Showing papers on "Vortex shedding published in 1970"

Solution of the equations of rotational motion for a class of torque-free gyrostats

Abstract: with the same cylinders fitted with end plates to simulate the case of infinite length. The cylinders were mounted sufficiently rigid to prevent oscillation. The results are presented in Fig. 2. In accordance with earlier findings the Strouhal number of the infinite cylinder is approximately 0.2, computed from the frequency peak protruding from the otherwise turbulent spectrum. In case of the finite cylinder with aspect ratio 4, a regular motion indicated by a distinct frequency in the spectral distribution with S « 0.45 was found at Rer> ~ 2.4 X 10s. Apparently the frequency peak tended to become weaker with decreasing Reynolds number and at RCD ~ 5 X 104 a distinct frequency could no longer be discerned. The spectra obtained with the cylinder of aspect ratio 8 showed a shedding frequency with S = 0.2 at subcritical Reynolds numbers with the indication to become stronger with ReD increasing. The evaluation of Roshko's "universal wake Strouhal number/' Sw = fDw/Uw showed for all measurements Sw « 0.2. Naumann2 found that due to the three dimensionality of the flow the separation line is no longer straight and thus the circulation of a separating vortex is no longer constant, which leads to a break up. This seems to be confirmed by some surface patterns presented by Gould, Raymer, and Ponsford.3 The surface patterns which were observed during this work, however, exhibit a very straight separation line and at the same time there was no indication of vortex shedding. It appears therefore that some additional explanations may be necessary. For any blunt body part of the flow going over the top of the body is being dragged into the wake. The strength of this downwash obviously decreases with increasing Reynolds number and is restricted to a certain length of the cylinder from top downwards, i.e., its over-all influence decreases with increasing aspect ratio. One may consider the downwash flow as a kind of air curtain acting to some extent like a splitter plate. Depending on its over-all strength it dampens the feedback from both sides of the cylinder arid thus the shedding mechanism. Two tests were made to check on this model. In the first case the cylinder with end plate was provided with a slit in the base open to atmosphere, so that by action of the low base pressure a weak jet was blown into the wake. This largely damped the shedding which was clearly observed when the slit was blocked. In the second test the downwash in the near region of the finite cylinder was prevented by a small plate behind the cylinder between half height and top. The presence of this plate accounted for the occurrence of regular shedding. The main observations may be summarized as follows: 1) the pressure distribution around a blunt cylinder, being similar to that of the infinite cylinder has the same Ren — dependence; 2) the region of highly three-dimensional flow in the wake is restricted to the first 3—4 cylinder diameters; 3) turbulence levels in the near wake reach values of approximate 80% of the local mean velocity; 4) macro scales in the nonperiodic wake are almost an order of magnitude smaller than in the periodic, i.e., shedding case. Their mean values over the cylinder height increase linearly with downstream distance after the first 2 to 3 cylinder diameters; 5) the universal wake Strouhal number appears to be a constant for finite and infinite cylinders alike;

Numerical Simulation Of Vortex Shedding From An Oscillating Circular Cylinder

Abstract: The interaction between cylinder oscillation and the shedding of vortices is investigated numerically in this paper. The near wake structure is presented for different values of reduced velocity of a cylinder free to oscillate transversely. One of the objectives of this paper is to compare the numerical results with experimental data obtained by Parra [11] in the water tank facility of IPT/University of Sao Paulo. The attraction of applying numerical methods to this problem is that the way the flow is modified can be studied in closer detail. In the computer it is possible to investigate many different flow conditions more easily. The method used for the simulation is based on the Vortex-in-Cell formulation incorporating viscous diffusion. The Navier-Stokes equations are solved using the operator-splitting technique, where convection and diffusion of vorticity are treated separately. The convection part is modelled assuming that the vorticity field is carried on a large number of discrete vortices. Force coefficients are calculated by considering the normal gradient of vorticity at the wall to evaluate the pressure contribution and the vorticity at the wall to obtain the skin friction.

Fluid vortex device

Abstract: FLUID VORTEX APPARATUS COMPRISING A A HOUSING ENCLOSING A VORTEX CHAMBER, A PRIMARY COUPLING ELEMENT SURROUNDING THE VORTEX CHAMBER, A CENTRAL FLUID OUTLET FROM THE VORTEX CHAMBER, AND SECONDARY COUPLING MEANS LOCATED WITHIN THE VORTEX CHAMBER BETWEEN THE PRIMARY COUPLING ELEMENT AND THE CENTRAL OUTLET. THE PRIMARY COUPLING ELEMENT IS STRUCTURE TO INTRODUCE FLUID INTO THE VORTEX CHAMBER SO THAT IT HAS SUBSTANTIALLY NOT RATIONAL VELOCITY WITH RESPECT TO THE CHAMBER HOUSING, FLUID WITHIN THE VORTEX CHAMBER ACQUIRING A ROTATIONAL VELOCITY WITH RESPECT TO THE HOUSING IN RESPONSE TO INPUT STIMULII. THE SECONDARY COUPLING MEANS MODIFIES ANY RATIONAL FLOW PATTERN WITHIN THE VORTEX CHAMBER SO AS TO PRODUCE A CHARACTERIZED TIME-VARYING ROTATIONAL FLOW PATTERN IN THE FLUID OUTLET. A SENSOR IN THE OUTLET PRODUCES A SIGNAL INDICATIVE OF THE RATIONAL VELOCITY OF FLOW ABOUT THE AXIS OF THE OUTLET, THEREBY RESULTING IN A CHARACTERIZED RESPONSE TO THE INPUT STIMULII.

Investigation on the Nonconstant Behavior of a Vortex Flow Meter with Narrow Gauge Pipe via Conducting Measurements and Numerical Simulations

Abstract: Vortex shedding flowmeters can be used for a wide range of flow measurement applications with various kinds of fluids. The critical point in applying this method comes from the assumption that the Strouhal number is constant for the given Reynolds number range. In some cases – typically regarding flowmeters with narrow gauge pipes –, this assumption is only partially met, thus limiting the widespread use of these instruments in certain industrial appliances. The paper presents a diagnostic investigation on the effects of this nonconstant behavior. The method elaborated in this report can be applied to vortex flowmeters with narrow gauge pipes. In these instruments – usually due to the narrow cross-sections of the gauge pipe – measurement possibilities are limited, thus it is not possible for the user to determine the effects of the nonconstant behavior. To conduct these investigations, a calibration rig was designed and assembled. The presented diagnostic method combines measurements and numerical simulations. The results of the investigations can be used in the data processing phase, in order to reduce the uncertainty of the volume flow rate measured by vortex flowmeters.

Vortex wakes from flexible circular cylinders at low reynolds numbers.

Abstract: : The study is related to the flexible circular cylinder in the Reynolds number range from 30 to 500. The shedding features of flexible cables are studied and general characteristics of vortex shedding are interpreted from diagnostic observations. The study has two objectives: (1) to observe and analyze the vortex shedding features characteristic of a flexible cable that is flow-excited into standing wave oscillations; and (2) to perform a diagnostic investigation of the spanwise shedding phenomenon when the vortex shedding is both dependent and independent of the oscillating motion. (Author)

Theoretical analysis of vortex shedding from bodies of revolution in coning motion

Abstract: Flow field model for steady asymmetric vortex system shed from slender body of revolution in coning motion

Surface Dipole Strength for Flow Past Airfoils

Abstract: A new correlation technique enables the determination of local acoustic source strength on the surface of flat plates and simple airfoil shapes. The method is based on Curle's equation for surface generated noise and involves cross correlation between local surface pressure and the farfield acoustic pressure. Flat plate airfoils of circular planform were positioned in a quiet open jet airflow. The distribution of dipole strength was obtained by moving the point of surface pressure measurement around on the surface. Distinctively different distributions were obtained for cases of vortex shedding (airfoil at zero angle of attack in core of jet), separated flow (airfoil at 16° angle of attack in core of jet), and incident turbulence (airfoil in turbulent mixing layer). The popular notion that noise comes dominantly from the edges of a plate was not strongly supported. In some cases, however, definite localized source regions were identified. The technique also enabled estimates of correlation area for the su...

Fluid turbulence study apparatus and method

Abstract: A rotating arm carrying vortex generators generates outwardly spiralling vortices in a fluid-medium. Measurements are made in the fluid disturbances caused by the vortices.