External Corners Research Articles

Simple layer potential method for domains having external corners

This note investigates the simple layer potential method for domains having external corners. The singular behaviour of simple layer density at the corners is studied for the Neumann problem of Helmholtz's equation. A numerical technique of solving the integral equation for this problem is proposed. This technique takes the singularity of the solution into consideration. Some numerical examples are given to show the applicability of the present method.

Numerical study of flowfields about asymmetric external conical corners

A numerical study of the flowfield about asymmetrical external axial corners formed by the juncture of swept compressive wedges is presented. The geometrical configuration allows a unified treatment of external corners typical of delta wings and rectangular inlets. The study investigates how the flow transitions from a symmetrical flowfield with a cross-flow stagnation point at the corner to an asymmetrical flowfield for which the flow spills over the corner. The effects of leading-edge sweep, wedge compression, and corner radius are investigated.

Potential flow near conical stagnation points

Flow patterns near conical stagnation points in supersonic flow have been investigated on the basis of potential flow. Near the conical stagnation point the nonlinear equation for the conical velocity potential reduces to the equation of Laplace. Solutions of the equation of Laplace for incompressible plane flow are then used as a guide to generate conical stagnation-point solutions. Apart from known types of streamline patterns, such as nodes and saddle points, new types are found. Among them are oblique saddle points, saddle-nodes, topological nodes and topological saddle points. They may be used to clarify certain questions in a number of practical conical-flow problems. The oblique saddle point may be used to describe the inviscid flow associated with flow separation and also certain features of the flow over an external corner. The saddlenode, being structurally unstable, may fall apart into a saddle and a node. It may then be used to interpret the lift-off phenomenon of the singularity in the flow around a circular cone at incidence as a bifurcation. Similarly, this may be done for the appearance of a dividing streamline in the same flow at still higher angles of incidence, where a vortex system is formed at the leeward side of the cone.

Careful Numerical Study of Flowfields about Symmetric External Conical Corners

A numerical study of the flowfield about asymmetrical external axial corners formed by the juncture of swept compressive wedges is presented. The geometrical configuration allows a unified treatment of external corners typical of delta wings and rectangular inlets. The study investigates how the flow transitions from a symmetrical flowfield with a cross-flow stagnation point at the corner to an asymmetrical flowfield for which the flow spills over the corner. The effects of leading-edge sweep, wedge compression, and corner radius are investigated.

Computation of the Viscous Supersonic Flow over External Axial Corners

The viscous supersonic flowfield surrounding symmetric and asymmetric swept external axial corners is computed using existing second-order, implict and explicit finite-difference computer codes. The governing partial differential equations in conservation-law form are hyperbolic with respect to time and are assumed to be conical; that is, any variation of the radial convective or diffusive terms is assumed to be negligible. An inviscid numerical study for symmetric 90 deg dihedral rounded corners reveals both single and triple crossflow stagnation point flows, depending on the corner radius of curvature. For asymmetrical 90 deg dihedral configurations (i.e., those obtained by varying one of the wedge angles), both single and triple stagnation point flows are also observed. For certain highly asymmetrical configurations, the inviscid flow spills over the corner and in so doing generates a local embedded supersonic bubble. Viscous numerical solutions are obtained for both symmetric and highly asymmetric axial corners for which experimental surface oil flow and vapor screen data are available. For the symmetric configuration, both the laminar and turbulent numerical solutions result in flow away from the corner, which agrees with the experimental data. For the highly asymmetrical configuration, the viscous numerical solution and the experimental data result in flow around the corner. The computed shock locations for both configurations agree fairly well with the experimental vapor screen results.

Structure of the Conical Flowfield about External Axial Corners

A theoretical and experimental investigation of the flowfield about symmetrical and asymmetrical external axial corners formed by the juncture of swept compressive wedges is presented. A study is made of the nature of inviscid conical cross-flow stagnation points, and the dependence of the streamline pattern on certain flow parameters is derived. The importance of imposing the physically relevant boundary condition for numerical simulations is discussed. For the asymmetrical wedge configuration, the proper boundary condition along the axial corner is shown to be a conical analog of Prandtl-Meyer flow. For the symmetrical configuration, a local solution of the irrotational equations is obtained. The solution is shown to be applicable to cones and internal and external corners. For symmetrical internal corners, the solution is unique; the corner is a nodal point of streamlines. The possible multiple solutions for external corners and cones are discussed. Further insight into the flow structure is revealed by the experimental results. The consistency of the derived flow models with the Euler limit of the Navier-Stokes equations is substantiated by the experimental data.

Obstacle detection using ambient or self-generated noise.

OBJECT ranging can be achieved by humans using the sound reflected or scattered from obstacles. For a range of wave-lengths short compared with the size of its surfaces, and long compared with the size of the irregularities in these surfaces, specular reflexion will be obtained and an acoustic image of the sound source will be formed analogous to an optical image. In many situations, however, such as the approach of an external corner, an acoustic image may not be audible from the observer's position. In these cases sound scattered from the edges and irregularities may, or frequently may not, give the necessary warning. Such signals are, however, weak compared with those of the acoustic image with which we are chiefly concerned.

Haemaphysalis megalaimae sp. n., a New Tick from the Small Green Barbet (Megalaima viridis) in India

Haemaphysalis megalaimae sp.n. is described from males, females, nymphs, and a larva collected from small green barbets (Megalaima viridis Boddaert) taken in Shimoga District, Mysore State, India. The species appears to be host-specific on the small green barbet. It is closely related to the Haemaphysalis hoodi-doenitzi-centropi group of bird parasitizing haemaphysalids but differs in several distinct morphological features. While studying ticks of birds of Shimoga District, Mysore State, South India, several adults, nymphs, and one larva of a distinctive Haemaphysalis tick were collected from the small green barbet Megalaima viridis. In consultation with Dr. Harold Trapido and Dr. Harry Hoogstraal these were recognized as close to, but differing from, Haemaphysalis centropi Kohls, 1949. The species has thus far been found only on one host species, Megalaima viridis, and is named for this genus of birds. In the following description measurements given are the averages from three specimens. Haemaphysalis megalaimae sp. n. Holotype: Male, A 27957, collected on small green barbet Megalaima viridis from Sagar (elevation approx 1,900 feet), 1 February 1960. Allotype: Female, A 36352, collected on Megalaima viridis from Gilalagundi (elevation approx 1,800 feet), 28 July 1960. Paratypes: Specimens listed in Table I other than the holotype and allotype. The holotype and allotype are deposited in the collection of the Rocky Mountain Laboratory, Hamilton, Montana. Paratypes will be deposited in the collections of the Zoological Survey of India, Calcutta, the Virus Research Centre, Poona, the British Museum (Natural History), and the collection of Harry Hoogstraal. Male (Figs. 1, 2, 5 to 8) Body: Length from tips of palpi to posterior margin, 1.62 mm. Width, 1.11 mm. Brownish yellow in color, ovoid, widest at about the level of the spiracle. Capitulum (Figs. 5, 6): Length from tips of palpi to tips of cornua, 0.37 mm. Length of basis, 0.17 mm. Width, 0.31 mm. Dorsal basis finely punctate, rectangular, lateral margins slightly divergent anteriorly, width about twice the length. Cornua moderate, sharp. Ventral basis broadly rectangular, with external corners rounded. Dorsal internal margins of palps straight. Palpal article 2 v ry salient laterally, flared, basal margin semicircular in outlin . Basal margin dorsally broken midway between inner and outer margins by commencement of more heavily chitinized distal portion of margin. Lateral margins acutely recurved from basolateral salience approximately to the level of juncture between articles 2 and 3, thence converging to moderately rounded apex. Palpal articles 2 and 3 subequal in length, dorsally and ventrally. A posteriorly directed short, broad, triangular, bladelike spur situated at the distal margin of palpal article 3 on the ventral side. Three to four infrainternal bristles on article 2 and two infrainternal bristles on article 3, situated near ventral spur. Hypostomal teeth 5/5 apically, diminishing to 3/3 proximally, about ten per file. Length of hypostome 0.17 mm. Scutum: Length, 1.41 mm. Punctations fine, numerous, and evenly distributed. Prominent lateral grooves, beginning at a point between legs II and III and continuing posteriorly across two festoons on either side. Scapulae acute. Cervical grooves moderate, deep anteriorly, and slightly diverging posteriorly. Festoons long, well separated, eleven in number. Spiracular plate (Fig. 7): Ovoid in shape, without dorsal process. Genital aperture: At level of coxa II. Legs: Coxae I to III with short ridgelike projections, that of coxa I larger and more prominent than II and III. Coxa IV with a short triangular spur. Distinct dorsal spur on trochanter I; trochanters I to III with weak ventral spurs, decreasing from I to III. Tarsi as illustrated in Figure 8. Received for publication 18 December 1962. * The Virus Research Centre is jointly maintained by the Indian Council of Medical Research and the Rockefeller Foundation.