An overview of aerospace gas turbine technology of relevance to the development of the automotive gas turbine engine

Technology areas related to gas turbine propulsion systems with potential for application to the automotive gas turbine engine are discussed. Areas included are: system steady-state and transient performance prediction techniques, compressor and turbine design and performance prediction programs and effects of geometry, combustor technology and advanced concepts, and ceramic coatings and materials technology

Variable geometry aft-fan for takeoff quieting or thrust augmentation of a turbojet engine

A concept is presented that combines the low-noise and high-thrust characteristics of a turbofan at takeoff, together with its high efficiency at subsonic flight speeds, with the high efficiency of a turbojet at supersonic cruise. It consists of a free turbine with tip fan mounted behind the turbine of a conventional turbojet engine. Fan air is supplied from blow-in doors or is ducted from the main engine inlet. At high flight speeds where fan augmentation is not desirable, the fan inlet is closed and the free turbine is stopped by adjustment of its variable-camber stators. Estimates of noise, cycle performance, and example configurations are presented for a typical supersonic transport application

2D and 3D Dense-Fluid Shear Flows via Nonequilibrium Molecular Dynamics. Comparison of Time-and-Space-Averaged Tensor Temperature and Normal Stresses from Doll's, Sllod, and Boundary-Driven Shear Algorithms

Homogeneous shear flows (with constant strainrate du/dy) are generated with the Doll's and Sllod algorithms and compared to corresponding inhomogeneous boundary-driven flows. We use one-, two-, and three-dimensional smooth-particle weight functions for computing instantaneous spatial averages. The nonlinear stress differences are small, but significant, in both two and three space dimensions. In homogeneous systems the sign and magnitude of the shearplane stress difference, P(xx) - P(yy), depend on both the thermostat type and the chosen shearflow algorithm. The Doll's and Sllod algorithms predict opposite signs for this stress difference, with the Sllod approach definitely wrong, but somewhat closer to the (boundary-driven) truth. Neither of the homogeneous shear algorithms predicts the correct ordering of the kinetic temperatures, T(xx) > T(zz) > T(yy).Comment: 34 pages with 12 figures, under consideration by Physical Review

Fluctuation theorem for stochastic systems

The fluctuation theorem describes the probability ratio of observing trajectories that satisfy or violate the second law of thermodynamics. It has been proved in a number of different ways for thermostatted deterministic nonequilibrium systems. In the present paper we show that the fluctuation theorem is also valid for a class of stochastic nonequilibrium systems. The theorem is therefore not reliant on the reversibility or the determinism of the underlying dynamics. Numerical tests verify the theoretical result

Nonequilibrium, thermostats and thermodynamic limit

The relation between thermostats of "isoenergetic" and "frictionless" kind is studied and their equivalence in the thermodynamic limit is proved in space dimension $d=1,2$ and, for special geometries, $d=3$.Comment: 22 pages PRA 2-columns format v3: Typos corrected as acknowledge

Note on nonequilibrium stationary states and entropy

In transformations between nonequilibrium stationary states, entropy might be a not well defined concept. It might be analogous to the ``heat content'' in transformations in equilibrium which is not well defined either, if they are not isochoric ({\it i.e.} do involve mechanical work). Hence we conjecture that un a nonequilbrium stationary state the entropy is just a quantity that can be transferred or created, like heat in equilibrium, but has no physical meaning as ``entropy content'' as a property of the system.Comment: 4 page

Note on the Kaplan-Yorke dimension and linear transport coefficients

A number of relations between the Kaplan-Yorke dimension, phase space contraction, transport coefficients and the maximal Lyapunov exponents are given for dissipative thermostatted systems, subject to a small external field in a nonequilibrium stationary state. A condition for the extensivity of phase space dimension reduction is given. A new expression for the transport coefficients in terms of the Kaplan-Yorke dimension is derived. Alternatively, the Kaplan-Yorke dimension for a dissipative macroscopic system can be expressed in terms of the transport coefficients of the system. The agreement with computer simulations for an atomic fluid at small shear rates is very good.Comment: 12 pages, 5 figures, submitted to J. Stat. Phy

Duality in Shearing Rheology Near the Athermal Jamming Transition

We consider the rheology of soft-core frictionless disks in two dimensions in the neighborhood of the athermal jamming transition. From numerical simulations of bidisperse, overdamped, particles, we argue that the divergence of the viscosity below jamming is characteristic of the hard-core limit, independent of the particular soft-core interaction. We develop a mapping from soft-core to hard-core particles that recovers all the critical behavior found in earlier scaling analyses. Using this mapping we derive a duality relation that gives the exponent of the non-linear Herschel-Bulkley rheology above jamming in terms of the exponent of the diverging viscosity below jamming.Comment: 5 pages, 4 figures. Manuscript revisions: new title, additional text concerning connections to experiment, revised Fig. 4, other minor changes and clarifications in text. Conclusions remain essentially unchanged. Accepted for publication in Phys. Rev. Let

Generalized fluctuation relation and effective temperatures in a driven fluid

By numerical simulation of a Lennard-Jones like liquid driven by a velocity gradient \gamma we test the fluctuation relation (FR) below the (numerical) glass transition temperature T_g. We show that, in this region, the FR deserves to be generalized introducing a numerical factor X(T,\gamma)<1 that defines an ``effective temperature'' T_{FR}=T/X. On the same system we also measure the effective temperature T_{eff}, as defined from the generalized fluctuation-dissipation relation, and find a qualitative agreement between the two different nonequilibrium temperatures.Comment: Version accepted for publication on Phys.Rev.E; major changes, 1 figure adde