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1
IMAICHI, Kensaku, and Eiichi TADA. "Determination of vortex shedding frequency and drag for karman vortex street (1st report, Vortex shedding frequency)." Transactions of the Japan Society of Mechanical Engineers Series B 51, no. 471 (1985): 3685–88. http://dx.doi.org/10.1299/kikaib.51.3685.
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Hu, Jian, Zibin Wang, Wang Zhao, Shili Sun, Cong Sun, and Chunyu Guo. "Numerical Simulation on Vortex Shedding from a Hydrofoil in Steady Flow." Journal of Marine Science and Engineering 8, no. 3 (March 12, 2020): 195. http://dx.doi.org/10.3390/jmse8030195.
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This paper presents a numerical modeling procedure for the idealization of vortex shedding effects in the wake flow field of a NACA0009 hydrofoil. During the simulation, the lift and drag acting on the hydrofoil were monitored, and the vortex-shedding frequency of the hydrofoil was analyzed. The effects of inflow velocity, trailing-edge thickness, angle of attack, and maximum hydrofoil thickness on vortex shedding were investigated. The results indicate that an increase in the inflow velocity led to an increase in the vortex-shedding frequency and a negligible change in the Strouhal number. Furthermore, as the thickness of the trailing edge increased, the vortex-shedding frequency decreased gradually, whereas the Strouhal number first increased and then decreased. Vortex shedding and lift curve oscillations ceased altogether after the angle of attack of the hydrofoil increased beyond a certain threshold. When the maximum hydrofoil thickness was increased while keeping the thickness and chord length of the trailing edge constant, the vortex-shedding frequency decreased.
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Zhang, Mingming, and Anping Hou. "Numerical Investigation on Unsteady Separation Flow Control in an Axial Compressor Using Detached-Eddy Simulation." Applied Sciences 9, no. 16 (August 12, 2019): 3298. http://dx.doi.org/10.3390/app9163298.
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Unsteady excitation has proved its effectiveness in separation flow control and has been extensively studied. It is observed that disordered shedding vortices in compressors can be controlled by unsteady excitation, especially when the excitation frequency coincides with the frequency of the shedding vortex. Furthermore, former experimental results indicated that unsteady excitation at other frequencies also had an impact on the structure of shedding vortices. To investigate the impact of excitation frequency on vortex shedding structure, the Detached-Eddy Simulation (DES) method was applied in the simulation of shedding vortex structure under unsteady excitations at different frequencies in an axial compressor. Effectiveness of the DES method was proved by comparison with URANS results. The simulation results showed a good agreement with the former experiment. The numerical results indicated that the separation flow can be partly controlled when the excitation frequency coincided with the unsteady flow inherent frequency. It showed an increase in stage performance under the less-studied separation flow control by excitation at a certain frequency of pressure side shedding vortex. Compared with other frequencies of shedding vortices, the frequency of pressure side shedding vortex was less sensitive to mass-flow variation. Therefore, it has potential for easier application on flow control in industrial compressors.
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Britto, Abraham Benjamin, and Sathesh Mariappan. "Lock-in phenomenon of vortex shedding in oscillatory flows: an analytical investigation pertaining to combustors." Journal of Fluid Mechanics 872 (June 7, 2019): 115–46. http://dx.doi.org/10.1017/jfm.2019.353.
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An analytical investigation is performed to understand the lock-in phenomenon, observed in vortex shedding combustors. Several aeroengine afterburners and ramjets use a bluff body to stabilize the flame. The bluff body sheds vortices. During the occurrence of high-amplitude combustion instability, the frequency of vortex shedding locks in to the frequency of the chamber acoustic field. This phenomenon is termed vortex-acoustic lock-in. In general, there is a two-way coupling between the vortex shedding process and the acoustic field, making analytical investigation difficult. Since the frequency of the latter remains largely unaltered, performing an investigation to study the response of vortex shedding to external excitation not only allows one to gain insights, but also make the problem analytically tractable. We begin with a lower-order model available in the literature to describe the vortex shedding process in non-reacting flows, arising from sharp corners in the presence of upstream velocity excitation. The continuous time domain model is transformed to a discrete map, which connects the time instances of two successive vortex shedding events. The frequency and amplitude of excitation are varied to study the instantaneous vortex shedding time period, as the response of the system. In the absence of forcing, the iterates of the map form a period-1 solution with the frequency equalling the natural vortex shedding frequency. On increasing the amplitude of excitation, quasi-periodic behaviour of the iterates is observed, followed by a period-1 lock-in solution, where vortex shedding occurs at the excitation frequency. On further increasing the amplitude, de-lock-in occurs. From the map, an analytical solution is extracted, which represents the lock-in state. The condition and thereby the region in the frequency–amplitude parameter space where a general$p:1$lock-in occurs is then identified. Several important analytical expressions, such as for (1) critical threshold frequency above which lock-in occurs, (2) boundary of lock-in region in the parameter space, that are of direct importance to the design of quieter combustors are obtained. The study also identifies the transition of higher-order$p:1$to$1:1$lock-in state, through a series of lock-in and de-lock-in steps, whose occurrence could be verified from future experiments.
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Bejan, A. "Predicting the Pool Fire Vortex Shedding Frequency." Journal of Heat Transfer 113, no. 1 (February 1, 1991): 261–63. http://dx.doi.org/10.1115/1.2910540.
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Konstantinidis, E., S. Balabani, and M. Yianneskis. "A Study of Vortex Shedding in a Staggered Tube Array for Steady and Pulsating Cross-Flow." Journal of Fluids Engineering 124, no. 3 (August 19, 2002): 737–46. http://dx.doi.org/10.1115/1.1487359.
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This paper describes an experimental investigation of the vortex shedding phenomena in a staggered tube array with streamwise and transverse spacing to diameter ratios of 2.1 and 3.6, respectively. LDA measurements were employed to monitor the flow fluctuations and a visualization technique was implemented to reveal the underlying flow patterns in the array for steady and pulsating cross-flow. The results obtained in steady flow are in general agreement with results from previous investigations and show that vortex shedding occurs at two distinct frequencies in the front and inner rows. A lower frequency component was detected at the exit of the array, which has not been previously identified. Pulsating flow caused the frequency of vortex shedding to lock-on at the subharmonic of the imposed frequency. In the lock-on range, vortex shedding from all the tubes was synchronized and in-phase and velocity fluctuations at the shedding frequency increased considerably compared to their counterparts in steady flow.
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Xiong, Zhongying, and Xiaomin Liu. "Very Large-Eddy Simulations of the Flow Past an Oscillating Cylinder at a Subcritical Reynolds Number." Applied Sciences 10, no. 5 (March 9, 2020): 1870. http://dx.doi.org/10.3390/app10051870.
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This work focuses on flow past a circular cylinder at a subcritical Reynolds number. Although this classical study has been a concern for many years, it is still a challenging task due to the complexity of flow characteristics. In this paper, a high-efficiency very large-eddy simulation method is adopted and verified in order to handle the oscillating boundary. A series of numerical simulations are conducted to investigate the transient flow around the oscillating cylinder. The results show that the vortex shedding mode varies with an increase in the excitation amplitude and the excitation frequency. Vortex shedding is a lasting process under the condition of a low excitation amplitude that leads to irregular fluctuations of the lift and drag coefficients. For a vortex shedding mode that exhibits a strong vortex pair and a weak vortex pair or a weak single vortex, the temporal evolution of the lift coefficient of the oscillating cylinder shows irregular ”jumping” at a specific time per cycle corresponding to the shedding of the strong vortex pair. The vortex shedding mode and the frequency and time of the vortex shedding co-determine the temporal evolutions of the lift and drag coefficient.
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Leontini, Justin S., David Lo Jacono, and Mark C. Thompson. "A numerical study of an inline oscillating cylinder in a free stream." Journal of Fluid Mechanics 688 (November 3, 2011): 551–68. http://dx.doi.org/10.1017/jfm.2011.403.
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AbstractSimulations of a cylinder undergoing externally controlled sinusoidal oscillations in the free stream direction have been performed. The frequency of oscillation was kept equal to the vortex shedding frequency from a fixed cylinder, while the amplitude of oscillation was varied, and the response of the flow measured. With varying amplitude, a rich series of dynamic responses was recorded. With increasing amplitude, these states included wakes similar to the Kármán vortex street, quasiperiodic oscillations interleaved with regions of synchronized periodicity (periodic on multiple oscillation cycles), a period-doubled state and chaotic oscillations. It is hypothesized that, for low to moderate amplitudes, the wake dynamics are controlled by vortex shedding at a global frequency, modified by the oscillation. This vortex shedding is frequency modulated by the driven oscillation and amplitude modulated by vortex interaction. Data are presented to support this hypothesis.
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Perrot-Minot, Clément, Emmanuel Mignot, Nicolas Riviere, and Richard Perkins. "Predicting the vortex shedding frequency at the interface of the lateral cavities." E3S Web of Conferences 40 (2018): 05011. http://dx.doi.org/10.1051/e3sconf/20184005011.
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The vortex shedding frequency in the mixing layer between a cavity and a main stream has been examined experimentally in absence of large oscillation of the free surface inside the cavity, called seiching. It was observed that the vortex shedding frequency follows a monotonically increasing trends with possible jumps from one to another with increasing Froude number of the main stream. These trends are obtained by solving a model based on the Rossiter approach. This model considers that the vortices shed in the mixing layer create some water depth variation at the impingement corner of the cavity. This water depth variation in turn generate pressure waves that propagates upstream and influence the vortex shedding process. Finally the measured vortex shedding frequencies correspond quite accurately to the frequencies predicted by the model. This highlights the existence of a resonant phenomena between vortices in the mixing layer of a lateral cavity and gravity waves even without any seiching phenomena.
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Okafor, Chinedum Vincent. "Finite Element Analysis of Vortex Induced Responses of Multistory Rectangular Building." European Journal of Engineering Research and Science 3, no. 2 (February 25, 2018): 35. http://dx.doi.org/10.24018/ejers.2018.3.2.612.
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High-rise buildings may experience high levels of vibrations under the actions of wind which cause building motions, adversely affecting serviceability and occupant comfort. The paper analyzed the vortex shedding responses of a multistory building with moment resisting frame. It presents a numerical model based on computational wind engineering technique to simulate the wind action over a typical high-rise building using wind speed data of Lagos state Nigeria. The vortex shedding frequency of the vortices and the natural frequency of vibration of the entire high-rise building structural system were calculated by computing fast Fourier transform algorithm (FFT) of the force coefficient and finite element analysis (FEA) of the structural system respectively. From the result obtained, the vortex shedding frequency of the wind vortices was lower than the fundamental frequency of vibration of the typical high-rise building. Hence, vortex shedding was not responsible for the failure of high-rise buildings in the locality being considered due to the reasons stated in the author’s conclusion.
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MILLS, RICHARD, JOHN SHERIDAN, and KERRY HOURIGAN. "Particle image velocimetry and visualization of natural and forced flow around rectangular cylinders." Journal of Fluid Mechanics 478 (March 10, 2003): 299–323. http://dx.doi.org/10.1017/s0022112002003439.
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Particle image velocimetry (PIV) measurements and flow visualization in a water tunnel show that vortex shedding at the leading and trailing edges of rectangular cylinders can be simultaneously phase-locked to transverse velocity perturbations when the applied perturbation Stp is close to an impinging leading-edge vortex/trailing-edge vortex shedding (ILEV/TEVS) frequency. The transverse perturbations, analogous to β-mode duct acoustic resonances, are generated through harmonic oscillations of the sidewalls. When this occurs, the leading-edge vortices are found always to pass the trailing edge at the same phase in the perturbation cycle regardless of the chord-to-thickness (c/t) ratio. Applying perturbations at an Stp not equal to the natural global frequency also results in phase-locked vortex shedding from the leading edge, and a near wake with a frequency equal to the perturbation frequency. This is consistent with previous experimental findings. However, vortex shedding at the trailing edge is either weaker or non-existent. PIV results and flow visualization showed trailing-edge vortex growth was weaker because leading-edge vortices arrive at the trailing edge at a phase in the perturbation cycle where they interfere with trailing-edge shedding. The frequencies at which trailing-edge vortices form for different c/t ratios correspond to the natural ILEV/TEVS frequencies. As in the case of natural shedding, peaks in base suction occur when the leading-edge vortices pass the trailing edge at the phase in the perturbation cycle (and thus in the leading-edge shedding cycle) that allows strong trailing-edge shedding. This is the reason for the similarity in the Stvs.c/t relationship for three seemingly different sets of experiments.
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Zhu, Baoshan, Jun Lei, and Shuliang Cao. "Numerical Simulation of Vortex Shedding and Lock-in Characteristics for a Thin Cambered Blade." Journal of Fluids Engineering 129, no. 10 (April 28, 2007): 1297–305. http://dx.doi.org/10.1115/1.2776964.
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In this paper, vortex-shedding patterns and lock-in characteristics that vortex-shedding frequency synchronizes with the natural frequency of a thin cambered blade were numerically investigated. The numerical simulation was based on solving the vorticity-stream function equations with the fourth-order Runge–Kutta scheme in time and the Chakravaythy–Oscher total variation diminishing (TVD) scheme was used to discretize the convective term. The vortex-shedding patterns for different blade attack angles were simulated. In order to confirm whether the vortex shedding would induce blade self-oscillation, numerical simulation was also carried out for blade in a forced oscillation. By changing the pitching frequency and amplitude, the occurrence of lock-in at certain attack angles was determined. Inside the lock-in zone, phase differences between the blade’s pitching displacement and the torque acting on the blade were used to infer the probability of the blade self-oscillation.
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WANG, Z. JANE. "Vortex shedding and frequency selection in flapping flight." Journal of Fluid Mechanics 410 (May 10, 2000): 323–41. http://dx.doi.org/10.1017/s0022112099008071.
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Chen, Jian, Linlin Geng, and Xavier Escaler. "Numerical Investigation of the Cavitation Effects on the Vortex Shedding from a Hydrofoil with Blunt Trailing Edge." Fluids 5, no. 4 (November 21, 2020): 218. http://dx.doi.org/10.3390/fluids5040218.
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Vortex cavitation can appear in the wake flow of hydrofoils, inducing unwanted consequences such as vibrations or unstable behaviors in hydraulic machinery and systems. To investigate the cavitation effects on hydrofoil vortex shedding, a numerical investigation of the flow around a 2D NACA0009 with a blunt trailing edge at free caviation conditions and at two degrees of cavitation developments has been carried out by means of the Zwart cavitation model and the LES WALE turbulence model which permits predicting the laminar to turbulent transition of the boundary layers. To analyze the dynamic behavior of the vortex shedding process and the coherent structures, two identification methods based on the Eulerian and Lagrangian reference frames have been applied to the simulated unsteady flow field. It is found that the cavitation occurrence in the wake significantly changes the main vortex shedding characteristics including the morphology of the vortices, the vortex formation length, the effective height of the near wake flow and the shedding frequency. The numerical results predict that the circular shape of the vortices changes to an elliptical one and that the vortex shedding frequency is significantly increased under cavitation conditions. The main reason for the frequency increase seems to be the reduction in the transverse separation between the upper and lower rows of vortices induced by the increase in the vortex formation length.
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MILLS, RICHARD, JOHN SHERIDAN, and KERRY HOURIGAN. "Response of base suction and vortex shedding from rectangular prisms to transverse forcing." Journal of Fluid Mechanics 461 (June 25, 2002): 25–49. http://dx.doi.org/10.1017/s0022112002008534.
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In previous experiments, the vortex-shedding frequency in the flow around rectangular prisms has been found to follow a stepwise variation with chord-to-thickness ratio for two different situations: the natural shedding at low Reynolds number and the excitation of a resonant transverse acoustic mode of a duct for flows at moderate Reynolds numbers. This stepwise variation disappears for natural shedding at Reynolds number higher than approximately 2000; however, it is present at the higher Reynolds numbers for the acoustically perturbed case. The present experimental study shows that if the flow is forced by small transverse oscillations, similar in form to the resonant transverse acoustic mode, the leading-edge and trailing-edge vortex shedding are locked over a wide range of forcing frequencies. However, a stepwise variation in the frequency at which peak base drag occurs is found even at these higher Reynolds numbers. The stepwise frequency variation of vortex shedding in the natural shedding case and the acoustic resonance case are then explained in terms of preference of the flow to shed trailing-edge vortices at peak base drag.
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Wroblewski, D. E., and P. A. Eibeck. "Turbulent Heat Transport in a Boundary Layer Behind a Junction of a Streamlined Cylinder and a Wall." Journal of Heat Transfer 114, no. 4 (November 1, 1992): 840–49. http://dx.doi.org/10.1115/1.2911891.
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Measurements of the turbulent velocity and temperature fields were made in a heated boundary layer 14 diameters downstream of a junction of a tapered cylinder and a wall (ReD = 24,700). The boundary layer is strongly affected by the presence of large-scale unsteadiness arising from vortex shedding, which appears in the measurements as “turbulence” with a strong spectral component at the shedding frequency. The boundary layer exhibits three distinct spanwise regions: (1) the innerwake region, z/D<0.8, where vortex shedding effects are observed only in the spanwise component of the fluctuations; (2) the middle-wake region, 0.8<z/D<1.6, where strong vortex shedding is seen in all three components of the fluctuations; and (3) the outer-wake region, z/D>1.6, where the flow is approaching a two-dimensional boundary-layer flow. Cross-spectra of νθ indicate that vortex shedding increases the turbulent heat flux in the middle-wake region. However, peak values of the Stanton number and the eddy diffusivity are observed in the inner-wake region, where the cross-spectra of turbulent heat flux do not exhibit a peak near the shedding frequency, but do show an increase compared to a two-dimensional boundary layer over a much broader frequency range.
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Piccirillo, Paul S., and C. W. Van Atta. "An experimental study of vortex shedding behind linearly tapered cylinders at low Reynolds number." Journal of Fluid Mechanics 246 (January 1993): 163–95. http://dx.doi.org/10.1017/s0022112093000084.
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Experiments were performed to study vortex shedding behind a linearly tapered cylinder. Four cylinders were used, with taper ratios varying from 50:1 to 100:1. The cylinders were each run at four different velocities, adjusted to cover the range of laminar vortex shedding for a non-tapered cylinder. The flow was confirmed to consist of discrete shedding cells, each with a constant frequency. For a centrespan Reynolds number greater than 100, the dimensionless mean cell length was found to be a constant. Individual cell size was found to be roughly self-similar. New shedding cells were created on the ends of the cylinders, or in regions adjacent to areas not shedding. Successful scalings were found for both the cell shedding frequencies and their differences, the modulation frequencies. The modulation frequencies were found to be constant along the cylinder span. The shedding frequency Strouhal number versus Reynolds number curve was found to have a slightly steeper slope than the Strouhal number curve for a non-tapered cylinder. Vortex shedding was found to begin at a local Reynolds number of about 60, regardless of any other factors. End effects were found to be of little importance.The vortex splits, which form the links between shedding cells, were found to be similar in some respects to those found by earlier investigators. Amplitude results suggested that the splits at different spanwise locations are temporally sequenced by an overall flow mechanism, a supposition confirmed by flow visualization. Wavelet analysis results showed that while the behaviour of the shedding frequencies in time was relatively unaffected by changing taper ratio, the behaviour of the modulation frequency in time was greatly affected. Comparisons with other experiments point out the universality of vortex splitting phenomena.
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Silva-Leon, Jorge, and Andrea Cioncolini. "Effect of Inclination on Vortex Shedding Frequency Behind a Bent Cylinder: An Experimental Study." Fluids 4, no. 2 (May 31, 2019): 100. http://dx.doi.org/10.3390/fluids4020100.
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This paper presents experimental results on the vortex shedding frequency measured behind a bent cylinder. Experiments were conducted in a wind tunnel covering Reynolds numbers between 50 and 500, a range of interest for flow sensing, flow control, and energy harvesting applications. The bent cylinder comprised a vertical leg always oriented at normal incidence with respect to the free-stream flow, and an inclined leg whose inclination was varied during the tests between 90° and 15°. The bent cylinder was oriented in the wind tunnel with the vertical leg upstream and the inclined leg downstream, and the vortex shedding frequency was measured with hot-wire anemometry at several locations behind the inclined leg. The present bent cylinder design improves upon those previously considered by providing a finer control on the upstream boundary condition acting upon the inclined leg, which in the present design is not affected by the yaw angle of the inclined leg. With the exception of free-end effects, only noticeable for certain inclinations and Reynolds number values, inclination effects were surprisingly not observed, and the frequency of vortex shedding measured behind the inclined leg of the bent cylinder was consistent (within a few percent) with the cross-flow vortex shedding frequency at the same flow velocity. The present results corroborate and significantly extend the limited observations on bent cylinders available in the literature, further highlighting the importance of the upstream boundary condition on the vortex shedding process with inclined cylinders.
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Fischer, Raymond. "Singing Propellers—Solutions and Case Histories." Marine Technology and SNAME News 45, no. 04 (October 1, 2008): 221–27. http://dx.doi.org/10.5957/mt1.2008.45.4.221.
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This paper examines the hydroacoustic processes involved with "singing propellers" aboard marine vessels. Methods are presented to determine the potential for a resonant response of a propeller to a vortex shedding excitation—a phenomenon known as "singing." Methods are provided to determine the likely shedding frequency and structural natural frequency for propeller blades. Diagnostics procedures to determine the presence of singing are explored. Measured and theoretical differences between the blade's natural frequency response in air and in-water are explored. Treatments are identified to change the vortex shedding frequency or to de-tune the structure. Case histories are detailed showing the potential magnitude of the problem and effective solutions.
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Liu, Yongwei, Yalin Li, and Dejiang Shang. "The Generation Mechanism of the Flow-Induced Noise from a Sail Hull on the Scaled Submarine Model." Applied Sciences 9, no. 1 (December 29, 2018): 106. http://dx.doi.org/10.3390/app9010106.
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Flow-induced noise from the sail hull, which is induced by the horseshoe vortex, the boundary layer separation and the tail vortex shedding, is a significant problem for the underwater vehicles, while has not been adequately studied. We have performed simulations and experiments to reveal the noise generation mechanism from these flows using the scaled sail hull with part of a submarine body. The large eddy simulation and the wavenumber–frequency spectrum are adopted for simulations. The frequency ranges from 10 Hz to 2000 Hz. The simulation results show that the flow-induced noise with the frequency less than 500 Hz is mainly generated by the horseshoe vortex; the flow-induced noise because of the tail vortex shedding is mainly within the frequency of shedding vortex, which is 595 Hz in the study; the flow-induced noise caused by the boundary layer separation lies in the whole frequency range. Moreover, we have conducted the experiments in a gravity water tunnel, and the experimental results are in good accordance with the simulation results. The results can lay the foundation for the design of flow control devices to suppress and reduce the flow-induced noise from the sail hull.
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Sondak, D. L., and D. J. Dorney. "Simulation of Vortex Shedding in a Turbine Stage." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 428–35. http://dx.doi.org/10.1115/1.2841335.
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Vortex shedding in a turbomachine blade row is affected by the passing of blades in the adjacent downstream blade row, but these effects have not been examined in the literature. A series of flow simulations has been performed to study vortex shedding in a turbine stage, and to quantify the blade interaction effects on the unsteady pressure response. The numerical issues of spatial order of accuracy and the use of Newton subiterations were investigated first. Second-order spatial accuracy was shown to be inadequate to model the shedding frequency response and time-averaged base pressure accurately. For the small time step employed for temporal accuracy, Newton iterations were shown to be unnecessary. The effects of the adjacent blade row were examined by comparing the shedding frequency response for the stage simulations to the response for isolated cascades. The vane shedding was shown to occur exactly on a series of harmonics of the blade passing frequency for the stage case, compared to a single predominant frequency for the isolated cascade. Losses were also examined in the wake region. It was shown that close to the trailing edge, losses were mainly due to wake mixing. Farther downstream of the trailing edge, losses were predominantly due to the trailing edge shock wave.
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Leontini, Justin S., David Lo Jacono, and Mark C. Thompson. "Wake states and frequency selection of a streamwise oscillating cylinder." Journal of Fluid Mechanics 730 (July 30, 2013): 162–92. http://dx.doi.org/10.1017/jfm.2013.332.
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AbstractThis paper presents the results of an in-depth study of the flow past a streamwise oscillating cylinder, examining the impact of varying the amplitude and frequency of the oscillation, and the Reynolds number of the incoming flow. These findings are presented in a framework that shows that the relationship between the frequency of vortex shedding ${f}_{s} $ and the amplitude of oscillation ${A}^{\ast } $ is governed by two primary factors: the first is a reduction of ${f}_{s} $ proportional to a series in ${A}^{\ast 2} $ over a wide range of driving frequencies and Reynolds numbers; the second is nonlinear synchronization when this adjusted ${f}_{s} $ is in the vicinity of $N= {(1- {f}_{s} / {f}_{d} )}^{- 1} $, where $N$ is an integer. Typically, the influence of higher-order terms is small, and truncation to the first term of the series (${A}^{\ast 2} $) well represents the overall trend of vortex shedding frequency as a function of amplitude. However, discontinuous steps are overlaid on this trend due to the nonlinear synchronization. When ${f}_{s} $ is normalized by the Strouhal frequency ${f}_{St} $ (the frequency of vortex shedding from an unperturbed cylinder), the rate at which ${f}_{s} / {f}_{St} $ decreases with amplitude, at least for ${f}_{d} / {f}_{St} = 1$, shows a linear dependence on the Reynolds number. For a fixed $\mathit{Re}= 175$, the truncated series shows that the rate of decrease of ${f}_{s} / {f}_{St} $ with amplitude varies as ${(2- {f}_{d} / {f}_{St} )}^{- 1/ 2} $ for $1\leqslant {f}_{d} / {f}_{St} \leqslant 2$, but is essentially independent of ${f}_{d} / {f}_{St} $ for ${f}_{d} / {f}_{St} \lt 1$. These trends of the rate of decrease of ${f}_{s} $ with respect to amplitude are also used to predict the amplitudes of oscillation around which synchronization occurs. These predicted amplitudes are shown to fall in regions of the parameter space where synchronized modes occur. Further, for the case of varying ${f}_{d} / {f}_{St} $, a very reasonable prediction of the amplitude of oscillation required for the onset of synchronization to the mode where ${f}_{s} = 0. 5{f}_{d} $ is given. In a similar manner, amplitudes at which ${f}_{s} = 0$ are calculated, predicting where the natural vortex shedding is completely supplanted by the forcing. These amplitudes are found to coincide approximately with those at which the onset of a symmetric vortex shedding mode is observed. This result is interpreted as meaning that the symmetric shedding mode occurs when the dynamics crosses over from being dominated by the vortex shedding to being dominated by the forcing.
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ZHU, LUODING. "Viscous flow past a flexible fibre tethered at its centre point: vortex shedding." Journal of Fluid Mechanics 587 (August 31, 2007): 217–34. http://dx.doi.org/10.1017/s002211200700732x.
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Motivated by a laboratory experiment reported in Alben, Shelley & Zhang (Nature, vol. 420, 2002, p. 479), we performed simulations of an elastic fibre anchored at its centre point and immersed in a flowing viscous incompressible fluid by the immersed boundary (IB) method. We focus on the influence of some dimensionless parameters on vortex shedding from the fibre for Re in the range [30, 800]. Three sets of simulationswere designed to investigate the influence of Reynolds number Re, dimensionless fibre flexure modulus b, and dimensionless fibre length on vortex shedding. According to the simulation results, Re, b, and each has a significant influence on the structure of shed vortices. However, Re has little influence on the vortex shedding frequency. With the increase of dimensionless bending modulus, the dimensionless vortex shedding frequency (fvs) and the critical Reynolds number (Rec) decrease approximately as power-law functions. Both fvs and Rec increase approximately linearly as dimensionless fibre length increases.
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Cravero, Carlo, Nicola Marogna, and Davide Marsano. "A Numerical Study of Correlation Between Recirculation Length and Shedding Frequency in Vortex Shedding Phenomena." WSEAS TRANSACTIONS ON FLUID MECHANICS 16 (March 5, 2021): 48–62. http://dx.doi.org/10.37394/232013.2021.16.6.
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The purpose of this paper is to characterize and to estimate the recirculating length behind an aerodynamic profile in ground effect with Gurney Flap. The flow characterization at high Reynolds numbers was performed by means of numerical analysis. A correlation between the size of the recirculation length and the frequency of vortex shedding was studied. The vortex shedding has a characteristic frequency, which, in this work, is correlated to the size of a recirculation length defined by the authors. The numerical investigation methodology applied to the profile with Gurney Flap, was previously developed on the well-documented test case of the flow around a cylinder at high Reynolds. The case was chosen to investigate and to validate the numerical approach with experimental data.
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HUANG, R. F., J. Y. WU, J. H. JENG, and R. C. CHEN. "Surface flow and vortex shedding of an impulsively started wing." Journal of Fluid Mechanics 441 (August 15, 2001): 265–92. http://dx.doi.org/10.1017/s002211200100489x.
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The particle tracking flow visualization method (PTFV) and particle image velocimetry (PIV) are used to obtain a clear picture of vortex evolution on the suction surface of an impulsively started NACA 0012 wing. The experiments are conducted in a towing water tank. The formation, evolution, and shedding of the vortex system on the suction surface are observed and analysed by streak pictures of particle images. Five characteristic vortex evolution regimes are identified in the parameter domain of angle of attack and chord Reynolds number. The pathline patterns, instantaneous streamlines, and vorticity of various vortex evolution processes are presented. Stable vortex shedding in the wake is eventually established after the initial period of complex vortex evolution on the suction surface of the wing. Various types of instabilities in the wake, e.g. instability wave, surface vortex shedding, and bluff-body vortex shedding, are found to correspond to different evolution processes of the surface flow. The shedding frequency of the vortices is correlated and compared with several conventional results. Topological critical points, separatrices, and alleyways are identified and discussed to elucidate the unsteady structure of the instantaneous streamline patterns. The topological rule for the number of singular points is verified.
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Mohd Haris, Siti Nur Aishah, Mohamed Sukri Mat Ali, Sheikh Ahmad Zaki Shaikh Salim, Sallehuddin Muhamad, and Muhammad Iyas Mahzan. "Numerical Simulation of Noise Radiated from a Blunt Trailing Edge." Applied Mechanics and Materials 629 (October 2014): 3–8. http://dx.doi.org/10.4028/www.scientific.net/amm.629.3.
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The Lighthill acoustic analogy is applied to estimate the noise radiation from flow over a blunt trailing edge. The blunt trailing edge is an effective vortex generator. Periodic vortex shedding near the trailing edge induces fluctuating lift that radiates a strong Aeolian tone. The frequency of the Aeolian tone is similar to that of the vortex shedding. A 50.1 dB of Aeolian tone level is radiated from this blunt trailing edge.
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Michálek, Petr, and David Zacho. "Wind Tunnel Study of Vortex Shedding behind Cooling Tower Models." Applied Mechanics and Materials 617 (August 2014): 280–84. http://dx.doi.org/10.4028/www.scientific.net/amm.617.280.
Full textAbstract:
Wind tunnel measurements of vortex shedding behind cooling tower models were performed in VZLU. Two variants of cooling tower models were used, i.e. model with smooth wall outer surface and model with rough wall surface. Measurements were conducted using hot-wire anemometer. Time signal from the anemometer was transformed using Fast-Fourier routine into frequency spectrum. Measurements have shown significant differences between smooth and rough variant of model surface and dependency of vortex shedding frequency on Reynolds number.
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Azadi Yazdi, E. "Optimal control of a broadband vortex-induced vibration energy harvester." Journal of Intelligent Material Systems and Structures 31, no. 1 (November 22, 2019): 137–51. http://dx.doi.org/10.1177/1045389x19888711.
Full textAbstract:
A vortex-induced vibration energy harvester consists of a relatively long cylinder mounted on a flexible structure. In a flow field, the periodically shedding vortices induce transverse vibrations in the cylinder that is converted to electricity by means of piezoelectric generators. In most vortex-induced vibration harvesters, the output power is considerable only in a narrow band around the wind speed where the vortex shedding frequency matches the natural frequency of the structure. To overcome this limitation, a tuned mass mechanism is employed in the proposed vortex-induced vibration energy harvester that can change the natural frequency of the turbine to match the vortex shedding frequency in a broad band of wind speeds. The tuned mass mechanism should work in close cooperation with the piezoelectric generators to maximize the electric power of the turbine. To this end, a nonlinear piezoaeroelastic model of the system is derived, and a model predictive control technique is formulated to find the optimal control inputs for the tuned mass actuator and the piezoelectric generators. Results of numeric simulations confirmed that the tuned mass mechanism not only increases the velocity band over which the turbine is effective but also increases the peak power output of the turbine by 294%.
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Huang, Li-Zhong, and De-Ming Nie. "Vortex shedding patterns in flow past inline oscillating elliptical cylinders." Thermal Science 16, no. 5 (2012): 1395–99. http://dx.doi.org/10.2298/tsci1205395h.
Full textAbstract:
Vortex shedding patterns in flow past inline oscillating elliptical cylinder are simulated by lattice Boltzmann and direct forcing/fictitious domain method which is validated by finite volume method when this cylinder is fixed. The modes of vortex shedding are analyzed in detail by changing the amplitude and the frequency of oscillation by using the first method in this paper.
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Modi, V. J., and J. E. Slater. "Unsteady Aerodynamics and Vortex-Induced Aeroelastic Response of a Structural Angle Section." Journal of Vibration and Acoustics 116, no. 4 (October 1, 1994): 449–56. http://dx.doi.org/10.1115/1.2930448.
Full textAbstract:
Wake-body interactions for a two-dimensional structural angle member during stationary and vortex induced oscillatory conditions are studied using a conventional low turbulence wind tunnel. The response of an angle section with combined plunging and torsion indicates that the oscillations occur essentially in one of the two degrees-of-freedom. The measurements of frequency and phase substantiated this observation. The plunging resonance exhibits the familiar vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control phenomenon where the vortex shedding governs the frequency of oscillation. The vortex-induced torsional resonance was found to be severe even at moderate damping levels. The results should prove useful in structural designs such as high-voltage transmission towers, antenna masts, bridges, etc., where angle sections are often used as secondary members.
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PRASAD, ANIL, and CHARLES H. K. WILLIAMSON. "Three-dimensional effects in turbulent bluff-body wakes." Journal of Fluid Mechanics 343 (July 25, 1997): 235–65. http://dx.doi.org/10.1017/s002211209700579x.
Full textAbstract:
There has recently been a surge in activity concerning the development of three-dimensionality in the wakes of nominally two-dimensional bluff bodies, yielding the realization that end effects can influence the wake vortex shedding pattern over long spanlengths. Much of this work has been focused on low Reynolds numbers (Re), but virtually no studies have investigated to what extent it is possible to control shedding patterns at higher Reynolds numbers, through the use of end manipulation. In the present paper, we demonstrate that it is possible to induce parallel shedding, oblique shedding and vortex dislocations, by manipulation of the end conditions, over a large range of Reynolds number. Such patterns affect the frequency of primary wake instability and its amplitude of fluctuation, as they do at low Reynolds number, although distinct differences are found at the higher Reynolds numbers.We find that imposition of oblique shedding conditions at high Reynolds number leads to a spatial variation of both the oblique shedding angle and shedding frequency across the span, and to sparse dislocations which are not restricted to the spanwise end regions, as they are at low Reynolds numbers (under similar geometrical conditions). In the wake transition regime (Re=190–250), it is confirmed that the spontaneous appearance of vortex dislocations in mode-A shedding precludes the control of shedding patterns using end manipulation. However, it has proven possible to extend the regime of Reynolds number where dislocations ‘naturally’ exist to Re>250, by introducing them artificially through end control, where they would otherwise not occur. The possibility of introducing dislocations and of inducing oblique vortex shedding at higher Reynolds numbers has practical significance, if one can deliberately decorrelate the vortex shedding, and hence reduce the spanwise-integrated unsteady fluid forces on the body.We confirm the existence of a transition in the mode of shedding at Re≈5000 (originally found by Norberg 1987) under conditions where parallel shedding is attempted. This mode transition displays similarities to an inverse of the mode A→mode B transition that is found in the wake transition regime. It is clear that vortex dislocations occur beyond Re=5000, although it is not clear why the flow is unstable to such a mode. Furthermore, there appears to be some support for the suggestion that vortex dislocations may be a feature of the flow for Re at least up to 30×103, as evidenced by the work of Norberg (1994).
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Zhong, Xing Fu, Li Ming Lin, Ying Xiang Wu, and Shi Ying Shi. "New Method in Suppressing Vortex-Induced Vibration of Marine Riser." Applied Mechanics and Materials 226-228 (November 2012): 9–12. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.9.
Full textAbstract:
Marine risers are key apparatus in connecting the subsea wells to the oil production platform. When the ocean current flow past a riser, the vortex shedding behind riser may induce vibration. If the frequency of vortex shedding is approaching or equal to the natural frequency of riser, the resonance will be generated. Such phenomenon leads to the potential fatigue damage of riser. Therefore, the safety and assurance of marine risers are widely arousing the interest of offshore engineering. In present paper, previous apparatus or methods in suppressing vortex-induced vibration (VIV) of risers used in marine engineering are firstly analyzed, and correspondingly the conditions in design of VIV suppressors are proposed. Based on the Bernoulli equation, the disturbance in flow around a bluff body and the relationship of vortex shedding in span-wise direction, a new method of VIV suppression is proposed. The numerical results have shown that the vibration of risers could be reduced by such disturbance.
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Peltzer, R. D., and D. M. Rooney. "Near Wake Properties of a Strumming Marine Cable: An Experimental Study." Journal of Fluids Engineering 107, no. 1 (March 1, 1985): 86–91. http://dx.doi.org/10.1115/1.3242446.
Full textAbstract:
Resonant flow-induced oscillations of a flexible cable can occur when the damping of the cable system is sufficiently small. The changes in the flow field that occur in the near wake of the cable during these resonant oscillations are closely related to the changes in the fluid forces that accompany these oscillations. The present wind tunnel experiments were undertaken to examine the effects that forced synchronized vibration and the helically-wound cross section of the cable have on near wake vortex shedding-related parameters; specifically the shedding frequency, vortex formation length Lf, reduced velocity Ur, vortex strength and the wake width Lw. The range of flow speeds over which the vortex shedding was locked on to the vibration frequency varied directly with the vibration amplitude. The helical cross section and the synchronized vibration caused significant changes in the near wake development that could be directly related to the increase in hydrodynamic forces associated with unforced synchronized vibration.
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MURALIDHAR, PRANESH, NANGELIE FERRER, ROBERT DANIELLO, and JONATHAN P. ROTHSTEIN. "Influence of slip on the flow past superhydrophobic circular cylinders." Journal of Fluid Mechanics 680 (May 24, 2011): 459–76. http://dx.doi.org/10.1017/jfm.2011.172.
Full textAbstract:
Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large- and small-scale channels. In this paper, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from polydimethylsiloxane with well-defined micron-sized patterns of surface roughness. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction, the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. Thus, in this paper we demonstrate that vortex shedding dynamics is very sensitive to changes of feature spacing, size and orientation along superhydrophobic surfaces.
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Sakamoto, H., and H. Haniu. "A Study on Vortex Shedding From Spheres in a Uniform Flow." Journal of Fluids Engineering 112, no. 4 (December 1, 1990): 386–92. http://dx.doi.org/10.1115/1.2909415.
Full textAbstract:
Vortex shedding from spheres at Reynolds numbers from 3 × 102 to 4 × 104 in a uniform flow was investigated experimentally. Standard hot-wire technique were used to measure the vortex shedding frequency from spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important results from the investigation were that (i) the variation of the Strouhal number St (=fD/U0, U0: freestream velocity, D: diameter of the sphere, f: vortex shedding frequency) with the Reynolds number (= U0D/v, v: kinematic viscosity) can be classified into four regions, (ii) the Reynolds number at which the hairpinshaped vortices begin to change from laminar to turbulent vortices so that the wake structure behind the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (vi) at Reynolds numbers ranging from 8X102 to 1.5X104, the higher and lower frequency modes of the Strouhal number coexist.
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Qu, Yuan, Jinjun Wang, Mao Sun, Lihao Feng, Chong Pan, Qi Gao, and Guosheng He. "Wake vortex evolution of square cylinder with a slot synthetic jet positioned at the rear surface." Journal of Fluid Mechanics 812 (January 9, 2017): 940–65. http://dx.doi.org/10.1017/jfm.2016.833.
Full textAbstract:
Wake vortex evolution of a square cylinder with a slot synthetic jet issuing from the cylinder’s rear surface has been experimentally investigated using the time-resolved particle image velocimetry technique. The Reynolds number based on the side length of the square cylinder is $Re=836$. The excitation frequency normalized by the natural shedding frequency $f_{e}/f_{0}$ varies from 0 to 6 at the dimensionless stroke length $L_{0}/w=72.6$. The distributions of the time-averaged Reynolds stresses present significant differences as the excitation frequency increases. With control, the mean streamwise velocity deficit of the wake recovers more quickly in comparison with the natural case, and the vertical velocity fluctuation intensity becomes weaker. Moreover, a drag reduction can be achieved for the control cases, especially, for $f_{e}/f_{0}=4$ and $f_{e}/f_{0}=6$, a thrust instead of drag reduction can be obtained. The profiles of the mean streamwise velocity tend to have jet-like distributions. The wake vortex dynamics and its evolution with the excitation frequency are revealed. (i) For the low excitation frequency cases ($f_{e}/f_{0}=0.5$, 1, 2), no significant changes in the dominant frequency and the spanwise vortex structures are observed in comparison with the natural case. (ii) For the moderate excitation frequency case ($f_{e}/f_{0}=3$), the wake vortex shedding frequency is locked on half of the control frequency. In this case, the shear layer is divided into two parts by the synthetic jet vortex, and the wake vortices with smaller scales still shed asymmetrically and appear closer to the square cylinder. (iii) For the high excitation frequency case ($f_{e}/f_{0}=6$), the flow is governed by the synthetic jet. As a result of strong perturbations of the synthetic jet, the wake vortex shedding becomes symmetric with the shedding frequency consistent with the control frequency. And the separation is suppressed effectively. The different control effects of the slot synthetic jet on a square cylinder and a circular cylinder are also compared in detail. Generally speaking, the circular cylinder is easier to be controlled due to its non-fixed separation points.
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Yang, Guang Jun, and Jing Sun. "Numerical Simulation of Non-Equal Diameter Cylinder." Applied Mechanics and Materials 249-250 (December 2012): 527–32. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.527.
Full textAbstract:
Numerical simulation has been carried out on the wake flow structure of some simplified antenna model which is shaped as a non-equal diameter slender cylinder. The unsteady flow parameter-Strouhal number is confirmed to be a constant approximately in the subcritical state. The results show that at levels of different diameters, when the length-diameter ratio is large enough, each level can still maintain stable periodical vortex shedding phenomenon, the vortex shedding frequency of each level, the flow velocity and the equivalent diameter still meet the Strouhal relationship. The effect of connect transition area on vortex shedding stabilize region are close to the freestream velocity.
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Mirzaei, Masoud, A. Shams Taleghani, and A. Shadaram. "Experimental Study of Vortex Shedding Control Using Plasma Actuator." Applied Mechanics and Materials 186 (June 2012): 75–86. http://dx.doi.org/10.4028/www.scientific.net/amm.186.75.
Full textAbstract:
This paper aims at experimental investigation of the active flow control with plasma actuator over an airfoil. The method involved application of single dielectric barrier discharge in order to change the frequency of vortex shedding and the turbulence characteristics from a NACA4412 airfoil. The objective was to reduce control flaps noise in transporting aircraft via an effective body force generated by the actuators. Results indicated that the use of plasma actuator led to a significant decrease in the frequency of vortex shedding around the flap whereas a significant increase in turbulence levels was achieved at a distance away from the actuator.
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Li, Fei, and He Juan Chen. "Numerical Analysis of Vortex Shedding Behavior of Piezoelectric Microgenerator from Dynamic Airflow-Induced Vibration." Advanced Materials Research 694-697 (May 2013): 1595–601. http://dx.doi.org/10.4028/www.scientific.net/amr.694-697.1595.
Full textAbstract:
Computational fluid dynamics (CFD) method is applied to analyze airflow field of acoustic-induced vibration piezoelectric generator. In this paper, numerical simulation has been performed for the unsteady flow field of nozzle vortex shedding with inlet and outlet boundary conditions. Distribution of velocity, pressure and vortices field has been calculated and analyzed in the process of vortex shedding in order to provide a reference for optimizing source frequency. The result shows that jetting initially shows vortex shedding when adopting the nozzle of variable flow tube structure, which is an equal section flow tube with necking cross section flow tube. The analysis method of this paper is laid the foundation for the design of power airflow acoustic source generator.
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Popescu, Mihaela, Stein Tore Johansen, and Wei Shyy. "Flow-Induced Acoustics in Corrugated Pipes." Communications in Computational Physics 10, no. 1 (July 2011): 120–39. http://dx.doi.org/10.4208/cicp.301209.230710a.
Full textAbstract:
AbstractWhen gas flows through corrugated pipes, pressure waves interacting with vortex shedding can produce distinct tonal noise and structural vibration. Based on established observations, a model is proposed which couples an acoustic pipe and self-excited oscillations with vortex shedding over the corrugation cavities. In the model, the acoustic response of the corrugated pipe is simulated by connecting the lossless medium moving with a constant velocity with a source based on a discrete distribution of van der Pol oscillators arranged along the pipe. Our time accurate solutions exhibit dynamic behavior consistent with that experimentally observed, including the lock-in frequency of vortex shedding, standing waves and the onset fluid velocity capable of generating the lock-in.
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MIAU, J. J., J. T. WANG, J. H. CHOU, and C. Y. WEI. "CHARACTERISTICS OF LOW-FREQUENCY VARIATIONS EMBEDDED IN VORTEX-SHEDDING PROCESS." Journal of Fluids and Structures 13, no. 3 (April 1999): 339–59. http://dx.doi.org/10.1006/jfls.1999.0206.
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Wang, C. T., and C. T. Chen. "Self-Similar Analysis on Vortex Shedding Process." Journal of Mechanics 22, no. 4 (December 2006): 263–70. http://dx.doi.org/10.1017/s1727719100000915.
Full textAbstract:
AbstractChaos theory has been seen as an efficient tool for studying the turbulent flow, the findings of attractor were also important and made in the study to investigate the wake flow behind the bluff body. Here, the fractal dimension value would then be found by Hurst analysis. According to the results found, the Hurst empirical formula derived by the self-similar laceration of vortex plane would be applied by self-similar property to decide the band of the frequency variations in the vortex shedding process. The three kinds of flow mode with their individual attractors and characteristics could be decomposed and shown as following: self-similar laceration, energy input and white noise band. Finally, the energy ratio for the three kinds of flow mode had been confirmed. Hence, these findings would be helpful to further study the wake flow in the vortex shedding process.
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Barbi, C., D. P. Favier, C. A. Maresca, and D. P. Telionis. "Vortex shedding and lock-on of a circular cylinder in oscillatory flow." Journal of Fluid Mechanics 170 (September 1986): 527–44. http://dx.doi.org/10.1017/s0022112086001003.
Full textAbstract:
An experimental study has been made of a circular cylinder in steady and oscillatory flow with non-zero mean velocity up to a Reynolds number of 40000. The results for the stationary cylinder are in close agreement with previously published data. Skin-friction measurements revealed the amplitude of fluctuation of the boundary layer for different angular locations. It has been universally accepted that bluff bodies shed vortices at their natural frequency of shedding (Strouhal frequency), or, when synchronized with an external unsteadiness, at the frequency of the disturbance or half of it, depending of the direction of the unsteadiness. Our findings, instead, indicate that the shedding frequency may vary smoothly with the driving frequency before locking on its subharmonic. Moreover, the present results indicate that, at the lowest frequency limit of lock-on, vortices are shed simultaneously on both sides of the model. A more traditional alternate pattern of vortex shedding is then recovered at higher driving frequencies.
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Rooney, D. M., J. Rodichok, and K. Dolan. "Finite Aspect Ratio Effects on Vortex Shedding Behind Two Cylinders at Angles of Incidence." Journal of Fluids Engineering 117, no. 2 (June 1, 1995): 219–26. http://dx.doi.org/10.1115/1.2817133.
Full textAbstract:
Wind tunnel tests were undertaken at subcritical Reynolds numbers to determine the vortex shedding characteristics behind a pair of finite circular cylinders at distances from one to six diameters apart and at all angles to one another. In addition, individual finite cylinders with aspect ratios 0.67 ≤ L/D ≤ 11.33 were examined to determine the effect of aspect ratio on shedding frequency, and to measure the frequency of the tip vortex when it is present. Aspect ratio was found to be a significant factor in the difference between shedding frequencies of the two cylinders at oblique angles. It was also found that “lock-on” of the two frequencies occurred when longer aspect ratio cylinders were upstream of shorter ones, but not in the reverse case.
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Hsu, Li-Chieh, De-Chang Lai, and Jian-Zhi Ye. "Suppression of Vortex Shedding of Circular Cylinder by a Small Control Rod." Applied Mechanics and Materials 477-478 (December 2013): 265–70. http://dx.doi.org/10.4028/www.scientific.net/amm.477-478.265.
Full textAbstract:
The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.
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Ferreira, R. L., and E. D. R. Vieira. "FLOW AROUND MODIFIED CIRCULAR CILYNDERS." Revista de Engenharia Térmica 3, no. 1 (June 30, 2004): 62. http://dx.doi.org/10.5380/reterm.v3i1.3482.
Full textAbstract:
The flow around a circular cylinder has awaken the attention of different
researchers since the historic Strouhal's work of 1878. Ever since, many
experimental and numeric works have been carried out in order to
determine the relationship between the vortex shedding frequency and the
flow regime. Recently, a number of studies have been developed using
several small modifications in circular cylinder. In this work a circular
cylinder modified with a longitudinal concave notch, has been tested in
order to determine the relationship between the non-dimensional vortex
shedding frequency (Strouhal number) and the Reynolds number has been
determined to Reynolds up to 600. Additionally a modified circular
cylinder with a longitudinal slit also has been tested in order to determine
the Strouhal-Reynolds relationship in several attack angle configurations.
The experiments have been carried out in a vertical low turbulence
hydrodynamic tunnel with 146x146x500 mm of test section operating in
continuous mode. Flow visualization by direct liquid dye injection has been
utilized in order to produce vortex images. These images have been
captured in still chemical photography for different Reynolds numbers. A
hot-film probe has been adequately positioned in the vortex wake to
determine the vortex shedding frequency and consequently the Strouhal
number.
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FENG, LI HAO, and JIN JUN WANG. "Circular cylinder vortex-synchronization control with a synthetic jet positioned at the rear stagnation point." Journal of Fluid Mechanics 662 (August 25, 2010): 232–59. http://dx.doi.org/10.1017/s0022112010003174.
Full textAbstract:
The flow over a circular cylinder controlled by a two-dimensional synthetic jet positioned at the mean rear stagnation point has been experimentally investigated in a water channel at the cylinder Reynolds number Re = 950. This is an innovative arrangement and the particle-image-velocimetry measurement indicates that it can lead to a novel and interesting phenomenon. The synthetic-jet vortex pairs induced near the exit convect downstream and interact with the vorticity shear layers behind both sides of the cylinder, resulting in the formation of new induced wake vortices. The present vortex synchronization occurs when the excitation frequency of the synthetic jet is between 1.67 and 5.00 times the natural shedding frequency at the dimensionless stroke length 99.5. However, it is suggested that the strength of the synthetic-jet vortex pair plays a more essential role in the occurrence of vortex synchronization than the excitation frequency. In addition, the wake-vortex shedding is converted into a symmetric mode from its original antisymmetric mode. The symmetric shedding mode weakens the interaction between the upper and lower wake vortices, resulting in a decrease in the turbulent kinetic energy produced by them. It also has a significant influence on the global flow field, including the velocity fluctuations, Reynolds stresses and flow topology. However, their distributions are still dominated by the large-scale coherent structures.
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Sakamoto, Hiroshi, and Hiroyuki Haniu. "The formation mechanism and shedding frequency of vortices from a sphere in uniform shear flow." Journal of Fluid Mechanics 287 (March 25, 1995): 151–71. http://dx.doi.org/10.1017/s0022112095000905.
Full textAbstract:
Experiments to investigate the formation mechanism and frequency of vortex shedding from a sphere in uniform shear flow were conducted in a water channel using flow visualization and velocity measurement. The Reynolds number, defined in terms of the sphere diameter and approach velocity at its centre, ranged from 200 to 3000. The shear parameter K, defined as the transverse velocity gradient of the shear flow non-dimensionalized by the above two parameters, was varied from 0 to 0.25. The critical Reynolds number beyond which vortex shedding from the sphere occurred was found to be lower than that for uniform flow and decreased approximately linearly with increasing shear parameter. Also, the Strouhal number of the hairpin-shaped vortex loops became larger than that for uniform flow and increased as the shear parameter increased.The formation mechanism and the structure of vortex shedding were examined on the basis of series of photographs and subsequent image processing using computer graphics. The range of Reynolds number in the present investigation, extending up to 3000, could be classified into three regions on the basis of this study, and it was observed that the wake configuration did not differ substantially from that for uniform flow. Also, unlike the detachment point of vortex loops in uniform flow, which was irregularly located along the circumference of the sphere, the detachment point in shear flow was always on the high-velocity side.
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Scanlon, T. J., M. T. Stickland, and A. Oldroyd. "A numerical analysis of vortex shedding within a confined channel flow." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 213, no. 5 (May 1, 1999): 477–90. http://dx.doi.org/10.1243/0954406991522716.
Full textAbstract:
The numerical analysis of two-dimensional laminar vortex shedding from a rectangular cylinder within a confined channel flow is presented. This study, carried out using a computational fluid dynamics (CFD) code based on the SIMPLEST algorithm, considers the influence of numerical diffusion on the prediction of the vortex shedding frequency. The computational analysis compares the commonly used first-order accurate UPWIND scheme with the well-known third-order scheme QUICK and its derivative SMART, used for the discretization of convective transport. For the temporal differencing, a fully implicit scheme has been adopted. Plots of Strouhal number against Reynolds number suggest that the implementation of a higher-order scheme is beneficial for the accurate capture of the vortex shedding transient in unsteady flows of this nature.
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Ausoni, Philippe, Mohamed Farhat, Xavier Escaler, Eduard Egusquiza, and François Avellan. "Cavitation Influence on von Kármán Vortex Shedding and Induced Hydrofoil Vibrations." Journal of Fluids Engineering 129, no. 8 (March 16, 2007): 966–73. http://dx.doi.org/10.1115/1.2746907.
Full textAbstract:
The present study deals with the shedding process of the von Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds number Reh=25×103–65×103. This research focuses mainly on the effects of cavitation and fluid-structure interaction on the mechanism of the vortex generation. The vortex shedding frequency, derived from the flow-induced vibration measurement, is found to follow the Strouhal law provided that no hydrofoil resonance frequencies are excited, i.e., lock-off. For such a regime, the von Kármán vortices exhibit strong spanwise 3D instabilities and the cavitation inception index is linearly dependent on the square root of the Reynolds number. In the case of resonance, the vortex shedding frequency is locked onto the hydrofoil eigenfrequency and the spatial coherence is enhanced with a quasi-2D shape. The measurements of the hydrofoil wall velocity amplitude and phase reveal the first torsion eigenmotion. In this case, the cavitation inception index is found to be significantly increased compared to lock-off conditions. It makes clear that the vortex roll-up is amplified by the phase locked vibrations of the trailing edge. For the cavitation inception index, a new correlation relationship that encompasses the entire range of Reynolds numbers, including both the lock-off and the lock-in cases, is proposed and validated. In contrast to the earlier models, the new correlation takes into account the trailing edge displacement velocity. In addition, it is found that the transverse velocity of the trailing edge increases the vortex strength linearly. This effect is important in the context of the fluid-structure interaction, since it implies that the velocity of the hydrofoil trailing edge increases the fluctuating forces on the body. It is also demonstrated that cavitation developing in the vortex street cannot be considered as a passive agent for the turbulent wake flow. In fact, for fully developed cavitation, the vortex shedding frequency increases up to 15%, which is accompanied by the increase of the vortex advection velocity and reduction of the streamwise vortex spacing. In addition, a significant increase of the vortex-induced vibration level is found at cavitation onset. These effects are addressed and thought to be a result of the increase of the vorticity by cavitation.