lift, regime. The PTC-to-FIM Map, developed in previous work, revealed zones of weak suppression, strong suppression, hard galloping, and soft galloping. In this paper the sensitivity of the PTC-to-FIM Map to: (a) the width of PTC covering, (b) PTC covering a single or multiple zones, (c) PTC being straight or staggered is studied experimentally. Experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan. Fixed parameters are: cylinder diameter D = 8.89cm, m* = 1.725, spring stiffness K = 763N/m, aspect ratio l/D = 10.29, and damping ratio ζ = 0.019. Variable parameters are: circumferential PTC location αPTC ∈ [0°−180°], Reynolds number Re ∈ [30,000–120,000], flow velocity U ∈ [0.36m/s–1.45m/s]. Measured quantities are: amplitude ratio A/D, frequency ratio fosc/fn,w, and synchronization range. As long as the roughness distribution is limited to remain within a zone, the width of the strips does not affect the FIM response. When multiple zones are covered, the strong suppression zone dominates the FIM.

Understanding In-Cylinder Flow Variability Using Large-Eddy Simulations

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Noah Van Dam ◽  
Chris Rutland
Keyword(s):  
Flow Direction ◽  
Large Eddy Simulations ◽  
University Of Michigan ◽  
Variable Flow ◽  
Stagnation Points ◽  
Optical Engine ◽  
Velocity Magnitude ◽  
Large Eddy ◽  
Cylinder Flow ◽  
The University

Multicycle large-eddy simulations (LES) of motored flow in an optical engine housed at the University of Michigan have been performed. The simulated flow field is compared against particle image velocimetry (PIV) data in several cutting planes. Circular statistical methods have been used to isolate the contributions to overall turbulent fluctuations from changes in flow direction or magnitude. High levels of turbulence, as indicated by high velocity root mean square (RMS) values, exist in relatively large regions of the combustion chamber. But the circular standard deviation (CSD), a measure of the variability in flow direction independent of velocity magnitude, is much more limited to specific regions or points, indicating that much of the turbulence is from variable flow magnitude rather than variable flow direction. Using the CSD is also a promising method to identify critical points, such as vortex centers or stagnation points, within the flow, which may prove useful for future engine designers.

RANS Simulation vs. Experiments of Flow Induced Motion of Circular Cylinder With Passive Turbulence Control at 35,000

2011 ◽  
Author(s):  
Wei Wu ◽  
Michael M. Bernitsas ◽  
Kevin Maki
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Cylinder Wall ◽  
Turbulence Control ◽  
Induced Motion ◽  
High Reynolds ◽  
Vortex Patterns ◽  
Cylinder Flow ◽  
The University ◽  
Passive Turbulence Control

Two-dimensional RANS equations with the Spalart-Allmaras turbulence model are used to simulate the flow and body kinematics of a rigid circular cylinder mounted on springs, transversely to a steady uniform flow in the high-lift, TrSL3 regime with 35,000<Re<130,000. Passive Turbulence Control (PTC) in the form of selectively distributed surface roughness is used to alter the cylinder Flow Induced Motion (FIM). Simulation is performed by using a solver based on the open source CFD tool OpenFOAM, which solves continuum mechanics problems with a finite volume discretization method. Roughness parameters of PTC are simulated modeling tests conducted in the Marine Renewable Energy Lab (MRELab) of the University of Michigan. The numerical tool is first tested on smooth cylinder in VIV and results are compared with available experimental measurements and RANS simulations. For the cylinder with PTC cases, the sandpaper grit (k) on the cylinder wall is modeled as a rough-wall boundary condition. Two sets of cases with different system parameters (spring constant, damping) are simulated and the results are compared with experimental data measured in the MRELab. The amplitude-ratio curve shows clearly three different branches, including the VIV initial and upper branches and a galloping branch, similar to those observed experimentally. Frequency ratio, vortex patterns, transitional behavior, and lift are also predicted well for PTC cylinders at such high Reynolds numbers.

Suppression of the Vortex-Induced Vibration of a Circular Cylinder With Permeable Meshes

2014 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Cesar M. Freire ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Vortex Formation ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Vortex Induced Vibrations ◽  
Image Velocimetry ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of the dynamic response are presented for models with low mass and damping which are free to respond in the cross-flow direction. Reynolds number ranged from 1,000 to 10,000 and reduced velocity was varied between 2 and 13. Also presented are measurements of the wake of static models with Particle Image Velocimetry (PIV) at Reynolds number equal to 4000. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. Visualisation of the flow by PIV around static cylinders revealed that all suppressors disrupt the vortex shedding and increase the formation length when compared to the bare cylinder. The VT mesh, which presented the best suppression, also presented the largest vortex formation length.

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