Effect of acoustic resonance on the dynamic lift forces acting on two tandem cylinders in cross-flow

2009 ◽  
Vol 25 (3) ◽  
pp. 461-478 ◽  
Author(s):  
A. Mohany ◽  
S. Ziada
Keyword(s):  
Cross Flow ◽  
Acoustic Resonance ◽  
Tandem Cylinders ◽  
Lift Forces

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.

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.

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.

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.

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.

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.

Parametric Investigation of the Flow-Sound Interaction Mechanism for Single Cylinders in Cross-Flow

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Omar Afifi ◽  
Atef Mohany
Keyword(s):  
Heat Exchangers ◽  
Interaction Mechanism ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Industrial Applications ◽  
Resonance Excitation ◽  
Acoustic Damping ◽  
Radiation Losses ◽  
Cylinder Diameter ◽  
Tube Bundles

Abstract Flow-excited acoustic resonance is a design concern in many industrial applications. If not treated, it may lead to excessive vibrational loads, which could subsequently result in premature structural failure of critical equipment. For the case of tube bundles in heat exchangers, several acoustic damping criteria were proposed in the literature to predict the occurrence of resonance excitation. However, these criteria, in some cases, are not reliable in differentiating between the resonant and nonresonant cases. A primary reason for that is the geometrical differences between reduced scale models and full-scale tube bundles, and their effect on the flow-sound interaction mechanism. Therefore, the effect of two geometrical aspects, namely, the duct height and the cylinder diameter, on the self-excited acoustic resonance for single cylinders in cross-flow is experimentally investigated in this work. Changing the duct height changes the natural frequency of the excited acoustic modes and the duct's acoustic damping and radiation losses. Changing the cylinder diameter changes the flow velocity at frequency coincidence, the pressure drop, and Reynolds number. It is found that increasing the duct height decreases the acoustic impedance, which makes the system more susceptible to resonance excitation. This, in turn, changes the magnitude of the acoustic pressure at resonance, even for cases where the dynamic head of the flow is kept constant. The acoustic attenuation due to visco-thermal losses is quantified theoretically using Kirchhoff's acoustical damping model, which takes into account the geometrical aspects of the different ducts. Results from the experiments are compared with the acoustic damping criteria from the literature for similar cases. It is revealed that the height of the duct is an important parameter that should be included in damping criteria proposed for tube bundles of heat exchangers, as it controls the acoustic damping and radiation losses of the system, which have been over-looked in the past.

Further Study of Quasiperiodic Vibration Excitation Forces in Rotated Triangular Tube Bundles Subjected to Two-Phase Cross Flow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
C. Zhang ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Fretting Wear ◽  
Force Frequency ◽  
Two Phase ◽  
Vibration Excitation ◽  
Tube Bundles ◽  
Excitation Force ◽  
Lift Forces ◽  
Drag And Lift

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. Some of this work has already been done. Somewhat unexpected but significant quasiperiodic forces in both the drag and lift directions were measured. These forces are generally larger in the drag direction. However, the excitation force frequency is relatively low (i.e., 3–6 Hz) and not directly dependent on flow velocity in the drag direction. On the other hand, much higher frequencies (up to 16 Hz) were observed in the lift direction at the higher flow velocities. The frequency appears directly related to flow velocity in the lift direction. The present work aims at (1) providing further evidence of the quasiperiodic lift force mechanism, (2) determining the effect of cylinder position on such quasiperiodic drag and lift forces, and (3) verifying the existence of quasiperiodic drag and lift forces in a more realistic larger tube array. The program was carried out with two rotated triangular tube arrays of different width subjected to air/water flow to simulate two-phase mixtures from liquid to 95% void fraction. Both the dynamic lift and drag forces were measured with strain gauge instrumented cylinders.

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