Hydrokinetic Energy Harnessing Using the VIVACE Converter With Passive Turbulence Control

2011 ◽  
Author(s):  
Che-Chun Chang ◽  
Michael M. Bernitsas
Keyword(s):  
Turbulent Shear ◽  
Motion Mechanism ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Turbulent Shear Layer ◽  
Induced Motion ◽  
Layer Flow ◽  
Set Up ◽  
Energy Harnessing ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of selectively applied surface roughness is used on a rigid circular cylinder supported by two end-springs in transverse steady flow. The flow-induced motions are enhanced dramatically reaching the limits of the experimental facility and motion mechanism at amplitude to diameter ratio A/D ≅ 3. In comparison to a smooth cylinder, in the fully turbulent shear layer flow regime at Reynolds number on the order of 100,000, PTC initiates VIV earlier at reduce velocity U* ≅ 4, reduces VIV amplitude depending on damping, and initiates galloping at U* ≅ 10 rather than 20. Thus, back-to-back VIV and galloping are achieved expanding the synchronization range of Flow Induced Motion (FIM) beyond U* ≅ 15 and the capabilities of the experimental set-up. The harnessed horizontal hydrokinetic power increased by a factor of four due to increased velocities in the synchronization range without any adjustment of the motion mechanism particulars.

Simulation of inviscid vortex-stretched turbulent shear-layer flow

AIAA Journal ◽  
1986 ◽  
Vol 24 (4) ◽  
pp. 680-682
Author(s):  
Arthur Rizzi ◽  
Charles J. Purcell
Keyword(s):  
Shear Layer ◽  
Turbulent Shear ◽  
Turbulent Shear Layer ◽  
Layer Flow

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.

Flow-Induced Vibration (FIV) and Hydrokinetic Power Conversion of Two Staggered, Low Mass-Ratio Cylinders, With Passive Turbulence Control in the TrSL3 Flow Regime (2.5×104

2017 ◽  
Author(s):  
Wanhai Xu ◽  
Chunning Ji ◽  
Hai Sun ◽  
Wenjun Ding ◽  
Michael M. Bernitsas
Keyword(s):  
Flow Regime ◽  
Total Power ◽  
Mass Ratio ◽  
Flow Induced Vibration ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Staggered Arrangement ◽  
Low Mass ◽  
Low Mass Ratio ◽  
Passive Turbulence Control

Flow-induced vibration (FIV), primarily vortex-induced vibrations (VIV) and galloping have been used effectively to convert hydrokinetic energy to electricity in model-tests and field-tests by the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan. The developed device, called VIVACE (VIV for Aquatic Clean Energy), harnesses hydrokinetic energy from river and ocean flows. One of the methods used to improve its efficiency of harnessed power efficiency is Passive Turbulence Control (PTC). It is a turbulence stimulation method that has been used to alter FIV of a cylinder in a steady flow. FIV of elastically mounted cylinders with PTC differs from the oscillation of smooth cylinders in a similar configuration. Additional investigation of the FIV of two elastically mounted circular cylinders in staggered arrangement with a low mass ratio in the TrSL3 flow-regime is required and is contributed by this paper. A series of experimental studies on FIV of two PTC cylinders in staggered arrangement were carried out in the recirculating water channel of MRELab. The two cylinders were allowed to oscillate in the transverse direction to the oncoming fluid flow. Cylinders tested have, diameter D = 8.89cm, length L = 0.895m and mass ratio m* = 1.343. The Reynolds number was in the range of 2.5×104<Re<1.2×105, which is a subset of the TrSL3 flow-regime. The center-to-center longitudinal and transverse spacing distances were T/D = 2.57 and S/D = 1.0, respectively. The spring stiffness values were in the range of 400<K<1200N/m. The values of harnessing damping ratio tested were ζharness = 0.04, 0.12, 0.24. For the values tested, the experimental results indicate that the response of the 1st cylinder is similar to a single cylinder; however more complicated vibration of the 2nd cylinder is observed. In addition, the oscillation system of two cylinders with stiffer spring and higher ζharness could initiate total power harness at a larger flow velocity and harness much higher power. These findings are very meaningful and important for hydrokinetic energy conversion.

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.

Investigation of a Reattaching Turbulent Shear Layer: Flow Over a Backward-Facing Step

1980 ◽  
Vol 102 (3) ◽  
pp. 302-308 ◽  
Author(s):  
J. Kim ◽  
S. J. Kline ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Eddy Viscosity ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Turbulence Structure ◽  
Backward Facing Step ◽  
Turbulent Shear Layer ◽  
Separated Shear Layer ◽  
Layer Flow

Incompressible flow over a backward-facing step is studied in order to investigate the flow characteristics in the separated shear-layer, the reattachment zone, and the redeveloping boundary layer after reattachment. Two different step-heights are used: h/δs = 2.2 and h/δs = 3.3. The boundary layer at separation is turbulent for both cases. Turbulent intensities and shear stress reach maxima in the reattachment zone, followed by rapid decay near the surface after reattachment. Downstream of reattachnent, the flow returns very slowly to the structure of an ordinary turbulent boundary layer. In the reattached layer the conventional normalization of outerlayer eddy viscosity by U∞ δ* does not collapse the data. However, it was found that normalization by U∞ (δ − δ*) does collapse the data to within ± 10% of a single curve as far downstream as x/xR ≈ 2, the last data station. This result illustrates the strong downstream persistence of the energetic turbulence structure created in the separated shear layer.

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

2015 ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Michael M. Bernitsas
Keyword(s):  
Parametric Design ◽  
Fluid Dynamic ◽  
Circular Cylinders ◽  
Design Parameters ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Flow Features ◽  
Induced Motion ◽  
Marine Hydrokinetic ◽  
The University

In the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan, Flow Induced Motion (FIM) is studied as a means to convert marine hydrokinetic energy to electricity using the VIVACE energy harvester [1–4]. Turbulence stimulation in the form of sand-strips, referred to as Passive Turbulence Control (PTC), were added to oscillating cylinders in 2008 [5]. PTC enabled VIVACE to harness hydrokinetic energy from currents/tides over the entire range of FIM including VIV and galloping. In 2011, the MRELab produced experimentally the PTC-to-FIM Map defining the induced cylinder motion based on the location of PTC [6]. In 2013, the robustness of the map was tested and dominant zones were identified [7]. Even though the PTC-to-FIM Map has become a powerful tool in inducing specific motions of circular cylinders, several parameters remain unexplored. Experiments, though the ultimate verification tool, are time consuming and hard to provide all needed information. A computational tool that could predict the FIM of a cylinder correctly would be invaluable to study the full parametric design space. A major side-benefit of PTC was the fact that PTC enabled computational fluid dynamic (CFD) simulations to generate results in good agreement with experiments by forcing the location of the separation point [8]. This valuable tool, along with experiments, is used in this paper to investigate PTC design parameters such as width and thickness and their impact on flow features with the intent of maximizing FIM and, thus, hydrokinetic energy conversion.

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