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Research Papers: Fundamental Issues and Canonical Flows

# PIV Investigation of Flow Behind Surface Mounted Detached Square Cylinder

[+] Author and Article Information
P. K. Panigrahi

Department of Mechanical Engineering, IIT Kanpur, Kanpur UP 208016, Indiapanig@iitk.ac.in

J. Fluids Eng 131(1), 011202 (Nov 26, 2008) (16 pages) doi:10.1115/1.3026721 History: Received July 02, 2007; Revised September 29, 2008; Published November 26, 2008

## Abstract

The flow field behind surface mounted detached square ribs under the approaching flat plate turbulent boundary layer has been experimentally studied using the particle image velocimetry (PIV) (two-component and stereo) technique in both streamwise and cross stream measurement planes. An oil film visualization study has been carried out for correlating the surface flow patterns to the flow structures. The Reynolds number based on the rib height is equal to 11,075. The ratio of the gap height to the square rib size is set equal to 0.2, 0.37, 0.57, and 1.0. The ratio of approaching boundary layer thickness to rib height is equal to 0.2. The mean and rms velocity fields, streamwise and spanwise vorticity fields, velocity gradient and velocity vector fields, turbulent kinetic energy budgets, and stream trace results are reported. The second invariant of the velocity gradient tensor results are presented to distinguish between the rotational and shear contribution of the vorticity field. The recirculation bubbles with a focilike structure are observed behind the detached ribs. These structures are displaced upward, i.e., away from the wall surface with an increase in gap size of the detached cylinder. The size of the recirculation bubble also drops with an increase in the gap size. The stream traces in the cross stream plane show node-saddle patterns, whose near wall concentration is high for a lower gap size detached cylinder. The oil film visualization images show saddle patterns at the meeting point between the flow through the gap and the reattaching shear layer for the lower gap size detached cylinder. The $v$-velocity magnitude distribution shows greater wall-normal motion across the wake for the detached cylinder of lower gap size. There is a significant near wall velocity fluctuation for the lower gap size detached cylinder. The higher velocity fluctuation due to the near wall flow structures contributes toward an increase in the near wall mixing of a detached cylinder geometry. Overall, the present study clearly demonstrates the flow structures behind detached ribs, which are responsible for effective near wall mixing. The results from this study provide useful understanding for the design of turbulators in various practical applications.

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## Figures

Figure 3

The normalized u-velocity field (top) and v-velocity field (bottom) behind detached ribs for gap to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 4

The time averaged stream traces superposed on the normalized velocity magnitude for detached ribs of gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 5

The stream traces using the y and z components of velocity (v,w) superposed on the normalized streamwise (u) velocity in the cross stream (y-z) plane at x∕h=0.5 (top) and x∕h=1.5 (bottom) for detached ribs with gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 6

The normalized urms∕Uo velocity behind the detached ribs in the x-y plane for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 7

The normalized urms, vrms, wrms and total rms velocity behind detached ribs in the cross stream y-z plane (x∕h=0.5) for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 8

The instantaneous velocity vector (with three data points skipped in both x and y directions) and instantaneous vorticity (ωz) plots behind detached ribs for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 9

The instantaneous u-velocity, ωx-vorticity, and velocity gradients (δu∕δz and δu∕δy) in the y-z plane (x∕h=1.5) behind detached ribs for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 1

The schematic of the experimental setup

Figure 2

(a) The schematic of the detached rib mounted over flat plate and (b) different measurement zones (streamwise and cross stream planes) for the PIV measurements

Figure 10

The oil film visualization pictures of different detached rib configurations for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 11

The average coherent structure evaluation parameters, i.e., vorticity (ωz) and invariance of the velocity gradient tensor (Q2D-Z) behind detached ribs for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 12

The normalized total turbulent kinetic energy and the normalized production of turbulent kinetic energy behind detached ribs for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

Figure 13

The normalized turbulent kinetic energy budget terms behind detached ribs for gap size to rib height ratio: (a) G∕h=0.2, (b) G∕h=0.37, (c) G∕h=0.57, and (d) G∕h=1.0

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