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Showing papers on "Starting vortex published in 1968"


Journal ArticleDOI
TL;DR: In this article, a study has been made of the varicose instability of an axisymmetrical jet with a velocity distribution radially uniform at the nozzle mouth except for a laminar boundary layer at the wall.
Abstract: A study has been made of the varicose instability of an axisymmetrical jet with a velocity distribution radially uniform at the nozzle mouth except for a laminar boundary layer at the wall. The evolutionary phenomena of instability, such as the rolling up of the cylindrical vortex layer into ring vortices, the coalescence of ring vortex pairs, and the eventual disintegration into turbulent eddies, have been investigated as a function of the Reynolds number using smoke photography, stroboscopic observation, and the light-scatter technique.Emphasis has been placed on the wavelength with maximum growth rate. The jet is highly sensitive to sound and the effects of several types of acoustic excitation, including pure tones, have been determined.

241 citations




Patent
06 Mar 1968

10 citations



ReportDOI
01 Jun 1968
TL;DR: In this paper, the kinematics of the motion of trailing vortex sheets in the wake of a propeller and the dynamics of the tip vortex were investigated for a lifting line wing model and results applied to propeller theory.
Abstract: : This report concerns the kinematics of the motion of trailing vortex sheets in the wake of a propeller and the dynamics of the tip vortex. The problem is solved numerically for a lifting line wing model and the results applied to propeller theory. Special consideration is given to the subjects of tip vortex cavitation, changes in loading on a blade due to rollup of the trailing vortex sheet, and the trajectory of the tip vortex. Experimental confirmation was obtained for the pressure at which cavitation appeared and the motion of the vortex sheet through testing a hydrofoil in a propeller tunnel.

4 citations


Journal ArticleDOI
TL;DR: In this article, a thin airfoil theory is developed for airfoils spanning a slowly diverging or converging channel, the motivation being to predict, theoretically, the effect of varying axial velocity on the cascade performance of axial flow compressor rows.
Abstract: A thin airfoil theory is developed for airfoils spanning a slowly diverging or converging channel, the motivation being to predict, theoretically, the effect of varying axial velocity on the cascade performance of axial flow compressor rows.

3 citations



01 Dec 1968
TL;DR: In this article, the authors present a model of the tip vortex line of a helicopter rotor, which is best represented by a vortex line with a finite vortex core where viscous effects dominate, and is responsible for the sharp peaks in the rotor airloads distribution.
Abstract: : The wake of a helicopter rotor consists of a relatively concentrated tip vortex generated by the rapid decrease in bound circulation at the tip of the rotor blade and distributed vortex sheets generated by spanwise variation of the bound circulation over the inboard portion of the blade (the inboard trailing wake) and by azimuthal variations of the bound vorticity (the shed wake). The tip vortex, because of its concentration, is best represented by a vortex line, with a finite vortex core where viscous effects dominate, and is responsible for the sharp peaks in the rotor airloads distribution. Thus accurate geometry is much more important for the tip vortex than for the rest of the wake and effort has been concentrated on the accurate and efficient computation of the tip vortex geometry.

2 citations


Journal ArticleDOI
TL;DR: In this article, the modifications that must be made to two-dimensional calculations of the flow past an airfoil when the flow takes place in a symmetric channel with slightly non-parallel walls are investigated.
Abstract: An investigation is presented of the modifications that must be made to two-dimensional calculations of the flow past an airfoil when the flow takes place in a symmetric channel with slightly non-parallel walls.

1 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that a vortex, which is formed at one edge of the sample, moves across it, and is destroyed at the other edge, has a ''zipper'' effect on the phase of the order parameter.
Abstract: Electrical resistance observed1 in superconductors in the mixed state is interpreted as a measure of the motion of Abrikosov vortices in a direction transverse to the imposed net current. Additional evidence of flow of vortices has been provided by dc transformer action2,3 and by heat transport4 in the direction of vortex flow. The connection between the resistive voltage drop and the flow of vortices is understood5 in terms of the superconducting order parameter, which is a complex number varying in space and time. A vortex, which is formed at one edge of the sample, moves across it, and is destroyed at the other edge, has a ``zipper'' effect on the phase of the order parameter. On one side of the path of the vortex, the phase is raised by π (for a single quantum vortex); on the other side it is lowered by the same amount. This process makes no net change in the physical state of the sample; yet it requires a pulse of voltage difference between the ends of the sample, because the time derivative of phase of the order parameter is proportional6 to electrostatic potential (more generally, to the chemical potential for electrons). A state of steady flow of vortices thus involves a steady difference of potential between the ends of the sample. A voltmeter registers this difference. There is no net induced emf to be registered. The dissipation associated with the electrical resistance of a sample in which there is vortex flow occurs in the form of Joule heating produced by normal (i.e., nonsuper) currents.7 Most of this dissipation is in the cores of the vortices, where the material is at least approximately normal and where the electric field is strongest. The electric field in a moving core is partly induced magnetically but is mostly the gradient of electrostatic potential which is associated with the rapid changes of order parameter on opposite sides of the core. A moving vortex not only produces heat but also carries heat along with it, transversely to the electric current and to the magnetic field. A plausible model for the mechanism of this heat transport is based on the available excited states of the superconducting system of electrons as described by BCS. Each available level has a thermal probability of being occupied. The spectrum of levels available varies from place to place in the material according to the local value of the energy gap, which practically vanishes in the core of each vortex, but is significantly large between cores. A particular excitation can migrate only in regions where the energy gap is less than the excitation energy. Each low‐energy excitation is therefore trapped, rattling about within a definite core. When a core moves, the trapped excitations are carried along. When a vortex is eventually destroyed at the edge of the sample, its trapped excitations are stranded at the last position of the core. As the gap there goes up, so does the energy of each excitation. The excitation probability which corresponded to thermal equilibrium at the orignal energy is excessive at higher energies. Until the energy becomes so great that the excitation is no longer trapped, the excitation probability can readjust only by a net probability of conversion of energy from the electronic excitation into lattice heat. Similarly, when a vortex is formed, its core absorbs heat from the lattice. The net result is transportation of heat from the location of formation to the location of destruction. The detailed mechanisms by which forces are applied to vortices remain obscure. But by thermodynamic arguments8 we find a force in the direction of j×B due to net electrical current and a thermal force in the direction of − ▿T. In a superconductor in which the pinning of vortices is slight, we should be able (at least as laboratory curiosities) to use vortex flow as the basis of an electrically driven low‐temperature refrigerator and of a thermally driven source of electrical energy.

01 Apr 1968
TL;DR: Wall injection area and axial bypass effects on flow pattern of stagnation surface in radial inflow vortexes were studied in this paper, where the authors showed that the wall injection area can affect the flow pattern.
Abstract: Wall injection area and axial bypass effects on flow pattern of stagnation surface in radial inflow vortexes