Showing papers on "Vortex shedding published in 1976"
TL;DR: In this paper, a study of the wake of a cylinder vibrating in line with an incident steady flow was made, and the vortex shedding was at all times synchronized with the vibrations of the cylinder, which were in a range of frequencies near twice the Strouhal shedding frequency for the stationary cylinder.
Abstract: A study has been made of the wake of a cylinder vibrating in line with an incident steady flow. The Reynolds number for the experiments was 190, and the vortex shedding was at all times synchronized with the vibrations of the cylinder, which were in a range of frequencies near twice the Strouhal shedding frequency for the stationary cylinder. Two distinct vortex wake patterns were encountered. The first is a complex regime in which two vortices are shed during each cycle of the vibration and form an alternating pattern of vortex pairs downstream. The second pattern is an alternating street which results from the shedding of a single vortex during each cycle of the cylinder's motion. The street geometry in the latter case shares many basic characteristics with the wake of a cylinder vibrating in cross-flow. These include the effects of vibration amplitude and frequency on the longitudinal and transverse spacing of the vortices. The results obtained from these experiments in air are in agreement with previous findings from free- and forced-vibration experiments in water at both higher and lower Reynolds numbers.
239 citations
TL;DR: In this paper, the frequency of vortex shedding from circular cylinders forced to oscillate transversely in low-turbulence uniform and shear flows was investigated and it was conjectured that the wake width jumps from being greater to being less than that for the stationary cylinder at a particular cylinder frequency near mid-range.
Abstract: The frequencies of vortex shedding from circular cylinders forced to oscillate transversely in low-turbulence uniform and shear flows were investigated. The stream velocity in the shear flow varied linearly with spanwise distance.In both flows the vortex shedding frequency locked on to the cylinder frequency and to submultiples of the cylinder frequency. In uniform flow the range of cylinder frequencies for locking-on was dependent on the amplitude of oscillation and Reynolds number. At the boundaries of locking-on at the cylinder frequency locked-on shedding was intermittent with unforced shedding and locking-on was accompanied by a change in wake width. At a particular cylinder frequency near mid-range it is conjectured that the wake width jumped from being greater to being less than that for the stationary cylinder. In shear flow the spanwise extent of locking-on at the cylinder frequency was explained by considering the uniform flow results and the inclination of shed vortices in shear flow. At the spanwise boundaries of this locking-on, locked-on cells were shed intermittently with unforced cells which were more stable in frequency than the corresponding cells for the stationary cylinder.
178 citations
TL;DR: In this article, the wake interaction effects between two identical flexible circular cylinders in flowing water were examined and the stability of the two cylinders was explained by reference to oscillatory mode shapes and from considerations of two possible types of vortex shedding (symmetric and alternate).
134 citations
02 Feb 1976
TL;DR: In this paper, the in-line and transverse forces acting on smooth and rough circular cylinders placed in oscillatory water flow at Reynolds numbers up to 700,000, Keulegan-Carpenter number up to 150, and relative roughness from 0. 002 to 0.02 were determined through the use of the Fourier analysis and the least squares method.
Abstract: : This report presents the results on an extensive experimental investigation of the in-line and transverse forces acting on smooth and rough circular cylinders placed in oscillatory water flow at Reynolds numbers up to 700,000, Keulegan-Carpenter numbers up to 150, and relative roughnesses from 0. 002 to 0.02. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least-squares method. The transverse force (lift) has been analyzed in terms of its maximum, semi-peak-to-peak, and root- mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined.
108 citations
TL;DR: In this paper, a conditional averaging technique is used to extract the underlying vortex pattern from a turbulent bluff body wake, and ensemble averages of wake velocities are developed on the basis of a reference phase position, determined from the outer flow irrotational fluctuations.
Abstract: A conditional averaging technique to extract the underlying vortex pattern from a turbulent bluff body wake is described. Ensemble averages of wake velocities are developed on the basis of a reference phase position, determined from the outer flow irrotational fluctuations. The method is applied to the wakes of a stationary and oscillating D-shape cylinder, where, in the latter case, the vortex shedding is locked to the frequency of body movement. Direct comparisons of average circulation and vortex street spacings are obtained and these demonstrate the significant change in wake structure that accompanies and sustains vortex-induced vibrations. It is observed in both conditions that only 25% of the estimated shed vorticity is found in the fully developed wake. In addition the analysis produces profiles of vorticity and velocity in an ‘average vortex cycle’. A model, developed to help interpret these results, suggests that a good representation of an average wake situation is obtained by the addition of considerable mean shear to a street of finite area axisymmetric vortices.
108 citations
TL;DR: In this article, the authors discuss the theory of sound generation when a frozen turbulent eddy is convected in a mean flow past an airfoil or a semi-infinite plate, with and without the application of a Kutta condition.
Abstract: This paper discusses the theory of the generation of sound which occurs when a frozen turbulent eddy is convected in a mean flow past an airfoil or a semi-infinite plate, with and without the application of a Kutta condition and with and without the presence of a mean vortex sheet in the wake. A sequence of two-dimensional mathematical problems involving a prototype eddy in the form of a line vortex is examined, it being argued that this constitutes the simplest realistic model. Important effects of convection are deduced which hitherto have not been revealed by analyses which assume quadrupole sources to be at rest relative to the plate or airfoil. It is concluded that, to the order of approximation to which the sound from convected turbulence near a scattering body is usually estimated, the imposition of a Kutta condition at the trailing edge leads to a complete cancellation of the sound generated when frozen turbulence convects past a semi-infinite plate, and to the cancellation of the diffraction field produced by the trailing edge in the case of an airfoil of compact chord.
105 citations
TL;DR: In this paper, a fan for moving a gaseous fluid, e.g., air, is described in which the high audible frequency noise resulting from the phenomenon occurring at the trailing edges of the blades, known as vortex shedding, is reduced.
Abstract: A fan for moving a gaseous fluid, e.g., air, is described in which the high audible frequency noise resulting from the phenomenon occurring at the trailing edges of the blades, known as vortex shedding, is reduced. This is accomplished by notching an edge of each of the blades so that the pattern of vortices leaving the blade, which causes the noise, is disturbed and a turbulence condition engendered. The turbulence distributes the pressure fluctuations resulting from movement of the blades through the fluid over a relatively broad band of frequencies and reduces the annoying noise frequencies. Various notch configurations are disclosed.
74 citations
56 citations
TL;DR: In this article, an experimental investigation was conducted to determine the effect of a uniform pitching motion on a slender axisymmetric body while undergoing large excursions in angle of attack.
Abstract: : An experimental investigation was conducted to determine the effect of a uniform pitching motion on a slender axisymmetric body while undergoing large excursions in angle of attack Force and moment measurements were obtained for a slender tangent-ogive/cylindrical body over a range of Reynolds numbers from 50,000 to 140,000 while varying the angle of attack from zero to 90 degrees and the pitch rate between zero and 281 degrees per second Smoke flow visualization studies were used as an aid in assessing wake vortex transitions
49 citations
01 Jan 1976
TL;DR: In this article, the in-line and transverse forces acting on smooth and rough circular cylinders placed in oscillatory flow at Reynolds numbers up to 700,000, Keulegan-Carpenter number up to 150, and relative roughness from 0.002 to 0.02 were investigated.
Abstract: The design of structures for the marine environment requires the prediction of the forces generated by waves and currents. This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on smooth and rough circular cylinders placed in oscillatory flow at Reynolds numbers up to 700,000, Keulegan-Carpenter numbers up to 150, and relative roughness from 0.002 to 0.02. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least squares method. The transverse force (lift) has been analyzed in terms of its maximum, semi peak-to-pe and root-mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined.
48 citations
TL;DR: A flow visualization study showed that strong Karman vortices are developed behind the blunt trailing edge of a plate when the free stream velocities over both surfaces are equal.
Abstract: A flow visualization study showed that strong Karman vortices are developed behind the blunt trailing edge of a plate when the free stream velocities over both surfaces are equal. These vortices tend to disappear when the surface velocities are unequal. This observation provided an explanation for the occurrence and disappearance of the lip noise often present in coaxial jets. Vortex formation and lip noise occurred at a Strouhal number of about 0.2 based on the lip thickness and the average of the external steady-state velocities. Results from theoretical calculations of the vortex formation, based on an inviscid, incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.
TL;DR: In this article, an extensive series of experimental vibration tests has been conducted on tube bundles of contemporary interest in a large water tunnel and the main objective of these tests was to develop a design criterion to limit vibration amplitudes.
Abstract: An extensive series of experimental vibration tests has been conducted on tube bundles of contemporary interest in a large water tunnel. The main objective of these tests has been to develop a design criterion to limit vibration amplitudes. It has been found that the main excitation mechanisms are turbulence, some vortex shedding, and hydroelastic instability. The results of these tests are correlated and presented. It is found that the most serious excitation mechanism is hydroelastic instability. Criteria are advanced for establishing upper velocity limits based on the experimental findings. The vortex shedding mechanism is found to only be a problem for tubes in the inlet region of some bundles. Strouhal numbers associated with observed resonances are tabulated and discussed. Tube response to random turbulence has been studied for numerous bundles but is found to be of secondary significance.
TL;DR: In this article, a theory was developed for calculating the wavelength of the waves produced at the welded interface between two identical and explosively projected (flyer) plates using the so-called symmetric welding arrangement.
Abstract: A theory is developed for calculating the wavelength of the waves produced at the welded interface between two identical and explosively projected (flyer) plates using the so-called symmetric welding arrangement. The theory appeals to the analogy between interface wave formation and the formation of a vortex street behind an obstacle in a fluid stream which has been discussed elsewhere (1)‡. It is a notional theory in the sense that the results of an inviscid analysis of jet collision are combined with a semi-empirical vortex shedding theory. In spite of this, the authors believe that it provides a useful first approximation to a more rigorous analysis, and this belief is supported by the agreement found between the theory and certain experimental results obtained from the welding of steel flyer plates.
TL;DR: In this paper, the locking-on of vortex shedding at the cylinder frequency, associated with vortex-induced vibrations, was carefully studied, and it was found to produce especially low base pressures, i.e., high drags.
Abstract: Experiments have been made to investigate the base pressure coefficients of circular cylinders oscillating transversely in a stream for a wide range of cylinder amplitudes and frequencies. This is thought to give a good indication of the variation in drag coefficient. The locking-on of vortex shedding at the cylinder frequency, associated with vortex-induced vibrations, was carefully studied. Locking-on at a third of the cylinder frequency was found to produce especially low base pressures, i.e., high drags.
TL;DR: In this article, a rapidly rotating flow that exhibits periodic vortex detachment is examined, where the rotation/symmetry axis of a fluid-filled cylinder is set perpendicular to gravity and a free buoyant cylindrical float placed within the container is acted upon by both centrifugal and gravitational forces.
Abstract: We examine a rapidly rotating flow that exhibits periodic vortex detachment. Specifically, the rotation/symmetry axis of a fluid-filled cylinder is set perpendicular to gravity. A free buoyant cylindrical float placed within the container is acted upon by both centrifugal and gravitational forces, the competition of which causes fluid motion and, in certain parameter ranges, flow instability. The motion is determined, a criterion for separation is advanced, preliminary experiments and data are described and the relationship of this phenomenon to other examples of vortex shedding in rotating fluids is discussed.
TL;DR: In this paper, it is suggested that the frequency of vortex shedding is equal to the highest frequency with complete correlation over the width of the body, which is the same as the Strouhal number.
Patent•
07 Sep 1976
TL;DR: In this article, a vibratory planar sensor, preferably ferromagnetic, is placed in a sensor chamber within the support member for vibrating in response to received pressure fluctuations.
Abstract: A fluid flowmeter includes a bluff body for producing vortex shedding free of intermittency. The body has at one end a support member for mounting in a conduit and has proximate its downstream surfaces a pair of orifices. A vibratory planar sensor, preferably ferromagnetic, is situated in a sensor chamber within the support member for vibrating in response to received pressure fluctuations. A magnetic detector is situated in proximity to the sensor for producing an electrical signal when the sensor vibrates in response to vortex shedding. Fluid in the conduit, and thus vortex shedding, is coupled from the orifices through a pair of parallel channels, which are in non-fluid-flow communication with one another, to opposite sides of the sensor. In one embodiment, the sensor comprises a diaphragm rigidly mounted along its periphery whereas in another embodiment the sensor comprises a rigid, substantially planar disc vibratorily mounted along its periphery.
TL;DR: In this paper, the effects of free-stream turbulence and of sinusoidal free stream pulsations of controlled frequencies and amplitudes on the periodic wake of a circular cylinder are investigated experimentally by employing hot-wire and smoke visualisation techniques.
Abstract: The effects of free-stream turbulence and of sinusoidal free-stream pulsations of controlled frequencies and amplitudes on the periodic wake of a circular cylinder are investigated experimentally by employing hot-wire and smoke visualisation techniques. In addition, the effects of cylinder yaw and mild favourable and adverse pressure gradients on the vortex shedding mechanism have been explored. The data relating frequency to mean velocity follow Berger’s relation; this relation is uninfluenced by free-stream turbulence intensities up to 8 per cent. As the longitudinal turbulence intensity increases from 0.3 to 8 per cent, the downstream distance Lp behind the cylinder over which the hot-wire signal is periodic decreases progressively, indicating that the otherwise steady periodic wake interacts non-linearly with the three-dimensional free-stream turbulence and undergoes either transition or rapid diffusion by turbulence, depending on both the Reynolds number and the turbulence intensity. For a given turbulence intensity, Lp decreases also with increasing Reynolds number. The shedding frequency behind a yawed cylinder does not vary as the cosine of the yaw angle ϕ for ϕ < 50°; the signal switches intermittently between periodic and irregular form as the yaw is increased from 0 to 70°. Mild pressure gradients (favourable as well as adverse) do not affect the shedding frequency; this is confirmed by smoke visualisation, which also shows that the pressure gradient changes the longitudinal vortex spacing downstream; the measured frequency is that determined by the local Reynolds number corresponding to the Berger relation. Sinusoidal streamwise pulsations of controlled frequencies, and of amplitudes up to 10 per cent of free-stream velocity, have no effect on the natural shedding frequency; this is confirmed by smoke visualisation of the cylinder wake. However, the wake signal is amplitude-modulated at a frequency equal to the difference between the pulsation frequency and the natural shedding frequency corresponding to the free-stream mean velocity. The vortices are diffused faster in the presence of pulsation. When the pulsation amplitude is increased beyond 20 per cent, the hot-wire signal frequency in the wake equals the driving frequency; the frequency in the wake centre is also that of the pulsation. The effect of free-stream pulsation on the periodic wake is different from that due to longitudinal or transverse cylinder vibration, when lock-in has been observed. It appears that free-stream disturbances – random or periodic – cannot account for the “Tritton jump”.
TL;DR: In this paper, the authors used an electrolytic flow visualization technique to observe the turbulent motions of vortex rings in a stably stratified fluid, of which the density profile has a gradual step change, and observed new types of distorted vortex rings wave observed to from in the nonhomogeneous fluid.
Abstract: Unsteady motions of vortex rings in a stably stratified fluid, of which the density profile has a gradual step change, have been observed using an electrolytic flow visualization technique. Some new types of distorted vortex rings wave observed to from in the nonhomogeneous fluid.
TL;DR: In this article, the free fall of small spheres through vertically oscillated liquids has been studied theoretically and experimentally for liquid accelerations up to 130g, and several modifications to the complete equation of motion for slow or creeping flow have been solved numerically and compared with experimental results in terms of the amplitude ratio, phase lag and mean fall velocity.
TL;DR: In this article, it was shown that the Strouhal number and dimensionless frequency of an elliptical cylinder vary with flow incidence angle in the Reynolds-number range between 300 and 1200.
Abstract: Experiments on the vortex shedding frequencies of selected bluff cylinders were conducted in the 1 1/2 ft by 4 ft (0.46 m by 1.2 m) test section of the Maryland University wind tunnel. The resulting data show how the Strouhal number and dimensionless frequency of an elliptical cylinder vary with flow incidence angle in the Reynolds-number range between 300 and 1200. These results are discussed in the light of the results of other investigations. Similar data are also presented for a square cylinder in the same range of Reynolds numbers. It is shown that the data for elliptical cylinders with eccentricities between 0.6 and 0.8 can be correlated over the range of Reynolds numbers between 500 and 10 to the fifth power. A correlation of data on Strouhal-number variation with angle of incidence, based on the projected height of the model, is obtained for both the square and elliptical models in the range of Reynolds numbers between 300 and 1200. The validity of the Independence Principle for flow past a yawed circular cylinder is examined. Experimental data, based on the velocity component normal to the cylinder, are presented for flow past a circular cylinder yawed 40 deg. These data are compared with those of other investigators. The combined data, which cover a wide range of Reynolds numbers, show a definite departure from the Independence Principle.
26 Jan 1976
TL;DR: In this article, a series of tests has been run at the McDonnell Douglas Aerophysics Laboratory to observe the noise generation, and it has been shown that the sound pressure level generated at a liner surface can be as large as 158 dB for a duct Mach number of 0.4.
Abstract: A problem that occurs in the application of perforated plate acoustic duct liners is the noise generated by the. turbulent boundary-layer flow over the holes in the liner surface. This flow not only generates noise but also thickens the boundary layer. To observe the noise generation, a series of tests has been run at the McDonnell Douglas Aerophysics Laboratory. These tests demonstrated that the sound pressure level generated at a liner surface can be as large as 158 dB for a duct Mach number of 0.4. The liner self-noise as measured in one liner panel was found to be affected by changes in the impedance of other liner panels. The tests showed that liner self-noise can be an important consideration in liner design. ELF-NOISE caused by flow over solid and porous surfaces, and in particular noise generated by airflows over perforated plate acoustic liners has been known to exist for some time.1'2'3 Such flows not only generate noise but also increase boundary-layer thicknesses and reduce jet thrust from aircraft engine ducts. It is possible that self-noise in an engine duct with a large amount of acoustic lining could be high enough so that an increase in lining area would actually increase the duct noise level. Recently, tests were conducted at the Douglas Aircraft Company to measure the impedance of acoustic liners using the two-microphone method. A specially designed siren was used to generate the high amplitude sound waves needed for the tests. It was a surprise to find that the self-noise amplitude could be of the same order as the high amplitude sound introduced into the duct from the siren. The self-noise waveform was periodic, with a frequency much different from the liner resonant frequency. Because selfnoise appears to be a basic problem connected with the use of perforated plate liners, a separate study of liner self-noise was carried out. The phenomenon of self-noise reminds the authors of two related problems in unsteady aeroacoustics, that of the edge tone,4'5 and that of vortex shedding behind a twodimensional body.6 In both problems an unsteady and periodic motion is generated by airflow over a rigid surface. Furthermore, the acoustic wavelength is much larger than a characteristic dimension of the surface so that near the surface the flowfield is primarily a hydrodynamic or a pseudosound7 field. That is, pressure fluctuations in the near field are of the order pu2 rather than pew, where p is the fluid density, c is the speed of sound, and u is the magnitude of the fluid velocity at a typical location in the flowfield. In both the edge tone and the self-noise problems a jet of air impinges on a rigid surface; in the vortex shedding problem the "jet" is really the entire freestream, which comes to rest on the forward part of the bluff body. In each case hydrodynamic instability is responsible for the unsteady motion, and a portion of the stream energy is radiated as acoustic energy. This portion is quite small if the freestream Mach number Uao/c is small compared to one, but it grows rapidly with Mach number.
TL;DR: In this paper, the Strouhal number for shedding of vortices from a circular cylinder is calculated by computing an unsteady viscous fluid flow at Reynolds number 200 under natural boundary conditions with a fine mesh near the surface of the cylinder.
Patent•
11 Feb 1976
TL;DR: In this article, a vibration densitometer probe is employed with a shield that produces vortex shedding, and the probe has a vane that is vibrated at an amplitude modulated acoustic frequency.
Abstract: A vibration densitometer probe is employed with a shield that produces vortex shedding. The probe has a vane that is vibrated at an amplitude modulated acoustic frequency. The envelope may be employed to compute mass flow rate. The said acoustic frequency may be employed to compute density and/or mass flow rate.
01 Jan 1976
TL;DR: In this article, the Strouhal number is a function of the gap below the cylinder and the added mass coefficient is much larger when the cylinder is near the boundary than when it is a free stream.
Abstract: Where wake effects are negligible, potential flow calculations predict well the lift and added mass forces acting on pipelines near the ocean floor when subjected to time dependent flows. Wake effects have a significant influence on the flow conditions and measured frequencies of vortex shedding can predict the drag force acting on the cylinder. The Strouhal number is a function of the gap below the cylinder. The added mass coefficient is much larger when the cylinder is near the boundary than when it is a free stream.
TL;DR: The radar and surface structure of a severe thunderstorm's wake vortex on 25 June 1969 are examined in this paper, where two probable aerodynamic causes for wake vortex formation are Karma vortices and starting vortex to the updraft lee.
Abstract: The radar and surface structure of a severe thunderstorm's wake vortex on 25 June 1969 are examined. Two probable aerodynamic causes for wake vortex formation are Karma vortices and starting vortices to the updraft lee. Karman vortices would form, as do those observed, within the echo core at the updraft lee “edges” and move downstream with the ambient flow. However, in contrast to Karman theory, radar reflectivity distributions consistently suggest anticyclonic flow. Starting vortices should develop as observed, during transition of a thunderstorm updraft from non-rotational to rotational state, as a vortex of comparable strength but opposite circulation. Four other thunderstorms examined also produced severe weather, increased intensity rapidly, and turned right or formed hook echoes contemporaneously with vortex shedding.
TL;DR: In this article, the theory of sound radiation from cylinders vibrating in resonance with vortex shedding is extended to consider the effects of vibration amplitude and mode shape, and closed form solutions for intensity are obtained when cylinder vibration velocity is either much smaller than or comparable to mean flow velocity.
Abstract: The theory of sound radiation from cylinders vibrating in resonance with vortex shedding is extended to consider the effects of vibration amplitude and mode shape. Farfield intensity and total radiated power are expressed as functions of given structural and flow parameters. Closed form solutions for intensity are obtained when cylinder vibration velocity is either much smaller than or comparable to mean flow velocity.Subject Classification: [43]28.65, [43]40.26, [43]50.55.
01 Sep 1976
TL;DR: In this paper, a mathematical model for flow-induced vibrations in heat exchanger tube banks is presented which includes the effects of vortex shedding, fluidelastic coupling, drag force, and fluid inertia coupling.
Abstract: A mathematical model for flow-induced vibrations in heat exchanger tube banks is presented which includes the effects of vortex shedding, fluidelastic coupling, drag force, and fluid inertia coupling Once the fluid forces are known, the model can predict the details of complex tube-fluid interactions: (1) natural frequencies and mode shapes of coupled vibrations; (2) critical flow velocities; (3) responses to vortex shedding, drag force, and other types of excitations; and (4) the dominant excitation mechanism at a given flow velocity The analytical results are in good agreement with the published experimental results