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.

Characteristics of Acoustic Resonance Excitation by Flow Around Inline Cylinders

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Mahmoud Shaaban ◽  
Atef Mohany
Keyword(s):  
Acoustic Pressure ◽  
Tube Bundle ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Environmental Risks ◽  
Critical Parameters ◽  
Resonance Excitation ◽  
Tube Bundles ◽  
Flow Oscillations

Excitation of acoustic resonance by flow over tube bundles in heat exchangers can cause hazardous levels of acoustic pressure that may pose operational and environmental risks. The previous studies have indicated that inline arrangements of cylinders excite acoustic resonance of a nature different from that of a single cylinder. In this work, the excitation of acoustic resonance by cross-flow around inline arrangements of cylinders is experimentally investigated to identify the role of critical parameters on resonance characteristics. Results show that flow around inline tube bundles can excite acoustic resonance due to periodic flow oscillations over the cavity formed between successive cylinders rather than periodic wake phenomena. Based on precoincidence resonance characteristics, a criterion is introduced to predict the occurrence of acoustic resonance in inline arrangements of cylinders. The proposed parametric criterion does not only identify the potential for resonance excitation for inline arrangements of cylinders experimentally investigated in this work but it also provides a method to separate resonant from nonresonant cases for inline tube bundle data from the literature.

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.

Aeroacoustic Response of a Single Cylinder With Straight Circular Fins in Cross-Flow

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Nadim Arafa ◽  
Atef Mohany
Keyword(s):  
Aspect Ratio ◽  
Acoustic Pressure ◽  
Interaction Mechanism ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Acoustic Excitation ◽  
Pressure Amplitude ◽  
Fin Thickness ◽  
Fin Spacing

The phenomenon of sound generation has been investigated in some detail for the case of bare cylinders; however, the effect of adding fins to the cylinder on the flow–sound interaction mechanism is not yet fully understood. Thus, the aeroacoustic response of a cylinder with straight circular fins in cross-flow is investigated experimentally in this work. During the experiments, the acoustic modes of the duct housing the cylinder are self-excited due to the vortex shedding that emerges from the cylinder's surface. In order to determine the effect of different fin parameters on the onset and intensity of acoustic resonance, 14 different finned cylinders with fin thickness ranging from 0.35 to 1.5 mm and fin density ranging from 4 to 13.7 fin/in. are investigated. It is observed that the finned cylinders experience an earlier acoustic resonance and higher levels of acoustic pressure compared to their equivalent bare cylinders. Moreover, it is observed that, for constant fin spacing, the acoustic pressure amplitude increases and the acoustic resonance occurs at earlier velocities as the fin thickness increases. On the other hand, for constant fin thickness, as the fin spacing increases the amplitude of the acoustic pressure decreases while the onset of the resonance is delayed. Finally, the effect of the cylinder's aspect ratio on the acoustic resonance excitation is presented. It is shown that as the finned cylinders' aspect ratio increases from 4.85 to 11.3, the normalized acoustic pressure during resonance increases drastically. However, for bare cylinders the normalized acoustic pressure during resonance is not highly dependent on the cylinders' aspect ratio. These results indicate that adding fins to the cylinder alters the flow field downstream of the cylinder in a manner that makes it more susceptible to acoustic excitation.

Effect of Flow Approach Angle on Acoustic Resonance Excitation of In-Line Tube Bundles in Cross-Flow

2019 ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany ◽  
Marwan Hassan
Keyword(s):  
Tube Bundle ◽  
Flow Direction ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Acoustic Energy ◽  
Resonance Excitation ◽  
Approach Angle ◽  
Tube Bundles ◽  
Lock In

Abstract This paper presents preliminary experimental results on the influence of the flow approach angle on the acoustic resonance excitation of in-line tube bundles in cross-flow. The pitch-to-diameter ratio (P/D) of the in-line tube bundles investigated is P/D = 1.733. The flow approach angle was investigated by physically rotating the tube bundle clockwise relative to the flow direction. The tube bundles are capable of rotating with increments of 5° up to an angle of 45°. For brevity, only the results for the 0° and 30° orientation will be presented herein. For the 0° orientation, two Strouhal frequencies (St1 = 0.437 and St2 = 0.252) were observed. However, only one of these frequencies (St1 = 0.437) was capable of exciting resonance. During resonance, a peak sound pressure level (SPL) of 170 dB was achieved. The Strouhal frequencies and peak SPL agrees well with what has been presented in the literature. For the 30° orientation, only one Strouhal frequency (St1 = 0.98) was measured. At this orientation, the lock-in phenomenon occurred at a much lower flow velocity compared to the 0° orientation with a peak SPL reaching 153 dB. Jumps in the lock-in frequency were observed at the 30° orientation. This phenomenon is associated with two reasons. The first reason is a partial lock-in with an acoustic resonant mode, due to the acoustic energy not being fully trapped within the tube bundle. The second reason is related to the changes in the apparent speed of sound resulting in variations in the acoustic cross-mode frequency depending on where the excitation source is emanating from within the tube bundle. A brief summary of the results is presented in this paper.

Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

2021 ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Interaction Mechanism ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Effective Diameter ◽  
Finned Tubes ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

Experimental Investigation of Forced Convection Enhancement by Acoustic Resonance Excitations in Turbulated Heat Exchangers

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Samuel Gendebien ◽  
Alex Kleiman ◽  
Boris Leizeronok ◽  
Beni Cukurel
Keyword(s):  
Heat Exchanger ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Minimal Form ◽  
Resonance Frequencies ◽  
Double Pipe ◽  
The Impact

Abstract The present research deals with enhancing the thermal performance of turbulated heat exchangers through the application of sound pressure waves at acoustic resonance frequencies. Extending the findings of prior wind tunnel studies, where a standing wave greatly improved the forced convection in reattaching flows, this paper exploits such a phenomenon in a practical heat exchanger setting. The current experiments are conducted in representative turbulated plate and double-pipe heat exchanger geometries, mounted in a dedicated facility. After identifying the inherent acoustic resonance frequencies of the passageways, the impact of excitation is studied in various sound pressure levels, blockage ratios, as well as Strouhal and Reynolds numbers. The acoustic resonance excitation resulted in heat transfer enhancement of 20% and 10% in the plate and double-pipe designs, respectively, absence of additional pressure penalties. To the best knowledge of the authors, this is the first demonstration of acoustic forced convection enhancement in turbulated heat exchanger geometries. Such a technology can pave the way toward future designs that require low-pressure losses, minimal form factor, and/or process controllability.

Experimental Investigation of Forced Convection Enhancement by Acoustic Resonance Excitations in Turbulated Heat Exchangers

2019 ◽  
Author(s):  
S. Gendebien ◽  
A. Kleiman ◽  
B. Leizeronok ◽  
B. Cukurel
Keyword(s):  
Heat Exchanger ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Minimal Form ◽  
Resonance Frequencies ◽  
Double Pipe ◽  
The Impact

Abstract The present research deals with enhancing thermal performance of turbulated heat exchangers through application of sound pressure waves at acoustic resonance frequencies. Extending the findings of prior wind tunnel studies, where a standing wave greatly improved the forced convection in reattaching flows, this paper exploits such a phenomenon in a practical heat exchanger setting. The current experiments are conducted in representative turbulated plate and double pipe heat exchanger geometries, mounted in a dedicated facility. After identifying the inherent acoustic resonance frequencies of the passageways, the impact of excitation is studied in various sound pressure levels, blockage ratios, as well as Strouhal and Reynolds numbers. The acoustic resonance excitation resulted in heat transfer enhancement of 20% and 10% in the plate and double pipe designs respectively, absent of additional pressure penalties. To the best knowledge of the authors, this is the first demonstration of acoustic forced convection enhancement in turbulated heat exchanger geometries. Such a technology can pave the way towards future designs that require low pressure losses, minimal form factor and/or process controllability.

Modeling and Simulation of Cross-Flow Induced Vibration in a Multi-Span Tube Bundle

2004 ◽  
Author(s):  
Shahab Khushnood ◽  
Zaffar M. Khan ◽  
M. Afzaal Malik ◽  
Zafarullah Koreshi ◽  
Mahmood Anwar Khan
Keyword(s):  
Heat Exchanger ◽  
Tube Bundle ◽  
Cross Flow ◽  
Fatigue Cracking ◽  
Acoustic Resonance ◽  
Computer Code ◽  
Variable Geometry ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Tube Bundles

Flow-induced vibration in steam generator and heat exchanger tube bundles has been a source of major concern in nuclear and process industry. Tubes in a bundle are the most flexible components of the assembly. Flow induced vibration mechanisms, like fluid-elastic instability, vortex shedding, turbulence induced excitation and acoustic resonance results in failure due to mechanical wear, fretting and fatigue cracking. The general trend in heat exchanger design is towards larger exchangers with increased shell side velocities. Costly plant shutdowns have been the motivation for research in the area of cross-flow induced vibration in steam generators and process exchangers. The current paper focuses on the development of a computer code (FIVPAK) for the design (natural frequencies, variable geometry, tube pitch & pattern, mass damping parameter, reduced velocity, strouhal and damage numbers, added mass, wear work rates, void fraction for two-phase, turbulence and acoustic considerations etc.) of tube bundles with respect to cross flow-induced vibration. The code has been validated against Tubular Exchanger Manufacturers (TEMA), Flow-Induced Vibration code (FIV), and results on an actual variable geometry exchanger, specially manufactured to simulate real systems. The proposed code is expected to prove a useful tool in designing a tube bundle and to evaluate the performance of an existing system.

Strouhal Numbers for Heat Exchanger Tube Arrays in Cross Flow

1987 ◽  
Vol 109 (2) ◽  
pp. 219-223 ◽  
Author(s):  
D. S. Weaver ◽  
J. A. Fitzpatrick ◽  
M. ElKashlan
Keyword(s):  
Heat Exchangers ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Peak Frequency ◽  
Heat Exchanger Tube ◽  
Turbulence Spectrum ◽  
Tube Arrays ◽  
Exchanger Tube ◽  
Array Geometry

The prediction of tube or acoustic resonance due to cross-flow in heat exchangers is dependent upon knowledge of the flow characteristics for a given tube array geometry. For this, a Strouhal number relating a peak frequency in the turbulence spectrum to the velocity of the flow is required. The data available in the literature for this are rather confusing and the prediction methods appear somewhat contradictory. This paper reports the results from experiments conducted to determine Strouhal numbers for eight tube array models. These results together with the data available in the literature are then compared and appropriate conclusions drawn.

The Impact of Perforation Geometry on Acoustic Damping Attributes of a Perforated Liner With Bias Flow

2012 ◽  
Author(s):  
Alireza Mazdeh ◽  
Reza Kashani
Keyword(s):  
Fluid Dynamic ◽  
Perforated Plate ◽  
Interaction Mechanism ◽  
Industrial Applications ◽  
Radius Ratio ◽  
Damping Properties ◽  
Acoustic Damping ◽  
Spacing Ratio ◽  
Bias Flow ◽  
The Impact

Acoustic damping properties of perforated liners are highly dependent on a number of variables which can be categorized as “flow variables” such as the extent and Mach number of grazing flow as well as bias flow and “geometric variable” such as the shape of the hole which can be rectangular, cylindrical, conical with diverging or converging nozzle, thickness to radius ratio, radius to hole spacing ratio and hole orientation which can be normal to or inclined with respect to the perforated plate. Many of these variables were not incorporated in previous studies. Theoretical and empirical approaches have provided the foundation for understanding the damping properties of liners but they are based on certain simplifying assumptions making them inadequate in addressing the more realistic conditions encountered in industrial applications. These limitations have highlighted the importance of numerical methods for studying damping behavior of liners. Acoustic attributes of perforated plates (mainly in terms of impedance which is a frequency-dependent complex quantity) as a function of non-dimensional variables like Reynolds, Strouhal, Mach, and Helmholtz numbers have been studied by various researchers, including the authors, using a variety of numerical tools starting from the simple 1D network scheme based on linear acoustics and the wall compliance concept introduced by Howe all the way to the computationally intensive Large-Eddy Simulations (LES) and Scaled Adaptive Simulation (SAS) reconstructing the full unsteady turbulent structures. Although the impacts of some geometry variations such as hole inclination angle and diameter, in conjunction with various fluid dynamic parameters, have been investigated using 1D network tools, the focus of LES has been mainly on analysis of a single circular hole with periodic boundary conditions as the representation of multi-perforation (assuming the perforations are spaced far enough from each other so that there is no interaction between neighboring holes). There is certainly a need for thorough investigation of the acoustics impact of these geometric parameters as well as shape of the holes using LES. In an on-going research we are extending the numerical modeling work on characterizing the acoustic damping attributes of a perforation, beyond the current state of the art, by including the geometric variables including hole size, shape, orientation, and radius to thickness ratio, amongst others, in the study. In this paper, following a short review of the research conducted in the recent past for comprehension of the acoustic-vortex interaction mechanism in perforated liners resulting in acoustic absorption, we present the findings on the impact of thickness/radius ratio on the acoustic damping attribute of a perforation. The verification of the CFD results are done by comparing the data with analytical solutions.

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