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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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At least 271 records · Page 15
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NASA NTRS1974

Measurement of tilt rotor VTOL rotor wake-airframe ground aerodynamic interference for application to real time flight simulation

The hover and low speed rotor wake-airframe-ground aerodynamic characteristics of the XV-15 tilt rotor research aircraft were determined in wind tunnel tests of a scale model. Results of the wind tunnel tests were applied to real flight time simulation. The principal findings of the wind tunnel tests are summarized. The effect of aerodynamic interference on the handling qualities of the aircraft is analyzed. It was determined that aerodynamic interference effects are significant in hover and at low speeds, with the influence being more pronounced in ground effect than out of it. At airspeeds above 60 knots, aerodynamic interference does not have a significant effect on handling characteristics.

Gaffey, T. M.↗
NASA NTRS1974

SUSSA ACTS: A computer program for steady and unsteady, subsonic and supersonic aerodynamics for aerospace complex transportation systems

The computer program SUSSA ACTS (Steady and Unsteady, Subsonic and Supersonic Aerodynamics for Complex Transportation Systems) are presented in the final version. The numerical formulation and the description of the program and numerical results are included. In particular, generalized forces for fully unsteady (complex frequency) aerodynamics for a wing-body configuration, in both subsonic and supersonic flows, are discussed. The mathematical analysis includes completely arbitrary motion. The numerical implementation was limited to steady and oscillatory flows. A more general aerodynamic formulation in the form of a fully transient response for time-domain analysis and the aerodynamic transfer function (Laplace transform of the fully unsteady operator) for frequency-domain analysis is outlined.

Tseng, K.↗
NASA NTRS1975

The finite element method in low speed aerodynamics

The finite element procedure is shown to be of significant impact in design of the 'computational wind tunnel' for low speed aerodynamics. The uniformity of the mathematical differential equation description, for viscous and/or inviscid, multi-dimensional subsonic flows about practical aerodynamic system configurations, is utilized to establish the general form of the finite element algorithm. Numerical results for inviscid flow analysis, as well as viscous boundary layer, parabolic, and full Navier Stokes flow descriptions verify the capabilities and overall versatility of the fundamental algorithm for aerodynamics. The proven mathematical basis, coupled with the distinct user-orientation features of the computer program embodiment, indicate near-term evolution of a highly useful analytical design tool to support computational configuration studies in low speed aerodynamics.

Baker, A. J.↗
NASA NTRS1975

Aerodynamic lift effect on satellite orbits

Numerical quadrature is employed to obtain orbit perturbation results from the general perturbation equations. Both aerodynamic lift and drag forces are included in the analysis of the satellite orbit. An exponential atmosphere with and without atmospheric rotation is used. A comparison is made of the perturbations which are caused by atmospheric rotation with those caused by satellite aerodynamic effects. Results indicate that aerodynamic lift effects on the semi-major axis and orbit inclination can be of the same order as the effects of atmosphere rotation depending upon the orientation of the lift vector. The results reveal the importance of including aerodynamic lift effects in orbit perturbation analysis.

Karr, G. R.↗
NASA NTRS1976

On the formulation of the aerodynamic characteristics in aircraft dynamics

The theory of functionals is used to reformulate the notions of aerodynamic indicial functions and superposition. Integral forms for the aerodynamic response to arbitrary motions are derived that are free of dependence on a linearity assumption. Simplifications of the integral forms lead to practicable nonlinear generalizations of the linear superpositions and stability derivative formulations. Applied to arbitrary nonplanar motions, the generalization yields a form for the aerodynamic response that can be compounded of the contributions from a limited number of well-defined characteristic motions, in principle reproducible in the wind tunnel. Further generalizations that would enable the consideration of random fluctuations and multivalued aerodynamic responses are indicated.

Tobak, M.↗
NASA NTRS1959

Aerodynamic design for supersonic speeds

The aerodynamic phenomena that may profitably be employed by the designer at subsonic speeds seem now to be well understood. At supersonic speeds such phenomena show a greater and more interesting variety. Search for the minimum number of guiding principles of design thus becomes more difficult and more dangerous. Studies which can cover an adequate range of geometrical form are at present limited to the linearized version of aerodynamic theory. Such studies, especially those by variational methods, have disclosed certain basic principles of design for aerodynamic efficiency. In present-day experiments, however, the indicated trends are rather quickly confronted with effects of viscosity and nonlinearities. While the theory indicates that good values of aerodynamic efficiency are possible at supersonic speeds it is not yet clear how closely these expectations may be approached in practice. In the present paper several arrangements of supporting surfaces and bodies are discussed and in some cases comparisons of theory and experiment are made. Finally, certain phenomena connected with lift and drag in a rarefied medium are considered briefly.

Robert T. Jones↗
NASA NTRS1976

Aerodynamic performance of flared fan nozzles used as inlets

Tests were conducted in a low speed wind tunnel to determine the aerodynamic performance of several flared fan nozzles. Each of the flared nozzles was a downstream-facing inlet to a model fan that was used to simulate a variable pitch fan during reverse thrust operation. The total pressure recovery of each of the flared nozzles as well as that of an unflared nozzle and a serrated flare nozzle was obtained for comparison. The aerodynamic performance of a selected flared nozzle was considered in further detail. The nozzle surface pressures for a flared nozzle were also determined. Results indicated that the differences in aerodynamic performance among the nozzles were most apparent at the wind-tunnel-off condition. A nonzero free stream velocity significantly reduced the perforamnce of all the nozzles, and crosswind flow (free stream flow perpendicular to the model axis) further reduced the performance of the nozzles. The unflared nozzle and the serrated flare nozzle had reduced aerodynamic performance compared to a solid surface flared nozzle.

Dietrich, D. A.↗
NASA NTRS1975

Small scale noise and wind tunnel tests of upper surface blowing nozzle flap concepts. Volume 1. Aerodynamic test results

The results and analyses of aerodynamic and acoustic studies conducted on the small scale noise and wind tunnel tests of upper surface blowing nozzle flap concepts are presented. Various types of nozzle flap concepts were tested. These are an upper surface blowing concept with a multiple slot arrangement with seven slots (seven slotted nozzle), an upper surface blowing type with a large nozzle exit at approximately mid-chord location in conjunction with a powered trailing edge flap with multiple slots (split flow or partially slotted nozzle). In addition, aerodynamic tests were continued on a similar multi-slotted nozzle flap, but with 14 slots. All three types of nozzle flap concepts tested appear to be about equal in overall aerodynamic performance but with the split flow nozzle somewhat better than the other two nozzle flaps in the landing approach mode. All nozzle flaps can be deflected to a large angle to increase drag without significant loss in lift. The nozzle flap concepts appear to be viable aerodynamic drag modulation devices for landing.

Renselaer, D. J.↗
NASA NTRS1976

Steady incompressible variable thickness shear layer aerodynamics

A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales. The analysis begins with the elementary wavy wall problem and, through Fourier superpositions over the wave number space, the shear flow equivalents to the aerodynamic transfer functions of classical potential flow are obtained. The aerodynamic transfer functions provide integral equations which relate the wall pressure and the upwash. Computational results are presented for the pressure distribution, the lift coefficient, and the center of pressure travel along a two dimensional flat plate in a shear flow. The aerodynamic load is decreased by the shear layer, compared to the potential flow. The variable thickness shear layer decreases it less than the uniform thickness shear layer based upon equal maximum shear layer thicknesses.

Chi, M. R.↗
NASA NTRS1976

Theoretical and empirical low perigee aerodynamic heating during orbital flight of an atmosphere explorer

This document presents the results of an extensive, low perigee, orbital aerodynamic heating study undertaken in support of the Atmosphere Explorer-C Temperature Alarm. Based upon in-flight orbital temperature data from the Temperature Alarm tungsten resistance wire thermometer, aerodynamic heating rates have been determined for eight selected orbits by means of a reduced thermal analytical model verified by both ground test and flight data. These heating rates are compared with the classical free molecular and first order collision regime values. It has been concluded that, for engineering purposes, the aerodynamic heating rate of atmospheric gases at perigee altitudes between 170 and 135 km on pure tungsten wire is 30 to 60% of the value set by the classical free molecular limit. Relative to the more usual orbital thermal input attributable to direct solar radiation, the aerodynamic heating rate at the lowest altitude attempted with the spacecraft despun (135 km) is the equivalent of about 1.2 solar constants incident on a tungsten wire with a solar absorptivity of 0.85.

Caruso, P. S., Jr.↗
NASA NTRS1977

Investigation of real-gas and viscous effects on the aerodynamic characteristics of a 40 deg half-cone with suggested correlations for the shuttle orbiter

Parameters were evaluated that might be used to correlate shuttle orbiter aerodynamic data to be used in extrapolating from wind-tunnel to flight conditions. Preliminary calculations indicate that the lee-side forces will have an insignificant influence on the aerodynamic characteristics of the orbiter for moderate angle-of-attack entries; therefore, this work is focused on phenomena which have an overriding influence on windward forces, namely, real-gas (equilibrium and nonequilibrium) and viscous-interaction effects. Analytically determined flow fields previously obtained on 40 deg blunted cones were used as a data source to evaluate various correlation parameters. Inviscid effects were found to be the dominant contributor to the aerodynamic coefficients in the altitude range of 64 to 76.2 km. The most suitable correlation of the aerodynamic forces on these cones is based on local dynamic pressure and local Mach number.

Hunt, J. L.↗
NASA NTRS1977

Recent advances in aerodynamic energy concept for flutter suppression and gust alleviation using active controls

Control laws are derived, by using realizable transfer functions, which permit relaxation of the stability requirements of the aerodynamic energy concept. The resulting aerodynamic eigenvalues indicate that both the trailing edge and the leading edge-trailing edge control systems can be made more effective. These control laws permit the introduction of aerodynamic damping and stiffness terms in accordance with the requirements of any specific system. Flutter suppression and gust alleviation problems can now be treated by either a trailing edge control system or by a leading edge-trailing edge control system by using the aerodynamic energy concept. Results are applicable to a wide class of aircraft operating at subsonic Mach numbers.

Nissim, E.↗
NASA NTRS1977

Scramjet exhaust simulation technique for hypersonic aircraft nozzle design and aerodynamic tests

Current design philosophy for scramjet-powered hypersonic aircraft results in configurations with the entire lower fuselage surface utilized as part of the propulsion system. The lower aft-end of the vehicle acts as a high expansion ratio nozzle. Not only must the external nozzle be designed to extract the maximum possible thrust force from the high energy flow at the combustor exit, but the forces produced by the nozzle must be aligned such that they do not unduly affect aerodynamic balance. The strong coupling between the propulsion system and aerodynamics of the aircraft makes imperative at least a partial simulation of the inlet, exhaust, and external flows of the hydrogen-burning scramjet in conventional facilities for both nozzle formulation and aerodynamic-force data acquisition. Aerodynamic testing methods offer no contemporary approach for such vehicle design requirements. NASA-Langley has pursued an extensive scramjet/airframe integration R&D program for several years and has recently developed a promising technique for simulation of the scramjet exhaust flow for hypersonic aircraft. Current results of the research program to develop a scramjet flow simulation technique through the use of substitute gas blends are described in this paper.

Hunt, J. L.↗
NASA NTRS1978

Future requirements and roles of computers in aerodynamics

While faster computers will be needed to make solution of the Navier-Stokes equations practical and useful, most all of the other aerodynamic solution techniques can benefit from faster computers. There is a wide variety of computational and measurement techniques, the prospect of more powerful computers permits extension and an enhancement across all aerodynamic methods, including wind-tunnel measurement. It is expected that, as in the past, a blend of methods will be used to predict aircraft aerodynamics in the future. These will include methods based on solution of the Navier-Stokes equations and the potential flow equations as well as those based on empirical and measured results. The primary flows of interest in aircraft aerodynamics are identified, the predictive methods currently in use and/or under development are reviewed and two of these methods are analyzed in terms of the computational resources needed to improve their usefulness and practicality.

Gregory, T. J.↗
NASA NTRS1976

Powered-Lift Aerodynamics and Acoustics

Powered lift technology is reviewed. Topics covered include: (1) high lift aerodynamics; (2) high speed and cruise aerodynamics; (3) acoustics; (4) propulsion aerodynamics and acoustics; (5) aerodynamic and acoustic loads; and (6) full-scale and flight research.

Source record↗
NASA NTRS1978

Fundamental Aspects of the Aerodynamics of Turbojet Engine Combustors

Aerodynamic considerations in the design of high performance combustors for turbojet engines are discussed. Aerodynamic problems concerning the preparation of the fuel-air mixture, the recirculation zone where primary combustion occurs, the secondary combustion zone, and the dilution zone were examined. An aerodynamic analysis of the entire primary chamber ensemble was carried out to determine the pressure drop between entry and exit. The aerodynamics of afterburn chambers are discussed. A model which can be used to investigate the evolution of temperature, pressure, and rate and efficiency of combustion the length of the chamber was developed.

Barrere, M.↗
NASA NTRS1978

Effect of flow separation vortices on aircraft unsteady aerodynamics

The unsteady aerodynamic flow field over the space shuttle orbiter was studied. The results indicate at moderate to high angles of attack separation-induced vortices exact a dominating influence on the unsteady aerodynamics of the space shuttle orbiter and of high performance aircraft. The main characteristics are as follows: (1) The vortex-induced aerodynamic loads are large and highly nonlinear, sometimes discontinuous in character; and (2) the vortex-induced loads have opposite effects on static and dynamic stability characteristics. Analytic approximations are presented which can predict these vortex-induced aerodynamic effects with the accuracy needed for most engineering design.

Ericsson, L. E.↗
NASA NTRS1981

Aerodynamic preliminary analysis system 2. Part 1: Theory

A subsonic/supersonic/hypersonic aerodynamic analysis was developed by integrating the Aerodynamic Preliminary Analysis System (APAS), and the inviscid force calculation modules of the Hypersonic Arbitrary Body Program. APAS analysis was extended for nonlinear vortex forces using a generalization of the Polhamus analogy. The interactive system provides appropriate aerodynamic models for a single input geometry data base and has a run/output format similar to a wind tunnel test program. The user's manual was organized to cover the principle system activities of a typical application, geometric input/editing, aerodynamic evaluation, and post analysis review/display. Sample sessions are included to illustrate the specific task involved and are followed by a comprehensive command/subcommand dictionary used to operate the system.

Bonner, E.↗