Cylinder Width Research Articles

Aeroacoustics of a Square Finite-Wall-Mounted Cylinder in Pressure-Gradient Flows

An experimental investigation of the wake flow structures, surface pressure fluctuations, and noise production of a square finite-wall-mounted cylinder with an aspect ratio of 2.4 is presented. The cylinder was immersed in flows with favorable, near-zero, and adverse pressure gradients at a Reynolds number of 48,000, based on cylinder width. Far-field noise, unsteady surface pressure, and particle image velocimetry measurements were taken simultaneously using the open-jet pressure-gradient test rig in the UNSW Anechoic Wind Tunnel. Favorable and adverse pressure gradients were found to enhance and suppress the cylinder tonal noise, respectively. A favorable pressure gradient reduced the size of the recirculation region in the wake, which intensified the free-end downwash and suppressed the junction upwash. The intensities of the cylinder surface pressure fluctuations were slightly increased at the primary and secondary shedding Strouhal numbers (based on cylinder width) of approximately 0.1 and 0.2. Conversely, the recirculation region expanded under an adverse pressure gradient, with the downwash weakened and the upwash enhanced. The peaks in the surface pressure spectra were noticeably attenuated at the primary shedding Strouhal number and completely suppressed at the secondary Strouhal number. Wake flow structures correlated with the surface pressure fluctuations and far-field noise were identified to understand the enhancement or suppression mechanisms of the surface pressure fluctuations and the associated shedding regimes.

Numerical analysis of the flow over four side-by-side square cylinders with different gaps

This study conducts two-dimensional numerical simulations of the flow over four square cylinders arranged side by side at a low Reynolds number (Re) of 100. The investigation primarily centers on the influence of the gap to a square cylinder width ratio (g*) on the flow. The range of g* spans from 0.1 to 7.0. Within this parameter range, three distinct flow regimes emerge based on the inherent flow characteristics. These regimes are defined as follows: (1) single bluff body flow (g* ≤ 0.3), (2) flip-flopping flow (0.3 < g* < 2.0), and (3) modulated periodic flow (g* ≥ 2.0). Additionally, the modulated periodic flow is further categorized into three distinct flow patterns. Various aspects of these different flow regimes are examined, including vortex contours, velocity fields, and liquid force coefficients around the cylinders. Moreover, detailed illustrations are provided for the modulation behaviors in vortex structures and liquid force coefficients. Finally, the proper orthogonal decomposition technique is employed to identify and analyze the underlying spatial coherent structures in the flow field, offering further insights into the dynamic features of wakes.

Effects of taper ratio on the aerodynamic forces and flow field of two tandem square cylinders

To explore the influence of taper ratio on aerodynamic characteristics of tandem square cylinders, three-dimensional (3D) large eddy simulations of flow around two tandem square cylinders at the Reynolds number (Re) = 2 × 103 are carried out with a spacing ratio G/D = 4, where G is the cylinder center-to-center distance and D is the cylinder width. Different taper ratios of ξ = 0%, 5%, 10%, and 15% are considered. The influence of taper ratio on aerodynamic coefficient, wind pressure coefficient, mean, and instantaneous flow fields are comprehensively studied. The mechanism of variation in flow fields is revealed, and the mathematical relationship between the taper ratio and aerodynamic characteristics is established, which can provide theoretical reference for design and construction of tandem structures. The results indicate that the taper ratio has significant influence on the mean force coefficient, fluctuating force coefficient, surface mean and fluctuating pressure coefficients, and vortex shedding frequency (fvs). As increase in the taper ratio, the mean force in the along-wind direction, fluctuating force in the across-wind direction, and surface pressure of the two cylinders will be decreased, but the vortex shedding frequency will be increased. The taper ratio has negligible influence on the flow separation location of the upstream cylinder. However, reattachment location of the shear layer moves backward along the leeward surface of the downstream cylinder, and width of the shear layer gradually becomes narrower and closer to surface of the two cylinders. The vortex shedding strength and vortex energy distribution of the two cylinders will be reduced as a result of the narrower shear layer. Meanwhile, coherence and periodicity of the vortex shedding will also be weakened, which results in reduction in the aerodynamic forces and increase in the vortex shedding frequency.

Near-wake structures of a finite square cylinder with a flapping film at its free end

As a follow-up study of Wang et al. [“Control of the flow around a finite square cylinder with a flexible plate attached at the free end,” Phys. Fluids 34(2), 027109 (2022)], this paper presents an experimental study of flow around a wall-mounted finite square cylinder with a vertically clamped flapping film at its free end. The width (d) of the square cylinder was 40 mm, and the aspect ratio (H/d) was 5, where the height H was 200 mm. The flexible film was made of low-density polyethylene, with a thickness of 0.04 mm and the width and length (l) each of d. Flow visualization and particle image velocimetry were conducted in the central lateral plane and several horizontal planes to reveal the 3D structure of the flapping induced vortex (FIV) and its effects on the cylinder near wake. All measurements were done in a low-speed wind tunnel at a flow speed of U∞ = 5 m/s with a Reynolds number of 13 700 based on U∞ and d. Previous study suggests that the flapping film reduces aerodynamic forces of the cylinder significantly and that the fluctuating lateral force is reduced by 60% [Wang et al., “Control of the flow around a finite square cylinder with a flexible plate attached at the free end,” Phys. Fluids 34(2), 027109 (2022)]. Vortices that shed from the trailing edge of the flapping film connect those from the side edges, forming n-shape FIVs downstream. FIVs induce more high-speed flow downwards into the wake, which suppresses the mean recirculation zone near the free end but enlarges it in the lower part of the wake. The two legs of n-shape FIVs are symmetrically arranged near the cylinder free end, whose effects diminish gradually as approaching the bottom wall, where alternating Karman vortex shedding still prevails.

Varijacije u anatomiji iglica običnog bora (Pinus sylvestris L.) s obzirom na staništa i nadmorsku visinu u Turskoj

In this study, eight Scots pine populations from Turkiye were studied to explore the influence of different habitats and altitudinal zones on the needle anatomical traits. A total of 496 needles belonging to 64 individuals were examined using light microscopy with the aim to score variability of sixteen needle anatomical traits. Variance analysis showed significant differences in needle thickness, needle width, resin canal number, resin canal diameter, central cylinder width, central cylinder thickness, endodermis cell number, endodermis width and endodermis thickness of eight populations depending on habitat zones. However, only resin canal diameter, endodermis width and endodermis thickness differ significantly in examined populations depending on altitudinal gradients. Cluster analysis showed the greatest similarities between the Bolu-Aladağ and Ardahan-Yalnızçam populations, and the most distinguishable population was the Giresun-Espiye population based on the anatomical characteristics of the needles. Although principal component analysis showed that needle width, central cylinder width, needle thickness, and central cylinder thickness had the greatest influence on the delimitation of Scots pine populations distributed in Turkiye, discrimination analysis did not separate the examined populations depending on the anatomical characteristics of the needles.

On the performance of freestanding rolling mode triboelectric nanogenerators from rotational excitations for smart tires

In this study, we propose a novel freestanding rolling mode triboelectric nanogenerator (FR-TENG) for harvesting energy generated by tire rotation, located within the tire to achieve optimal energy capture. First, to investigate the operating principles of the FR-TENG, the finite element method (FEM) is conducted to predict the potential distribution of spherical rolling elements. Additionally, we employ an atomic-scale electron cloud potential well model to describe the electron transfer mechanism. Second, kinematic simulation is employed to examine the motion state of rolling elements of varying sizes and shapes at different rotation speeds. The results demonstrate that the cylindrical and spherical rolling elements exhibit more stable motion performance compared to the elliptical cylindrical rolling element. Third, the effect of rolling element shapes and sizes on the output performance of the FR-TENG is investigated through systematic experiments. At a rotation speed of 120 rpm, the maximum power of the sphere (diameter 20 mm) reaches 5.33 μW with a load resistance of 50 MΩ. The maximum volume power density of the FR-TENG reaches 3.29 W/m3 when the rolling element is a cylinder (width 22 mm). Regarding charging ability, the cylindrical rolling element outperforms the spherical rolling element by achieving a higher charging voltage. The FR-TENG can charge a 22 μF capacitor to 4.4 V and continuously drive a watch for 20 s. This study provides a comprehensive outlook on the design and configuration of freestanding triboelectric-layer mode TENGs, which can aid in the development of energy recovery systems for vehicle tire rotation.

Influence of different interface component distributions on Richtmyer-Meshkov instability

In this paper, the Richtmyer-Meshkov instability is studied numerically by using the high-resolution Roe scheme based on the two-dimensional unsteady Euler equation, which is caused by the interaction between shock wave and the helium circular light gas cylinder with different component distributions. The numerical results are used to further discuss the deformation process of the gas cylinder and the wave structure of the flow field, and also to quantitatively analyze the characteristic dimensions (length, height and central axial width) of the gas cylinder, the time-dependent volume compression ratio of the cylinder. In addition, the flow mechanism of shock-driven interface gas mixing is analyzed from multiple perspectives by combining the flow field pressure, velocity, circulation and gas mixing rate. Then the effects of different initial component distribution conditions on interface instability are investigated. The results show that when the diffusion interface transforms into the sharp interface, the reflection coefficient gradually increases on both sides of interface. When the incident shock wave interacts with the cylinder, the transmission of the shock wave will transform from conventional transmission into unconventional transmission. At the same time, the reflected shock wave is gradually strengthened and the transmitted shock wave is gradually weakened, which leads the Richtmyer-Meshkov instability to be strengthened. Moreover, the Atwood numbers on both sides of the interface also increase as the diffusion interface transforms into the sharp interface, which leads the Rayleigh-Taylor instability and the Kelvin-Helmholtz instability to be strengthened. Therefore, the increase of instability will cause the circulation to increase, resulting in the increase of the growth rate of gas mixing rate.

The Relationship Between the Emitter Position and the Wehnelt Cylinder Aperture Radius of the Thermionic Electron Gun

This paper includesfinding a mathematical relationship between the distance from the emitter to the width of the Wehnelt cylinder bore and the diameter of that bore, by studying the effect and correlation of these two parameterson the quality of the electron beam. A group of electron guns with identical and variable geometric parameters were designed for the values ​​of the Wehnelt cylinder aperture radius for each case from the emitter site, which represents the distance from the emitter head to the Wehnelt cylinder aperture. As well as the calculation of the electron beam diameter and the brightness and emittance, as the mathematical relationship between these two parameters was found to be linear.

Effect of incoming boundary layer thickness on the flow dynamics of a square finite wall-mounted cylinder

This paper investigates the flow dynamics around a square finite wall-mounted square cylinder of two different aspect ratios (AR=H/D=6 and 10, H and D are the height and width, respectively) under six boundary layer thickness (δ/D=0.5–4.0, δ is the boundary layer thickness) using the improved delayed detached eddy simulation turbulence model. The Reynolds number based on the square cylinder width and incoming velocity is Re=1.4×104. The aerodynamic force, surface mean and fluctuating pressure, wake closure length, Reynolds stresses, turbulence production, and the anisotropy of turbulence are analyzed in detail to investigate the effect of AR and δ/D combinations. The Q-criterion vortex identification method is adopted to identify and classify the vortex structures of different AR and δ/D combinations. The parametric diagram based on AR and δ/D to predict the dipole/quadrupole wake structure proposed in Yauwenas et al. [“The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders,” J. Fluid Mech. 875, 929–960 (2019)] is refined based on results of the present study (quadrupole wake for AR=6 with δ/D≥1.5 and AR=10 with δ/D≥1.0). The instantaneous space–time pressure distribution along the whole span proves the existence of cellular shedding (AR=10 for δ/D=0.5–2.0), and the spectral proper orthogonal decomposition technique is adopted to investigate the cellular shedding phenomenon and its distribution. With the increase in δ/D from 2.0 to 4.0, the cellular shedding process is absent, implying the inhibitory effect of increasing boundary layer thickness on the cellular shedding.

A Numerical Investigation of Turbulent Flow Over Single and Tandem Square Cylinders

This paper presents the three-dimensional flow investigations over the square cylinders placed in the tandem arrangement. Two different flow configurations were investigated in detail; one comprising of a single square cylinder and the other comprising of three square cylinders placed in a tandem arrangement with the spacing of six times the width (w) of each square cylinder. The Reynolds number based on the width of the square cylinder (w) and free stream velocity (Uo) is 22,000. The problem was solved numerically using an Unsteady Reynolds-Averaged Navier-Stokes (URANS) based model and Large Eddy Simulation (LES) based model. Strouhal Number, lift, and drag coefficients were computed for each configuration. By comparing both the models using contour plots of pressure, velocity and vorticity it is found that the LES model is more accurate to capture the turbulence around single and tandem square cylinders. In the tandem arrangement, complex periodic vortex shedding was observed in the wake of each square cylinder. The production of turbulent kinetic energy was also investigated to understand the roles of stresses during flow over the cylinders. The analysis showed that the production of turbulence by normal stresses is higher than that of shear stresses. Furthermore, it was observed that the flow over the first cylinder arranged in tandem is quite identical to that of the single square cylinder. Moreover, the upstream cylinder experienced a higher lift in comparison to the downstream cylinders.

Effect of inlet shear on turbulent flow past a wall-mounted finite-size square cylinder

The present study analyzes the effect of incoming shear flow on the wake behind a wall-mounted finite-length square cylinder of aspect ratio (AR=7) using large eddy simulation (LES). All the simulations were performed at a Reynolds number (Re) of 10000, based on cylinder width (d) and average inlet velocity (uavg), with different shear parameters, K=0.0,0.025,0.050 and 0.075. The shear-improved Smagorinsky model Lévêque et al. (2007) is used to account for the subgrid scale stress. It is found that the incoming flow shear has a profound effect on the modes of shedding. With increasing shear parameter anti-symmetric modes of shedding tends to dominate along the cylinder height, except close to the free-end where both symmetric and anti-symmetric modes of shedding co-exist. The incoming shear flow has also significant influence on the downwash flow from the free-end, the strength of which decreases with an increase in shear parameter. The resolved turbulent kinetic energy (TKE) associated with the cylinder wake is found to have maximum contribution from the transverse component of normal stress compared to the other components of normal stresses.

New insights into numerical simulations of flow around two tandem square cylinders

Flows around tandem square cylinders at Re = 100 are numerically studied using a characteristic-based penalty operator splitting finite element method based on a multistep algorithm. The validation of the code and numerical method is performed for flows around single square cylinders. L/D effects (with L being the center-to-center distance and D being the square cylinder width) on the flow structures and parameters are investigated for 1.5 ≤ L/D ≤ 9.0. The flow structures, especially far downstream of the square cylinder, indicate six distinct flow regimes. The two-layered vortex formation (TVF) and secondary vortices formation (SVF) modes are defined, and their mechanisms are analyzed. The evolution of TVF into SVF proceeds through the combination of single and binary vortex formations. Variations in the physical flow parameters, including the coefficients of fluctuating lift (CL′), time-averaged drag (C̄D), and amplitude lift (CLA), as well as the Strouhal number and phase lag (ϕ), are analyzed for various L/D values. Obvious jumps in the flow parameters occur at both square cylinders for L/D = 4.4–4.5 because of vortex impingement. Finally, insight into the physics underlying the relationship between CL−upA, CL−up′, and ϕ is derived from the simulation results. The local maximum and minimum of CL−upA and CL−up′ occur at ϕ = 2π and 3π, respectively, corresponding to in-phase and anti-phase vortex shedding by the cylinders. The pressures on the upper and lower sides of the upstream square cylinder decrease and increase, respectively, leading to reductions in CL−upA and CL−up′ as the flow pattern changes from in-phase to anti-phase.

Effects of side ratio on energy harvesting from transverse galloping of a rectangular cylinder

Rectangular cylinders have been identified as ideal bluff bodies for galloping-based energy harvesting, while a systematic study of the effects of the side ratio (i.e., the ratio between the cylinder width and the cylinder height) remains unavailable. This study investigates the influences of the side ratio on the piezoelectric energy harvesting from the transverse galloping of a rectangular cylinder based on a representative electro-aero-mechanical model, in which the aerodynamic force is calculated by the quasi-steady theory. The existing experimental aerodynamic coefficients for rectangular cylinders with side ratios of 0.62–3.0 are utilized as inputs of the quasi-steady aerodynamic force model. The influences of the side ratio and load resistance on the onset velocity, displacement, and power output of the galloping-based energy harvester are investigated. The results show that the onset velocity of galloping is dependent on the load resistance while this dependency becomes less significant with increasing the natural frequency. The onset galloping velocity of the energy harvester decreases with increasing the side ratio, and the lowest onset velocity is achieved by a rectangular cylinder with a side ratio of around 2.50. The largest vibration amplitude is achieved by the cylinder with a side ratio of 1.62 or 2.0 at low flow velocities, while the largest vibration amplitude is always achieved by the square cylinder at high flow velocities. Therefore, the side ratio of a galloping-based energy harvester should be designed according to its working environment: the optimal side ratio is around 1.0 if the harvester is expected to work at relatively high reduced flow velocities, while the optimal side ratio is around 1.62–2.0 if the harvester is expected to be effective at relatively low reduced flow velocities. These conclusions can provide references for designing galloping-based energy harvesters with rectangular cylinders as bluff bodies.

Laminar Flow over a Square Cylinder Undergoing Combined Rotational and Transverse Oscillations

This work numerically investigates the effects of combined rotational and transverse oscillations of a square cylinder on the flow field and force coefficients. The primary non-dimensional parameters that were varied are frequency ratio fR (0.5, 0.8), Re (50-200), phase difference (ϕ) between the motions and rotational amplitude (θ0) with the influence of the last three parameters being discussed in detail. The amplitude of transverse oscillations is fixed at 0.2D, where D is the cylinder width. The study has been validated using the mean drag coefficient for stationary and transversely oscillating square cylinders from literature. Output data was obtained in the form of force coefficient (Cd), vorticity and pressure contours. The governing equations for the 2dimensional model were solved from an inertial frame of reference (overset meshing) using finite volume method. The interplay between the convective field and prescribed motion has been used to explain many of the results obtained. The relative dominance of cylinder motion over the flow stream was determined using Discrete Fast Fourier Transform. The influence of Re on Cd disappears when the motions are completely out of phase (ϕ = π). In general, the Cd for low Re flows exhibited low sensitivity to change in other parameters. Direct correlation has been observed between frontal area, vortex patterns and drag coefficient

Stereovision measurement of layer geometry in wire and arc additive manufacturing with various stereo matching algorithms

Robust measurement of layer geometry can help better understand the complex deposition process and provide feedback control to increase process stability of wire and arc additive manufacturing (WAAM). In this study, a virtual binocular vision sensing system is designed to measure the layer width and torch height from top layer simultaneously. Considering that stereo matching is the most crucial step for 3-D reconstruction in stereovision sensing, various matching algorithms, i.e. adaptive Census transform (ACT), global-based crosswise iteration (GCI), and semi global matching (SGM), are employed to calculate disparity images of image pairs. The matching algorithms are tested based on the standard datasets, indicating that the highest matching accuracy comes from the GCI matching algorithm. Then, a standard cylinder is taken as an example to verify the effectiveness of the sensing system and algorithms. The results show that the cylinder width errors with the ACT, GCI and SGM matching algorithms are 3.17%, 3.02%, and 3.08%, respectively, while the cylinder height errors are 5.83%, 4.15%, and 4.83%, respectively. Finally, layer geometries in WAAM with various process parameters are determined. The width and height errors of layer geometry with the GCI matching algorithm are less than 3.2%. This study will lay a solid foundation for subsequent feedback control for layer geometry in WAAM.

Large Eddy Simulation of the flow around a finite-length square cylinder with free-end slot suction

Large Eddy Simulation (LES) is used to study the effects of steady slot suction on the aerodynamic forces of and flow around a wall-mounted finite-length square cylinder. The aspect ratio H/d of the tested cylinder is 5, where H and d are the cylinder height and width, respectively. The Reynolds number based on free-stream oncoming flow velocity Us/U∞) is is varied as Q = 0, 1 and 3, where Us is the velocity at the entrance of the suction slot. It is found that the free-end steady slot suction can effectively suppress the aerodynamic forces of the model. The maximum reduction of aerodynamic forces occurs at Q = 1, with the time-mean drag, fluctuating drag, and fluctuating lift reduced by 3.75%, 19.08%, 40.91%, respectively. For Q = 3, all aerodynamic forces are still smaller than those for Q = 0 (uncontrolled case), but obviously higher than those for Q = 1. The involved control mechanism is successfully revealed, based on the comparison of the flow around cylinder free end and the near wake for the three tested Q values.

Flow Around Three Side-by-Side Square Cylinders and the Effect of the Cylinder Oscillation

Abstract In this study, the flow field over three square cylinders (SCs) arranged side by side is investigated in a low-speed wind tunnel. The experiments are performed with three similar SCs for Reynolds number (Re) 295. The influences of spacing ratio on the wake size, drag coefficient, and flow interference of the cylinders are reported with the hotwire anemometry, particle image velocimetry (PIV), and the flow visualization techniques. Special attention is paid to the oscillation given to the middle cylinder and its effect on flow structure and related forces. The spacing ratio (s/D) ranges from 1.5 to 3, whereas the forcing frequency ratio ranges from 0.5 to 2 with amplitude of 10% of the cylinder width. It is observed that the spacing influences the flow structure, and the vortex shedding mechanism strongly. A secondary frequency appears in the flow field for spacing ratio s/D = 2 and 3. Depending upon the spacing ratios, the flow pattern is seen to be asymmetric biased, symmetric biased, and weakly interactive. The wake interaction decreases with increase in spacing ratios. With the oscillations, the wake becomes more unstable and complex. Additional wake oscillation frequency appears in the power spectra. With an increase in spacing ratios, the drag coefficient decreases, whereas with oscillations, higher drag force is observed compared to a stationary cylinder. A correlation is developed between the time-averaged drag coefficient with cylinder spacing and Reynolds number.

Scaling of the time-mean characteristics in the polygonal cylinder near-wake

The near wake of the polygonal cylinder with the side number N = 3–∞ is systematically studied based on particle image velocimetry (PIV) and load-cell measurements. Each cylinder is examined for two orientations, with either one leading side or leading corner. The Reynolds number Re = (1.0–6.0) × 104, defined by the longitudinally projected cylinder width. The dependence of the wake characteristic parameters on the cylinder orientation and N is discussed, and wake scaling analysis is conducted based on these parameters. It is found that the velocity deficit and half width of the wake scale well with the reverse flow zone length and recirculation bubble width, whilst the Strouhal number, drag and fluctuating lift coefficients scale well with the vortex formation length and wake width. The unveiled scaling relationships cast insight into the intrinsic physical connections between the aerodynamic forces and vortex formation and between the polygonal cylinder wakes of N = 3–∞, suggesting that the understanding of the time-mean wake behind individual polygonal cylinder can be unified to that of the circular cylinder wake.

Modulation of aerodynamic characteristics of a finite wall-mounted square cylinder through steady jet injection

This paper presents the results of an experimental study that investigates the flow behavior around a finite wall-mounted square cylinder (with the aspect ratio of AR = 7) subjected to a steady jet issued from the cylinder’s front face. Two wavy and continuous jets were considered to examine the jet velocity distribution effect. The wind tunnel measurements consist of smoke flow visualization, mean drag force, mean surface pressure, and velocity data obtained from hotwire probe, mostly at Reynolds number (Red, based on the cylinder width and inlet velocity) of 1.2 × 104. The ratio of the jet flow to the freestream, Г, was changed as 0 ≤ Г < 5. Both the wavy and continuous jets reduce the downwash flow contribution with the flow from the lateral faces. An increase of Г continuously amplifies this effect, and improves the flow control performance in drag reduction. The maximum pressure drag reduction of 29% and 16% were obtained for the wavy and continuous jets, respectively. Two characteristic continuous jet flow modes, namely deflected jet (Г < 1) and deflected oscillating jet (1 < Г < 2), were identified. The both continuous jet deflection mode have a leading role in the pressure reduction on the front face, and subsequently in drag reduction. Oscillation of the deflected continuous jet at high-Г also significantly increases the vortex shedding frequency in the upper half of the cylinder, and makes the mean wake flow asymmetrical. On the other hand, the base pressure recovery is the major reason for the drag reduction when the wavy jet is applied. The wavy jet shows a slight deflection at high-Г; however, the mean wake flow remains symmetrical. Finally, the influence of jet flow control on the flow topology was discussed.

The effect of the incoming boundary layer thickness on the aeroacoustics of finite wall-mounted square cylinders.

This paper is concerned with the influence of the incoming wall boundary layer thickness on the noise produced by a square finite wall-mounted cylinder in cross-flow. Acoustic and near wake velocity measurements have been taken in an anechoic wind tunnel for a cylinder in two different near-zero-pressure gradient turbulent boundary layers with thicknesses of 130% and 370% of the cylinder width, W. The cylinders have an aspect ratio of 0.29≤L/W≤22.9 (where L is the cylinder span) and were examined at a Reynolds number, based on width, of ReW = 1.4 × 104. The results presented in this paper demonstrate that increasing the height of the boundary layer delays the production of acoustic tones to higher aspect ratios. The height of the boundary layer changes the balance between upwash and downwash across the cylinder span, resulting in a delayed onset of the shedding regimes and correspondingly, the production of acoustic tones.