Characteristics of Aerodynamic Sound Radiated From Two Finned Cylinders

2014 ◽  
Author(s):  
Hiromitsu Hamakawa ◽  
Hiroki Matsuoka ◽  
Kazuki Hosokai ◽  
Eiichi Nishida ◽  
Eru Kurihara
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Transverse Direction ◽  
Flow Direction ◽  
Cross Flow ◽  
Near Wake ◽  
Aerodynamic Sound ◽  
Spacing Ratio ◽  
Staggered Arrangement ◽  
Karman Vortex

In the present paper the attention is focused on the characteristics of aerodynamic sound radiated from two finned cylinders with tandem and staggered arrangement exposed to cross-flow. We measured the spectrum of SPL and flow velocity for the cylinder spacing ratios ranged from 0 to 1.05 in the transverse direction and the ratios from 1.24 to 6.8 in the flow direction at Reynolds number of 1.0×105−1.9×105. As a result, we found that the peak SPL and Strouhal number of vortex shedding for two finned cylinders depend on the cylinder spacing ratios as well as those for bare cylinders. The peak SPL of the spectrum varied complexly with the tube spacing ratio. The peak levels of SPL for tandem finned cylinders were approximately 8 dB lower than that for the tandem bare cylinders. At the cylinder spacing ratio of 1.24 in the flow direction, the peak SPL for two finned cylinders at the cylinder spacing ratio of 0.72 in the transverse direction was about 8 dB larger than that for tandem finned cylinders. The peak SPL depended on the spanwise correlation length of the Karman vortex formed in the near wake of the downstream of two finned cylinders.

Flow Induced Oscillation of a Set-In Circular Cylinder

2009 ◽  
Author(s):  
F. Oviedo-Tolentino ◽  
R. Romero-Mendez ◽  
A. Hernandez-Guerrero ◽  
J. M. Luna
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Flow Behavior ◽  
Cross Flow ◽  
Close Relation ◽  
Structure Interaction ◽  
Visualization Techniques ◽  
Flow Experiments

This work studies the fluid-structure interaction of a set-in, large aspect-ratio circular cylinder in cantilever subjected to a cross flow. Experiments were conducted in a water tunnel and observations were obtained using flow visualization techniques and direct observation of the deflection of the cylinder. The flow behavior was observed using dye injection. The experiments show that the dominant vibration of the cylinder is transversal to the flow direction, and that the first mode of vibration of the cylinder appears at a particular Reynolds number, which is a function of the mechanical properties of the cylinder. The deflection stops when the Reynolds number is increased. The peak deflection and frequency of oscillation, as a function of the Reynolds number, were also determined. The analysis shows a close relation between the frequency of oscillation and the frequency of appearance of a vortex shedding. For large deflections of the cylinder the flow structure is modified substantially, and the frequency at which vortex appears is different to the frequency that occurs for fixed cylinders.

The Role of Axial Flow in Near Wake on the Cross-Flow Vibration of the Inclined Cable of Cable-Stayed Bridges

2010 ◽  
Author(s):  
Masaru Matsumoto
Keyword(s):  
Vortex Shedding ◽  
Cross Flow ◽  
Axial Flow ◽  
Splitter Plate ◽  
Near Wake ◽  
Karman Vortex ◽  
The Cross ◽  
Wind Induced Vibration ◽  
Cable Stayed Bridges

Nowadays, the violent wind-induced vibration, including “rain-wind induced vibration” and “dry-galloping”, of stay-cables of cable-stayed bridges has become the most serious issue for bridge design. Up-to-date, the major factors for excitation of inclined cables have been clarified to be, for “rain-wind” induced vibration, the formation of “water-rivulet” on the particular position of upper cable surface, and, for “dry galloping”, the “axial flow” which flows in the near wake along cable-axis, and the effect of drag-force associated with Reynolds number, separately. However, the details of the effect of “axial flow” remain unsolved. Thus, this study aims to clarify the effect of axial flow in near wake on the aero-elastic vibration of inclined cables basing on various experiments. The mean velocity of axial flow was almost 60% of approaching wind velocity. Furthermore, the aerodynamic effect of the “axial flow” on cross-flow vibration of inclined cables is discussed in relation to the mitigation of Karman vortex shedding in near wake. Since the role of axial flow seems to be similar to the splitter plate installed in wake from the point of mitigation of Karman vortex shedding, to clarify the cross-flow response in relation to the mitigation of Karman vortex, the perforated ratio of the splitter plate was variously changed, then the similarity of effect of axial flow and the one of splitter plate was verified comparing their unsteady lift force-characteristics. In summary, it is shown that the axial flow on aerodynamic cross-flow vibration might excite like galloping similarly with the splitter plate by mitigation of Karman vortex.

Numerical Study on Cross-Flow around Three Cylinders Using Lattice Boltzmann Method

2014 ◽  
Vol 525 ◽  
pp. 311-315
Author(s):  
Xiang Cui Lv ◽  
Wei Zhang ◽  
Dian Xin Zhang
Keyword(s):  
Reynolds Number ◽  
Lattice Boltzmann Method ◽  
Vortex Shedding ◽  
Lattice Boltzmann ◽  
Numerical Study ◽  
Cross Flow ◽  
Evolution Process ◽  
Spacing Ratio ◽  
The Right ◽  
Boltzmann Method

The flow around three cylinders in isosceles left-triangle and right-triangle configurations at Reynolds number of 200 are investigated using lattice Boltzmann method (LBM). Vortex shedding pattern and evolution process in the wake of each cylinder in the two cases are analyzed with a spacing ratio of 4. Results show that the flow pattern in the right-triangle configuration is symmetrical and the vortex shedding is anti-phase. Meanwhile, vortex shedding in-phase is observed in the left-triangle configuration which is due to the effect of the periodical vortex shedding behind upstream cylinder. The evolution process of vortex in the wakes of the cylinders for left-triangle configuration is simulated numerically.

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.

scholarly journals Flow past a square-section cylinder with a wavy stagnation face

2001 ◽  
Vol 426 ◽  
pp. 263-295 ◽  
Author(s):  
RUPAD M. DAREKAR ◽  
SPENCER J. SHERWIN
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Physical Structure ◽  
Near Wake ◽  
Hairpin Vortices ◽  
Independent State ◽  
Flow Past ◽  
Edge Surface

Numerical investigations have been performed for the flow past square-section cylinders with a spanwise geometric deformation leading to a stagnation face with a sinusoidal waviness. The computations were performed using a spectral/hp element solver over a range of Reynolds numbers from 10 to 150.Starting from fully developed shedding past a straight cylinder at a Reynolds number of 100, a sufficiently high waviness is impulsively introduced resulting in the stabilization of the near wake to a time-independent state. It is shown that the spanwise waviness sets up a cross-flow within the growing boundary layer on the leading-edge surface thereby generating streamwise and vertical components of vorticity. These additional components of vorticity appear in regions close to the inflection points of the wavy stagnation face where the spanwise vorticity is weakened. This redistribution of vorticity leads to the breakdown of the unsteady and staggered Kármán vortex wake into a steady and symmetric near-wake structure. The steady nature of the near wake is associated with a reduction in total drag of about 16% at a Reynolds number of 100 compared with the straight, non-wavy cylinder.Further increases in the amplitude of the waviness lead to the emergence of hairpin vortices from the near-wake region. This wake topology has similarities to the wake of a sphere at low Reynolds numbers. The physical structure of the wake due to the variation of the amplitude of the waviness is identified with five distinct regimes. Furthermore, the introduction of a waviness at a wavelength close to the mode A wavelength and the primary wavelength of the straight square-section cylinder leads to the suppression of the Kármán street at a minimal waviness amplitude.

scholarly journals Effect of Cylinder Gap Ratio on The Wake of a Circular Cylinder Enclosed by Various Perforated Shrouds

CFD letters ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 51-68
Author(s):  
Nurul Azihan Ramli ◽  
Azlin Mohd Azmi ◽  
Ahmad Hussein Abdul Hamid ◽  
Zainal Abidin Kamarul Baharin ◽  
Tongming Zhou
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Control Method ◽  
Lift Coefficient ◽  
Base Case ◽  
Bluff Bodies ◽  
Ansys Fluent ◽  
Gap Ratio ◽  
Spacing Ratio

Flow over bluff bodies produces vortex shedding in their wake regions, leading to structural failure from the flow-induced forces. In this study, a passive flow control method was explored to suppress the vortex shedding from a circular cylinder that causes many problems in engineering applications. Perforated shrouds were used to control the vortex shedding of a circular cylinder at Reynolds number, Re = 200. The shrouds were of non-uniform and uniform holes with 67% porosity. The spacing gap ratio between the shroud and the cylinder was set at 1.2, 1.5, 2, and 2.2. The analysis was conducted using ANSYS Fluent using a viscous laminar model. The outcomes of the simulation of the base case were validated with existing studies. The drag coefficient, Cd, lift coefficient, Cl and the Strouhal number, St, as well as vorticity contours, velocity contours, and pressure contours were examined. Vortex shedding behind the shrouded cylinders was observed to be suppressed and delayed farther downstream with increasing gap ratio. The effect was significant for spacing ratio greater than 2.0. The effect of hole types: uniform and non-uniform holes, was also effective at these spacing ratios for the chosen Reynolds number of 200. Specifically, a spacing ratio of 1.2 enhanced further the vortex intensity and should be avoided.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Performance characteristics of a chilled water spirally coiled finned tube in cross flow for air conditioning applications

2012 ◽  
Vol 227 (2) ◽  
pp. 320-331 ◽  
Author(s):  
Abdalla Gomaa ◽  
Wael IA Aly ◽  
Ashraf Mimi Elsaid ◽  
Eldesuki I Eid
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Flow Direction ◽  
Cross Flow ◽  
Finned Tube ◽  
Performance Characteristics ◽  
Curvature Ratio ◽  
Coiled Tube ◽  
Chilled Water

In the present study, the thermo-fluid characteristics of a spirally coiled finned tube in cross flow were experimentally investigated. This investigation covered different design parameters such as curvature ratio, air velocity, flow direction, fin pitch and flow rate of chilled water on performance characteristics of the spirally coiled finned tube. The purpose was to evaluate this kind of the spirally finned-tube cooling coils with particular reference to bare coiled tube. Six test specimens were designed and manufactured with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30 mm and fin pitches of (33, 22, 11 mm). Experiments were carried out in a pilot wind tunnel with air Reynolds number ranging from 35,500 to 245,000. Two types of chilled water flow directions entering the spiral coil were tested at Reynolds number ranging from 5700 to 25,300, the first was inward flow direction and the other was to outward flow direction. The results revealed that the inward flow direction has significant enhancement effect on the Nusselt number compared with outward flow direction by 37.0% for tube pitch of 18 mm and curvature ratio of 0.027. The decrease of fin pitch enhances the Nusselt number by 21.92% on expense of friction factor by 10.9%. In the case of spirally coiled bare tube, the decreasing of the curvature ratio increases air side Nusselt number by 33.69% on expense of friction factor by 18.36%. General correlations of Nusselt number and air friction factor for bare and finned spirally coiled tube were correlated based on reported experimental data.

Development of a Fluids Laboratory Experience in Dimensional Analysis and Similitude Applied to Vortex Shedding From a Cylinder in Cross-Flow

2013 ◽  
Author(s):  
Matthew Anderson ◽  
Dylan Shiltz ◽  
Christopher Damm
Keyword(s):  
Reynolds Number ◽  
Data Acquisition ◽  
Strouhal Number ◽  
Dimensional Analysis ◽  
Vortex Shedding ◽  
Free Stream ◽  
Cross Flow ◽  
Laboratory Experience ◽  
Analysis And Design ◽  
Wide Range

A fluids laboratory experience that introduces students to dimensional analysis and similitude was designed and performed in a junior-level first course in fluid mechanics. After students are given an introduction to dimensional analysis, the technique is applied to the phenomenon of vortex shedding from a cylinder in cross-flow. With help from the instructor, lab groups use dimensional analysis to ascertain the relevant dimensionless pi terms associated with the phenomenon. After successfully determining that the pi terms are the Strouhal number and the Reynolds number, experiments are performed to elucidate the general functional relationship between the dimensionless groups. To conduct the experiments, a wind-tunnel apparatus is used in conjunction with a Pitot tube for measurements of free stream velocity and a platinum-plated tungsten hot-wire anemometer for rapid (up to 400 kHz) measurements of velocity fluctuations downstream of the cylinder. Utilizing an oscilloscope in parallel with a high-speed data acquisition system, students are able to determine the vortex shedding frequency by performing a spectral analysis (via Fourier transform) of the downstream velocity measurements at multiple free stream velocities and for multiple cylinder diameters (thus a varying Reynolds number). The students’ experimental results were found to agree with relationships found in the technical literature, showing a constant Strouhal number of approximately 0.2 over a wide range of Reynolds numbers. This exercise not only gives students valuable experience in dimensional analysis and design of experiments, it also provides exposure to modern data acquisition and analysis methods.

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