Numerical Simulation of the Flow-Sound Interaction Mechanisms of Two Side-by-Side Cylinders in Cross-Flow

2011 ◽  
Author(s):  
Atef Mohany ◽  
Marwan Hassan ◽  
Samir Ziada
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Single Frequency ◽  
Interaction Mechanisms ◽  
Spacing Ratio ◽  
Volume Method

A numerical simulation of the flow-excited acoustic resonance for the case of two side-by-side cylinders in cross-flow is performed. One spacing ratio between the cylinders, T/D = 1.25, is investigated, where D is the diameter of the cylinders and T is the center-to-center distance between them. The unsteady flow field is simulated using a finite-volume method at a Reynolds number of 25000. This simulation is then coupled with a finite element simulation of the resonant sound field, by means of Howe’s theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. At the off resonance conditions two distinct vortex shedding frequencies are observed. These are associated with the wider and narrower wakes of the cylinders. However, when acoustic resonance is initiated the bi-stable flow phenomenon is eliminated and the vortex shedding from both cylinders occurs at a single frequency that is between those observed before the onset of acoustic resonance. Moreover, three main aeroacoustic sources are observed in the wake of the two cylinders. Two aeroacoustic sources are located just downstream of each cylinder and one aeroacoustic source is located in the gap between the cylinders. The numerical results are compared with the experimental results presented in a previous investigation and favourable agreement is obtained.

Numerical Simulation of the Flow-Sound Interaction Mechanisms of a Single and Two-Tandem Cylinders in Cross-Flow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Mohany ◽  
S. Ziada
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Positive Energy ◽  
Single Cylinder ◽  
Interaction Mechanisms ◽  
Tandem Cylinders

A numerical simulation of the flow-excited acoustic resonance for the case of two-tandem cylinders in cross-flow is performed. The spacing ratio between the cylinders (L/D=2.5) is inside the proximity interference region. Similar simulation is performed for the case of a single cylinder. The unsteady flow field is simulated using a finite-volume method. This simulation is then coupled with a finite-element simulation of the resonant sound field, by means of Howe’s theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. For the case of a single cylinder, acoustic resonance is excited over a single range of flow velocity. The main aeroacoustic source, which causes a positive energy transfer from the flow field to the acoustic field, is found to be located just downstream of the cylinder. For the case of two-tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity: the precoincidence and the coincidence resonance ranges. For the coincidence resonance range, the main aeroacoustic source is found to be located just downstream of the downstream cylinder, and the excitation mechanism of this resonance range is found to be similar to that of a single cylinder. However, for the precoincidence resonance range, the primary acoustic source is found to be located in the gap between the cylinders. Moreover, flow visualization of the wake structure for the two-tandem cylinders during acoustic resonance shows that for the precoincidence resonance range there is a phase shift of about 90 deg between the vortex shedding from the upstream and the downstream cylinders, which is different from the coincidence resonance range, where the vortex shedding from both cylinders seems to be in-phase.

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.

Experimental Investigation of the Acoustic Power Around Two Tandem Cylinders

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
S. L. Finnegan ◽  
C. Meskell ◽  
S. Ziada
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Acoustic Resonance ◽  
Low Flow ◽  
Interaction Mechanisms ◽  
Tandem Cylinders ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Flow Velocities

Aeroacoustic resonance of bluff bodies exposed to cross flow can be problematic for many different engineering applications and knowledge of the location and interaction of acoustic sources is not well understood. Thus, an empirical investigation of the acoustically coupled flow around two tandem cylinders under two different resonant conditions is presented. It is assumed that the resonant acoustic field could be decoupled from the hydrodynamic flow field, resolved separately, and then recoupled to predict the flow/sound interaction mechanisms using Howe's theory of aerodynamic sound. Particle image velocimetry was employed to resolve the phase-averaged flow field characteristics around the cylinders at various phases in an acoustic wave cycle. It was found that the vortex shedding patterns of the two resonant conditions exhibit substantial differences. For the first condition, which occurred at low flow velocities where the natural vortex shedding frequency was below the acoustic resonance frequency, fully developed vortices formed in both the gap region between the cylinders and in the wake. These vortices were found to be in phase with each other. For the second resonant condition, which occurred at higher flow velocities where the natural vortex shedding frequency was above the acoustic resonant frequency, fully developed vortices only formed in the wake and shedding from the two cylinders were not in phase. These differences in the flow field resulted in substantial variation in the flow-acoustic interaction mechanisms between the two resonant conditions. Corresponding patterns of the net acoustic energy suggest that acoustic resonance at the lower flow velocity is due to a combination of shear layer instability in the gap and vortex shedding in the wake, while acoustic resonance at the higher flow velocity is driven by the vortex shedding in the wake of the two cylinders.

Numerical Simulation of Cross-Flow around Four Cylinders in a Square Configuration Using Lattice Boltzmann Method

2013 ◽  
Vol 405-408 ◽  
pp. 3259-3262 ◽  
Author(s):  
Wei Zhang ◽  
Hui Hua Ye ◽  
Jian Hua Tao
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Lattice Boltzmann Method ◽  
Vortex Shedding ◽  
Lattice Boltzmann ◽  
Cross Flow ◽  
Spacing Ratio ◽  
Square Configuration ◽  
Boltzmann Method ◽  
Four Cylinders

The flow around four cylinders in a square configuration with a spacing ratio 4 and Reynolds number of 200 are investigated using lattice Boltzmann method for angles of incidence α=0 and 45º, respectively. The results show that no biased flow occurs and the flow pattern is symmetrical at α=0, and the vortex shedding exists after the upstream cylinders which is completely different from the experimental results. It is hard to explain the discrepancy at present. The phenomenon of vortex shedding in-phase observed in the experiment reappears in the numerical simulation at α=45º.

Vortex Shedding and Acoustic Resonance of Single and Tandem Finned Cylinders

2010 ◽  
Author(s):  
Mohammed Eid ◽  
Samir Ziada
Keyword(s):  
Vortex Shedding ◽  
Sound Pressure ◽  
Interaction Mechanism ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Number Range ◽  
Tandem Cylinders ◽  
Spacing Ratio ◽  
High Reynolds ◽  
The Impact

The effect of fins on vortex shedding and acoustic resonance is investigated for isolated and two tandem cylinders exposed to cross-flow in a rectangular duct. Three spacing ratios between the tandem cylinders (S/De = 1.5, 2 and 3) are tested for a Reynolds number range from 1.6×104 to 1.1×105. Measurements of sound pressure and flow velocity are performed for bare and finned cylinders with three different fin densities. The effect of fins on the sound pressure generated before the onset of acoustic resonance as well as during the pre-coincidence and coincidence resonance is found to be rather complex and depends on the spacing ratio between cylinders, the fin density and the nature of the flow-sound interaction mechanism. For isolated cylinders, the fins reduce the strength of vortex shedding only slightly, but strongly attenuate the radiated sound before and during the acoustic resonance. This suggests that the impact of the fins on correlation length is stronger than on velocity fluctuations. In contrast to isolated cylinders, the fins in the tandem cylinder case enhance the vortex shedding process at off-resonant conditions, except for the large spacing case which exhibits a reversed effect at high Reynolds numbers. Regarding the acoustic resonance of the tandem cylinders, the fins promote the onset of the coincidence resonance, but increasing the fin density drastically weakens the intensity of this resonance. The fins are also found to suppress the pre-coincidence resonance for the tandem cylinders with small spacing ratios (S/De = 1.5 and 2), but for the largest spacing case (S/De = 3), they are found to have minor effects on the sound pressure and the lock-in range.

Numerical Simulation of Vortex Shedding Past a Circular Cylinder in a Cross-Flow at Low Reynolds Number With Finite Volume-Technique: Part 1 — Forced Oscillations

2007 ◽  
Author(s):  
Antoine Placzek ◽  
Jean-Franc¸ois Sigrist ◽  
Aziz Hamdouni
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Finite Volume ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Cross Flow ◽  
Forced Oscillations ◽  
Lift And Drag ◽  
Wake Characteristics

The numerical simulation of the flow past a circular cylinder forced to oscillate transversely to the incident stream is presented here for a fixed Reynolds number equal to 100. The 2D Navier-Stokes equations are solved with a classical Finite Volume Method with an industrial CFD code which has been coupled with a user subroutine to obtain an explicit staggered procedure providing the cylinder displacement. A preliminary work is conducted in order to check the computation of the wake characteristics for Reynolds numbers smaller than 150. The Strouhal frequency fS, the lift and drag coefficients CL and CD are thus controlled among other parameters. The simulations are then performed with forced oscillations f0 for different frequency rations F = f0/fS in [0.50–1.50] and an amplitude A varying between 0.25 and 1.25. The wake characteristics are analysed using the time series of the fluctuating aerodynamic coefficients and their FFT. The frequency content is then linked to the shape of the phase portrait and to the vortex shedding mode. By choosing interesting couples (A,F), different vortex shedding modes have been observed, which are similar to those of the Williamson-Roshko map.

Numerical Simulation of Cross-Flow around Four Square Cylinders in a Square Configuration at Low Reynolds Number

2013 ◽  
Vol 423-426 ◽  
pp. 1700-1704
Author(s):  
Wei Zhang ◽  
Wen Jie Li ◽  
Hui Hua Ye ◽  
Dian Xin Zhang
Keyword(s):  
Cross Flow ◽  
Reynold Number ◽  
Drag And Lift Coefficients ◽  
Square Cylinders ◽  
Spacing Ratio ◽  
Low Reynolds ◽  
Four Square ◽  
Drag And Lift ◽  
Square Configuration ◽  
Volume Method

A two-dimensional finite volume method with unstructured mesh is used to simulate the flow around four square cylinders in a square configuration at low Reynolds numbers.The vorticity field, drag and lift coefficients, and Strouhal number are resolved at different spacing ratios. The vortex-shedding process and fluid-structure interactions of four square cylinders are analyzed at Reynold number of 100. The results show that the spacing ratio has important effect on the drag and lift coefficients. The accuracy of the numerical scheme are validated against other numerical and experimental data.

Flow Excited Acoustic Resonance of Two Side-by-Side Cylinders in Cross Flow

2006 ◽  
Author(s):  
Ronald Hanson ◽  
Atef Mohany ◽  
Samir Ziada
Keyword(s):  
Flow Regime ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonance Mechanism ◽  
Flow Phenomenon ◽  
Stable Flow ◽  
Center Distance

The aeroacoustic response of two side-by-side cylinders in cross-flow is investigated experimentally. In order to investigate the effect of the gap between the cylinders on the acoustic resonance mechanism, six spacing ratios between the cylinders have been investigated. These spacing ratios are in the range of T/D = 1.25 to 3, where D is the diameter of the cylinders and T is the center-to-center distance between them. Special attention is given to the bi-stable flow regime, which is reported in the literature for intermediate spacing ratios. During the tests, the acoustic cross-modes of the duct housing the cylinders are self-excited. For the intermediate spacing ratios, T/D = 1.25, 1.35, 1.46 and 1.75, two distinct vortex shedding frequencies at the off-resonance conditions are observed. These are associated with the wider and narrower wakes of the cylinders, as described in the literature. In this case, acoustic resonance occurs at a Strouhal number that is between those observed before the onset of resonance. In addition, the acoustic resonance synchronizes vortex shedding in the two wakes and thereby eliminates the bi-stable flow phenomenon. For large spacing ratios, T/D = 2.5 and 3, vortex shedding occurs at a single Strouhal number at which the acoustic resonance is initiated.

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