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Showing papers on "Starting vortex published in 1971"


Journal ArticleDOI
TL;DR: In this paper, the Schlieren method was used to visualize the vortex formation region and the vortex shedding frequency for two tubes at various spacings, and it was found that the size of the vortex forming domain has a dominant effect on the frequency.
Abstract: A gas flow in and behind tube banks with tuber axes normal to the gas flow is highly turbulent containing numerous vortices of different sizes and intensities. Each vortex in this complicated wake is the result of a periodic generation, and the periodicity sometimes induces serious vibration problems in steam generators and heat exchangers. The structure of the flow may be treated ass a complex synthesized result of Karman vortex flow. This paper is the first report of a series of studies carried out form the above mentioned viewpoint, and presents the experimental results about a Karman vortex flow from two tubes at various spacings. The vortex formation region was visualized by means of the Schlieren method and was recorded by a 16mm movie camera. The vortex shedding frequency was systematically studied. The frequency for two tubes is entirely different from that for a single tube. It was found that the size of the vortex formation domain has a dominant effect on the frequency.

171 citations



Journal ArticleDOI
TL;DR: In this paper, the Strouhal numbers for flow past a circular and a blunt jet are in qualitative agreement with those for corresponding solid bodies, provided that the width of the spreading jet some distance from the surface is used rather than the jet exit plane dimension.
Abstract: Measurements in the wake behind turbulent jets exhausting from a solid surface into a cross-wind indicate that vortex shedding occurs as in the case of flow past solid bluff bodies. The Strouhal numbers for flow past a circular and a blunt jet are in qualitative agreement with those for corresponding solid bodies, provided that the width of the spreading jet some distance from the surface is used rather than the jet exit plane dimension.

84 citations


Patent
06 Dec 1971
TL;DR: In a vortex type de-aerator, a vortex stabilizing baffle device is located adjacent to the inlet for stabilising the vortex flow and for shielding separated gas from any disturbances at the vortex inlet as discussed by the authors.
Abstract: In a vortex type de-aerator for separating air and other gases from a flowing liquid, having a central perforate tube located within a vessel having a tangential inlet and a tangential outlet, a vortex stabilising baffle device is located adjacent to the inlet for stabilising the vortex flow and for shielding separated gas from any disturbances at the inlet.

81 citations


Journal ArticleDOI
TL;DR: In this article, the effect of axial flow on the stability of a single vortex filament and a pair of vortices has been investigated and the stability boundary has been obtained.
Abstract: Previous results concerning the effects of axial velocity on the motion of vortex filaments are reviewed. These results suggest that a slender-body force balance between the Kutta–Joukowski lift on the vortex cross-section and the momentum flux within the curved filament will give some insight into the behaviour of the filament. These simple ideas are exploited for both a single vortex filament and a vortex pair, both containing axial flow. The stability of a straight vortex filament containing an axial flow to long wave sinusoidal displacements of its centre-line is investigated and the stability boundary obtained. The effect of axial flow on the stability of a vortex pair is explored. It is shown that to lowest order (in the ratio of vortex core radius to distance between the vortices) the effect of axial flow is to reduce the self-induced rotation of a single filament and that this effect can be considered as a change in effective core radius. To the next order, travelling waves appear in the instability, the instability mode for the vortex pair becomes non-planar but the amplification rate of the instability is not affected.

35 citations


Book ChapterDOI
01 Jan 1971
TL;DR: In the NASA-Ames 7-by-10-foot wind tunnel, an experimental study was carried out on a rectangular wing as mentioned in this paper, where flow visualization studies were made using a tuft grid and smoke, and it was shown that the dissipater caused a significant reduction in the maximum tangential velocities in the trailing vortex.
Abstract: An experimental study was carried out on a rectangular wing in the NASA-Ames 7- by 10-Foot Wind Tunnel. Flow visualization studies were made using a tuft grid and smoke. Preliminary studies showed that the introduction of a bluff body into the trailing vortex downstream of the wing resulted in modification of the vortex. Further studies showed that a small vertical panel, termed a vortex dissipater, mounted on the wing upper surface near the wing tip also caused modification of the vortex. Both the smoke and tuft grid visualization studies indicated that the dissipater caused a significant reduction in the maximum tangential velocities in the trailing vortex. Additional studies using a hot wire anemometer showed significant reductions in the magnitude of the tangential velocities, increases in the cross-sectional dimensions of the core of the dissipated vortex and changes in the turbulence structure. Limited flight tests with a dissipater fitted to a Convair 990 wing tip and using a Lear jet aircraft as a probe indicated that the rolling acceleration and the degree of roll control required was less in the modified vortex than in the unmodified vortex.

30 citations


Patent
09 Nov 1971
TL;DR: An airfoil having an upper surface shaped to control flow acceleration and pressure distribution over the upper surface and to prevent separation of the boundary layer due to a shock wave formulation at high subsonic speeds well above the critical Mach number is considered in this article.
Abstract: An airfoil having an upper surface shaped to control flow accelerations and pressure distribution over the upper surface and to prevent separation of the boundary layer due to shock wave formulation at high subsonic speeds well above the critical Mach number. A highly cambered trailing edge section improves overall airfoil lifting efficiency.

30 citations


Book ChapterDOI
01 Jan 1971
TL;DR: In this article, a model of a trailing vortex pair behind an aircraft is presented which is thought to represent a case of extreme vortex persistency and which therefore is relevant from the safety point of view.
Abstract: A model of a trailing vortex pair behind an aircraft is presented which is thought to represent a case of extreme vortex persistency and which therefore is relevant from the safety point of view. Three stages are considered in the analysis: a rolling-up stage directly behind the aircraft, a second stage in which the vortices act independently as constant strength equilibrium turbulent vortices, and a third stage where the vortices physically interact and decay in strength. An overall theory is presented encompassing all three stages and aimed at obtaining equilibrium solutions. Calculative examples are presented for all stages.

23 citations



Journal ArticleDOI
TL;DR: In this article, a method is presented for the prediction of the spatial distribution of the trailing vorticity during the rolling up process, thus giving the overall downwash field behind the wing.
Abstract: A wing of finite span in flight generates trailing vorticity which “rolls up” into two “discrete” vortices. During the rolling up process the trailing vorticity is displaced vertically downward (assuming that the aircraft is in horizontal flight) under the influence of the wing circulation and the self-induced downwash velocities. In this note a method is presented for the prediction of the spatial distribution of the trailing vorticity during the rolling up process, thus giving the overall downwash field behind the wing.

17 citations


Journal ArticleDOI
TL;DR: In this article, a method of weighted residuals for the computation of rotationally symmetric quasicylindrical viscous incompressible vortex flow is presented, which approximates the axial velocity and circulation profiles by series of exponentials having (N + 1) and TV free parameters.
Abstract: A method of weighted residuals for the computation of rotationally symmetric quasicylindrical viscous incompressible vortex flow is presented. The method approximates the axial velocity and circulation profiles by series of exponentials having (N + 1) and TV free parameters, respectively. Exponentials are also used as weighting functions. Formal integration results in a set of (2N + 1) ordinary differential equations for the free parameters. The governing equations are shown to have an infinite number of discrete singularities. Sample solutions for different swirl parameters and three typical vortex flows (initially uniform axial flow, leading edge vortex, and trailing vortex) are presented, and the effects of external axial velocity and circulation gradients are investigated. The computations point to the controlling influence of the inner core flow on vortex behavior. They also confirm the existence of two particular critical swirl parameter values: So, which separates vortex flow which decays smoothly from vortex flows which eventually "breaks down," and Si, the first singularity of the quasi-cylindrical system, at which point physical vortex breakdown is thought to occur. The results are close to the inviscid values for S0 and Si[(2)lf2 and 3.8317/2 for initially uniform axial flow].

Patent
16 Mar 1971
TL;DR: An airfoil for fixed and rotary wing aircraft comprising a continuous upper surface that joins with a generally planar portion of the under surface at the leading edge to form the apex of a wedge-like airfoiler section that extends toward and terminates abruptly in advance of the trailing edge was proposed in this article.
Abstract: An airfoil for fixed and rotary wing aircraft comprising a continuous upper surface that joins with a generally planar portion of the under surface at the leading edge to form the apex of a wedge-like airfoil section that extends toward and terminates abruptly in advance of the trailing edge.

Journal ArticleDOI
Kenichi Nanbu1
TL;DR: In this paper, the boundary-layer equations under the boundary condition of distributed suction were solved, and a formal similarity solution was obtained for suction parameter greater than a certain value.
Abstract: Introduction B the use of momentum integral methods, Taylor and Cooke calculated the laminar boundary-layer development on the interior surface of a frustum of a cone, with a potential vortex as the outer flow. Taylor's swirl atomizer problem has also been examined by means of similarity transformations of the boundary-layer equations by Moore, Mager, and Rott and Lewellen, and in Ref. 3 it is concluded that no valid solution can be found. However, in Ref. 4 it is noted that the valid solution may be found if the velocity profile of secondary flow changes sign somewhere in the boundary layer. Contrary to this, in Ref. 5 the existence of similarity solution is denied by a simple and clear consideration. Here, for simplicity we restrict our attention to the vortex flow over an infinite flat surface, i.e., to the case when the vertex angle of a cone is equal to 180°. For this problem, even the complete Navier-Stokes equations have a similarity solution only for a limited range of the Reynolds number." In this Note, we attempt to solve the boundary-layer equations under the boundary condition of distributed suction, and show without any speculation to the singularity on the vortex axis that a formal similarity solution can be obtained for suction parameter greater than a certain value.


01 Jan 1971
TL;DR: In this article, an experimental program was conducted to investigate the modifications of a tip vortex which could be obtained by injecting the core of the tip vortex core with a stream of air.
Abstract: : An experimental program was conducted to investigate the modifications of a tip vortex which could be obtained by injecting the core of a tip vortex with a stream of air. Wind tunnel tests of an airfoil model were conducted. The results obtained from flow-visualization studies, balance data, and vortex-meter measurements show how the strength of the tip vortex can be reduced significantly by the injection of a linear mass flow of air into the core of the tip vortex. The reduction in drag obtained with injection is important since it allows the recovery of power required to inject the tip vortex core with mass flow.


01 Dec 1971
TL;DR: In this article, the authors determined the vortex shedding noise characteristics of isolated airfoils in a Reynolds number range applicable to full-scale helicopter rotors, and the frequency dependence of this noise on velocity and chord was found to be well predicted by a constant Strouhal number near 0.2 referenced to laminar wake thickness at the airfoil trailing edge.
Abstract: : The purpose of the study was to determine the vortex shedding noise characteristics of isolated airfoils in a Reynolds number range applicable to full-scale helicopter rotors. Measurements of far-field noise, airfoil surface pressure fluctuations, and correlation coefficients were obtained for three airfoils. Two models of differing thickness were tested as two-dimensional models (NACA 0012 and 0018 airfoils) and the third has a span of half the tunnel width (NACA 0012 airfoil). Airfoil vortex shedding noise was found to be discrete rather than broadband. The frequency dependence of this noise on velocity and chord was found to be well predicted by a constant Strouhal number near 0.2 referenced to laminar wake thickness at the airfoil trailing edge. The presence of a laminar boundary layer on the pressure surface of the airfoils was found to be critical to the presence of vortex shedding noise. (Author)

Journal ArticleDOI
TL;DR: In this article, local heat transfer coefficients to an airfoil in an oscillating stream have been measured for a range of frequencies and oscillation amplitudes for moderate angles of attack, including those associated with stall in steady flow.
Abstract: Local heat transfer coefficients to an airfoil in an oscillating stream have been measured for a range of frequencies and oscillation amplitudes. Results at moderate angles of attack are in agreement with previously reported findings. However, at large angles of attack, including those associated with stall in steady flow, a strong periodic starting vortex shed from the leading edge leads to a dramatic reattachment of the flow and consequent increase in local Nusselt Numbers of as much as five-fold. These effects are shown to be amplified by increasing oscillation frequency and amplitude.

Journal ArticleDOI
TL;DR: In this paper, steady axially symmetric small Rossby number flows in which the driving consists of prescribed axial heat sources are investigated, by letting the velocity be proportional to the shear at the bottom surface.
Abstract: We investigate steady axially symmetric small Rossby number flows in which the driving consists of prescribed axial heat sources. By letting the velocity be proportional to the shear at the bottom surface we study the effects of that boundary condition on the resulting flows. A multi-boundary-layer structure is found in the core, surrounding the heat sources. That structure depends on the relative magnitudes of the aspect ratio, stratification parameter and Ekman number.

Journal ArticleDOI
TL;DR: In this article, it was shown that the common analysis of centrifugal separators does not adequately predict the separation of small particles in j et-driven swirl separators, since the particle with a density much higher than that of the flow medium can move toward the vortex center instead of being separated.
Abstract: Two vortex experiments are cited that show that the common analysis of centrifugal separators does not adequately predict the separation of small particles in j et-driven swirl separators. The common analysis ignores the interference of the particle with the vortex flow in cases where the flow deviates from the solid vortex type. This interference, in connection with viscous effects, causes substantial fluid pressure forces opposing the separation of the particle. With the viscous effects approximated by analogy with straight flow conditions, the limit for the separation of particles in a free vortex is derived. It becomes apparent that particles with a density much higher than that of the flow medium can move toward the vortex center instead of being separated. In zones where the flow deviates from the free vortex conditions, the inward movement may be stopped resulting in the stabilization of the particles. The present considerations pertain quite generally to the movement of small particles in curved flow's.


01 Jan 1971
TL;DR: In this article, the effects of a drooped wing tip on its Trailing Vortex System were investigated. But the authors focused on the dynamics of the system and did not consider the effect of the drift of the wing tip in the wake of the aircraft.
Abstract: Keynote Address.- Aircraft Wakes: A New Look at a Classical Problem.- Fundamental Problems.- The Velocity of Viscous Vortex Rings.- Studies in the Motion and Decay of Vortices.- Transport of a Vortex Wake in a Stably Stratified Atmosphere.- Experimental Methods.- Split-Film Anemometer Sensors for Three-Dimensional Velocity-Vector Measurement.- Sub-Scale Modeling of Aircraft Trailing Vortices.- The Utility of Doppler Radar in the Study of Aircraft Wing-Tip Vortices.- Application of Laser Doppler Systems to Vortex Measurement and Detection.- Wake Formation and Character.- An Analysis of Flight Measurements in the Wake of a Jet Transport Aircraft.- Vortex Control.- The Effect of a Drooped Wing Tip on Its Trailing Vortex System.- Some Work at the Royal Aircraft Establishment on the Behaviour of Vortex Wakes.- Span Loading and Formation of Wake.- An Experimental Investigation of Trailing Vortices Behind a Wing with a Vortex Dissipator.- Vortex Wake Development and Aircraft Dynamics.- Measurements of Boeing 747, Lockheed C5A and Other Aircraft Vortex Wake Characteristics by Tower Fly-by Technique.- Flight Evaluation of the Wing Vortex Wake Generated by Large Jet Transports.- Stability and Decay.- An Assessment of Dominant Mechanisms in Vortex-Wake Decay.- Theoretical and Experimental Study of the Stability of a Vortex Pair.- Structure of a Line Vortex in an Imposed Strain.- A New Look at the Dynamics of Vortices with Finite Cores.- Decay of an Isolated Vortex.- Decay of a Vortex Pair Behind an Aircraft.- Results of Trailing Vortex Studies in a Towing Tank.- Interactions with Vortex Wakes.- Results of the Boeing Company Wake Turbulence Test Program.- Aircraft Response to Turbulence Including Wakes.- Airloads and Moments on an Aircraft Flying Over a Pair of Inclined Trailing Vortices.- Aircraft Wake Turbulence Controllability Experiment.- Fog Formation and Dispersal by Trailing Vortices.- An Estimate of the Power Required to Eliminate Trailing Vortices by Suction.- Panel Discussion.- Conclusions.- Author Index.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the geometry of the trailing vortex generated behind a jet-flapped wing and found that these vortices persist for some time and have maximum tangential velocities which increase linearly with the lift coefficient.
Abstract: : The purpose of the investigation was to measure the geometry of the trailing vortex generated behind a jet-flapped wing Such vortices can pose a serious hazard to aircraft that penetrate them Previous investigations performed on conventional wings indicate that these vortices persist for some time and have maximum tangential velocities which increase linearly with the lift coefficient As future aircraft may employ high lift devices such as jet-flapped wings, the vortices generated could be even stronger Two semispan models of a jet-flapped wing were tested in a subsonic wing tunnel Parameters varied during testing included the jet flap angle, angle of attack, aspect ratio, and jet momentum coefficient Vortex measurements were obtained using a vortex meter which measured the rotational speed of the fluid within the vortex Values obtained were numerically integrated to yield the tangential velocity and circulation distributed through the vortex Experimental results indicate that the maximum tangential velocity increases to a maximum and then decreases with continually increasing jet blowing At high values of jet blowing, the vortex was found to decay rapidly downstream (Author)