Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

Equivalent Diameter for Predicting Vortex Shedding of Finned Cylinders in Cross-Flow

10.1115/pvp2021-63015 ◽

2021 ◽

Author(s):

Mohammed Alziadeh ◽

Atef Mohany

Keyword(s):

Vortex Shedding ◽

Tube Bundle ◽

Cross Flow ◽

Acoustic Resonance ◽

Finned Tube ◽

Resonance Excitation ◽

Equivalent Diameter ◽

Frequency Scaling ◽

Abstract This article explores different equivalent diameter equations found in the literature for shedding frequency scaling and applying it to various types of finned cylinders in industrial heat exchangers. The focus is on three finned cylinder types: straight, twist-serrated, and crimped spirally finned cylinders. Within each finned cylinder category, at least three different finned cylinders are investigated. The results indicate that utilizing the appropriate equivalent diameter for vortex shedding frequency scaling collapses the data within the Strouhal bounds of a bare cylinder away from resonance excitation. However, the onset of flow-excited acoustic resonance and peak acoustic pressure in all the finned cylinder cases occur at a reduced flow velocity earlier than their equivalent diameter bare cylinder. This suggests that although utilizing the appropriate equivalent diameter can predict the shedding frequency away from resonance, it cannot be used in velocity scaling to predict the onset of acoustic resonance in finned tube bundle.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

Journal of Energy Resources Technology ◽

10.1115/1.3231028 ◽

1984 ◽

Vol 106 (1) ◽

pp. 70-78 ◽

Cited By ~ 78

Author(s):

A. J. Grass ◽

P. W. J. Raven ◽

R. J. Stuart ◽

J. A. Bray

Keyword(s):

Boundary Layer ◽

Strouhal Number ◽

Vortex Shedding ◽

Combined Effects ◽

Maximum Increase ◽

Velocity Gradients ◽

Large Velocity ◽

Layer Velocity ◽

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

Wake Flow Behind a Cylinder With a Detached Splitter Plate

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2005-77045 ◽

2005 ◽

Cited By ~ 1

Author(s):

Minter Cheng

Keyword(s):

Strouhal Number ◽

Vortex Shedding ◽

Formation Process ◽

Vortex Formation ◽

Splitter Plate ◽

Wake Flow ◽

Plate Length ◽

Splitter Plates ◽

Fluid flow across a bluff body can induce a series alternating vortices in the downstream flow field. The vortex flow can produce adverse effects on many engineering applications. A number of studies have shown that the wake splitter plate is one of the means to stabilize the vortex formation process. However, most of the previous studies are confined to cylinders with attached splitter plates. Very few studies investigate the effects of the spacing between the cylinder and the splitter plate on the formation of wake vortices. In the present study, the effects of the splitter plate length as well as the gap distance between the splitter plate and the cylinder on the wake flow behind a cylinder have been studied experimentally for low Reynolds number of 400. Both circular and square cylinders are studied in this research. Four splitter plates with different length, 1 ≤ L/D ≤ 4, have been used and a range of cylinder and splitter plate gap distance, 0 < G/D < 6, have been studied. By using flow visualization technique and hot-film anemometer measurement, detailed measurements of the velocity distribution, the vortex shedding frequency, the wake width, and the wake formation length are carried out in order to get a clear understanding of the flow interference behavior. The experimental results indicate that splitter plates alter the vortex formation process in the wake causing a decrease in vortex shedding frequency. The Strouhal number decreases with increasing the splitter plate length as well as the gap distance between the cylinder and the splitter plate. It is shown that a jump in Strouhal number occurs at G/D of 3 to 6. The jump is splitter plate length dependent, and generally the gap distance at which jump takes place increases as the splitter plate length increases.

A Study on Vortex Shedding From Spheres in a Uniform Flow

Journal of Fluids Engineering ◽

10.1115/1.2909415 ◽

1990 ◽

Vol 112 (4) ◽

pp. 386-392 ◽

Cited By ~ 268

Author(s):

H. Sakamoto ◽

H. Haniu

Keyword(s):

Reynolds Number ◽

Strouhal Number ◽

Vortex Shedding ◽

Water Channel ◽

Reynolds Numbers ◽

Uniform Flow ◽

Freestream Velocity ◽

Shedding Frequency ◽

Visualization Experiments

Vortex shedding from spheres at Reynolds numbers from 3 × 102 to 4 × 104 in a uniform flow was investigated experimentally. Standard hot-wire technique were used to measure the vortex shedding frequency from spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important results from the investigation were that (i) the variation of the Strouhal number St (=fD/U0, U0: freestream velocity, D: diameter of the sphere, f: vortex shedding frequency) with the Reynolds number (= U0D/v, v: kinematic viscosity) can be classified into four regions, (ii) the Reynolds number at which the hairpinshaped vortices begin to change from laminar to turbulent vortices so that the wake structure behind the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (vi) at Reynolds numbers ranging from 8X102 to 1.5X104, the higher and lower frequency modes of the Strouhal number coexist.

A Numerical Study of Geometrical Effects on the Strouhal Number of a Circular Cylinder

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2008-69034 ◽

2008 ◽

Author(s):

Farzan Kazemifar ◽

Mehdi Molai ◽

Bahar Firoozabadi ◽

Goodarz Ahmadi

Keyword(s):

Circular Cylinder ◽

Strouhal Number ◽

Vortex Shedding ◽

Numerical Study ◽

Circular Cylinders ◽

Percentage Reduction ◽

Blade Angle ◽

Shedding Frequency ◽

Geometrical Effects

In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α = 0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d = 0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α = 0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was increased from zero to 90°, the percentage reduction in Strouhal number decreased; however, as the blade angle was further increased from 90° to 150°, the percentage reduction in Strouhal number increased. Although the modifications studied here decrease the vortex shedding frequency they make the vortices shed from the cylinder farther and stronger hence increasing the magnitude of the fluctuating forces.

Vorticity Shedding and Acoustic Resonance Excitation of Two Tandem Spirally Finned Cylinders in Cross-Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.4048102 ◽

2020 ◽

Vol 143 (2) ◽

Author(s):

Mohammed Alziadeh ◽

Atef Mohany

Keyword(s):

Reynolds Number ◽

Strouhal Number ◽

Flow Characteristics ◽

Cross Flow ◽

Acoustic Resonance ◽

Root Diameter ◽

Circular Cylinders ◽

Resonance Excitation ◽

Equivalent Diameter ◽

Spacing Ratio

Abstract The aeroacoustic response of two tandem spirally finned cylinders is experimentally investigated. Three different pairs of finned cylinders are studied with fin pitch-to-root diameter ratios (p/Dr) ranging between 0.37≤p/Dr≤0.74. The spiral fins are crimped similar to those used in industrial heat exchangers. The results of the finned cylinders are compared with bare, circular cylinders with a modified equivalent diameter (Deq). The spacing ratio (L/Deq) between the cylinders are kept constant at L/Deq=2.00. The Strouhal number (StDeq) of the tandem finned cylinders is found to be higher compared to the tandem bare cylinders, resulting in an earlier onset of coincidence resonance. Moreover, unlike the tandem bare cylinders, the Strouhal number of the finned cylinders did not depend on the Reynolds number, suggesting that the flow characteristics around the finned cylinders are unaffected by Reynolds number. Only the tandem finned cylinders with the lowest fin pitch-to-root diameter ratio (p/Dr=0.37) were capable of exciting precoincidence acoustic resonance. The precoincidence resonance mechanism is similar to that observed in in-line tube bundles.

Numerical Simulation on Vortex Shedding from a Hydrofoil in Steady Flow

Journal of Marine Science and Engineering ◽

10.3390/jmse8030195 ◽

2020 ◽

Vol 8 (3) ◽

pp. 195

Author(s):

Jian Hu ◽

Zibin Wang ◽

Wang Zhao ◽

Shili Sun ◽

Cong Sun ◽

...

Keyword(s):

Strouhal Number ◽

Vortex Shedding ◽

Angle Of Attack ◽

Wake Flow ◽

Trailing Edge ◽

Inflow Velocity ◽

Lift Curve ◽

Shedding Frequency ◽

Lift And Drag

This paper presents a numerical modeling procedure for the idealization of vortex shedding effects in the wake flow field of a NACA0009 hydrofoil. During the simulation, the lift and drag acting on the hydrofoil were monitored, and the vortex-shedding frequency of the hydrofoil was analyzed. The effects of inflow velocity, trailing-edge thickness, angle of attack, and maximum hydrofoil thickness on vortex shedding were investigated. The results indicate that an increase in the inflow velocity led to an increase in the vortex-shedding frequency and a negligible change in the Strouhal number. Furthermore, as the thickness of the trailing edge increased, the vortex-shedding frequency decreased gradually, whereas the Strouhal number first increased and then decreased. Vortex shedding and lift curve oscillations ceased altogether after the angle of attack of the hydrofoil increased beyond a certain threshold. When the maximum hydrofoil thickness was increased while keeping the thickness and chord length of the trailing edge constant, the vortex-shedding frequency decreased.

FLOW AROUND MODIFIED CIRCULAR CILYNDERS

Revista de Engenharia Térmica ◽

10.5380/ret.v3i1.3482 ◽

2004 ◽

Vol 3 (1) ◽

Author(s):

R. L. Ferreira ◽

E. D. R. Vieira

Keyword(s):

Circular Cylinder ◽

Strouhal Number ◽

Vortex Shedding ◽

Reynolds Numbers ◽

Continuous Mode ◽

Longitudinal Slit ◽

Shedding Frequency ◽

Hot Film ◽

The Relationship

The flow around a circular cylinder has awaken the attention of different researchers since the historic Strouhal's work of 1878. Ever since, many experimental and numeric works have been carried out in order to determine the relationship between the vortex shedding frequency and the flow regime. Recently, a number of studies have been developed using several small modifications in circular cylinder. In this work a circular cylinder modified with a longitudinal concave notch, has been tested in order to determine the relationship between the non-dimensional vortex shedding frequency (Strouhal number) and the Reynolds number has been determined to Reynolds up to 600. Additionally a modified circular cylinder with a longitudinal slit also has been tested in order to determine the Strouhal-Reynolds relationship in several attack angle configurations. The experiments have been carried out in a vertical low turbulence hydrodynamic tunnel with 146x146x500 mm of test section operating in continuous mode. Flow visualization by direct liquid dye injection has been utilized in order to produce vortex images. These images have been captured in still chemical photography for different Reynolds numbers. A hot-film probe has been adequately positioned in the vortex wake to determine the vortex shedding frequency and consequently the Strouhal number.

Synchronization Characteristics of Vortex Shedding From Tube Banks on Acoustic Resonance

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2013-97682 ◽

2013 ◽

Author(s):

Hiromitsu Hamakawa ◽

Eiichi Nishida ◽

Kenta Asakura

Keyword(s):

Vortex Shedding ◽

Pressure Fluctuation ◽

Acoustic Pressure ◽

Broad Band ◽

Acoustic Resonance ◽

Modeling Method ◽

Acoustic Damping ◽

Shedding Frequency ◽

Tube Banks

In the present paper the attention is focused on vortex shedding synchronization on acoustic resonance in in-line tube banks which occurred in the two-dimensional model of boiler. And we have examined the verification of proposed modeling method. We measured the characteristics of acoustic resonance, acoustic damping, the pressure fluctuation on the surface of tubes at the nodes of acoustic pressure and the acoustic pressure fluctuation on the side wall of the duct. As the acoustic mode number increased, the acoustic damping ratio decreased. As the tube pitch ratio in the flow direction decreased, the acoustic damping increased for all acoustic modes and the vortex shedding frequency became broad-band. The multiple resonance modes of lower acoustic damping were generated within the broad-band vortex shedding frequency. If the acoustic resonance occurred, the peak level of spectrum of surface pressure fluctuation and the coherence between vortex shedding and wall acoustic pressure in the tube banks also increased. The features of experimental results agree well with those obtained by using the proposed modeling method. We have discussed the characteristics of vortex shedding synchronization by using proposed the modeling method.

Numerical Simulation of Non-Equal Diameter Cylinder

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.249-250.527 ◽

2012 ◽

Vol 249-250 ◽

pp. 527-532

Author(s):

Guang Jun Yang ◽

Jing Sun

Keyword(s):

Numerical Simulation ◽

Vortex Shedding ◽

Wake Flow ◽

Subcritical State ◽

Equivalent Diameter ◽

Freestream Velocity ◽

Transition Area ◽

Shedding Frequency ◽

Different Diameters

Numerical simulation has been carried out on the wake flow structure of some simplified antenna model which is shaped as a non-equal diameter slender cylinder. The unsteady flow parameter-Strouhal number is confirmed to be a constant approximately in the subcritical state. The results show that at levels of different diameters, when the length-diameter ratio is large enough, each level can still maintain stable periodical vortex shedding phenomenon, the vortex shedding frequency of each level, the flow velocity and the equivalent diameter still meet the Strouhal relationship. The effect of connect transition area on vortex shedding stabilize region are close to the freestream velocity.