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TECHNICAL PAPERS

Mean and Fluctuating Velocity Characteristics of a Separated Shear Layer Past a Surface Mounted Block

[+] Author and Article Information
Ü. Özkol

Department of Mechanical Engineering, İzmir Yüksek Teknoloji Enstitüsü, İzmir, Turkeyunverozkol@iyte.edu.tr

C. Wark

Mechanical, Materials and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616wark@iit.edu

D. Fabris

Mechanical Engineering Department, Santa Clara University, Santa Clara, CA 95053dfabris@scu.edu

J. Fluids Eng 129(2), 200-208 (Aug 05, 2006) (9 pages) doi:10.1115/1.2409359 History: Received January 02, 2006; Revised August 05, 2006

Abstract

The mean velocity, Reynolds stress, and mean vorticity regions of a separated shear layer over a surface mounted block are investigated by 2D Digital Particle Image Velocimetry (DPIV) for three Reynolds numbers ($Rea=500$, $1000$, and $2500$) and two channel-to-block height ratios ($H∕a=1.825$ and $4.6$). The recirculation region’s height and length are determined for the separated shear layer by means of $U¯=0$ contours. It is observed that the high Reynolds stress regions lay just outside of the $U¯=0$ contours. The flow visualization and DPIV measurement of vorticity indicate that the differing normalized Reynolds stresses between $Rea=500$ and 1000 are most probably due to the initiation of the vortex shedding between these two Reynolds numbers while, differences are minimal between $Rea=1000$ and 2500. A sign change in the Reynolds shear stress distribution of the separated shear layer near the leading edge of the block was recognized for every Reynolds number and channel width.

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Figures

Figure 1

Water flow facility, top view and side view

Figure 2

Schematic of model geometry and measurement regions. The orientation of the coordinate system is based on the leading edge of the upper surface, indicated by l.e.

Figure 3

Joint histogram of U′ and V′ along with the normalized Reynolds shear stress contours, Rea=1000, H∕a = 4.6. The data for this figure result from the ensemble average of 1000 DPIV realizations.

Figure 4

Path used in the calculation of the circulation estimate

Figure 5

Normalized flow rate for H∕a=1.825. (…; Rea=500), (ooo; Rea=1000), (xxx; Rea=2500).

Figure 6

Mean velocity contours for the flow in the top region for Rea=1000 at H∕a=1.825. Note that the measurement region is scaled with block height (a) and block’s leading and trailing edges are located at (x∕a,y∕a)=(0,0) and (2.5,0), respectively.

Figure 7

Recirculation height versus Reynolds number

Figure 8

Recirculation length versus Reynolds number

Figure 9

Long exposure imaging of seeding particles identifying vortex shedding events over the top of the block for Rea=1000, H∕a=4.6. Arrows indicating the rotational motion are superimposed on the image.

Figure 10

Normalized streamwise Reynolds stress distributions, u′u′¯∕Uinlet2, for three Reynolds numbers at H∕a=1.825. The U¯=0 velocity contour is superimposed to indicate the size of the recirculation region.

Figure 11

Normalized wall-normal Reynolds stress distributions, v′v′¯∕Uinlet2, for two different channel widths at Rea=500

Figure 12

Normalized Reynolds shear stress distributions, u′v′¯∕Uinlet2, for three Reynolds numbers at H∕a=1.825

Figure 13

Normalized instantaneous vorticity distribution, ωz¯a∕Uinlet, for Rea=1000, H∕a=1.825

Figure 14

Mean vorticity field for Reynolds numbers 500, 1000, and 2500 at H∕a=1.825

Errata

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