# Vortex shedding characteristics of a cylinder with a parallel slit placed in a circular pipe

### Abstract

Visualization experiments for flow around a cylinder with parallel slit placed inside a circular pipe are carried out with water as the working medium. Two different color dyes are employed to visualize the complex vortex formation mechanism behind the bluff bodies. The objective of this study is to explore the potential of cylinder with parallel slit as an improved vortex generator for various practical applications. Wake parameters, such as Strouhal Number, wake width, and vortex formation length, are calculated from the recorded images. Three different slit widths with non-dimensional separation ratio of 0.1, 0.2, and 0.4 are chosen to study the effect on the vortex formation mechanism and the corresponding wake parameters. The Reynolds number range covered in this study is *Re* _{ D } = 200–2300. Symmetric vortex formation from the outer surface is observed for lower slit widths, whereas for high slit widths, both in-phase and anti-phase shedding are observed. A separation bubble from each of the inner surface is formed which detaches from the bluff body to form a vortex at higher Reynolds numbers. The separation bubble is found to be both bi-stable and symmetric for lower slit widths. The interaction of the separation bubble with the outer vortices is seen to affect the strength of the primary/outer vortex. The slit width is seen to be an important parameter in determining the strength of the vortices. At higher slit width, the configuration behaves like a dual bluff body and strong crisscross vortex shedding is observed. Such novel kind of vortex formation mechanism can be utilized to improve the performance of numerous practical applications, such as flowmeters, heat exchangers, etc.

### Graphical abstract

## Keywords

Flow visualization Vortex shedding Parallel slit Wake Separation bubble## List of symbols

*B*Blockage ratio (

*d/D*)*D*Inner diameter of circular pipe (m)

*d*Diameter of bluff body (m)

*f*Frequency of vortex shedding (Hz)

*L′*Vortex formation length (m)

*L*_{c}Characteristic length (m)

*s*Slit width (m)

*U*_{m}Mean velocity (m/s)

*W*Wake width (m)

## Non-dimensional numbers

*Re*_{D}Reynolds number \(\left( {\frac{{\rho U_{\text{m}} D}}{\mu }} \right)\)

*St*Strouhal number \(\left( {St = \frac{fd}{{U_{\text{m}} }}} \right)\)

## Greek symbols

*ρ*Density of fluid (kg/m

^{3})*μ*Dynamic viscosity of fluid (Pa s)

## Notes

### Acknowledgments

The authors acknowledge funding support for this research from Department of Science and Technology, New Delhi.

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