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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.

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NASA NTRS1987

Optical measurement systems

Some of the areas of research conducted at Lewis on optical measurement techniques are described. Two laser anemometer systems developed at Lewis are used to illustrate the special instrumentation needs encountered in aeropropulsion research. Velocity measurements to be made through small viewing ports, close to surfaces within the propulsion system components, and in turbulent or highly-accelerating flows are some of the significant challenges. The application to research facilities of two advanced optical systems, the rainbow schlieren and the combustor viewing system, is presented. The calibration and verification of commercial optical measuring systems, such as droplet sizing systems, are also discussed. Calibration techniques capable of simulating moving droplets for flight-type sizing systems are being developed at Lewis. The presentation concludes with a brief look at the forces driving future research on optical instrumentation.

Lesco, Daniel J.↗
NASA NTRS1988

McDonnell Douglas Helicopter Company independent research and development: Preparing for the future

During the 1970's and 80's, research has produced the technology that is seen in aircraft such as the LHX and future models. The technology is discussed that is reaching maturity and moving into the application stage of future programs. Technology is discussed in six major areas: advanced concepts, analysis techniques, structures, systems, simulation, and research and development facilities. The partnership of McDonnell Douglas Helicopter Co. and the government in developing these technologies is illustrated in several programs.

Haggerty, Allen C.↗
NASA NTRS1987

Design and validation of fault-tolerant flight systems

Flight systems must be validated to show that they are consistent with the requirements of their intended applications. While high reliability is difficult to validate, the additional complexity of fault tolerance further compounds the validation problem. The objective of NASA’s research is to develop a methodology for designing validatable fault-tolerant systems. Under the design-for-validation philosophy, emphasis is placed on developing validation methods that can be incorporated into the design process right from the start and design methods and guidance which, while incorporating fault tolerance, can assure validatability. This paper examines the statistical issues of validating highly reliable, fault tolerant system. There are many problems associated with traditional methods of designing and validating these potentially complex hardware and software systems. Useful design-for-validation methods, which include structured specification and design methodologies, mathematical proof techniques, analytical modeling, simulation and emulation, and physical testing, are discussed. Important design issues associated with fault tolerance are presented along with the related validation concerns which must be addressed. Experience has shown that synchronization and Byzantine resilience must accompany fault tolerance. Other design attributes associated with fault tolerance may be used by a designer on the basis of cost, weight, performance, and validation considerations.

Computer systems↗
NASA NTRS1988

Development of a two-dimensional skin friction balance nulling circuit using multivariable control theory

Measurement of planar skin friction forces in aerodynamic testing currently requires installation of two perpendicularly mounted, single-axis balances; consequently, force components must be sensed at two distinct locations. A two-axis instrument developed at the Langley Research Center to overcome this disadvantage allows measurement of a two-dimensional force at one location. This paper describes a feedback-controlled nulling circuit developed for the NASA two-axis balance which, without external compensation, is inherently unstable because of its low friction mechanical design. Linear multivariable control theory is applied to an experimentally validated mathematical model of the balance to synthesize a state-variable feedback control law. Pole placement techniques and computer simulation studies are employed to select eigenvalues which provide ideal transient response with decoupled sensing dynamics.

Tripp, John S.↗
NASA NTRS1988

Trajectory optimization and guidance law development for national aerospace plane applications

The work completed to date is comprised of the following: a simple vehicle model representative of the aerospace plane concept in the hypersonic flight regime, fuel-optimal climb profiles for the unconstrained and dynamic pressure constrained cases generated using a reduced order dynamic model, an analytic switching condition for transition to rocket powered flight as orbital velocity is approached, simple feedback guidance laws for both the unconstrained and dynamic pressure constrained cases derived via singular perturbation theory and a nonlinear transformation technique, and numerical simulation results for ascent to orbit in the dynamic pressure constrained case.

Calise, A. J.↗
NASA NTRS1988

An investigation of turbulence models

The accuracy to which a turbulent boundary layer or wake can be predicted numerically depends on the validity of the turbulence closure model used. The modeling of turbulence physics is one of the most difficult problems in computational fluid dynamics (CFD). In fact, it is one of the pacing factors in the development of CFD. In general, there are three main approaches to the description of trubulence physics. First is turbulence modeling in which the Reynolds averaged Navier-Stokes equations are used and some closure approximation is made for the Reynolds stresses. A second approach to turbulence is large eddy simulation (LES) in which the computational mesh is taken to be fine enough that the large scale structure of the turbulence can be calculated directly. An empirical assumption must be made for the small scale sub-grid turbulence. The third approach is direct simulation. In this technique the Navier-Strokes equations are solved directly on a mesh which if fine enough to resolve the smallest length scale of the turbulence. The Reynolds averaged equations are not used and no closure assumption is required. These last two approaches require extensive computer resources and as such are not engineering tools. The purpose of the work was to investigate the various engineering turbulence models for accuracy and ease of programming. This involved comparison of the models with each other and with experimental data.

Doria, Michael L.↗
NASA NTRS1989

Three-dimensional flow simulation about the AFE vehicle in the transitional regime

The direct-simulation Monte Carlo technique is used to analyze the hypersonic rarefied flow about the three-dimensional NASA Aeroassist Flight Experiment vehicle. Results are given for typical transitional flows encountered during the vehicle's atmospheric entry from altitudes of 200-100 km with an entry velocity of 9.9 km/s. It is found that dissociation is important at altitudes of 110 km and below, and that transitional effects are significant even at an altitude of 200 km.

Celenligil, M. Cevdet↗
NASA NTRS1989

Computation of rarefied hypersonic flows

Numerical techniques for the simulation of hypersonic flows of rarefied gases are examined in an analytical review. The direct-simulation Monte Carlo (DSMC) method developed to interpret measurement data obtained by the Space Shuttle in the SUMS project is described; the fundamental limitations of the DMSC approach are discussed; and modifications to improve the physical plausibility of DSMC predictions are proposed. Particular attention is given to the use of a double-peaked molecular distribution function for the internal flow in the SUMS probe, a downstream vacuum-reservoir condition as a simplifying assumption, and an explicit forward-time centered-space differencing scheme for the discretization of the SUMS problem. Typical simulation results are presented in extensive graphs and briefly characterized.

Cheng, Sin-I↗
NASA NTRS1989

Nonequilibrium molecular motion in a hypersonic shock wave

Molecular velocities have been measured inside a hypersonic, normal shock wave, where the gas experiences rapid changes in its macroscopic properties. As first hypothesized by Mott-Smith, but never directly observed, the molecular velocity distribution exhibits a qualitatively bimodal character that is derived from the distribution functions on either side of the shock. Quantitatively correct forms of the molecular velocity distribution function in highly nonequilibrium flows can be calculated, by means of the Direct Simulation Monte Carlo technique.

Pham-Van-diep, G.↗
NASA NTRS1989

Evidence for accurate temperatures from the inflatable falling sphere

The experiments performed with the inflatable falling sphere technique, for middle atmosphere studies, are reported. It is shown to be a potentially high accurate and independent source of temperature measurement and an intrinsic method for establishing accuracy of other atmospheric measurement techniques. Theoretical derivation, simulations, and actual measurements show that the sphere's temperature data are accurate. It is demonstrated that retrieved temperatures from falling spheres are not significantly affected by linear bias in density caused by uncertainties in sphere mass, volume, or cross sectional area. Case studies illustrate the sphere's capability to produce accurate temperatures. Comparisons with Datasonde temperature measurements obtained close in time and space are in agreement below 60 km.

Schmidlin, F. J.↗
NASA NTRS1990

Quiet mode for nonlinear rotor models

High frequency harmonics are generated by helicopter rotor systems, and nonlinear blade-element models of these systems create the same harmonics. In discrete real-time rotorcraft simulation, however, especially for handling qualities research, they are more of a nuisance than a benefit. The cycle times required to adequately represent them are rarely obtainable. The result is that distinct frequencies alias into the pilot and simulator bandwidths, thereby decreasing simulation fidelity. However, use of an interpolation procedure permits the observation of harmonics at their proper frequency locations, and an accompanying notch filter may then be used to attenuate the harmonics prior to decimation. Rotorcraft simulations using these techniques are not contaminated with the spurious frequencies that create variable trim points, produce erroneous stability and control derivative data, and obscure time histories.

Mcfarland, R. E.↗
NASA NTRS1990

Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

An efficient method is presented for estimating the high-cycle fatigue lives of complex nonlinear structures. The procedure is based on an application of the method of equivalent linearization to construct a time-domain representation of the stress or strain response of a nonlinear structure. Fatigue estimates are obtained by processing the time-domain signal, and it is a simple matter to incorporate any damage accumulation model desired in the procedure. The method may also be applied to a wide range of complex nonlinear systems. Comparisons are presented of estimated fatigue lives for a nonlinear beam with random excitation obtained using the approximate method and using a conventional numerical simulation. The two techniques are found to give nearly identical results regardless of the level of nonlinearity. The number of calculations required in the approximate method is nearly the same as in a linear system and is not significantly affected by the type and level of nonlinearity in the structure.

Sun, J. Q.↗
NASA NTRS1989

Design of an orbital debris radar ground demonstration

A breadboard radar system is being designed and tested at NASA Johnson for dealing with the space debris problem that could present a growing threat to Space Station Freedom. The major design problems are due to the small radar cross section of such debris (below -30 dBm2), the high closing velocities of the particles with respect to the Space Station (10 km/sec and higher), and the stringent weight, power-consumption, maintenance, and reliability constraints on spaceborne systems. Consideration is given to the preliminary implementation of a ground demonstration radar for testing concepts, technologies, and performance envelopes for application to the space-borne debris detection and tracking radar. Simulation results and techniques developed for predicting system performance and for evaluating antenna parameters are given. The design process of the electronically steered phased array antenna is briefly described, and block diagrams for the implementation of the radar system are given.

Paz, I.↗
NASA NTRS1989

Computational fluid dynamics at the Lewis Research Center: An overview

Lewis is a multidisciplinary Center with strong research and development programs in aeronautical and space propulsion, power, space communications, space experiments and materials. Computational fluid dynamics (CFD) is playing an important and growing role in most of these areas. Described here is how CFD is integrated into these programs and highlights elements of the CFD activities. Examples are presented of codes developed to predict flow fields in advanced propulsion systems and several of the code validation experiments are described. The CFD effort at Lewis ranges from basic research on new and improved algorithms through code development to the application of these codes to specific engineering problems. Because of the substantial improvement in CFD's predictive capability, its use at Lewis is on a steep growth path, spreading rapidly into new areas which had not traditionally taken advantage of the techniques of numerical simulation. Multidisciplinary codes and the future direction of CFD at Lewis are discussed.

Stubbs, Robert M.↗
NASA NTRS1990

Techniques for hot structures testing

Hot structures test techniques developed and applied by the Aerostructures Branch of the NASA Ames Research Center, Dryden Flight Research Facility, are presented. Topics covered include the data acquisition and control of testing, the quartz lamp heater systems, current strain and temperature sensors, and hot structures test techniques used to simulate the flight thermal environment in the laboratory.

Deangelis, V. Michael↗
NASA NTRS1991

Vibration-dissociation coupling in nonequilibrium flows

The purpose of the study is to evaluate all important physical phenomena contributing to the vibration-dissociation problem by developing a numerical technique for the simulation of the vibrational relaxation and dissociation/recombination of N(2) in an isothermal box. A set of coupled master equations representing each vibrational level of N(2) is solved, and both V-V and V-T exchanges between molecules and atoms are included, along with the effects of dissociation and recombustion from/to each level. It is observed that the inverse range parameter has a strong impact on the vibrational exchange rates and relaxation. In a heating case, the lower vibrational levels relax through a series of equilibrium distributions, while in a cooling case, a population inversion is formed in the upper levels. Other cases of heating and cooling will be simulated, and together with this work, used to develop a matrix of nonequilibrium relaxation runs.

Landrum, D. Brian↗
NASA NTRS1992

Interplanetary program to optimize simulated trajectories (IPOST). Volume 4: Sample cases

The Interplanetary Program to Optimize Simulated Trajectories (IPOST) is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence of trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the cost function. Targeting and optimization are performed using the Standard NPSOL algorithm. The IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Hong, P. E.↗
NASA NTRS1992

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 1: User's guide

IPOST is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence fo trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the coat function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Hong, P. E.↗