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.

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.

Self-Excited Acoustic Resonance of Isolated Cylinders in Cross-Flow

2012 ◽  
Vol 1 (1) ◽  
pp. 45-55 ◽  
Author(s):  
A. Mohany
Keyword(s):  
Flow Velocity ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonance Phenomenon ◽  
Flow Conditions ◽  
Resonance Mechanism ◽  
Single Cylinder ◽  
Tandem Cylinders ◽  
Tube Bundles

Self-excited acoustic resonance is a design concern in many engineering applications such as tube bundles of heat exchangers and boilers. Since this phenomenon is not yet fully understood, it can be dangerously unpredictable. Due to the complexity of the flow-sound interaction mechanisms in tube bundles, the simplified cases of a single cylinder and two cylinders in various arrangements, tandem and staggered, are investigated in some detail. A summary of these investigations is presented in the current paper. It is found that the aeroacoustic response of two-tandem and side-by-side cylinders in cross-flow can be considerably different from that of a single cylinder under similar flow conditions. Moreover, for the case of two tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity; the pre-coincidence and the coincidence resonance ranges. The pre-coincidence acoustic resonance phenomenon is found to be similar to the acoustic resonance mechanism of in-line tube bundles.

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.

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.

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.

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

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 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.

Effect of Acoustic Resonance on the Dynamic Lift Forces Acting on Two Tandem Cylinders in Cross-Flow

2006 ◽  
Author(s):  
Atef Mohany ◽  
Samir Ziada
Keyword(s):  
Lift Force ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Transverse Modes ◽  
Tandem Cylinders ◽  
Abrupt Changes ◽  
Drastic Increase ◽  
Lift Forces ◽  
Force Components

Direct measurement of the dynamic lift force for the case of two tandem cylinders in cross-flow during acoustic resonance is performed. Two spacing ratios inside the proximity interference region, L/D = 2.5 and 3, are considered. During the tests, the acoustic transverse-modes of the duct housing the cylinder are self-excited. In the absence of acoustic resonance, the measured dynamic lift coefficient agrees well with those reported in the literature. When the acoustic resonance is initiated, a drastic increase in the dynamic lift coefficient is observed, especially on the downstream cylinder. This is associated with abrupt changes in the phase between the lift forces and the acoustic pressure. The dynamic lift forces on both cylinders are also decomposed into in-phase and out-of-phase components, with respect to the resonant sound pressure. The lift force components for the downstream cylinder are found to be dominant. Moreover, the out-of-phase component of the lift force on the downstream cylinder is found to become negative over two different ranges of flow velocity and to virtually vanish between these two ranges. Acoustic resonance is therefore generated over two ranges of reduced velocity separated by a non-resonant range near the velocity of frequency coincidence. The out-of-phase lift component of the downstream cylinder is found to control the occurrence of acoustic resonance, whereas the in-phase lift component seems to cause slight variations in the acoustic resonance frequency.

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