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Research Papers: Fundamental Issues and Canonical Flows

Investigations on Bluff Bodies as Improved Vortex Shedders Placed Inside a Circular Pipe

[+] Author and Article Information
A. Venugopal

School of Mechanical Sciences,
Indian Institute of Technology Bhubaneswar,
Bhubaneswar 752050, Orissa, India
e-mail: venugopal@iitbbs.ac.in

Amit Agrawal, S. V. Prabhu

Department of Mechanical Engineering,
Indian Institute of Technology Bombay,
Powai,
Mumbai 400076, India

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received July 13, 2016; final manuscript received November 30, 2016; published online February 15, 2017. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 139(4), 041204 (Feb 15, 2017) (9 pages) Paper No: FE-16-1449; doi: 10.1115/1.4035465 History: Received July 13, 2016; Revised November 30, 2016

In the present study, we visualize the turbulent wake of various bluff bodies placed inside a circular pipe. The objective is to identify shapes which are strong vortex generators and incur minimum irrecoverable pressure loss. The shapes of the bluff bodies are chosen such that they exhibit distinct separation point for strong and stable vortex shedding. The dye used for flow visualization is a shear-thickening and high extension viscosity fluid, which can sustain turbulent separated flows. The planar illumination of the flow field with laser sheet improves the visibility of coherent structures for qualitative and quantitative assessment of the images. The vortex shedding frequency, wake width, and vortex formation length are computed from image analysis. The results highlight that streamlined shapes possess lower wake width and larger vortex formation length, whereas blunt shapes (like triangle and trapezoid) show a larger wake width and a shorter vortex formation length. The vortex shedding frequency is also measured with a piezoelectric sensor to aid flow visualization studies. The optimum location of the piezoelectric sensor is explained based on the vortex formation length to obtain high amplitude signals. Among all the shapes studied, trapezoidal bluff body appears to be the most appropriate shape with strong and stable vortex shedding. This information is useful in the design of vortex flowmeters and other similar applications.

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Figures

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Fig. 2

Summary of results for various shapes

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Fig. 1

Orientation of piezoelectric sensor behind bluff body

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Fig. 3

Sequence of images showing vortex formation: (a) trapezoid (l/d = 1.25), (b) bullet shape body (l/d = 1.5), and (c) triangular body (l/d = 1.2) at ReD = 1.0 × 104

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Fig. 5

Strouhal number variation with Reynolds number for various bluff bodies (flow visualization)

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Fig. 9

Strouhal number variations with Reynolds number for trapezoidal shape

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Fig. 6

Strouhal number variation with Reynolds number for elliptic shape body with truncated edge facing the flow

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Fig. 7

Strouhal number variation with Reynolds number for triangular body

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Fig. 8

Normalized wall pressure distribution for various shapes

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Fig. 10

Vortex street for trapezoidal shape: (a) ReD = 10,000 and (b) ReD = 15,000

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Fig. 11

Power spectrum at various Reynolds numbers for trapezoidal bluff body obtained from flow visualization at plane a (a) and plane b (b). PSD: power spectral density.

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