Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “kinetic stabilization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Influence of temperature and hydroxyl concentration on incipient soot formation in premixed flames

Critical equivalence ratios phi(c) have been measured as a function of temperature (1600-1880 K) for premixed flames at atmospheric pressure. The five fuels studied are methane, ethane, propane, ethylene, and acetylene. The flames were stabilized on a flat flame burner and the temperatures were measured using sodium D-line reversal. A linear relationship is found between In phi(c) and 1/T for each fuel. Based on a global kinetic model in which soot precursors are formed by fuel pyrolysis and oxidized by OH, a predictive correlation has been developed which shows the influence of temperature, OH concentration, and C/H ratio on sooting tendency. This correlation describes all of the measured phi(c) versus temperature data, suggesting that the overall mechanism of soot formation is similar among aliphatic fuels.

Harris, M. M.↗
NASA NTRS1947

An Investigation of Convergent-Divergent Diffusers at Mach Number 1.85

An investigation has been conducted in the Cleveland 18- by 18-inch supersonic tunnel at a Mach number of 1.85 and angles of attack from 0 deg to 5 deg to determine optimum design configurations for a convergent-divergent type of supersonic diffuser with a subsonic diffuser of 5 deg included divergence angle. Total pressure recoveries in excess of theoretical recovery across a normal shock at a free-stream Mach number of 1.85 wore obtained with several configurations. The highest recovery for configurations without a cylindrical throat section was obtained with an inlet having an included convergence angle of 20 deg. Insertion of a 2-inch throat section between a 10 deg included angle inlet and the subsonic diffuser stabilized the shock inside the diffuser and resulted in recoveries as high as 0.838 free-stream total pressure at an angle of attack of 0 deg, corresponding to recovery of 92.4 percent of the kinetic energy of the free air stream. Use of the throat section also lessened the reduction in recovery of all configurations due to angle of attack.

Wyatt, Demarquis D↗
NASA NTRS1984

Inviscid fluid in high frequency excitation field

The influence of high frequency excitations (HFE) on a fluid is investigated. The response to these excitations is decomposed in two parts: 'slow' motion, which practically remains unchanged during the vanishingly small period tau, and 'fast' motion whose value during this period is negligible in terms of displacements, but is essential in terms of the kinetic energy. After such a decomposition the 'slow' and 'fast' motions become nonlinearly coupled by the corresponding governing equations. This coupling leads to an 'effective' potential energy which imparts some 'elastic' properties to the fluid and stabilizes laminar flows.

Zak, M.↗
NASA NTRS1973

A movable mass control system to detumble a disabled space vehicle

An internal autonomous control system to either completely detumble a spacecraft or lessen the tumbling motions until the rescue craft arrives is discussed. Such a device would become active upon loss of control. The development of a movable mass control system to convert the tumbling motions of a disabled vehicle into simple spin is presented. A simple spin state would greatly facilitate crew evacuation and final despinning by an external means. The system moves a control mass, according to a selected control law, in the acceleration environment created by the tumbling motion. By moving the mass properly, the rotational kinetic energy of the system may be increased or decreased creating simple spin states about the minimum or maximum moment of inertia axis, respectively. The control system is designed for the latter case due to its associated stability in the presence of perturbing forces.

Edwards, T. L.↗
NASA NTRS1988

Effect of surface catalysis on heating to ceramic coated thermal protection systems for transatmospheric vehicles

This paper describes the effect of surface catalysis on the heat transfer rate to the heat shield of a typical Transatmospheric Vehicle (TAV) during ascent and atmospheric entry. Surface kinetics and optical properties obtained from arc-jet tests on candidate thermal protection systems (coated metals) were used in a reacting boundary layer code to estimate the heating distribution along the surface of a TAV. Thermochemical stability of the coatings is described in terms of reduction in emittance and loss of opacifiers from the coatings during the arc-jet tests.

Stewart, David A.↗
NASA NTRS1990

Current-driven plasma acceleration versus current-driven energy dissipation. I - Wave stability theory

The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime.

Kelly, A. J.↗
NASA NTRS1973

Chemical reactivity of hydrogen, nitrogen, and oxygen atoms at temperatures below 100 k

The synthesis of unusual compounds by techniques employing cryogenic cooling to retard their very extreme reactivity was investigated. Examples of such species that were studied are diimide (N2H2), cyclobutadiene (C4H4), cyclopropanone (C3H4O), oxirene (C2H2O), and many others. Special purpose cryogenically cooled inlet arrangements were designed such that the analyses incurred no warm-up of the cold, and frequently explosively unstable, compounds. Controlled energy electron impact techniques were used to measure critical potentials and to develop the molecular energetics and thermodynamics of these molecules and to gain some insight into their kinetic characteristics as well. Three and four carbon strained ring molecules were studied. Several reactions of oxygen and hydrogen atoms with simple molecules of H, N, C, and O in hard quench configurations were studied. And the quench stabilization of BH3 was explored as a model system in cryochemistry.

Mcgee, H. A., Jr.↗
NASA NTRS2006

Water as a matrix for life

"Follow the water" is the canonical strategy in searching for life in the universe. Conventionally, discussion of this topic is focused on how solvent supports organic chemistry sufficiently rich to seed life. Perhaps more importantly, solvent must promote self-organization of organic matter into functional structures capable of responding to environmental changes. This process is based on non-covalent interactions. They are constantly formed and broken in response to internal and external stimuli. This requires that their strength must be properly tuned. If they were too weak, the system would exhibit undesired, uncontrolled response to natural fluctuations of physical and chemical parameters. If they were too strong kinetics of biological processes would be slow and energetics costly. Non-covalent interactions are strongly mediated by the solvent. Specifically, high dielectric solvents for life are needed for solubility of polar species and flexibility of biological structures stabilized by electrostatic interactions. Water exhibits a remarkable trait that it promotes solvophobic interactions between non-polar species, which are responsible for self-organization phenomena such as the formation of cellular boundary structures, and protein folding and aggregation. Unusual temperature dependence of hydrophobic interactions - they often become stronger as temperature increases - is a consequence of the temperature insensitivity of properties of the liquid water. This contributes to the existence of robust life over a wide temperature range. Water is not the only liquid with favorable properties for supporting life. Other pure liquids or their mixtures that have high dielectric constants and simultaneously support some level of self-organization will be discussed.

Pohorille, Andrew↗
NASA NTRS1993

Low-frequency mobility response functions for the central plasma sheet with application to tearing modes

Consideration is given to the effect of constant cross-tail magnetic field By on the collisionless conductivity produced by chaotic scattering and stochastic diffusion of particles in the current sheet for a parabolic geometry. It is shown that the correlation time scales as (By/Bz)-squared, and from this strong By scaling a strong tendency toward stabilization of the linear tearing modes with increasing values of By is inferred. This effect of increased dawn-dusk mobility is particularly dramatic when electrons are introduced in the calculation, and is in agreement with the results of kinetic particle simulations. The collisionless conductivity is expressed in terms of the ensemble-averaged power spectrum of the single particle trajectories, which makes it possible to calculate directly the linear conductivity instead of deriving it from the calculation of the irreversible heating rates.

Hernandez, J.↗
NASA NTRS2004

Energy Management of Manned Boost-Glide Vehicles: A Historical Perspective

As flight progressed from propellers to jets to rockets, the propulsive energy grew exponentially. With the development of rocket-only boosted vehicles, energy management of these boost-gliders became a distinct requirement for the unpowered return to base, alternate landing site, or water-parachute landing, starting with the X-series rocket aircraft and terminating with the present-day Shuttle. The problem presented here consists of: speed (kinetic energy) - altitude (potential energy) - steep glide angles created by low lift-to-drag ratios (L/D) - distance to landing site - and the bothersome effects of the atmospheric characteristics varying with altitude. The primary discussion regards post-boost, stabilized glides; however, the effects of centrifugal and geopotential acceleration are discussed as well. The aircraft and spacecraft discussed here are the X-1, X-2, X-15, and the Shuttle; and to a lesser, comparative extent, Mercury, Gemini, Apollo, and lifting bodies. The footprints, landfalls, and methods developed for energy management are also described. The essential tools required for energy management - simulator planning, instrumentation, radar, telemetry, extended land or water range, Mission Control Center (with specialist controllers), and emergency alternate landing sites - were first established through development of early concepts and were then validated by research flight tests.

Day, Richard E.↗
NASA NTRS1987

Nonlinear stability of Taylor's vortex array

It is proved that the two-dimensional Taylor vortex array, which is an exact unsteady solution of the Navier-Stokes equation, is globally and asymptotically stable in the mean with respect to three-dimensional periodic disturbances. A time-dependent bound on the decay rate of the kinetic energy of disturbances is obtained.

Lin, S. P.↗
NASA NTRS1978

Studies of vorticity imbalance and stability, moisture budget, atmospheric energetics, and gradients of meteorological parameters during AVE 3

Four diagnostic studies of AVE 3. are presented. AVE 3 represents a high wind speed wintertime situation, while most AVE's analyzed previously represented springtime conditions with rather low wind speeds. The general areas of analysis include the examination of budgets of vorticity, moisture, kinetic energy, and potential energy and a synoptic and statistical study of the horizontal gradients of meteorological parameters. Conclusions are integrated with and compared to those obtained in previously analyzed experiments (mostly springtime weather situations) so as to establish a more definitive understanding of the structure and dynamics of the atmosphere under a wide range of synoptic conditions.

Scoggins, J. R.↗
NASA NTRS1995

Reliability enhancement of Navier-Stokes codes through convergence acceleration

Methods for enhancing the reliability of Navier-Stokes computer codes through improving convergence characteristics are presented. The improving of these characteristics decreases the likelihood of code unreliability and user interventions in a design environment. The problem referred to as a 'stiffness' in the governing equations for propulsion-related flowfields is investigated, particularly in regard to common sources of equation stiffness that lead to convergence degradation of CFD algorithms. Von Neumann stability theory is employed as a tool to study the convergence difficulties involved. Based on the stability results, improved algorithms are devised to ensure efficient convergence in different situations. A number of test cases are considered to confirm a correlation between stability theory and numerical convergence. The examples of turbulent and reacting flow are presented, and a generalized form of the preconditioning matrix is derived to handle these problems, i.e., the problems involving additional differential equations for describing the transport of turbulent kinetic energy, dissipation rate and chemical species. Algorithms for unsteady computations are considered. The extension of the preconditioning techniques and algorithms derived for Navier-Stokes computations to three-dimensional flow problems is discussed. New methods to accelerate the convergence of iterative schemes for the numerical integration of systems of partial differential equtions are developed, with a special emphasis on the acceleration of convergence on highly clustered grids.

Merkle, Charles L.↗
NASA NTRS2019

Preliminary Soot Computations Based on a Model Aircraft Combustor With OpenNCC

In a preliminary effort to extend our current capabilities used in the design & testing of aero-engine combustors to particulate emissions, we incorporated several existing 2- equation soot models into the Open National Combustion Code (OpenNCC). The paper presents results from a validation study based on a well-characterized, swirl-stabilized, turbulent sooting flame generated by a model aero-engine combustor developed at DLR, Germany. The calculations are based on a Reynolds-Averaged Navier Stokes (RANS) simulation with standard k-e turbulence model & a finite-rate chemical kinetic mechanism. A separate transport equation is solved for all individual species involved in ethylene/air combustion. The predicted velocity and temperature are mostly in good agreement with the measured data and reasonable agreement was found for soot. While the calculated SVF (Soot Volume Fraction) behavior is similar to some other predicted results reported in literature, the measured soot lasts farther downstream than the calculated soot indicating a need for further improvement in the soot models employed.

Raju, Manthena↗
NASA NTRS1958

Survey of Hydrogen Combustion Properties

This literature digest of hydrogen-air combustion fundamentals presents data on flame temperature, burning velocity, quenching distance, flammability limits, ignition energy, flame stability, detonation, spontaneous ignition, and explosion limits. The data are assessed, recommended values are given, and relations among various combustion properties are discussed. New material presented includes: theoretical treatment of variation in spontaneous ignition lag with temperature, pressure, and composition, based on reaction kinetics of hydrogen-air composition range for 0.01 to 100 atmospheres and initial temperatures of 0 degrees to 1400 degrees k.

Drell, Isadore L↗
NASA NTRS1976

Split Space-Marching Finite-Volume Method for Chemically Reacting Supersonic Flow

A space-marching finite-volume method employing a nonorthogonal coordinate system and using a split differencing scheme for calculating steady supersonic flow over aerodynamic shapes is presented. It is a second-order-accurate mixed explicit-implicit procedure that solves the inviscid adiabatic and nondiffusive equations for chemically reacting flow in integral conservation-law form. The relationship between the finite-volume and differential forms of the equations is examined and the relative merits of each discussed. The method admits initial Cauchy data situated on any arbitrary surface and integrates them forward along a general curvilinear coordinate, distorting and deforming the surface as it advances. The chemical kinetics term is split from the convective terms which are themselves dimensionally split, thereby freeing the fluid operators from the restricted step size imposed by the chemical reactions and increasing the computational efficiency. The accuracy of this splitting technique is analyzed, a sufficient stability criterion is established, a representative flow computation is discussed, and some comparisons are made with another method.

Rizzi, Arthur W.↗
NASA NTRS1975

A generalized hyperbolic marching method for chemically reacting 3-D supersonic flow using a splitting technique

A generalized hyperbolic marching method employing a nonorthogonal coordinate system and using a split differencing scheme for calculating steady supersonic flow over aerodynamic shapes is presented. It is a second-order-accurate mixed explicit-implicit procedure that solves the inviscid adiabatic and nondiffusive equations for chemically reacting flow in integral conservation-law form. The relationship between the integral and differential forms of the equations are examined and the relative merits of each discussed. The method admits initial Cauchy data situated on any arbitrary surface and integrates them forward along a general curvilinear coordinate, distorting and deforming the surface as it advances. The chemical kinetics term is split from the convective terms which are themselves dimensionally split, thereby freeing the fluid operators from the restricted step-size imposed by the chemical reactions and increasing the computational efficiency. The accuracy of this splitting technique is analyzed, a sufficient stability criterion is established, and comparisons are made with another method.

Rizzi, A. W.↗