Boundary-layer influences on the subsonic near-wake of bluff bodies

1994 ◽  
Vol 31 (2) ◽  
pp. 443-444 ◽  
Author(s):  
Colin P. Britcher ◽  
Charles W. Alcorn
Keyword(s):  
Boundary Layer ◽  
Bluff Bodies ◽  
Near Wake

An Experimental Study of the Flow Above the Free Ends of Surface-Mounted Bluff Bodies

2012 ◽  
Author(s):  
Noorallah Rostamy ◽  
David Sumner ◽  
Donald J. Bergstrom ◽  
James D. Bugg
Keyword(s):  
Boundary Layer ◽  
Flow Pattern ◽  
Vortex Shedding ◽  
Ground Plane ◽  
Separated Flow ◽  
The Body ◽  
Bluff Bodies ◽  
Near Wake ◽  
Square Prism ◽  
Karman Vortex

The flow around surface-mounted finite-height bluff bodies is more complex than the flow around a two-dimensional or “infinite” cylinder. The flow over the free end and the boundary layer flow around the body-wall junction strongly influence the near-wake flow pattern. Streamwise tip vortex structures interact in a complex manner with Kármán vortex shedding from the sides of the body, and are responsible for a downward-directed local velocity field in the upper part of the wake known as “downwash.” A second pair of streamwise vortex structures, known as the base vortices, is found close to the ground plane. Upstream of the body the familiar horseshoe vortex is found. The interactions between the tip vortices, base vortices, and Kármán vortex shedding are strongly influenced by the aspect ratio, AR = H/D (for height, H, and width, D), the Reynolds number, Re, and the relative thickness of the boundary layer, δ/D. The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied in a low-speed wind tunnel using particle image velocimetry (PIV). Cylinders and prisms of AR = 9, 7, 5, and 3 were tested at Re = 4.2 × 104. The bodies were mounted normal to a ground plane and were partially immersed in a turbulent flat-plate boundary layer with δ/D = 1.7. PIV measurements were made above the free ends in three vertical planes at different cross-stream locations (y/D = 0, 0.25, and 0.375). The ensemble-averaged streamlines, turbulence intensity and Reynolds shear stress fields were obtained in these planes. The PIV results provide insight into the separated flow above the free ends, including the effects of AR and body shape. For the finite square prism, the large, separated, recirculating flow region extends into the near-wake. For the finite circular cylinder, this region is smaller and the separated flow reattaches onto the free-end surface. For the square prism of AR = 3, considerable difference is seen in the free-end flow pattern compared to the more slender prisms of AR = 9, 7 and 5. In particular, a cross-stream vortex is formed due to interaction between the separated flow from the leading edge of the prism and the reverse flow over the free end. This vortex is seen in all three planes for AR = 3 but only in the symmetry plane for AR = 9, while for the finite circular cylinder the flow pattern above the free end seems to be the same in all three planes for all aspect ratios, consisting of a cross-stream vortex at approximately x/D = 0.

Formation of Vortex Street in Laminar Boundary Layer

1980 ◽  
Vol 47 (2) ◽  
pp. 227-233 ◽  
Author(s):  
M. Kiya ◽  
M. Arie
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Laminar Boundary Layer ◽  
Solid Wall ◽  
Vortex Sheet ◽  
Vortex Street ◽  
Bluff Bodies ◽  
Uniform Shear ◽  
Uniform Shear Flow ◽  
Vortex Patterns

Main features of the formation of vortex street from free shear layers emanating from two-dimensional bluff bodies placed in uniform shear flow which is a model of a laminar boundary layer along a solid wall. This problem is concerned with the mechanism governing transition induced by small bluff bodies suspended in a laminar boundary layer. Calculations show that the background vorticity of shear flow promotes the rolling up of the vortex sheet of the same sign whereas it decelerates that of the vortex sheet of the opposite sign. The steady configuration of the conventional Karman vortex street is not possible in shear flow. Theoretical vortex patterns are experimentally examined by a flow-visualization technique.

Numerical Investigation of Flow Around Bluff Bodies

1998 ◽  
Vol 14 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Chou-Jiu Tsai ◽  
Ger-Jyh Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Near Wake ◽  
Navier Stokes Equations ◽  
Physical Description ◽  
Geometrical Shapes ◽  
Flow Phenomena ◽  
Volume Method

ABSTRACTIn this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.

Similarity in the turbulent near wake of bluff bodies

AIAA Journal ◽  
1975 ◽  
Vol 13 (11) ◽  
pp. 1425-1429 ◽  
Author(s):  
R. K. Sullerey ◽  
A. K. Gupta ◽  
C. S. Moorthy
Keyword(s):  
Bluff Bodies ◽  
Near Wake

Non-uniqueness in wakes and boundary layers

1984 ◽  
Vol 391 (1800) ◽  
pp. 1-26 ◽  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Algebraic Decay ◽  
Scale Separation ◽  
Boundary Layer Equations ◽  
Classical Boundary ◽  
Streamlined Flow ◽  
High Reynolds

In streamlined flow past a flat plate aligned with a uniform stream, it is shown that ( a ) the Goldstein near-wake and ( b ) the Blasius boundary layer are non-unique solutions locally for the classical boundary layer equations, whereas ( c ) the Rott-Hakkinen very-near-wake appears to be unique. In each of ( a ) and ( b ) an alternative solution exists, which has reversed flow and which apparently cannot be discounted on immediate grounds. So, depending mainly on how the alternatives for ( a ), ( b ) develop downstream, the symmetric flow at high Reynolds numbers could have two, four or more steady forms. Concerning non-streamlined flow, for example past a bluff obstacle, new similarity forms are described for the pressure-free viscous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include non-uniqueness, singularities and algebraic behaviour, consistent with non-entraining shear layers with algebraic decay. Non-uniqueness also seems possible in reattachment onto a solid surface and for non-symmetric or pressure-controlled flows including the wake of a symmetric cascade.

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