Aeronautical Engineering: A continuing bibliography with indexes, supplement 99

This bibliography lists 292 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1978

Specific heat effects in two-dimensional shock refractions

Compressible mixtures in supersonic flows are subject to significant temperature changes via shock waves and expansions, which affect several properties of the flow. Besides the widely studied variable transport effects such as temperature-dependent viscosity and conductivity, vibrational and rotational molecular energy storage is also modified through the variation of the heat capacity cp and heat capacity ratio gamma , especially in hypersonic flows. Changes in the composition of the mixture may also modify its value through the species mass fraction Yalfa, thereby affecting the compression capacity of the flow. Canonical configurations are studied here to explore their sharply conditioned mechanical equilibrium under variations of these thermal models. In particular, effects of cp(T , Yalfa) and gamma (T , Yalfa) on the stability of shock-impinged supersonic shear and mixing layers are addressed, on condition that a shock wave is refracted. It is found that the limits defining regular structures are affected (usually broadened out) by the dependence of heat capacities with temperature. Theoretical and high-fidelity numerical simulations exhibit a good agreement in the prediction of regular shock reflections and their post-shock aerothermal properties.Work produced with the support of a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation and Project PID2019-108592RB-C41 and PID2019-108592RA-C43 (MICINN/ FEDER, UE). Numerical simulations were carried out on the MareNostrum 4 supercomputer with the Grant RES FI-2019-1-0046. The authors gratefully acknowledge Arnaud Mura, CNRS researcher at Institut PPRIME in France, for the numerical tool CREAMS.Publicad

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Astrophysical Accretion as an Analogue Gravity Phenomena

In recent years, strong analogies have been established between the physics of acoustic perturbations in an inhomogeneous dynamical fluid system, and some kinematic features of space-time in general relativity. An effective metric, referred to as the `acoustic metric', which describes the geometry of the manifold in which acoustic perturbations propagate, can be constructed. This effective geometry can capture the properties of curved space-time in general relativity. Physical models constructed utilizing such analogies are called `analogue gravity models'. Classical analogue gravity effect may be observed when acoustic perturbations propagate through a inhomogeneous transonic classical fluid. The acoustic horizon, which resembles a black hole event horizon in many ways, is generated at the transonic point in the fluid flow. The acoustic horizon is essentially a null hyper surface, generators of which are the acoustic null geodesics, i.e. the phonons. The acoustic horizon emits acoustic radiation with quasi thermal phonon spectra, which is analogous to the actual Hawking radiation. The temperature of the radiation emitted from the acoustic horizon is referred to as the analogue Hawking temperature. It has been demonstrated that, in general, the transonic accretion in astrophysics can be considered as an example of the classical analogue gravity model naturally found in the Universe.Comment: 56 pages, 11 figures, revtex4. Send email request to the author for high resolution version of the manuscrip

The supernova-regulated ISM. I. The multi-phase structure

We simulate the multi-phase interstellar medium randomly heated and stirred by supernovae, with gravity, differential rotation and other parameters of the solar neighbourhood. Here we describe in detail both numerical and physical aspects of the model, including injection of thermal and kinetic energy by SN explosions, radiative cooling, photoelectric heating and various transport processes. With 3D domain extending 1 kpc^2 horizontally and 2 kpc vertically, the model routinely spans gas number densities 10^-5 - 10^2 cm^-3, temperatures 10-10^8 K, local velocities up to 10^3 km s^-1 (with Mach number up to 25). The thermal structure of the modelled ISM is classified by inspection of the joint probability density of the gas number density and temperature. We confirm that most of the complexity can be captured in terms of just three phases, separated by temperature borderlines at about 10^3 K and 5x10^5 K. The probability distribution of gas density within each phase is approximately lognormal. We clarify the connection between the fractional volume of a phase and its various proxies, and derive an exact relation between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100 pc and tends to grow with distance from the mid-plane. We use two distinct parameterizations of radiative cooling to show that the multi-phase structure of the gas is robust, as it does not depend significantly on this choice.Comment: 28 pages, 22 figures and 8 table

Aeronautical enginnering: A cumulative index to a continuing bibliography (supplement 312)

This is a cumulative index to the abstracts contained in NASA SP-7037 (301) through NASA SP-7073 (311) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled by the Center for AeroSpace Information of the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, foreign technology, contract number, report number, and accession number indexes