1,015 research outputs found
Computational fluid dynamics applications at McDonnel Douglas
Representative examples are presented of applications and development of advanced Computational Fluid Dynamics (CFD) codes for aerodynamic design at the McDonnell Douglas Corporation (MDC). Transonic potential and Euler codes, interactively coupled with boundary layer computation, and solutions of slender-layer Navier-Stokes approximation are applied to aircraft wing/body calculations. An optimization procedure using evolution theory is described in the context of transonic wing design. Euler methods are presented for analysis of hypersonic configurations, and helicopter rotors in hover and forward flight. Several of these projects were accepted for access to the Numerical Aerodynamic Simulation (NAS) facility at the NASA-Ames Research Center
Measurements of Turbulent Skin Friction on a Flat Plate at Transonic Speeds
The present report describes the design and construction of a floating-element skin-friction balance. This instrument, which is essentially an improved version of Dhawan's balance, was applied to measurements of local skin friction in the turbulent boundary layer of a smooth flat plate at high-subsonic Mach numbers and supersonic Mach
numbers up to 1.75. The measured skin-friction coefficients are consistent with the results of other investigations at subsonic and also at supersonic speeds. The principal difficulties which exist in comparing
skin-friction coefficients at various Mach numbers are discussed
Trapping of 27 bp - 8 kbp DNA and immobilization of thiol-modified DNA using dielectrophoresis
Dielectrophoretic trapping of six different DNA fragments, sizes varying from
the 27 to 8416 bp, has been studied using confocal microscopy. The effect of
the DNA length and the size of the constriction between nanoscale fingertip
electrodes on the trapping efficiency have been investigated. Using finite
element method simulations in conjunction with the analysis of the experimental
data, the polarizabilities of the different size DNA fragments have been
calculated for different frequencies. Also the immobilization of trapped
hexanethiol- and DTPA-modified 140 nm long DNA to the end of gold
nanoelectrodes was experimentally quantified and the observations were
supported by density functional theory calculations.Comment: 17 pages (1 column version), 8 figure
Theoretical and Experimental Investigation of Random Gust Loads Part I : Aerodynamic Transfer Function of a Simple Wing Configuration in Incompressible Flow
Sinusoidally oscillating downwash and lift produced on a simple rigid airfoil were measured and compared with calculated values. Statistically stationary random downwash and the corresponding lift on a simple rigid airfoil were also measured and the transfer functions between their power spectra determined. The random experimental values are compared with theoretically approximated values. Limitations of the experimental technique and the need for more extensive experimental data are discussed
Is there screwiness at the end of the QCD cascades?
We discuss what happens at the end of the QCD cascades. We show that, with
just a few reasonable assumptions, the emission of soft gluons is constrained
to produce an ordered field in the form of a helix. We describe how to modify
the Lund fragmentation scheme in order to fragment such a field. Our modified
fragmentation scheme yields results which are consistent with current
experimental measurements, but predicts at least one signature which should be
observable.Comment: 21+1 page
The Interaction of an Oblique Shock Wave with a Laminar Boundary Layer
The results of some experimental and theoretical studies of the interaction of oblique shock waves with laminar boundary layers are presented. Detailed measurements of pressure distribution, shear distribution, and velocity profiles were made during the interaction of oblique shock waves with laminar boundary layers on a flat plate. From these measurements a model was derived to predict the pressure levels characteristic of separation and the length of the separated region
Para to Ortho transition of metallic dimers on Si(001)
Extensive electronic structure calculations are performed to obtain the
stable geometries of metals like Al, Ga and In on the Si(001) surface at 0.5 ML
and 1 ML coverages. Our results coupled with previous theoretical findings
explain the recent experimental data in a comprehensive fashion. At low
coverages, as shown by previous works, `Para' dimers give the lowest energy
structure. With increasing coverage beyond 0.5 ML, `Ortho' dimers become part
of low energy configurations leading toward a `Para' to `Ortho' transition at 1
ML coverage. For In mixed staggered dimers (`Ortho' and `Para') give the lowest
energy configuration. For Ga, mixed dimers are non-staggered, while for Al
`Para' to `Ortho' transition of dimers is complete. Thus at intermediate
coverages between 0.5 and 1 ML, the `Ortho' and `Para' dimers may coexist on
the surface. Consequently, this may be an explanation of the fact that the
experimental observations can be successfully interpreted using either
orientation. A supported zigzag structure at 0.5 ML, which resembles , does not undergo a dimerization transition, and hence stays
semi-metallic. Also, unlike the soliton formation is ruled out
for this structure.Comment: 8 pages, 6 figure
Determining North Atlantic meridional transport variability from pressure on the western boundary: a model investigation.
In this paper we investigate the possibility of determining North
Atlantic meridional transport variability using pressure on the western boundary, focusing on the 42degN latitude of the Halifax WAVE array. We start by
reviewing the theoretical foundations of this approach. Next we present results from a model analysis, both statistical and dynamic, that demonstrate
the feasibility of the approach. We consider how well we can quantify the meridional transport variability at 42degN given complete knowledge of bottom pressure across the basin, and to what degree this quantification is degraded by first ignoring the effect of intervening topography, and then by using only bottom pressure on the western boundary. We find that for periods of greater
than one year we can recover more than 90% of the variability of the main
overturning cell at 42degN using only the western boundary pressure, provided
we remove the depth-average boundary pressure signal. This signal arises from
a basin mode of bottom pressure variability, which has power at all timescales,
but that does not in truth have a meridional transport signal associated with
it, and from the geostrophic depth-independent compensation of the Ekman
transport. An additional benefit of the removal of the depth-average pressure is that this high-frequency Ekman signal, which is essentially noise as
far as monitoring the MOC for climatically important changes is concerned,
is clearly separated from other modes
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