The Aeroacoustic Response of a Single Square Cylinder in Confined Cross Flow

2021 ◽  
Author(s):  
Mahmoud Shaaban ◽  
Atef Mohany
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Edge Length ◽  
Bluff Bodies ◽  
Square Cylinder ◽  
Unstable Flow ◽  
Response Characteristics ◽  
Flow Fluctuations

Abstract Unstable flow patterns around arrangements of bluff bodies in different engineering applications can give rise to pressure oscillations, leading to excitation of strong acoustic resonance that can interrupt operation. In certain conditions, flow fluctuations arising from vortex shedding downstream of a circular cylinder are reported to excite severe acoustic resonance. On the other hand, cylinders of a square cross section are known to be particularly susceptible to mechanisms that involve coupling between the flow and a structural mode. It is not documented, however, if such coupling would occur between an acoustic mode and flow fluctuations downstream of a square cylinder. In this work, the possibility of excitation of acoustic resonance due to coupling between unsteady flow downstream of a single square cylinder with an acoustic cross mode of a rectangular duct is experimentally investigated. During the experiments, acoustic resonance was self-excited. Measurements of the acoustic pressure and the flow velocity are carried out for a single square cylinder of an edge length of 25.4 mm. Results show that aeroacoustic response characteristics for this configuration are not completely analogous to the case of a circular cylinder, with a number of features not reported before. A brief summary of the results is presented in this work.

Simulation of Flow-Induced Acoustic Resonance of Bluff Bodies in Duct Flow

2010 ◽  
Author(s):  
Erick Reyes ◽  
Shane Finnegan ◽  
Craig Meskell
Keyword(s):  
Boundary Condition ◽  
Rigid Body ◽  
Acoustic Field ◽  
Potential Flow ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Bluff Bodies ◽  
Duct Flow ◽  
Body Vibration ◽  
Spacing Ratio

It is well known that the periodic vortex shedding from bluff bodies in a duct can excite the transverse acoustic mode if the frequencies are comparable. There is a considerable body of experimental work investigating this phenomenon for multiple cylinders. Numerical studies are somewhat less common, partially because it is difficult to couple the acoustics and the hydrodynamic field. This paper implements a hydrodynamic analogy proposed by Tan et al. in which the acoustic field is represented by a velocity excitation of the incompressible hydrodynamics at the domain extents. Two alternatives to this boundary condition are considered: rigid body vibration and surface potential flow. In all three cases, the flow field for two tandem cylinders with a spacing ratio of 2.5D has been simulated with uRANS and an RSM turbulence model. It has been found that a rigid body vibration is not a good model of acoustic excitation. However, imposing a potential flow at the surface of the cylinders yields promising results. The success of the new boundary condition implies that the coupling between the acoustic field and the hydrodynamics is not reorganizing the wake directly, but rather simply modifying the generation of vorticity at the surface. Furthermore, it is envisaged that the new modeling approach will be easier to implement for complex geometries, such as tube arrays.

A Parametric Study of the Resonance Mechanism of Two Tandem Cylinders in Cross-Flow

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
A. Mohany ◽  
S. Ziada
Keyword(s):  
Parametric Study ◽  
Small Diameter ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Resonance Phenomenon ◽  
Resonance Mechanism ◽  
Flow Parameters ◽  
Tandem Cylinders ◽  
Spacing Ratio

A parametric study has been performed to investigate the effect of cylinder diameter on the acoustic resonance mechanism of two tandem cylinders exposed to cross-flow in a duct. Three spacing ratios corresponding to different flow regimes inside the “proximity interference” region are considered, L∕D=1.5, 1.75, and 2.5, where L is the spacing between the cylinders and D is the diameter. For each spacing ratio, six cylinder diameters in the range of D=7.6–27.5mm have been tested. For small diameter cylinders, the acoustic resonance mechanism of the tandem cylinders seems to be similar to that observed for single cylinders; i.e., it occurs near frequency coincidence as the vortex shedding frequency approaches that of an acoustic resonance mode. However, for larger diameter cylinders, the resonance of a given acoustic mode occurs over two different ranges of flow velocity. The first resonance range, the precoincidence resonance, occurs at flow velocities much lower than that of frequency coincidence. The second resonance range, the coincidence resonance, is similar to that observed for single and small diameter tandem cylinders. Interestingly, the observed precoincidence resonance phenomenon is similar to the acoustic resonance mechanism of in-line tube bundles. It is shown that increasing the diameter of the tandem cylinders affects several flow parameters such that the system becomes more susceptible to the precoincidence resonance phenomenon. The occurrence and the intensity of the precoincidence resonance are therefore strongly dependent on the diameter of the cylinders.

Vortex-Induced In-Line Vibration and Random Vibration of a Circular Cylinder Under Various Inflow Conditions

2010 ◽  
Author(s):  
Takashi Nishihara ◽  
Yuzuru Eguchi
Keyword(s):  
Circular Cylinder ◽  
Random Vibration ◽  
Practical Importance ◽  
Cross Flow ◽  
Cylindrical Structures ◽  
Response Characteristics ◽  
Inflow Turbulence ◽  
Flow Induced Vibrations ◽  
Yaw Angle ◽  
Inflow Conditions

The flow-induced vibrations (FIV) of cylindrical structures subjected to a cross flow have been investigated in a number of studies owing to their practical importance. The results of these studies have been compiled into guidelines for the evaluation of FIV of cylindrical structures. However, the applicability of the guidelines to cases with upstream structures and with an oblique inflow has not been fully examined. In this paper, we describe the response characteristics of vortex-induced in-line vibration and random vibration of a circular cylinder under various inflow conditions. Water tunnel tests were conducted on a circular cylinder in a cross flow at three yaw angles of 0, 30 and 45 degrees to clarify the effects of the yaw angle on vortex-induced in-line vibration and random vibration. The vibration amplitudes of a circular cylinder downstream of another circular cylinder of five times larger diameter were also measured to investigate the effects of inflow turbulence generated by an upstream cylinder. The tests were conducted for two different relative locations of the upstream cylinder in the same reduced-velocity range as that of the single-cylinder tests. The response amplitudes and onset flow velocities obtained by the tests were compared with values predicted using the cosine law and the guidelines to verify the evaluation methods in the guidelines.

Numerical and Experimental Investigation of Flow-Acoustic Resonance of Side-by-Side Cylinders in a Duct

2013 ◽  
Author(s):  
Atef Mohany ◽  
David Arthurs ◽  
Michael Bolduc ◽  
Marwan Hassan ◽  
Samir Ziada
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Cross Flow ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Acoustic Power ◽  
Bluff Bodies ◽  
Aerodynamic Sound ◽  
Spacing Ratio ◽  
Piping Systems

The phenomenon of flow-excited acoustic resonance is a design concern in many engineering applications, especially when wakes of bluff bodies are encountered in ducts, piping systems, heat exchangers, and other confined systems. In this article, the case of self-excited acoustic resonance of two side-by-side cylinders in a duct with cross-flow is investigated both numerically and experimentally. A single spacing ratio between the cylinders, T/D = 2.5, is investigated, where D is the diameter of the cylinders and T is the center-to-center distance between them. The numerical investigation is performed using a finite-volume method at a Reynolds number of 30,000 to simulate the unsteady flow field, which is then coupled with a finite element simulation of the resonant sound field. The experimental investigation is performed using phase-locked Particle Image Velocimetry (PIV) during the occurrence of flow-excited acoustic resonance. The results of both methods reveal that the flow-excited acoustic resonance produces a strong oscillatory flow pattern in the cylinder wakes with strong in-phase vortex shedding being synchronized by the excited acoustic resonance. The distribution and strength of the aeroacoustic sources and sinks within the flow field have been computed by means of Howe’s theory of aerodynamic sound for both the experimental and numerical cases, with the results of the two methods comparing favorably, showing similar trends in the oscillating flow fields, and very similar trends in the distribution of net acoustic power.

A Parametric Study of the Resonance Mechanism of Two Tandem Cylinders in Cross-Flow

2006 ◽  
Author(s):  
Atef Mohany ◽  
Samir Ziada
Keyword(s):  
Parametric Study ◽  
Small Diameter ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Resonance Mechanism ◽  
Flow Parameters ◽  
Tandem Cylinders ◽  
Cylinder Diameter ◽  
Spacing Ratio

A parametric study has been performed to investigate the effect of cylinder diameter on the acoustic resonance mechanism of two tandem cylinders exposed to cross-flow in a duct. Three spacing ratios corresponding to different flow regimes inside the “proximity interference” region are considered, L/D = 1.5, 1.75 and 2.5, where L is the spacing between the cylinders and D is the diameter. For each spacing ratio, six cylinder diameters in the range of D = 7.6 mm to 27.5 mm, have been tested. For small diameter cylinders, the acoustic resonance mechanism of the tandem cylinders seems to be similar to that observed for single cylinders. However, for larger diameter cylinders, the resonance of a given acoustic mode occurs over two different ranges of flow velocity. The first resonance range, the pre-coincidence resonance, occurs at flow velocities much lower than that of frequency coincidence. The second resonance range, the coincidence resonance, is initiated near the condition of frequency coincidence. Thus, the occurrence and the intensity of the pre-coincidence resonance are found to be strongly dependent on the diameter of the cylinders. It is shown that increasing the cylinder diameter affects several flow parameters, which make the tandem cylinders more susceptible to the pre-coincidence acoustic resonance.

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