5,543 research outputs found
A new solution-adaptive grid generation method for transonic airfoil flow calculations
The clustering algorithm is controlled by a second-order, ordinary differential equation which uses the airfoil surface density gradient as a forcing function. The solution to this differential equation produces a surface grid distribution which is automatically clustered in regions with large gradients. The interior grid points are established from this surface distribution by using an interpolation scheme which is fast and retains the desirable properties of the original grid generated from the standard elliptic equation approach
A consistent spatial differencing scheme for the transonic full-potential equation in three dimensions
A full-potential steady transonic wing flow solver has been modified so that freestream density and residual are captured in regions of constant velocity. This numerically precise freestream consistency is obtained by slightly altering the differencing scheme without affecting the implicit solution algorithm. The changes chiefly affect the fifteen metrics per grid point, which are computed once and stored. With this new method, the outer boundary condition is captured accurately, and the smoothness of the solution is especially improved near regions of grid discontinuity
Evaluation of Navier-Stokes and Euler solutions for leading-edge separation vortices
Extensive study on the numerical simulation of the vortical flow over a double delta wing is carried out using the thin layer Navier-Stokes and Euler equations. Two important flow characteristics, vortex interaction and vortex breakdown, are successfully simulated. Grid resolution is one of the most important factors associated with the vortex problem. Computations were performed on a series of grids with various levels of refinement, coarse, medium, and fine. Computations using either the coarse or medium grids fail to capture the proper physical phenomena. The computed result using a fine grid shows flow unsteadiness once the vortex breakdown takes place. The C sub L - alpha characteristics are well predicted up to the breakdown angle of attack for all the grid distributions. The Euler solutions show fairly good agreement with the experiment on the C sub L - alpha characteristics. However, other aspects of the solution at each angle of attack, such as the locus of the leading edge separation vortex, are not consistent with the experiment. Even for the fine grid Navier-Stokes computations, further grid resolution is required to obtain good quantitative agreement with the experiment
Making Anti-de Sitter Black Holes
It is known from the work of Banados et al. that a space-time with event
horizons (much like the Schwarzschild black hole) can be obtained from 2+1
dimensional anti-de Sitter space through a suitable identification of points.
We point out that this can be done in 3+1 dimensions as well. In this way we
obtain black holes with event horizons that are tori or Riemann surfaces of
genus higher than one. They can have either one or two asymptotic regions.
Locally, the space-time is isometric to anti-de Sitter space.Comment: LaTeX, 10 pages, 6 postscript figures, uses epsf.te
Recent applications of the transonic wing analysis computer code, TWING
An evaluation of the transonic-wing-analysis computer code TWING is given. TWING utilizes a fully implicit approximate factorization iteration scheme to solve the full potential equation in conservative form. A numerical elliptic-solver grid-generation scheme is used to generate the required finite-difference mesh. Several wing configurations were analyzed, and the limits of applicability of this code was evaluated. Comparisons of computed results were made with available experimental data. Results indicate that the code is robust, accurate (when significant viscous effects are not present), and efficient. TWING generally produces solutions an order of magnitude faster than other conservative full potential codes using successive-line overrelaxation. The present method is applicable to a wide range of isolated wing configurations including high-aspect-ratio transport wings and low-aspect-ratio, high-sweep, fighter configurations
Black Holes and Wormholes in 2+1 Dimensions
A large variety of spacetimes---including the BTZ black holes---can be
obtained by identifying points in 2+1 dimensional anti-de Sitter space by means
of a discrete group of isometries. We consider all such spacetimes that can be
obtained under a restriction to time symmetric initial data and one asymptotic
region only. The resulting spacetimes are non-eternal black holes with
collapsing wormhole topologies. Our approach is geometrical, and we discuss in
detail: The allowed topologies, the shape of the event horizons, topological
censorship and trapped curves.Comment: 23 pages, LaTeX, 11 figure
De Sitter Space and Spatial Topology
Morrow-Jones and Witt have shown that generic spatial topologies admit
initial data that evolve to locally de Sitter spacetimes under Einstein's
equations. We simplify their arguments, make them a little more general, and
solve for the global time evolution of the wormhole initial data considered by
them. Finally we give explicit examples of locally de Sitter domains of
development whose universal covers cannot be embedded in de Sitter space.Comment: 21 pages, 7 figure
TAIR: A transonic airfoil analysis computer code
The operation of the TAIR (Transonic AIRfoil) computer code, which uses a fast, fully implicit algorithm to solve the conservative full-potential equation for transonic flow fields about arbitrary airfoils, is described on two levels of sophistication: simplified operation and detailed operation. The program organization and theory are elaborated to simplify modification of TAIR for new applications. Examples with input and output are given for a wide range of cases, including incompressible, subcritical compressible, and transonic calculations
One-dimensional conduction in Charge-Density Wave nanowires
We report a systematic study of the transport properties of coupled
one-dimensional metallic chains as a function of the number of parallel chains.
When the number of parallel chains is less than 2000, the transport properties
show power-law behavior on temperature and voltage, characteristic for
one-dimensional systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Examination of smears for tubercle bacilli by Fluorescence Microscopy
IN underdeveloped countries, laboratory facilities for the bacteriological
diagnosis of tuberculosis are at present, very limited. Cultural methods are
unlikely to be used on a large scale for many years to come. It is, therefore, important to
investigate the most economical method of examining smears for
tubercle bacilli. Fluorescence microscopy was introduced by Hagemann (1937)
and has since been described by many authors, including Tanner (1941, 1948), Lind
and Shaughnessy (1941), Lempert (1944), Norman and Jelks (1945), Clegg and
Foster-Carter (1946), Wilson (1952), Von Haebler and Murray (1954), and Needham
(1957). The great advantage claimed for this method is that stained bacilli can be
detected using a much lower magnification than with the usual Ziehl-Neelsen
method. Considerable time is saved in examining smears and larger areas can be
searched. The method has not been widely employed for two reasons. In the
first place, the light source must be very bright and many of the optical systems
described previously have only supplied sufficient light if the equipment was used in
a darkened room. Secondly, some workers (Ritterhoff and Bowman, 1945; Kuster,
1939; Holm and Plum, 1943) consider that false positive results can be obtained,
since some smears may contain small naturally fluorescent particles which can be
confused with bacilli.
Equipment for fluorescence microscopy that can be used in normal daylight
has been in use at the Tuberculosis Chemotherapy Centre, Madras, for over two
years. When it was first introduced, a comparison between this method and the
conventional Ziehl-Neelsen method was undertaken to test their relative sensitivities,
and to see whether fluorescence microscopy yielded false positive results.
The results of this comparison are described
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