12,657 research outputs found
A preliminary study of the use of intercooling and reheat in conjunction with regeneration for aircraft turbine engines
The effect on fuel consumption of turbofans with intercooled, regenerative cycles and with intercooled, regenerative, reheat cycles was studied. The technology level for both engine and aircraft was that projected for 1985. The simulated mission was a 5556 km flight carrying 200 passengers at Mach 0.8 at 11582 min. Results indicate that these relatively complex cycles offer little, if any, fuel savings potential relative to a conventional turbofan cycle of comparable advanced technology. The intercooled, regenerative cycle yields about the same fuel economy as a conventional cycle at close to the same overall pressure ratio
Rotorcraft convertible engines for the 1980s
Two rotorcraft studies were executed. The goal was to identify attractive techniques for implementing convertible powerplants for the ABC, Folded Tilt Rotor, and X-wing type high speed, high-L/D rotorcraft; to determine the DOC and fuel savings benefits achieved thereby; and to define research required to bring these powerplants into existence by the 1990's. These studies are reviewed herein and the different methods of approach are pointed out as well as the key findings. Fan shaft engines using variable inlet guide vanes or torque converters, and turboprop powerplants appear attractive. Savings in DOC and fuel consumption of over 15 percent are predicted in some cases as a result of convertible engine use rather than using separate engines for the thrust and the shaft functions. Areas of required research are fan performance (including noise), integrated engine/rotorcraft control, torque converters, turbine design, airflow for rotorcraft torque control, bleed for lift flow, and transmissions and clutches
Energetics of ion competition in the DEKA selectivity filter of neuronal sodium channels
The energetics of ionic selectivity in the neuronal sodium channels is
studied. A simple model constructed for the selectivity filter of the channel
is used. The selectivity filter of this channel type contains aspartate (D),
glutamate (E), lysine (K), and alanine (A) residues (the DEKA locus). We use
Grand Canonical Monte Carlo simulations to compute equilibrium binding
selectivity in the selectivity filter and to obtain various terms of the excess
chemical potential from a particle insertion procedure based on Widom's method.
We show that K ions in competition with Na are efficiently excluded
from the selectivity filter due to entropic hard sphere exclusion. The
dielectric constant of protein has no effect on this selectivity. Ca
ions, on the other hand, are excluded from the filter due to a free energetic
penalty which is enhanced by the low dielectric constant of protein.Comment: 14 pages, 7 figure
Thermodynamic anomalies in a lattice model of water: Solvation properties
We investigate a lattice-fluid model of water, defined on a 3-dimensional
body-centered cubic lattice. Model molecules possess a tetrahedral symmetry,
with four equivalent bonding arms. The model is similar to the one proposed by
Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified by
removing distinction between "donors" and "acceptors". We focus on solvation
properties, mainly as far as an ideally inert (hydrophobic) solute is
concerned. As in our previous analysis, devoted to neat water [J. Chem. Phys.
121, 11856 (2004)], we make use of a generalized first order approximation on a
tetrahedral cluster. We show that the model exhibits quite a coherent picture
of water thermodynamics, reproducing qualitatively several anomalous properties
observed both in pure water and in solutions of hydrophobic solutes. As far as
supercooled liquid water is concerned, the model is consistent with the second
critical point scenario.Comment: 12 pages, 9 figures, 1 tabl
Bottom-up derivation of an effective thermostat for united atoms simulations of water
In this article we derive the effective pairwise interactions in a Langevin
type united atoms model of water. The interactions are determined from the
trajectories of a detailed molecular dynamics simulation of simple point charge
water. A standard method is used for estimating the conservative interaction,
whereas a new "bottom-up" method is used to determine the effective dissipative
and stochastic interactions. We demonstrate that, when compared to the standard
united atoms model, the transport properties of the coarse-grained model is
significantly improved by the introduction of the derived dissipative and
stochastic interactions. The results are compared to a previous study, where a
"top-down" approach was used to obtain transport properties consistent with
those of the simple point charge water model.Comment: Submitted to J. Chem. Phy
Potential of liquid-methane fuel for Mach-3 commercial supersonic transports
Liquid methane fuel for commercial fixed arrow wing supersonic transport
Preliminary study of advanced turboprop and turboshaft engines for light aircraft
The effects of engine configuration, advanced component technology, compressor pressure ratio and turbine rotor-inlet temperature on such figures of merit as vehicle gross weight, mission fuel, aircraft acquisition cost, operating, cost and life cycle cost are determined for three fixed- and two rotary-wing aircraft. Compared with a current production turboprop, an advanced technology (1988) engine results in a 23 percent decrease in specific fuel consumption. Depending on the figure of merit and the mission, turbine engine cost reductions required to achieve aircraft cost parity with a current spark ignition reciprocating (SIR) engine vary from 0 to 60 percent and from 6 to 74 percent with a hypothetical advanced SIR engine. Compared with a hypothetical turboshaft using currently available technology (1978), an advanced technology (1988) engine installed in a light twin-engine helicopter results in a 16 percent reduction in mission fuel and about 11 percent in most of the other figures of merit
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