scholarly journals On Blockage Effects for a Tidal Turbine in Free Surface Proximity

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3325 ◽  
Author(s):  
Nitin Kolekar ◽  
Ashwin Vinod ◽  
Arindam Banerjee
Keyword(s):  
Free Surface ◽  
Rotational Speed ◽  
Surface Deformation ◽  
Wake Flow ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Near Wake ◽  
Tidal Turbine ◽  
Free Surface Deformation ◽  
Surface Proximity

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired through a submerged sensor. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on tip speed ratio and free surface to blade tip clearance. Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation. In addition, particle image velocimetry was carried out in the turbine near-wake using time- and phase-averaged techniques to understand the mechanism responsible for the variation of power coefficient with rotational speed and free surface proximity. Slower wake propagation for higher rotational velocities and increased asymmetry in the wake with increasing free surface proximity was observed. Improved performance at high rotational speed was attributed to enhanced wake blockage, and performance enhancement with free surface proximity was due to the additional blockage effects caused by the free surface deformation. Proper orthogonal decomposition analysis revealed a downward moving wake for the turbine placed in near free surface proximity.

scholarly journals Deformation and Bubble Entrapment of Free Surface Before Axisymmetric Bodies Detaching From Water Fully

2019 ◽  
Vol 35 (6) ◽  
pp. 863-874
Author(s):  
X. Song ◽  
Q. G. Wu ◽  
B. Y. Ni ◽  
H. L. Chen
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Surface Deformation ◽  
Circular Cone ◽  
Wake Flow ◽  
Experimental Apparatus ◽  
Free Surface Deformation ◽  
The Moment ◽  
Axisymmetric Bodies ◽  
Spike Patterns

ABSTRACTExperiments are presented on the deformation of free surface induced by water exit of axisymmetric bodies, particular at the moment before body detaching from water. A set of experimental apparatus is designed to provide driving force for the bodies. A high-speed camera is adopted to capture the motion and deformation of the free surface. Bodies of various shapes, including a stretched spheroid, a sphere, a circular cone and a combination of cylinder and circular cone, are lifted out of water with different velocities, by using a straight rod attached on the top of models. It is found that free-surface deformation is affected by the moving velocity a lot. Three wake flow or free-surface spike patterns are generated corresponding to different velocities. When the velocity is larger than a critical velocity, cavitation incepts and bubble is entrapped inside the water spike, which changes the flow pattern and shape of the spike. It is aimed to explore the spike phenomenon of free surface and explain the reasons behind it.

scholarly journals Blockage effects on the hydrodynamic performance of a marine cross-flow turbine

2013 ◽  
Vol 371 (1985) ◽  
pp. 20120299 ◽  
Author(s):  
Claudio A Consul ◽  
Richard H. J Willden ◽  
Simon C McIntosh
Keyword(s):  
Free Surface ◽  
Surface Deformation ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Hydrodynamic Performance ◽  
Power Coefficient ◽  
Surface Boundary ◽  
Useful Power ◽  
Free Surface Deformation ◽  
Surface Representations

This paper explores the influence of blockage and free-surface deformation on the hydrodynamic performance of a generic marine cross-flow turbine. Flows through a three-bladed turbine with solidity 0.125 are simulated at field-test blade Reynolds numbers, O (10 5 –10 6 ), for three different cross-stream blockages: 12.5, 25 and 50 per cent. Two representations of the free-surface boundary are considered: rigid lid and deformable free surface. Increasing the blockage is observed to lead to substantial increases in the power coefficient; the highest power coefficient computed is 1.23. Only small differences are observed between the two free-surface representations, with the deforming free-surface turbine out-performing the rigid lid turbine by 6.7 per cent in power at the highest blockage considered. This difference is attributed to the increase in effective blockage owing to the deformation of the free surface. Hydrodynamic efficiency, the ratio of useful power generated to overall power removed from the flow, is found to increase with blockage, which is consistent with the presence of a higher flow velocity through the core of the turbine at higher blockage ratios. Froude number is found to have little effect on thrust and power coefficients, but significant influence on surface elevation drop across the turbine.

Free-surface deformation measurement

1997 ◽  
Author(s):  
H. Stahl ◽  
Kevin Stultz ◽  
H. Stahl ◽  
Kevin Stultz
Keyword(s):  
Free Surface ◽  
Surface Deformation ◽  
Deformation Measurement ◽  
Free Surface Deformation

Numerical Analysis of Free Surface Deformation in Water Tank

2003 ◽  
Author(s):  
Fumio Shimizu ◽  
Kiyoshi Hatakenaka ◽  
Kazuhiro Tanaka ◽  
Hiroshi Shigefuji ◽  
Takeshi Shimizu
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Surface Deformation ◽  
Internal Flow ◽  
Oscillating Flow ◽  
Water Tank ◽  
Loud Noise ◽  
Two Phase ◽  
Free Surface Deformation ◽  
Good Agreement

A siphon phenomenon is one of gas/liquid two-phase flows including free surface deformation. Since the large-scale deformation of the free surface causes a loud noise, it is important to investigate the motion of the free surface. The purpose of the present study is to reproduce a siphon phenomenon in computer, and to analyze an internal flow field of the siphon phenomenon. An oscillating flow in two-dimensional U-tube was simulated to verify our computational codes, and good agreement compared with the theoretical period was obtained. After that, the numerical reproduction of a siphon phenomenon was succeeded and the behavior of the free surface was captured reasonably.

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