Relationship between vortex shedding noise and remotely-sensed surface pressure fluctuations of a structured porous-coated cylinder

An extensive experimental investigation was undertaken to control the flow and noise characteristics influenced by vortex shedding from a circular cylinder by implementing air blowing at the base of the cylinder. The study synchronised near-field pressure and far-field noise measurements with the wake velocity field to understand the noise reduction mechanism of base blowing. Surface pressure fluctuations were measured using pressure taps distributed around the cylinder's circumference through a remote-sensing method, while velocity measurements were obtained using planar particle image velocimetry at the midspan to examine the flow dynamics. The study unveiled the crucial role of near-field pressure, particularly induced at the shoulders of the cylinder, in generating far-field noise. The rapid vertical flow movement, arising from the interaction between shear layers, was identified as a mechanism responsible for inducing surface pressure fluctuations. This phenomenon occurred as high-momentum fluid moved from the free stream into the interior of the vortex-formation region. By applying base blowing, a remarkable reduction in both near-field pressure and far-field noise was achieved at the fundamental vortex-shedding frequency, with reductions of approximately 20 and 25 dB, respectively, compared with the baseline. Additionally, base blowing caused the shear layers to roll up farther downstream than in the baseline by decreasing the entrainment of fluid-bearing opposite vorticity by the shear layer upstream of the growing vortex. Consequently, there was a substantial decrease in turbulent kinetic energy and Reynolds stress near the cylinder, resulting in slower vertical flow movement and weaker near-field pressure.

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Flow and aerodynamic noise control of a circular cylinder by local blowing

Maryami,

Arcondoulis,

Liu

2024

J. Fluid Mech.

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In this experimental study, the impact of symmetric local blowing on suppressing the vortex-induced noise of a circular cylinder was investigated. A highly instrumented cylinder with pressure taps and a series of blowing chambers was used to inject air along the span (seven times the cylinder diameter) at circumferential angles $\theta _{b}={\pm }41^{\circ }$ , ${\pm }90^{\circ }$ and ${\pm }131^{\circ }$ corresponding to the boundary layer, shear layers on the cylinder and separated shear layers, respectively. The investigation aimed to understand the noise reduction mechanism of local blowing by conducting near-field pressure and far-field noise measurements in synchronisation with flow field velocity measurements. Near-field pressure was measured around the circumference of the cylinder using a remote-sensing technique and planar particle image velocimetry was implemented to measure the velocity of the wake flow field at a diameter-based Reynolds number of $Re=7\times 10^{4}$ . The results revealed that the interaction of the rolling up separated shear layers, under the influence of high-momentum fluid travelling from the free stream to the wake, induced significant vertical flow movement in the vortex-formation region. This movement led to strong alternating surface pressure fluctuations at the cylinder's shoulders, contributing to the scattering of noise. It was demonstrated that local blowing delayed vortex shedding for all cases, except at $\theta _{b}={\pm }90^{\circ }$ , which elongated the shear layers and pushed the high-momentum transfer area farther downstream. The application of local blowing at $\theta _{b}={\pm }41^{\circ }$ was particularly effective in increasing the vortex formation size due to reduced entrainment of fluid-bearing vorticity.

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Relationship between vortex shedding noise and remotely-sensed surface pressure fluctuations of a structured porous-coated cylinder

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Experimental investigation of active local blowing on the aerodynamic noise reduction of a circular cylinder

Experimental investigation of active local blowing on the aerodynamic noise reduction of a circular cylinder

Cylinder flow and noise control by active base blowing

Flow and aerodynamic noise control of a circular cylinder by local blowing

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