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NASA NTRS1992

Design of the advanced regional aircraft, the DART-75

This design analysis is intended to show the capabilities of the DART-75, a 75 passenger medium-range regional transport. Included are the detailed descriptions of the structures, performance, stability and control, weight and balance, and engine design. The design should allow for the DART to become the premier regional aircraft of the future due to some advanced features like the canard, semi-composite construction, and advanced engines.

Elliott, Steve↗

NASA NTRS1993

Time-dependent Computational Studies of Premixed Flames in Microgravity

This report describes the research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of NASA Microgravity Science and Applications Program. The primary focus of this research is on investigating fundamental questions concerning the propagation and extinction of premixed flames in earth gravity and in microgravity environments. Our approach is to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. Recently more advanced wall boundary conditions such as isothermal and no-slip have been added to the model. This enables the simulation of flames propagating in more practical systems than before. We have used the numerical simulations to investigate the effects of heat losses and buoyancy forces on the structure and stability of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the interaction between the various processes leading to flame instabilities and extinguishment, and to study the dynamics of cell formation and splitting. Our studies have been able to bring out the differences between upward- and downward-propagating flames and predict the zero-gravity behavior of these flames. The simulations have also highlighted the dominant role of wall heat losses in the case of downward-propagating flames. The simulations have been able to qualitatively predict the formation of multiple cells and the cessation of cell-splitting. Our studies have also shown that some flames in a microgravity environment can be extinguished due to a chemical instability and without any external losses. However, further simulations are needed to more completely understand upward-propagating and zero-gravity flames as well as to understand the potential effect of radiative heat losses.

Kailasanath, K.↗

NASA NTRS1993

Studies of Premixed Laminar and Turbulent Flames at Microgravity

The work of the Principal Investigator (PI) has encompassed four topics related to the experimental and theoretical study of combustion limits in premixed flames at microgravity, as discussed in the following sections. These topics include: (1) radiation effects on premixed gas flames; (2) flame structure and stability at low Lewis number; (3) flame propagation and extinction is cylindrical tubes; and (4) experimental simulation of combustion processes using autocatalytic chemical reactions.

Ronney, Paul D.↗

NASA NTRS1992

Two-dimensional viscous accretion disk models. I - On meridional circulations in radiative regions

It has been suggested that thin Keplerian disks, like rotating stars, cannot attain hydrostatic and thermal equilibrium simultaneously if the angular velocity is a function of radius only. To address the problem of vertical structure and stability of thin accretion disks, we performed 2D axisymmetric calculations by solving the set of fully nonlinear hydrodynamic equations, including radiation transport. The results indicate that the variation of the rotational velocity with height is too small to sustain hydrostatic equilibrium. Instead, the variation of the radial (inflow) velocity with height suffices to establish a stationary state. In particular, we find that for low values of the viscosity parameter alpha, there is mass outflow in the central parts of the disk close to the equatorial plane, and inflow only near the surface. Only for modestly high values of alpha, the flow throughout the disk is directed inward. Thus, the flow within the disk is the result of viscous radial inflow plus a circulatory flow directed outward in the midplane and inward near the surface.

Kley, W.↗

NASA NTRS1993

The X-15 airplane - Lessons learned

The X-15 rocket research airplane flew to an altitude of 354,000 ft and reached Mach 6.70. In almost 200 flights, this airplane was used to gather aerodynamic-heating, structural loads, stability and control, and atmospheric-reentry data. This paper describes the origins, design, and operation of the X-15 airplane. In addition, lessons learned from the X-15 airplane that are applicable to designing and testing the National Aero-Space Plane are discussed.

Aeroplane↗

NASA NTRS1993

Nuclear winds and the narrow-line emission from active galaxies

This paper discusses active galaxy narrow-line emission in the context of a supersonic wind generated by the active nucleus, a nuclear wind. Wind acceleration can naturally produce the inferred narrow-line cloud velocities as well as those of the broad-line and broad absorption line clouds with only a weak dependence on the parameters of the active nucleus. The primary obstacle to wind acceleration of emission-line clouds is the destructive effect of instabilities; however, the stability and structure of wind-confined clouds remain areas of future research. Observations, particularly of the Seyfert galaxy NGC 1068, are interpreted in the context of nuclear winds.

Smith, Steven J.↗

NASA NTRS1993

The cetaceopteryx: A global range military transport aircraft

This paper presents a design of a military transport aircraft capable of carrying 800,000 lbs of payload from any point in the United States to any other point in the world. Such massive airlift requires aggressive use of advanced technology and a unique configuration. The Cetaceopteyx features a joined wing, canard and six turbofan engines. The aircraft has a cost 1.07 billion (1993) dollars each. This paper presents in detail the mission description, preliminary sizing, aircraft configuration, wing design, fuselage design, empennage design, propulsion system, landing gear design, structures, drag, stability and control, systems layout, and cost analysis of the aircraft.

Brivkalns, Chad↗

NASA NTRS1995

Physics of intermediate shocks: A review

Intermediate shocks (ISs) lead to a transition from super-Alfvenic to sub-Alfvenic flow and are different from slow and fast shocks in that an IS rotates the component of the magnetic field tangent to the shock plane by 180 deg. Another peculiarity of ISs is that for the same upstream conditions an IS can have two different downstream states. There also exist a second class of ISs which rotate the magnetic field by an angle other than 180 deg. Due to their noncoplanar nature they cannot be time-stationary and are referred to as time-dependent intermediate shocks (TDIS). The existence of ISs has been the subject of much controversy over the years. Early studies questioned the physical reality of ISs. However, the studies of ISs found a new impetus when C.C. Wu showed that ISs do exist and are stable within the resistive MHD framework. In this paper, after a brief historical overview of the subject, we will review the latest developments in the study of ISs. In particular, we will address the questions of stability and structure of ISs and the relationship between ISs and other discontinuities. One of the recent developments has been the finding that ISs can be unsteady, reforming in time. Details of this process will be discussed. Finally, we examine the effect of anisotropy on the resolutions and discuss the relevance of ISs to the observed field rotations at the Earth's magnetopause.

Karimabadi, H.↗

NASA NTRS1995

Structure Of Flame Balls At Low Lewis-number (SOFBALL)

The work has encompassed several topics related to the experimental and theoretical study of combustion limits in premixed flames at microgravity. These topics include (1) flame structure and stability at low Lewis number (which is the basis for the SOFBALL space flight experiment), (2) flame propagation and extinction in cylindrical tubes, and (3) experimental simulation of combustion processes using autocatalytic chemical reactions. Progress on each of these topics is outlined.

Ronney, Paul D.↗

NASA NTRS1995

Evaluation of high temperature polymers

The purpose of this paper is to identify and develop arc-track resistant insulation materials that can operate reliably at 300 C. In the first phase, high performance polymers are evaluated based on structure, thermal stability and electrical properties. Next, the polymers are ranked according to performance and experimental characterization. Then, experimental evaluations in wire configuration are conducted. And selection is made based on performance and commerical potential.

Jayaraj, K.↗

NASA NTRS1997

Studies of Premixed Laminar and Turbulent Flames at Microgravity

Several topics related to the experimental and theoretical study of the combustion limits in premixed flames at reduced gravity have been investigated. The topics studied include: (1) numerical simulation of flame ball structure and stability; (2) interferometry for micro-g combustion experiments; (3) simulation of buoyancy effects in premixed flames using aqueous autocatalytic reactions; (4) premixed flame propagation in Hele-Shaw cells; and (5) experimental characterization of flame balls.

Ronney, Paul D.↗

NASA NTRS1996

Development of a Composite Tailoring Technique for Airplane Wing

Development of a new composite beam modeling technique to represent the principal load-carrying member in the wing is reported along with the development of a formal design optimization procedure to investigate the effect of composite tailoring on aeroelastic stability and structural characteristics of airplane wings. The developed procedure is used to perform design optimization studies on realistic airplane configurations to investigate the various aeroelastic/structural/dynamic design issues.

Chattopadhyay, Aditi↗

NASA NTRS1998

Aeroelastic Stability and Response of Rotating Structures

A summary of the work performed from 1996 to 1997 is presented. More details can be found in the cited references. This grant led to the development of aeroelastic analyses methods for predicting flutter and forced response in fans, compressors, and turbines using computational

Keith, Theo G., Jr.↗

NASA NTRS1999

Studies of Premixed Laminar and Turbulent Flames at Microgravity

Several topics relating to combustion limits in premixed flames at reduced gravity have been studied. These topics include: (1) flame balls; (2) numerical simulation of flame ball and planar flame structure and stability; (3) experimental simulation of buoyancy effects in premixed flames using aqueous autocatalytic reactions; and (4) premixed flame propagation in Hele-Shaw cells.

Abid, M.↗

NASA NTRS1999

Studies of Premixed Laminar and Turbulent Flames at Microgravity

Abid, M.↗

NASA NTRS1985

A Portable Battery for Objective, Nonobtrusive Measures of Human Performance

A need exists for a standardized battery of human performance tests in order to measure the effects of various treatments. The present paper reports on progress in such a program, funded jointly by NASA and the Navy. Three batteries are available which differ in length (7.5, 15, and 30 minutes), and number of tests in the battery (3, 10, and 15). All tests are implemented on a portable, lap-held, briefcase-sized microprocessor (NEC PC 8201A). Performances measured include information processing, memory, visual perception, reasoning, motor skills, etc. Current programs are underway to determine norms, reliabilities, stabilities, factor structure of tests, comparisons with marker tests, apparatus suitability, etc.

Kennedy, Robert S.↗

NASA NTRS2001

Studies of Premixed Laminar and Turbulent Flames at Microgravity

Several topics relating to premixed flame behavior at reduced gravity have been studied. These topics include: (1) flame balls; (2) flame structure and stability at low Lewis number; (3) experimental simulation of buoyancy effects in premixed flames using aqueous autocatalytic reactions; and (4) premixed flame propagation in Hele-Shaw cells.

Abid, M.↗

NASA NTRS1995

Resistance to Sliding on Atomic Scales

The structure and stability of agglomerates of micron-sized particles is determined by the mechanical properties of the individual contacts between the constituent particles. In this paper we study the possibility of aggregate rearrangements by sliding. Since the contacts between (sub)micron particles are only a few hundred atoms in diameter, processes on atomic levels will play the dominating roll. We study a theoretical model of sliding friction for surfaces that are either flat or contain steps in their grids. The results show that sliding over flat surfaces may produce a large range of friction coefficients, including zero if the adhesive forces are small compared to the binding forces inside a body. However, both grid alignment and steps in the surface will lead to high values for friction. These processes combined virtually eliminate the possibility of sliding in a collision of two (sub)micron sized particles at velocities low enough for sticking to occur. On the other hand we show that in collisions between aggregates sliding may be an important factor for energy dissipation and compaction.

Dominik, C.↗