Characterization of Flow Separation around Inline Cylinders within Oscillatory Flow

Yiding Zhao,Yao Shi

doi:10.1155/2018/7569432

Abstract

This paper has examined the effects of Reynolds number (Re), Keulegan–Carpenter number (KC), and gap ratio on flow separation around a cylinder array by PIV method in experiment. The vortex shedding in such situation occurs each half period of the oscillatory motion from the observation. No matter how many cylinders, KC is the key dominant parameter under low Re that has a great impact on the flow regime and flow motion in oscillatory flows. There is an influence area of vortex shedding around the cylinder. When two inline cylinders are in the flow, smaller gap ratio may extend the influence area of the vortex shedding. For s/d = 2, the vortex shedding that happens in each cylinder has a simultaneity and independence. For s/d = 1.5, the reduced gap ratio leads the upstream shed vortex to interact with downstream cylinder and makes the influence area of vortex shedding around downstream cylinder extends further. For s/d = 1, the interference in the central area is significantly obvious and the vortex shedding is suppressed and even follows the cross gap flow.

Highlights

Flow separation around a single cylinder is well understood [1] that hydrodynamics around a single cylinder in both steady current and oscillatory flows from two aspects which are flow regimes and forces
Vortex shedding occurs at either side at a certain frequency in the wake region when Reynolds number (Re) is above 40. e turbulent boundary layer separation occurs at one side of cylinder with laminar at the other side in 3∗105 < Re < 3.5∗105 [2], which can cause significant nonzero mean lift on the cylinder. e two-dimensional vortex shedding occurs in the range of 40 < Re < 200 and the model of vortex shedding is laminar [3]
E interaction of vortex systems between a pair of sideby-side square cylinders in numerical, which demonstrated that different gap ratio of cylinders, plays an important role in the vortex shedding of side-by-side cylinders for a certain Keulegan–Carpenter number (KC) value [10]. e effects of different KC values have been studied by finite-element simulation, which is based on the oscillatory flows around four cylinders in square arrangement of 2 times gap ratio [11]

Summary

Research Article

Characterization of Flow Separation around Inline Cylinders within Oscillatory Flow. is paper has examined the effects of Reynolds number (Re), Keulegan–Carpenter number (KC), and gap ratio on flow separation around a cylinder array by PIV method in experiment. e vortex shedding in such situation occurs each half period of the oscillatory motion from the observation. Characterization of Flow Separation around Inline Cylinders within Oscillatory Flow. Is paper has examined the effects of Reynolds number (Re), Keulegan–Carpenter number (KC), and gap ratio on flow separation around a cylinder array by PIV method in experiment. E vortex shedding in such situation occurs each half period of the oscillatory motion from the observation. Ere is an influence area of vortex shedding around the cylinder. When two inline cylinders are in the flow, smaller gap ratio may extend the influence area of the vortex shedding. For s/d 2, the vortex shedding that happens in each cylinder has a simultaneity and independence. For s/d 1, the interference in the central area is significantly obvious and the vortex shedding is suppressed and even follows the cross gap flow

Introduction

Methodology

Data set

Fourier transform