Research Papers: Fluid-Structure Interaction

Experimental Investigation on Vortex Shedding and Fluid Elastic Instability in Finned Tube Arrays Subjected to Water Cross Flow

[+] Author and Article Information
Sandeep R. Desai

Department of Automobile Engineering,
Rajarambapu Institute of Technology,
Islampur 415414, Maharashtra, India
e-mail: sandeep.desai@ritindia.edu

S. Pavitran

Mechanical Engineering Department,
Vishwakarma Institute of Technology,
Pune 400036, Maharashtra, India
e-mail: pavitra@vit.edu

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 20, 2016; final manuscript received June 20, 2017; published online August 1, 2017. Assoc. Editor: Tomomichi Nakamura.

J. Pressure Vessel Technol 139(5), 051301 (Aug 01, 2017) (10 pages) Paper No: PVT-16-1142; doi: 10.1115/1.4037263 History: Received August 20, 2016; Revised June 20, 2017

The paper presents results of an experimental study on fluid elastic instability and vortex shedding in plain and finned arrays exposed to water cross flow. The parallel triangular array with cantilever end condition is considered for the study. Pitch ratios considered are 2.1 and 2.6 while fin densities considered are 4 fpi (fins per inch) and 10 fpi. The results for critical velocity at instability for two finned tube arrays are presented. Apart from results on fluid elastic vibration behavior, extensive results on vortex shedding are also presented to study the phenomenon in tube arrays subjected to water cross flow. The test parameters measured are water flow rate, natural frequency, and vibration amplitudes of the tubes. The datum case results were first obtained by testing plain arrays with pitch ratios 2.1 and 2.6. This was then followed by experiments with finned arrays with pitch ratios 2.1 and 2.6, and each with two different fin densities. The higher pitch ratios typical of chemical process industries resulted in the delayed instability threshold due to weak hydrodynamic coupling between the neighboring tubes. The results indicated that finned arrays are more stable in water cross flow compared to plain arrays. The Strouhal numbers corresponding to small peaks observed before fluid elastic instability are computed and compared with the expected ones according to Owen's hypothesis. It was concluded that peaks observed are attributed to vortex shedding observed for all the arrays tested in water.

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Fig. 1

Flow loop schematic for fluid elastic instability experiments

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Fig. 2

Test section assembly

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Fig. 3

Tube array configuration

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Fig. 4

Outer box to hold support rod: (a) front view, (b) side view, and (c) top view

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Fig. 5

Spiral crimped type fin shape

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Fig. 6

Fin tube welded with support rod

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Fig. 7

Assembly of outer box to the test section

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Fig. 8

Mounting of accelerometer at the free end of the test tube

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Fig. 9

Amplitude ratio versus reduced velocity for single phase water cross flow

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Fig. 10

Strouhal numbers for parallel triangular tube arrays

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Fig. 11

Natural frequency in water versus gap velocity

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Fig. 12

Data presentation on stability map for tube arrays with Xp = 2.1

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Fig. 13

Data presentation on stability map for tube arrays with Xp = 2.6




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