Showing papers on "Starting vortex published in 1996"

Leading-edge vortices in insect flight

Abstract: INSECTS cannot fly, according to the conventional laws of aerodynamics: during flapping flight, their wings produce more lift than during steady motion at the same velocities and angles of attack1–5. Measured instantaneous lift forces also show qualitative and quantitative disagreement with the forces predicted by conventional aerodynamic theories6–9. The importance of high-life aerodynamic mechanisms is now widely recognized but, except for the specialized fling mechanism used by some insect species1,10–13, the source of extra lift remains unknown. We have now visualized the airflow around the wings of the hawkmoth Manduca sexta and a 'hovering' large mechanical model—the flapper. An intense leading-edge vortex was found on the down-stroke, of sufficient strength to explain the high-lift forces. The vortex is created by dynamic stall, and not by the rotational lift mechanisms that have been postulated for insect flight14–16. The vortex spirals out towards the wingtip with a spanwise velocity comparable to the flapping velocity. The three-dimensional flow is similar to the conical leading-edge vortex found on delta wings, with the spanwise flow stabilizing the vortex.

Tropical Cyclone Motion and Evolution in Vertical Shear

Abstract: The motion and the evolution of tropical cyclone-like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model. The study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear, the influence of vortex structure, and the role of diabatic heating. The results show that the initial response of the vortex to the vertical shear is to tilt downshear. As soon as the tilt develops, the upper-level anticyclonic and lower-level cyclonic circulations begin to interact with each other. As a result of these interactions, the tilted axis of the vortex reaches a stable state after an initial adjustment, which varies with the structure of the vortex, its environmental flow shear, and the cumulus convective heating. The motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms. Most of the vortices move with the environmental flow at about 650 hPa or ...

Experimental and numerical investigations of dynamic stall on a pitching airfoil

Abstract: The dynamic stall process on a pitching NACA 0012 airfoil was investigated by two experimental techniques-particle image velocimetry (PIV) and laser-sheet visualizations-and a numerical code based on the Navier-Stokes equations. The freestream velocity was 28 m/s, leading to a Reynolds number (based on airfoil chord) of 3.73 X 10 5 . The airfoil motion was a sinusoidal function between 5 and 25 deg of incidence, with a frequency of 6.67 Hz corresponding to a reduced frequency (based on airfoil half-chord) of 0.15. The out-of-plane component of the vorticity could be derived from the PIV velocity fields. The comparison between experimental and numerical results was conducted for the four main phases of the dynamic stall process, i.e., attached flow, development of the dynamic stall vortex, poststall vortex shedding, and reattachment. In general, the computational results agreed very well with the experimental results. However, some discrepancies were observed and discussed. The cycle-to-cycle nonreproducibility of the flowfield during the phase of massive separation is also mentioned.

Interaction of a shock with a longitudinal vortex

Abstract: In this paper we study the shock/longitudinal vortex interaction problem in axisymmetric geometry. Linearized analysis for small vortex strength is performed, and compared with results from a high order axisymmetric shock-fitted Euler solution obtained for this purpose. It is confirmed that for weak vortices, predictions from linear theory agree well with results from nonlinear numerical simulations at the shock location. To handle very strong longitudinal vortices, which may ultimately break the shock, we use an axisymmetric high order essentially non-oscillatory (ENO) shock capturing scheme. Comparison of shock-captured and shock-fitted results are performed in their regions of common validity. We also study the vortex breakdown as a function of Mach number ranging from 1.3 to 10, thus extending the range of existing results. For vortex strengths above a critical value, a triple point forms on the shock and a secondary shock forms to provide the necessary deceleration so that the fluid velocity can adjust to downstream conditions at the shock.

Ring Bubbles of Dolphins

Abstract: The article discusses how dolphins create and play with three types of air-filled vortices. The underlying physics is discussed. Photographs and sketches illustrating the dolphin's actions and physics are presented. The dolphins engage in this behavior on their own initiative without food reward. These behaviors are done repeatedly and with singleminded effort. The first type is the ejection of bubbles which, after some practice on the part of the dolphin, turn into toroidal vortex ring bubbles by the mechanism of baroclinic torque. These bubbles grow in radius and become thinner as they rise vertically to the surface. One dolphin would blow two in succession and guide them to fuse into one. Physicists call this a vortex reconnection. In the second type, the dolphins first create an invisible vortex ring in the water by swimming on their side and waving their tail fin (also called flukes) vigorously. This vortex ring travels horizontally in the water. The dolphin then turns around, finds the vortex and injects a stream of air into it from its blowhole. The air "fills-out" the core of the vortex ring. Often, the dolphin would knock-off a smaller ring bubble from the larger ring (this also involves vortex reconnection) and steer the smaller ring around the tank. One other dolphin employed a few other techniques for planting air into the fluke vortex. One technique included standing vertically in the water with tail-up, head-down and tail piercing the free surface. As the fluke is waved to create the vortex ring, air is entrained from above the surface. Another technique was gulping air in the mouth, diving down, releasing air bubbles from the mouth and curling them into a ring when they rose to the level of the fluke. In the third type, demonstrated by only one dolphin, the longitudinal vortex created by the dorsal fin on the back is used to produce 10-15 foot long helical bubbles. In one technique she swims in a curved path. This creates a dorsal fin vortex since centrifugal force has to be balanced by a lift-like force. She then re-traces her path and injects air into the vortex from her blowhole. She can even make a ring reconnect from the helix. In the second technique, demonstrated a few times, she again swims in a curved path, releases a cloud or group of bubbles from her blowhole and turns sharply away (Which presumably strengthens the vortex). As the bubbles encounter the vortex, they travel to the center of the vortex, merge and, in a flash, elongate along the core of the vortex. In all the three types, the air-water interface is shiny smooth and stable because the pressure gradient in the vortex flow around the bubble stabilizes it. A lot of the interesting physics still remains to be explored.

Study of aircraft wake vortex behavior near the ground

Abstract: Aircraft wake vortices have been modeled using an unsteady, two-dimensional laminar (constant eddy viscosity) approximation of the Navier-Stokes equations, to study the influence of ground coupling, stratification, and cross-wind on vortex system behavior and decay. Initialization and boundary conditions are developed and implemented systematically for a nonuniform grid representation of the semi-infinite domain containing a vortex pair. Subsequently, the physics of wake vortex interactions with the ground for different types of surface weather conditions are discussed.

Trailing-edge jet control of leading-edge vortices of a delta wing

Abstract: The effect of using a trailing-edge jet to control the leading-edge vortices of a delta wing is investigated experimentally in a water towing tank facility. The Reynolds number, based on the freestream velocity and the root chord, is 9.8 X 103. Both static and dynamic (pitching-up) conditions are tested. For the dynamic cases, the wing is pitched from 10- to 45-deg angle of attack with pitch rates varied from 0.043 to 0.26. From the dye flow visualization, it is shown that a downward vectored trailing-edge jet can significantly delay the vortex breakdown on a delta wing. Strong asymmetric breakdown of the leading-edge vortices can be induced by arranging the vectored jet in an asymmetric configuration. Transient pitching motion delays the onset of the vortex breakdown. The initial delay is independent of the pitch rate. Also, the use of jet control is found to be effective for the dynamic cases. During the initial pitching-up period, the use of jet control has a dominant influence on the propagation of the vortex breakdown. In general, with jet control, the propagation of the vortex breakdown slows down. From instantaneous particle image velocimetry measurements, a quasiperiodic variation of the leading-edge vorticity field is detected before the vortex breakdown. This variation appears to relate to the strong interaction between the separating shear layer, the secondary vortex, and the primary vortex. Along the vortex axis, the velocity distribution changes from a jet-type profile to a wake-type profile, signifying the onset of vortex breakdown.

Experimental studies of vortex disconnection and connection at a free surface

Abstract: An experimental study is presented that examines the interaction of a vortex ring with a free surface. The main objective of this study is to identify the physical mechanisms that are responsible for the self-disconnection of vortex filaments in the near-surface region and the subsequent connection of disconnected vortex elements to the free surface. The understanding of those mechanisms is essential for the identification and estimation of the appropriate spatial and temporal scales of the disconnection and connection process. In this regard, the velocity and vorticity fields of an obliquely approaching laminar vortex ring with a Reynolds number of 1150 were mapped by using Digital Particle Image Velocimetry (DPIV). The evolution of the near-surface vorticity field indicates that the connection process starts in the side regions of the approaching vortex ring where surface-normal vorticity already exists in the bulk. A local strain rate analysis was conducted to support this conclusion. Disconnection in the near-surface tip region of the vortex ring occurs because of the removal of surfaceparallel vorticity by the viscous flux of vorticity through the surface. Temporal and spatial mapping of the vorticity field at the surface and in the perpendicular plane of symmetry shows that the viscous flux is balanced by a local deceleration of the flow at the surface. It is found that the observed timescales of the disconnection and connection process scale with the near-surface vorticity gradient rather than with the core diameter of the vortex ring.

Transition to turbulence in an elliptic vortex

Abstract: Stability and transition to turbulence are studied in a simple incompressible two-dimensional bounded swirling flow with a rectangular planform – a vortex in a box. This flow is unstable to three-dimensional disturbances. The instability takes the form of counter-rotating swirls perpendicular to the axis which bend the vortex into a periodic wave. As these swirls grow in amplitude the primary vorticity is compressed into thin vortex layers. These develop secondary instabilities which roll up into vortex tubes. In this way the flow attains a turbulent state which is populated by intense elongated vortex tubes and weaker vortex layers which spiral around them. The flow was computed at two Reynolds numbers by spectral methods with up to 2563 resolution. At the higher Reynolds number broad three-dimensional shell-averaged energy spectra are found with nearly a decade of Kolmogorov k−5/3 law and small-scale isotropy.

Controlled leading-edge suction for management of unsteady separation over pitching airfoils

Abstract: The effect on the unsteady surface pressures of controlled suction from a spanwise slot, located at 2% chord in the suction surface of a two-dimensional NACA 0012 airfoil model, was examined in detail for a wide range of pitch rates with a constant velocity ramp motion. The experiments were conducted in the Andrew Fejer Wind Tunnel at the Illinois Institute of Technology's Fluid Dynamics Research Center. The optimum suction required to meet three different control objectives, suppression of the dynamic-stall vortex, delaying detachment of the vortex from the airfoil surface, and maximizing the unsteady lift, was determined for different pitch rates and angles of attack. The pressure data were used to develop specifications for the flow state over the airfoil surface that would meet these objectives. Such specifications are necessary for the development of on-line flow management systems. A procedure was also developed to account for variations in suction and motion history.

The Effect of Vortex Shedding on the Unsteady Pressure Distribution Around the Trailing Edge of a Turbine Blade

Abstract: The wakes behind turbine blade trailing edge are characterized by large scale periodic vortex patterns known as the von Karman vortex street. The failure of steady-state Navier-Stokes calculations in modeling wake flows appears to be mainly due to ignoring this type of flow instabilities. In an effort to contribute to a better understanding of the time varying wake flow characteristics behind turbine blades, VKI has performed large scale turbine cascade tests to obtain very detailed information about the steady and unsteady pressure distribution around the trailing edge of a nozzle guide vane. Tests are run at an outlet Mach number of M2,is,=0.4 and a Reynolds number of Rec = 2·106. The key to the high spatial resolution of the pressure distribution around the trailing edge is a rotatable trailing edge with an embedded miniature pressure transducer underneath the surface and a pressure slot opening of about 1.5° of the trailing edge circle. Signal processing allowed or differentiation between random and periodic pressure fluctuations. Ultra-short schlieren pictures help in understanding the physics behind the pressure distribution.Copyright © 1996 by ASME

Half-plow vortex generators for rotorcraft blades for reducing blade-vortex interaction noise

Abstract: In one embodiment for a helicopter main rotor assembly, a half-plow vortex generator is mounted in combination with the upper aerodynamic surface of each main rotor blade and is operative to generate a primary corotating vortex of sufficient strength to interact with and accelerate the dissipation of the tip vortex generated by the same main rotor blade, thereby reducing blade-vortex interaction noise radiating from the helicopter main rotor assembly. The half-plow vortex generator has a right triangular planform configuration defined by a length, a width, and an apex angle. The three-dimensional configuration of the vortex generator is further defined by an apex height. The apex height is the primary determinant of the strength of the generated primary corotating vortex and is defined in terms of the thickness of the main rotor blade at the local chord where the vortex generator is mounted. The apex height may be approximately equal to the local thickness, but preferably has a magnitude within the range of about one-eighth to about three-quarters of the local thickness. The length, width, and apex angle are secondary determinants of the strength of the primary corotating vortex generated by the half-plow vortex generator. The length and width of the vortex generator are defined in terms of the tip chord length of the main rotor blade, the length preferably having a magnitude within the range of about one-fourth to one-half of the tip chord length and the width preferably having a value of about one-third of the length of the vortex generator. The apex angle preferably has a value within the range of about twenty to about thirty degrees. The mounting site for the half-plow vortex generator is defined in terms of the length of the local and tip chords, respectively. The vortex generator is mounted inboardly from the tip of the main rotor or blade a spanwise distance having a magnitude preferably within the range of about one-half of to about equal to the tip chord length in substantial alignment with the local chord. The apex of the vortex generator is mounted inwardly from the leading edge of the main rotor blade by a chordal distance having a magnitude of about one-quarter the local chord length.

Boundary-layer-tripping studies of compressible dynamic stall flow

Abstract: The challenging task of properly tripping the boundary layer of a leading-edge-stalling airfoil experiencing compressible dynamic stall at Reynolds numbers between 3.6 X 10 5 and 8.1 X 10 5 has been addressed. Real-time interferometry data of the flow over an oscillating airfoil have been obtained at freestream Mach numbers of 0.3 and 0.45. The airfoil was tripped by separately placing five different trips of varying lengths near the leading edge. The trip heights ranged from 40 to 175 μm. The resulting flow and airfoil performance were evaluated using the criteria of elimination of the laminar separation bubble that otherwise forms, delay of dynamic stall onset to higher angles of attack, and production of consistently higher suction peaks. Quantitative analysis of the interferograms showed that the laminar separation bubble was still present with the smallest trip and premature dynamic stall occurred with the largest trip. The right trip was determined to be a distributed roughness element extending from 0.5 to 3% chord. Its height was found to compare reasonably with the airfoil boundary-layer thickness at the dynamic stall vortex formation angle of attack, at a location slightly upstream of the vortex origin in the adverse pressure gradient region.

High-Performance Airfoil with Moving Surface Boundary-Layer Control

Abstract: All airfoils are known to stall at high angles of attack as a result of flow separation, resulting in a sudden loss of the lift force. To avoid flow separation, it is necessary to introduce some form of boundary-layer control. The present study focuses on the performance of an airfoil with moving surface boundary-layer control (MSBC). Effects of the angles of attack, rate of momentum injection, as well as rotating cylinder surface condition on the surface pressure distribution and aerodynamic coefficients are assessed. A comprehensive study involving wind-tunnel investigation, numerical simulation, and flow visualization clearly demonstrates that the momentum injection through MSBC results in a significant delay in the stall angle (from 10 to 50 deg) and an increase in the lift coefficient by more than 200% at high angles of attack (α 30 deg). A multielement panel method, modeling the flow separation using free vortex lines, predicts the overall aerodynamics of an airfoil with the MSBC quite accurately. The airfoil performance can be improved further by judicious selection of the rotating cylinder surface condition

Measurements in the near wake of a hovering rotor

Abstract: AIAA, Fluid Dynamics Conference, 27th, New Orleans, LA, June 17-20, 1996 Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile- and induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter measurements on the vortex core and to assess the extent of the positional meandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex. (Author)

A model of stratified entrainment using vortex persistence

Abstract: A new model is proposed for the entrainment rate by vortices across stratified interfaces. In the model, different entrainment regimes are distinguished by the conventional parameters Richardson, Reynolds, and Schmidt number as well as a new parameter, the “vortex persistence”. Vortex persistence is defined as the number of rotations a vortex makes during the time it moves its own diameter with respect to the interface. It is further proposed that the concept of vortex persistence is important whenever a vortex is near any kind of surface, either stratified or solid. The model is in accord with most field and laboratory observations in a variety of stratified and bounded flows, including measurements of wall heat transfer and vortex formation in starting jets.

Airfoil vortex attenuation apparatus and method

Abstract: A vortex attenuating airfoil (24) includes an outboard area (28). The outboard area includes a deflector (40) which is disposed in the inboard direction from a tip (30). An air passage (46) extends through the airfoil from an inlet (48) on a high pressure side of said airfoil to an outlet (50) on a low pressure side of the airfoil. The outlet (50) is positioned in the outboard area between said deflector and the tip. In operation, air passes through the air passage to attenuate the naturally occurring vortex adjacent to the tip of the airfoil thereby reducing drag.

Flow field survey in trailing vortex system behind a civil aircraft model at high lift

Abstract: The roll-up of the trailing vortex system behind a generic civil aircraft windtunnel model with extended flaps and slats is studied up to 5 wing spans downstream. A laser light sheet flow visualisation technique is used and detailed flow field measurements are made with a spanwise traversable rake with five-hole probes. The measurement results are compared against calculations with the 2D vorticity transport equation.

Vortex shedding in segmented solid rocket motors

Abstract: This article is devoted to the numerical simulation of vortex shedding in the field of solid-propellant rocket motors resulting from the strong coupling between the shear-layer instability and acoustic waves in the chamber. Segmented solid rocket motors tend to develop thrust and pressure oscillations, linked to a periodic vortex shedding. An axisymmetric geometry close to the realistic configuration is computed. The computer code solves the unsteady Navier-Stokes equations by means of an explicit predictor/ corrector MacCormack scheme. Mesh dependence is studied by using three grid levels. In all cases, the vortex shedding process is observed. This mechanism is complex and vortex pairing occurs. The viscosity effect is analyzed by using three different viscosity values. The effect of the shape of diaphragms oh vortex shedding is also studied by comparing sharp and smooth diaphragms. HIS work is part of the overall combustion stability assessment of the Ariane 5 P230 MPS solid motor and has been supported by Centre National d'Etudes Spatiales (CNES) within a research program managed by ONERA. For this motor it is believed that there exists a severe risk for instability. Occurrence of low-amplitude , sustained oscillations pulsating at a frequency associated with one or more acoustic modes of the combustion cavity affects motor performances.1"3 One mechanism that drives pressure oscillations in rocket motors is the vortex shedding,1'4 which can interact with the chamber acoustics to generate pressure oscillations.5 Because of the segmented design of solid-propell ant rocket motors, shear layers induced by surface discontinuities appear and produce this vortex shedding. The dipole mechanism involving the interaction of the vortices with an impingement surface can be invoked as a typical source of energy transfer from the vortex fluctuations to the acoustic field. The observed periodic vortex shedding in rocket motors2'4 is the result of a strong coupling between the instability of mean shear flow and organ-pipe acoustic modes in the chamber. The feedback from the acoustic waves provides the control signal for the aerodynamic instability. Because of the complexity of the problem an analytical solution to the governing equations with complex boundary conditions does not exist. Numerical simulations may provide important help for understanding the complex physics. Such simulations would naturally couple mean-flow shear layer and acoustic waves. Numerical methods have been performed to isolate and study the interaction between acoustic waves and vortex structures.6"10 The present work is also concerned by a numerical simulation. The aim of this article is to present the ability of numerical codes to predict the unsteady behavior inside the combustion chambers of solid-propellant rocket motors and to analyze the acoustic and aerodynamic instability interaction. The computational domain corresponds to a 1/15 axisymmetric subscale motor representative of the Ariane 5 P230 solid rocket booster for which experimental results exist.11"13 For this subscale motor, the propellant is an unmetallized analog of Ariane 5 propellant and the inhibitors are

Computational Study of the Flowfields Associated with Oblique Shock/Vortex Interactions

Abstract: The interaction between a supersonic streamwise vortex and an oblique shock is solved numerically using the unsteady, three-dimensional Euler equations. The parametric study ascertains the effects of vortex strength, streamwise velocity deficit, and Mach number on the oblique shock/vortex interaction. The vortex, whose tangential and streamwise velocities are analytically modeled, is introduced upstream of the shock and allowed to interact with the shock. The interaction is examined at freestream Mach numbers of 3 and 5, using vortices of varying strength and possessing various velocity deficits. Three distinct types of interactions—weak, moderate, and strong—are observed, depending very strongly on the streamwise velocity deficit and, to a lesser degree, on the strength of the vortex. The weak interaction is characterized by a slight distortion of the shock and vortex with the resulting flowfield being supersonic everywhere. The moderate interaction, however, results in a more pronounced distortion of the shock, creating a small pocket of subsonic flow downstream of the interaction. In addition, the incident vortex is highly distorted by the shock and eventually splits up into two counter-rotating vortices. In the strong interaction, due to the formation of a large subsonic region, a dramatic reorganization of the original shock occurs, accompanied by a region of reversed subsonic flow, a stagnation point, and a drastic expansion of the vortex core, all of which are characteristics of vortex breakdown.

Dynamics of a vortex ring in a rotating fluid

Abstract: The formation and the evolution of axisymmetric vortex rings in a uniformly rotating fluid, with the rotation axis orthogonal to the ring vorticity, have been investigated by numerical and laboratory experiments. The flow dynamics turned out to be strongly affected by the presence of the rotation. In particular, as the background rotation increases, the translation velocity of the ring decreases, a structure with opposite circulation forms ahead of the ring and an intense axial vortex is generated on the axis of symmetry in the tail of the ring. The occurrence of these structures has been explained by the presence of a self-induced swirl flow and by inspection of the extra terms in the Navier–Stokes equations due to rotation. Although in the present case the swirl was generated by the vortex ring itself, these results are in agreement with those of Virk et al. (1994) for polarized vortex rings, in which the swirl flow was initially assigned as a ‘degree of polarization’.If the rotation rate is further increased beyond a certain value, the flow starts to be dominated by Coriolis forces. In this flow regime, the impulse imparted to the fluid no longer generates a vortex ring, but rather it excites inertial waves allowing the flow to radiate energy. Evidence of this phenomenon is shown.Finally, some three-dimensional numerical results are discussed in order to justify some asymmetries observed in flow visualizations.

Forced oscillations of airfoil flows

Abstract: The effect of background flow oscillations on a transonic airfoil (NACA 0012) flow was investigated experimentally. The oscillations were generated by means of a rotating plate placed downstream of the airfoil. Owing to the expansion and compression waves generated at the plate, the flow over the airfoil flow was drastically disturbed. This resulted in the presence of high intensity oscillations of a shock wave and a separation bubble on the suction surface of the airfoil. For relatively large values of the airfoil angle of attack, weak shock waves (transonic sound waves) were periodically shed upstream of the airfoil.

The three-dimensional interaction of a streamwise vortex with a large-chord lifting surface: theory and experiment

Abstract: The three-dimensional vortex flow that develops around a close-coupled canard-wing configuration is characterized by a strong interaction between the vortex generated at the canard and the aircraft wing. In this paper, a theoretical potential flow model is devised to uncover the basic structure of the pressure and velocity distributions on the wing surface. The wing is modelled as a semi-infinite lifting-surface set at zero angle of attack. It is assumed that the vortex is a straight vortex filament, with constant strength, and lying in the freestream direction. The vortex filament is considered to be orthogonal to the leading-edge, passing a certain height over the surface. An incompressible and steady potential flow formulation is created based on the three-dimensional Laplace's equation for the velocity potential. The boundary-value problem is solved analytically using Fourier transforms and the Wiener-Hopf technique. A closed-form solution for the velocity potential is determined, from which the velocity and pressure distributions on the surface and a vortex path correction are obtained. The model predicts an anti-symmetric pressure distribution along the span in region near the leading-edge, and a symmetric pressure distribution downstream from it. The theory also predicts no vertical displacement of the vortex, but a significant lateral displacement. A set of experiments is carried out to study the main features of the flow and to test the theoretical model above. The experimental results include helium-soap bubble and oil-surface flow pattern visualization, as well as pressure measurements. The comparison shows good agreement only for a weak interaction case, whereas for the case where the interaction is strong, secondary boundary-layer separation and vortex breakdown are observed to occur, mainly owing to the strong vortex-boundary layer interaction. In such a case the model does not agree well with the experiments.

An experimental study of viscous vortex rings

Abstract: The work focuses on the problem of stability and viscous decay of single vortex rings. A tentative classification scheme is proposed for vortex rings which is based on extensive hot-wire measurements of velocity in the ring core and wake, and flow visualization, viz. laminar, wavy, turbulence-producing, and turbulent. Prediction of vortex ring type is shown to be possible, at least approximately, based on the vortex ring Reynolds number alone. Linear growth rates of ring diameter with time are observed for all types of vortex rings, with different growth rates occurring for laminar and turbulent vortex rings. Data on the viscous decay of vortex rings are used to provide experimental confirmation of the accuracy of Saffman's equation for the velocity of propagation of a vortex ring.

Flow Past a Flat Plate With a Vortex/Sink Combination

Abstract: An attempt was made to model the so called leading edge vortex which forms over the leading edge of delta wings at high angles of attack. A simplified model was considered, namely that of a two-dimensional, inviscid, incompressible steady flow around a flat plate at an angle of attack with a stationary vortex detached on top, as well as a sink to simulate the strong spanwise flow. The results appear to agree qualitatively with experiments. A comparison was also made between the lift and the drag of this model and the corresponding results for two classical solutions: (1) that of totally attached flow over the plate with the Kutta condition satisfied at the trailing edge only: and (2) the Helmholtz solution of totally separated flow over the plate.

Vortex flow meter detector and vortex flow meter

Abstract: A vortex flowmeter detector is attached to or detachable from a vortex generation body for measurement of flow rate. The vortex flowmeter detector comprises a cylindrical oscillation tube having a bottom and a vortex detection part which is fixed by a fixing flange of the oscillation tube, wherein the oscillation tube is detachably inserted into a hole which is open to the vortex generation body at one end thereof, and the oscillation tube is fixed by a flange. An alternate pressure caused by a Karman vortex is introduced from both sides of the vortex generation body into the hole so as to oscillate the oscillation tube. This oscillation is received by a spring plate by way of an element cover, and it is transmitted to piezoelectric elements which are stuck to two chamfers of an elastic base material.

Scaling properties of vortex ring formation at a circular tube opening

Abstract: A vortex sheet model is applied to study vortex ring formation at the edge of a circular tube, for accelerating piston velocities Up∼tm. We determine properties of the vortex ring as a function of the piston motion and investigate the extent to which similarity theory for planar vortex sheet separation applies. For piston strokes up to half the tube diameter, we find that the ring diameter, core size and circulation are well predicted by the planar similarity theory. The axial ring translation is a superposition of an upstream component predicted by the theory and a downstream component which is linear in the piston stroke. The front of the fluid volume exiting the tube is also linear in the piston stroke and travels with 75% of the piston velocity. The core size decreases and the distribution of fluid near the core becomes more asymmetric as the parameter m increases.