Showing papers on "Starting vortex published in 1979"

On the formation of vortex rings: Rolling-up and production of circulation

Abstract: The temporal development of the rolling-up process of vortex rings produced in water at a circular nozzle is investigated by flow visualization. The results are compared with similarity laws for the rolling-up of vortex sheets in plane flow. The unsteady flow field in the nozzle-exit plane is measured by laser anemometry. The vorticity distribution in the boundary layers at the inner and outer nozzle wall and the vorticity flux through the exit plane are derived from the measurements. The flow conditions measured at the nozzle are used to explain the production of the ring-vortex circulation (measured three nozzle-diameters downstream) in relation to the generation conditions.

On the evolution of isolated, nonlinear vortices

Abstract: The evolution of an isolated, axially symmetric vortex is calculated with a quasi-geostrophic, adiabatic, hydrostatic. β-plane, two vertical mode model. The circumstances of greatest interest are those of weak friction and large vortex amplitude (strong nonlinearity). Systematic studies are made of the consequences of varying the frictional coefficient, the vortex amplitude, the vortex radius (relative to the deformation radius), the degree of nonlinear coupling between the two vertical modes and the initial vertical structure of the vortex. Results of note include the following. Within the approximation of a single vertical mode model (i.e., in the absence of modal coupling), a baroclinic vortex has an increased westward and a finite meridional propagation speed when its amplitude is greater than infinitesimal. Both of these speeds, however, are limited by the wave speeds (as determined from infinitesimal amplitude theory) of the weak dispersion field outside the vortex. The vortex amplitude dec...

Characteristics of Tornado-Like Vortices as a Function of Swirl Ratio: A Laboratory Investigation

Abstract: The investigation of tornado vortex dynamics by means of a laboratory simulation is described. Based on observations from nature and an examination of the Navier-Stokes equations, a laboratory simulator of the Ward type has been constructed. This simulator generates various vortex configurations as a function of swirl ratio, radial Reynolds number and aspect ratio. Configurations which are described are 1) a single laminar vortex; 2) a single vortex with breakdown bubble separating the upper turbulent region from the lower laminar region; 3) a fully developed turbulent core, where the breakdown bubble penetrates to the bottom of the experimental chamber; 4) vortex transition to two intertwined helical vortices; and 5) examples of higher order multiple-vortex configurations that form in the core region. Hot-film anemometry measurements of the magnitude of the velocity vector and inflow (swirl) angle have been obtained in a sequence of flows characterized by progressively increasing values of swirl...

Axial flow in trailing line vortices

Abstract: Axial flow in the core of a laminar steady trailing vortex from the tip of a semi‐infinite wing is analyzed assuming small departure of the axial velocity from the free‐stream velocity. It is further assumed that the axial pressure gradient is determined by the swirl velocities of an ideal infinite line vortex in which the radial and the associated axial velocity variations are neglected in the equation for the angular momentum. The axial and lateral variations of the axial velocity depend on the strength of the vortex and initial axial velocity distribution which must be specified at some station behind the wing except at the virtual origin of the vortex where a nonintegrable singularity exists. Numerical solutions for the axial velocity are obtained using the axial pressure gradient given by the line vortex and analytical solutions are obtained using an equivalent axial pressure gradient with good agreement between the two sets of axial velocity distributions. Resolution of the previous uncertainties in this field is given which were due to the unrecognized singularity at the virtual origin of the vortex. Using the calculated axial velocity the neglected radial and the associated axial fluxes of angular momentum are determined and the limits of validity of the theory presented here in terms of a suitably defined vortex Reynolds number and a nondimensional distance measured from the virtual origin of the vortex are given.

Inviscid Model of Two-Dimensional Vortex Shedding by a Circular Cylinder

Abstract: A discrete vortex model based on potential flow and boundary-layer interaction, rediscretization of shear layers, and circulation dissipation is developed to determine the characteristics of an impulsively started flow about a circular cylinder. The evolution of the flow from the start to very large times, lift and drag forces, Strouhal number, oscillations of the separation and stagnation points, and the vortex-street characteristics are calculated and compared with experiments. b CD CL Cpb c D fv h / j m N n q Re St s ds t At U u v w z F 7 6 X v p Nomenclature = longitudinal spacing of vortices = drag coefficient = lift coefficient = base pressure coefficient = radius of the cylinder - diameter of the cylinder ,D = 2c = vortex shedding frequency = transverse spacing of vortices = an index = distance to nascent vortex from cylinder = number of vortices on a sheet = an index = total velocity at a point = Reynolds number, UD/v = Strouhal number, fvD/ U = distance along a sheet = point vortex spacing = time or Ut/c for U= 1 and c = 1 - numerical step size = velocity of the ambient flow = x component of velocity -y component of velocity = complex velocity potential = complex variable = circulation = circulation per unit length = angle measured from ( - c,0) = dissipation parameter = kinematic viscosity of fluid = density of fluid = vorticity

A Study in Tornado-Like Vortex Dynamics

Abstract: Fine-resolution calculations using an axisymmetric numerical model of the flow within a Ward-type vortex chamber are discussed. Particular attention is paid to the vortex-ground interaction. Variations in the swirl ratio S from zero to unity lead to radically different vortex structure in the “corner” region (i.e., near r = z = 0). For S Lt; 1, a concentrated vortex forms in the upper chamber but not in the corner. At moderate S, we observe vortex breakdown, large-amplitude inertial waves, and very intense swirling motion in the corner. When S = 1, the central downdraft penetrates to the lower surface and the vortex breakdown occurs within the boundary layer. These results are consistent with experimental observations and suggest the explanation of a number of observed facets of tornadoes.

Formation of a Trailing Vortex

Abstract: The incompressible flowfield in the vicinity of a l ift ing rectangular finite wing is investigated experimentally to ascertain the nature and detailed characteristics of the formation of a trailing vortex. The mean velocity field was mapped directly using a linearized constant temperature hot-wire anemometry probe in conjunction with a precision wind-tunnel traversing mechanism. The associated vorticity field was inferred from these measurements through a spatial contour integration procedure. The existence of several identifiable flow regions exhibiting similar characteristics was established and verified with both hot-wire and flow visualization data. The nature of the near surface bound vorticity distribution is described including a map of the Prandtl-bound vortex filaments. Measurements at the wing trailing edge show that the properly nondimensionalized characteristic vorticity distribution in this region is independent of angle of attack. Shed vorticity emanating from the lower aerodynamic surface near the wing tip was observed to roll up adjacent to the tip and roll over onto the upper wing surface at a chordwise location which depends on the wing orientation. The presence and behavior of this structure which possesses an identifiable core is suggested as the cause of the modified pressure distribution (l ift increment) normally observed in this region.

Mutual slip‐through of a pair of vortex rings

Abstract: Mutual slip‐through of two identical vortex rings, traveling along a common axis in the same direction, was experimentally achieved in air at various Reynolds numbers between 800 and 2000 and observed by using the smoke wire technique and cigarette smoke. The motions of a pair of vortices agree very well with an approximate potential theory based on the Biot–Savart law.

Vortex fuel air mixer

Abstract: A vortex fuel air mixer is positioned between the air throttle and the intake manifold of an engine. Part of the expansion flow velocity past the air throttle flows tangentially into the vortex chamber of the mixer, providing angular momentum which drives the flow into a vortical pattern. The flow streamlines within the vortical flow form into a generally irrotational flow pattern which swirls from the outside wall of the vortex chamber inwardly to a central vortex chamber outlet. This outlet feeds the engine intake manifold. Centrifugal forces in the swirling flow fling fuel droplets to the outside wall of the vortex chamber (in the manner of a cyclone scrubber). This liquid fuel must evaporate in order to leave the vortex chamber. The interaction of the evaporation, flow structure and turbulence relations inside the vortex chamber produces an essentially homogeneous mixture at the vortex chamber outlet. Fuel evaporation time in the vortex chamber is quite short, so that the device exhibits excellent transient response.

Shapes for rotating airfoils

Abstract: This invention is an airfoil which has particular application to the blade or blades of rotor aircraft and aircraft propellers. The airfoil thickness distribution, camber and leading edge radius is shaped to locate the airfoil crest at a more aft position along the chord, and to increase the freestream Mach number at which sonic flow is attained at the airfoil crest. The upper surface of the airfoil has a general reduction in the surface slope back to the maximum ordinate which is about 40 percent of the airfoil chord. The reduced slope causes a reduction in velocity at the airfoil crest at lift coefficients from zero to the maximum lift coefficient. The leading edge radius is adjusted or shaped so that the maximum local Mach number at 1.25 percent chord and at the designed maximum lift coefficient is limited to about 0.48 when the Mach number normal to the leading edge is approximately 0.20. The lower surface leading edge radius is shaped so that the maximum local Mach number at the leading edge is limited to about 0.29 when the Mach number normal to the leading edge is approximately 0.20 and the lift coefficient is in the range of 0.0 to -0.2. This design moves the drag divergence Mach number associated with the airfoil to a higher Mach number over a range of lift coefficients resulting in superior aircraft performance.

On sound radiation from the trailing edge of an isolated airfoil in a uniform flow

Abstract: An experimental investigation has been conducted to determine the physical process of the noise production from the trailing edge of an isolated two-dimensional airfoil embedded in a low turbulence uniform mean flow. The Reynolds number of the airfoil based on chord was greater than 1,000,000 and that the boundary layer was fully turbulent at the trailing edge. Smoke injection technique and spark shadowgraphy were used to study the structural features of the boundary layer. Two point joint statistical analyses were made on the surface pressure, the radiated sound and the relationship between the two quantities. Operating conditions included two free stream velocities and two angles of attack for both a naturally developed and an artificially tripped boundary layer. Flow visualizations revealed the existence of large scale coherent motions in the outer region of the boundary layer. The observed coherent motions had scales of the order of boundary layer thickness and a convection velocity near the free stream velocity. The production process of the airfoil trailing edge noise was determined to be the convection of the large scale coherent eddies over the trailing edge of the airfoil. The noise field so generated was found to be rather coherent and dipole-like.

Fluid flow measuring apparatus

Abstract: A Karman vortex type flow rate measuring apparatus is provided with a plurality of vortex shedding members each having a different effective width, and a plurality of vortex detecting elements The distance between the vortex detecting elements is so selected that it coincides with the distance between the vortices of some one of the vortex trains induced by respective vortex shedding members The apparatus enables a positive and accurate detection of the vortices, and a compensation for drop out of the vortex shedding

Measured wake-vortex characteristics of aircraft in ground effect

Abstract: In support of the NASA wake vortex alleviation program, measurements were made of the influences of a ground plane on vortex trajectories and velocity profiles within lift-generated wakes. The wakes were generated by towing 0. 61-m (2-ft) span models of a B-747 and DC-10-30 under water in a ship model basin. The models were configured with landing flaps and flight spoilers to investigate the wake characteristics of these aircraft in ground effect at simulated full-scale distances of 19-116 m (62-380 ft) above the ground. The ground plane caused modifications in the vortex trajectories but did not alter vortex interactions and merging patterns in these multiple vortex wakes. Some distortions in vortex vertical (tangential) velocity profiles were recorded as a result of vortex lateral motions and vortex interactions with the viscous boundary layer on the ground plane; however, maximum tangential velocities remained unchanged.

Karman vortex flow meter

Abstract: PURPOSE:To improve instrumentation precision by increasing the resolution of a Karman vortex street by controlling the generation state of a vortex by arranging not less than two Karman vortex generating element plates at a desired interval behind a Karman vortex generating element rod CONSTITUTION:Inside flow-meter main body 2 equipped in duct 1, triangular vortex generating element rod 3 is provided and not less than two plate-shaped vortex generating element boards 5 of the same width as rod 3 are independently arranged at a fixed interval behind it This constitution generates an excellent Karman vortex under broad measurement conditions where the flow rate and flow velocity of a fluid are changeable As a result, the resolution is improved and the shape of vortex generating element rod 3 and the number and arrangement state of vortex generating element plates 5 are adequately set within the range of more than two in number so as to realize accurate instrumentation; and the structure is simple and various fluids can be measured Further, a closed pipe and open channel can be used for the duct

Observations of the Oscillatory Behavior of a Confined Ring Vortex

Abstract: Ring chambers with annular inflow and outflow through a radial exit tube find wide application in axial-flow turbomachinery as exit chambers to collect and divert the throughflow off-axis. Visual observations and detailed measurements of the flow in an idealized model exit chamber reveal that the flow in the ring is dominated by the vortex generated by the annular inflow. Coriolis forces, arising as a result of the longitudinal curvature imposed on the basic swirling flow, cause the vortex to adopt a helical form within the confines of the ring. Also, an interaction between the two ends of the vortex within the exit tube gives rise to oscillations of the flow which are strongly periodic for certain values of the ratio of the annular width t to the ring radius R. The periodic oscillations are characterized by a constant Strouhal number//?/ ^«0.03, where/is the fundamental frequency and V the inflow velocity. Although the flow oscillations can be suppressed by installing a splitter plate in the exit tube, when the vortex ends are separated and so cannot interact, the splitter plate has no direct influence on the vortex, the spatial structure of which is largely unaltered.

The prediction of two-dimensional airfoil stall progression

Abstract: A generalized boundary condition potential flow calculation method was combined with a momentum integral boundary layer method and a base flow theory of separation to predict airfoil viscous-inviscid interference up to and beyond stall. The resultant program considers laminar and turbulent separation and is, therefore, applicable to thin or thick airfoil stall. The calculated flow field includes the airfoil and the separation bubble recombination region behind the airfoil. Calculated pressure distributions and equivalent airfoil shapes, including the displacement thickness of the viscous regions, are compared with flow field measurements for several airfoils. The measured displacement thicknesses and wake centerlines corroborate the calculated shape. The comparison also suggests the use of the analytical solution to evaluate the measurements.

Fuel/air mixing device for engines

Abstract: A vortex fuel air mixer is positioned between the air throttle (4) and the intake manifold of an engine. Part (20,22) of the expansion flow velocity past the air throttle (4) flows tangentially into the vortex chamber (18) of the mixer, providing angular momentum which drives the flow into a vortical pattern. The flow streamlines within the vortical flow form into a generally irrotational flow pattern which swirls from the outside wall of the vortex chamber (18) inwardly to a central vortex chamber outlet (32). This outlet feeds the engine intake manifold. Centrifugal forces in the swirling flow fling fuel droplets to the outside wall of the vortex chamber (18) (in the manner of a cyclone scrubber). This liquid fuel must evaporate in order to leave the vortex chamber.

The static pressure in a vortex core

Abstract: Vortices are of interest in many situations in fluid mechanics. One type of vortex with which the gas turbine designer is concerned is the line vortex springing like a miniature tornado from a point on the ground (or from a nearby aircraft surface) and entering the engine intake. It is possible for these vortices to suck stones up into the engine (Refs. 1, 2) and also to reduce the compressor surge margin (Refs. 3, 4). They are unsteady, in that their point of origin wanders about and so does their point of entry into the intake. This unsteadiness makes it very difficult to measure them, and so far no one known to the author has reported measurements of ground vortex strength, in the course of several investigations of the phenomenon (Refs. 1-3, 5-8).

Sound diffraction at a trailing edge

Abstract: The diffraction of externally generated sound in a uniformly moving flow at the trailing edge of a semi-infinite flat plate is studied. In particular, the coupling of the sound field to the hydrodynamic field by way of vortex shedding from the edge is considered in detail, both in inviscid and in viscous flow. In the inviscid model the (two-dimensional) diffracted fields of a cylindrical pulse wave, a plane harmonic wave and a plane pulse wave are calculated. The viscous process of vortex shedding is represented by an appropriate trailing-edge condition. Two specific cases are compared, in one of which the full Kutta condition is applied, and in the other no vortex shedding is permitted. The results show good agreement nith Heavens' (1978) observations from his schlieren photographs, and confirm his conclusions. It is further demonstrated, by an explicit expression, that the sound power absorbed by the wake may be positive or negative, depending on Mach number and source position. So the process of vortex shedding does not necessarily imply an attenuation of the sound. In the viscous model a high-Reynolds-number approximation is constructed, based on a triple-deck boundary-layer structure, matching the harmonic plane wave outer solution to a known incompressible inner solution near the edge, to obtain the riscous correction to the Kutta condition.

A Study of Scattering, Production, and Stimulated Emission of Sound by Vortex Flows

Abstract: The basic theory of aeroacoustics of homentropic fluid media is applied to the problems of sound scattering, production, and stimulated emission. A general theory of scattering from low speed three-dimensional vortex flows is presented. Specific results are given for the horseshoe vortex and vortex ring. The noise of an elementary corotating vortex pair in various flows is calculated. It is shown that a potential flow and shear flow can substantially increase the basic pair noise. Small reverse shears can annihilate vortex pairs and eliminate the pair noise mechanism. The pair results are used to explain qualitatively the operation of noise suppression devices. The stimulated emission of a single vortex pair and four and six vortex arrays is demonstrated. The results for six vortices illustrate how external pure tones can amplify the broadband noise of a jet in agreement with recent experimental evidence.

An Investigation of Separation Models for the Prediction of Cl sub max.

Abstract: : Steady and unsteady analyses and computational methods have been developed for calculating the flow about two-dimensional airfoils up to and beyond the stall The steady-flow method adopts an iterative procedure between the potential flow an d boundary layer solutions The separated region is modeled in the potential flow analysis using free vortex sheets which require an inner iteration to establish their shapes The free vortex sheet length is an important parameter in the potential flow calculation Calculated and experimental results are compared for a GA (W) -1 airfoil and for several NACA airfoil series over a range of Reynolds numbers The calculated results, which include pressure, distributions as well as force and moment characteristics, are in very close agreement with experimental results, and are obtained for reasonable computing costs; typically, one incidence data point takes 15 to 20 cp seconds on a CDC 7600 computer

Simulation of the Pressure Field Near a Jet by Randomly Distributed Vortex Rings

Abstract: Fluctuations of the pressure field in the vicinity of a jet are simulated numerically by a flow model consisting of axially symmetric vortex rings with viscous cores submerged in a uniform stream. The time interval between the shedding of successive vortices is taken to be a random variable with a probability distribution chosen to match that from experiments. It is found that up to 5 diameters downstream of the jet exit, statistics of the computed pressure field are in good agreement with experimental results. Statistical comparisons are provided for the overall sound pressure level, the peak amplitude, and the Strouhal number based on the peak frequency of the pressure signals.

Investigation of Stable Atmospheric Stratification Effect on the Dynamics of Descending Vortex Pairs

Abstract: The physics of vortex flows in stratified fluids is studied with the objective of determining the influence of stable stratification on the descent of aircraft vortex pairs. Vortex rings descending into linear and discontinuous density stratifications are investigated experimentally and simulated numerically. The computer code used for this is based on a second-order closure turbulence model of the Reynolds stress equations in axisymmetric coordinates. Verification of the code is provided by the agreement found between the measured and calculated results. The two-dimensional version of the code is then used to simulate a measured Boeing-747 vortex descending in stable stratification. The strength and tightness of the measured vortex cores have necessitated developedment of a new method of numerically calculating strong vortex flows. The comparison of measured with calculated descent velocity, descent distance, swirl velocity, and circulation in the vortex is in agreement. It is concluded that turbulence effects must be accounted for in the study of aircraft vortex behavior. It is found that unaleviated vortices remain strong during descent, that the vortices stop descending due to a diffuse region of countersign vorticity outboard and above the cores, and that core separation does not primarily control descent. (Author)

Vortex Effects Resulting From Transverse Injection in Turbine Cascades, and Attempts at Their Reduction

Abstract: A preliminary experimental investigation has been made of the effects of vortices in the approach stream on turbine blade row performance. The vortex regime has been simulated by stationary vortex generators. The net pressure losses within the following blade row were reduced by 23 and 12 percent when the vortex generators were placed in line, respectively, with the mid-passages and with the leading edges. Further, the discrete inlet vortices had virtually disappeared at the exit plane. In addition, methods have been tested for reducing the exit vortex, particularly when enhanced by transverse injection. The most effective scheme examined was a fence location on the suction surface near the endwall. However, there is a pressure loss penalty.Copyright © 1979 by ASME