Near-wake flow structure of elliptic cylinders close to a free surface: effect of cylinder aspect ratio

2004 ◽  
Vol 36 (5) ◽  
pp. 748-758 ◽  
Author(s):  
Daichin ◽  
Sang Joon Lee
Keyword(s):  
Free Surface ◽  
Aspect Ratio ◽  
Flow Structure ◽  
Surface Effect ◽  
Wake Flow ◽  
Near Wake

Effect of aspect ratio on the near-wake flow structure of an Ahmed body

2015 ◽  
Vol 147 ◽  
pp. 95-103 ◽  
Author(s):  
M. Corallo ◽  
J. Sheridan ◽  
M.C. Thompson
Keyword(s):  
Aspect Ratio ◽  
Flow Structure ◽  
Wake Flow ◽  
Near Wake ◽  
Ahmed Body

scholarly journals Near-Wake Flow Structure of a Suspended Cylindrical Canopy Patch

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 84 ◽  
Author(s):  
Ayşe Yüksel Ozan ◽  
Didem Yılmazer
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Green Infrastructure ◽  
Nutrient Management ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Vegetation Patch ◽  
Comprehensive Picture ◽  
Flowing Waters

Urban stormwater is an important environmental problem, especially for metropolitans worldwide. The most important issue behind this problem is the need to find green infrastructure solutions, which provide water treatment and retention. Floating treatment wetlands, which are porous patches that continue down from the free-surface with a gap between the patch and bed, are innovative instruments for nutrient management in lakes, ponds, and slow-flowing waters. Suspended cylindrical vegetation patches in open channels affect the flow dramatically, which causes a deviation from the logarithmic law. This study considered the velocity measurements along the flow depth, at the axis of the patch, and at the near-wake region of the canopy, for different submerged ratios with different patch porosities. The results of this experimental study provide a comprehensive picture of the effects of different submergence ratios and different porosities on the flow field at the near-wake region of the suspended vegetation patch. The flow field was described with velocity and turbulence distributions along the axis of the patch, both upstream and downstream of the vegetation patch. Mainly, it was found that suspended porous canopy patches with a certain range of densities (SVF20 and SVF36 corresponded to a high density of patches in this study) have considerable impacts on the flow structure, and to a lesser extent, individual patch elements also have a crucial role.

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.

Comparison of Near Wake-Flow Structure Behind a Solid Cap With an Attached Bubble and a Solid Counterpart

2003 ◽  
Author(s):  
Hidekazu No ◽  
Michel Call ◽  
Akira T. Tokuhiro
Keyword(s):  
Flow Structure ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Equivalent Diameter ◽  
Velocity Measurements ◽  
Near Wake ◽  
Downward Flow ◽  
Air Bubble ◽  
Square Channel ◽  
Image Velocimetry

An experimental study was conducted on the flow structure in the near-wake of a hollow cap with an air bubble attached underneath and a solid object possessing a bubble-like shape. The objective of the study was to elucidate distinguishing wake flow characteristics of the capped bubble relative to the solid. The experiment was performed in a square channel, 80×80mm2 in cross section. The bubble and solid were separately suspended in downward flow of purified water. Both the capped bubble and the solid were ellipsoidal in shape (the cap was shaped to represent the front of an ellipsoidal bubble) and had an approximate volume of 0.8ml. The Reynolds number for the flow, based on the objects’ equivalent diameter and average downward flow velocity (U = 25cm/s), was Re ≅ 2800. Velocity measurements were taken using Particle Image Velocimetry. The obtained velocity data were analyzed to deduce vorticity, turbulent kinetic energy, production, and Reynolds stress. Graphic and numerical comparisons between the two cases were made. The results to date are discussed.

PIV Measurements of the Near-Wake Flow of an Airfoil Above a Free Surface

2007 ◽  
Vol 19 (4) ◽  
pp. 482-487 ◽  
Author(s):  
Daichin ◽  
Wen Kang ◽  
Li-li Zhao
Keyword(s):  
Free Surface ◽  
Wake Flow ◽  
Near Wake ◽  
Piv Measurements
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