Flow-Induced Acoustic Resonance of Finned Cylinders With Varying Fin Heights

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Md Rashidul Islam ◽  
Atef Mohany
Keyword(s):  
Acoustic Resonance ◽  
Root Diameter ◽  
Diameter Ratio ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Effective Diameter ◽  
Flow Perturbation ◽  
Lock In ◽  
Fin Thickness ◽  
Flow Blockage

Abstract The flow-excited acoustic resonance phenomenon, which is instigated by periodic flow perturbation, leads to the generation of acute sound pressure. In this work, we investigated the characteristics of the flow-excited acoustic resonance for circular finned cylinders with different fin heights. The fin height is expressed as a normalized form considering the ratio of the fin diameter to the root cylinder diameter. The experiments are performed with finned cylinders having a range of diameter ratios between 1.5<Df/Dr<2.5. The diameter ratios are varied by changing the root diameter and fin diameter separately as well as simultaneously while keeping the fin pitch and the fin thickness constant. The results show that the excitation of acoustic resonance has profound dependence on the diameter ratio. Increasing the diameter ratios of the finned cylinder results in strong acoustic resonance excitation. The lock-in width and the onset of the acoustic resonance excitation also depend on the diameter ratio of the cylinders. Moreover, the results show that using an effective diameter based on the geometrical flow blockage does not take into account the changes occurring in the source of resonance excitation due to the addition of fins.

Phase-Locked PIV Measurements of Vortex Shedding Characteristics Downstream of Straight Circular Finned Cylinders During Acoustic Resonance

2019 ◽  
Author(s):  
Rashid Islam ◽  
Mahmoud Shaaban ◽  
Atef Mohany
Keyword(s):  
Sound Pressure ◽  
Acoustic Pressure ◽  
Particle Image ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Effective Diameter ◽  
Piv Measurements ◽  
Flow Perturbation ◽  
Image Velocimetry

Abstract Excitation of acoustic resonance by flow perturbation downstream of cylinders can result in hazardous levels of acoustic pressure. Previous studies have shown that straight finned cylinders are susceptible to flow-excited acoustic resonance. In this work, the excitation of acoustic resonance by flow around finned cylinders of different fin parameters including the spacing between the fins, the thickness of the fin, and the height of the fin is investigated. All the investigated finned cylinders have the same equivalent diameter. Phase-locked particle image velocimetry (PIV) measurements are carried out during acoustic resonance to characterize the flow field downstream of the cylinders and identify the influence of the fins on the flow structures at the peak of resonance excitation. Results show that straight circular fins excite acoustic resonance at lower velocities and result in higher sound pressure level compared with a single bare cylinder of the same effective diameter. This behaviour is due to the effect of fin parameters on the strength and the formation length of vortices shed during the acoustic cycle. 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.

The Effect of Upstream Edge Geometry on the Acoustic Resonance Excitation in Shallow Rectangular Cavities

2014 ◽  
Author(s):  
Ahmed Omer ◽  
Nadim Arafa ◽  
Atef Mohany ◽  
Marwan Hassan
Keyword(s):  
Flow Instability ◽  
Acoustic Resonance ◽  
Resonance Mode ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Base Case ◽  
Pressure Amplitude ◽  
Cavity Depth ◽  
Edge Geometry ◽  
Aspect Ratios

The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes, which in turn generates acute noise problems and/or excessive vibrations. In this study, the effect of the upstream edge geometry on attenuating these undesirable effects is investigated experimentally for flows over shallow rectangular cavity with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, and for Mach number less than 0.5. The acoustic resonance modes of the cavity are self-excited. Twenty four different upstream cavity edges are investigated in this study; including round edges, chamfered edges, vortex generators and spoilers with different sizes and configurations. The acoustic pressure is measured with a flush-mounted microphone on the cavity floor and the velocity fluctuation of the separated shear layer before the onset of acoustic resonance is measured with a hot-wire probe. The results for each upstream cavity edge are compared with the base case when square cavity edge is used. It is observed that when chamfered edges are used, the amplitude of the first acoustic resonance mode is highly intensified with values reaching around 5000 Pa (compared to 2000 Pa for the base case) and a clear shift in its onset of resonance to higher flow velocities is observed. Similar trend is observed when round edges are used. The amplitude of the generated pressure of the first acoustic resonance mode is amplified with values exceeding 4000 Pa and a delay in its onset of acoustic resonance is observed as well. Most of the spoiler edges are found to be effective in suppressing the pressure amplitude of the excited acoustic resonance. However, the performance of each spoiler depends on its specific geometry (i.e. thickness, height, and angle) relative to the cavity aspect ratio. A summary of the results is presented in this paper.

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.

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.

Flow-Excited Acoustic Resonance of Single Finned Cylinder in Cross-Flow

2014 ◽  
Author(s):  
Nadim Arafa ◽  
Atef Mohany
Keyword(s):  
Aspect Ratio ◽  
Acoustic Pressure ◽  
Interaction Mechanism ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Effective Diameter ◽  
Pressure Amplitude ◽  
Resonance Amplitude ◽  
Fin Thickness ◽  
Fin Spacing

The flow-excited acoustic resonance of single straight finned cylinder in cross-flow is investigated experimentally in this work. This phenomenon has been investigated in some detail for the case of bare cylinders; however, the effect of adding fins to the cylinders on the flow-sound interaction mechanism is not yet fully understood. During the experiments, the acoustic cross-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, fourteen different finned cylinders with fin thickness ranging from 0.35 to 1.5 mm and fin density ranging from 4 to 13.7 fin/inch are investigated for a Reynolds number ranging from 3.2×104 to 2.6×105. The onset and intensity of the acoustic resonance generated from each finned cylinder are compared to those generated from an equivalent bare cylinder with the same effective diameter. It is observed that the finned cylinders experience an earlier acoustic resonance and higher levels of acoustic pressure compared to their equivalent bare cylinders. This suggests that adding fins to the cylinder enhances the flow coherence along the cylinder’s span and thus makes the flow more susceptible to acoustic excitation. 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 is investigated in three different test sections. It is observed that the amplitude of the excited acoustic resonance depends on the cylinder’s aspect ratio. The acoustic resonance amplitude is weaker for finned cylinders with aspect ratio less than 5 compared to their equivalent bare cylinders. However, finned cylinders with aspect ratio higher than 6 produces stronger acoustic resonance compared to their equivalent bare cylinders.

scholarly journals Numerical Study on Acoustic Resonance Excitation in Closed Side Branch Pipeline Conveying Natural Gas

2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Liuyi Jiang ◽  
Hong Zhang ◽  
Qingquan Duan ◽  
Yulong Zhang
Keyword(s):  
Natural Gas ◽  
Numerical Study ◽  
Acoustic Resonance ◽  
Side Branch ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Resonance Problem ◽  
Detached Eddy Simulation ◽  
Single Vortex ◽  
Excited Vibration

Flow-induced acoustic resonance in the closed side branch of a natural gas pipeline can cause intensive vibration which threatens the safe operation of the pipeline. Accurately modeling this excitation process is necessary for a workable understanding of the genetic mechanism to resolve this problem. A realizable k-ε Delayed Detached Eddy Simulation (DDES) model was conducted in this study to numerically simulate the acoustic resonance problem. The model is shown to accurately capture the acoustic resonance phenomenon and self-excited vibration characteristics with low calculation cost. The pressure pulsation component of the acoustic resonance frequency is gradually amplified and transformed into a narrowband dominant frequency in the process of acoustic resonance excitation, forming a so-called “frequency lock-in phenomenon.” The gas is pressed into and out of the branch in sinusoidal mode during excitation. The first-order frequency, single vortex moves at the branch inlet following the same pattern. A quarter wavelength steady standing wave forms in the branch. The mechanism and characteristics presented in this paper may provide guidelines for developing new excitation suppression methods.

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.

Frequency lock-in mechanism in flow-induced acoustic resonance of a cylinder in a flow duct

2019 ◽  
Vol 884 ◽  
Author(s):  
Zhiliang Hong ◽  
Xiaoyu Wang ◽  
Xiaodong Jing ◽  
Xiaofeng Sun
Keyword(s):  
Acoustic Resonance ◽  
Image Position ◽  
Lock In ◽  
Flow Duct

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