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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Acoustoelasticity - Review and extension

Research on the interaction between the sound pressure field and the flexible wall of an enclosure is reviewed. The topics discussed include: a mathematical model, simplified solutions for sinusoidal excitation, damping, random excitation, numerical results, including comparisons with representative experimental data, and design analysis methodology. Results of various authors using finite element techniques and modal analysis suggest that effective analytical models are available.

Dowell, E. H.↗
NASA NTRS1982

Physiological responses to prolonged bed rest and fluid immersion in man: A compendium of research (1974 - 1980)

Water immersion and prolonged bed rest reproduce nearly all the physiological responses observed in astronauts in the weightless state. Related to actual weightlessness, given responses tend to occur sooner in immersion and later in bed rest. Much research was conducted on humans using these two techniques, especially by Russian scientists. Abstracts and annotations of reports that appeared in the literature from January 1974 through December 1980 are compiled and discussed.

Greenleaf, J. E.↗
NASA NTRS1985

Development of a wind shear performance envelope

It is quite important that the airplane performance during a continuing headwind loss be understood. Lack of consideration of this characteristic can result in assuming almost twice the performance than that which the airplane actually has during severe wind shear at high descent rates. The example data relates to the Boeing 727-200, but the characteristics are applicable to any airplane.

Bliss, J. H.↗
NASA NTRS1985

A new approach to the free wake problem for hovering rotors

In the present approach to the hovering rotor free wake problem, an influence coefficient solution method is used to find that rotor wake solution which is steady in a reference frame that rotates with the blades; this scheme solves directly for the conditions of free wake equilibrium by a procedure that does not involve time-stepping and the associated use of numerical damping or special convergence methods. The solution method has been implemented in a hover wake computer program having a three-part wake model for the tip vortex. All three wake regions are represented by the new Basic Curved Vortex Elements. Sample hover calculations are presented for single blade and multiblade rotors.

Bliss, D. B.↗
NASA NTRS1986

Voyager 2 in the Uranian system - Imaging science results

Details of the characteristics of the Uranian atmosphere and the surface features and projected formation processes of the Uranian moons are surveyed on the basis of 7000 images obtained by Voyager 2. Brightness distribution curves are provided for the CH4 Uranian atmosphere, and various anomalies, e.g., banding, that are apparent are discussed. Attention is given to the detectable cloud structure, circulation patterns and wind effects, noting that at certain latitudes the wind speeds exceed the planetary rotational velocity. The physical dimensions, orientations and compositions of the nine rings are described, along with the locations and sizes of the 10 shepherd satellites discovered between Miranda and Uranus. Finally, the large database accumulated on the visual characteristics of the five major satellites is examined in detail, particularly in relation to the orbits, origins, formation processes and surface features.

Smith, B. A.↗
NASA NTRS1987

Analyzing Wakes From Hovering-Helicopter Rotor Blades

New method for analyzing free wake of hovering-helicopter rotor produces more reliable results and requires less computer time. Copes with wake instabilities, both physical and numerical, that afflict usual time-stepping analysis methods. Tip-vortex position, in coordinates moving with rotor blade, updated in relaxation procedure. Wake-airflow solution reached when updates converge to steady wake shape.

Bliss, D. B.↗
NASA NTRS1987

Interior noise reduction by alternate resonance tuning

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at low frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is studied which considers aircraft fuselages lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panel would oscillate at equal amplitude, to give equal acoustic source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to be cut off, and therefore be nonpropagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is being investigated theoretically and experimentally. Progress to date is discussed.

Bliss, Donald B.↗
NASA NTRS1988

Dowel Remover

Special tool pulls dowel pins straight out of blind holes. Removes dowels without damaging them or possibly injuring user. Accepts most common dowel sizes, 1/8 to 5/8 inch. Tool is simple and inexpensive. Made from screw, threader bar, slotted pipe, and nut.

Blisse, Jerry↗
NASA NTRS1987

Aircraft interior noise reduction by alternate resonance tuning

Model problem development and analysis continues with the Alternate Resonance Tuning concept. Various topics are presently at different stages of completion and are described. These topics included optimization of panel mass ratios, panel computer code verification and agreement with experimental data, and flexible frame modeling.

Gottwald, James A.↗
NASA NTRS1988

Reduced order models for nonlinear aerodynamics

Reduced order models are needed for reliable, efficient and accurate prediction of aerodynamic forces to analyze fluid structure interaction problems in turbomachinery, including propfans. Here, a finite difference, time marching Navier-Stokes code is validated for unsteady airfoil motion by comparing results with those from classical potential flow. The Navier-Stokes code is then analyzed for calculation of primitive and exact estimates of eigenvalues and eigenvectors associated with fluid-airfoil interaction. A variational formulation for the Euler equations and Navier-Stokes equations will be the basis for reduction of order through an eigenvector transformation.

Mahajan, Aparajit J.↗
NASA NTRS1988

Aircraft interior noise reduction by alternate resonance tuning

Model problem development and analysis continues with the Alternate Resonance Tuning (ART) concept. The various topics described are presently at different stages of completion: investigation of the effectiveness of the ART concept under an external propagating pressure field associated with propeller passage by the fuselage; analysis of ART performance with a double panel wall mounted in a flexible frame model; development of a data fitting scheme using a branch analysis with a Newton-Raphson scheme in multiple dimensions to determine values of critical parameters in the actual experimental apparatus; and investigation of the ART effect with real panels as opposed to the spring-mass-damper systems currently used in much of the theory.

Bliss, Donald B.↗
NASA NTRS1987

Prediction of tip vortex self-induced motion parameters in terms of rotor blade loading

The self-induced motion of curved vortex filaments at the tip of a helicopter rotor blade is investigated analytically. The derivation of a method for inviscid roll-up (IRU) is presented in detail, with attention to the cutoff-distance reformulation of the problem, a control-volume analysis of the self-induction properties of the vortex core, the adaptation of the roll-up method of Betz (1932) to IRU in three dimensions, the treatment of linear and elliptic loading, vortices with turbulent central cores, and the effect of cutoff distance on helicopter free-wake computations. Numerical results showing the significant effect of core properties on the geometry of a rotor wake in hover are presented in graphs and briefly characterized.

Bliss, Donald B.↗
NASA NTRS1988

Computational analysis of hover performance using a new free wake method

The development of EHPIC (Evaluation of Hover Performance using Influence Coefficients), a hover performance analysis code incorporating a new free wake analysis method based on the use of influence coefficients, is discussed. The technical principles underlying the EHPIC code are examined with emphasis on the extension of single-filament wake models to a multi-bladed multifilament wake suitable for realistic hover performance predictions. The coupling of the wake model to a lifting surface loads analysis is described, and sample problems are solved to demonstrate the robustness of the method.

Quackenbush, Todd R.↗
NASA NTRS1989

Aircraft interior noise reduction by alternate resonance tuning

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselages lines with panels alternately tuned to frequencies above and below the frequency to be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cut off and therefore be non-propagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior noise due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations. This program summarizes the work carried out at Duke University during the third semester of a contract supported by the Structural Acoustics Branch at NASA Langley Research Center.

Bliss, Donald B.↗
NASA NTRS1989

Performance optimization for rotors in hover and axial flight

Performance optimization for rotors in hover and axial flight is a topic of continuing importance to rotorcraft designers. The aim of this Phase 1 effort has been to demonstrate that a linear optimization algorithm could be coupled to an existing influence coefficient hover performance code. This code, dubbed EHPIC (Evaluation of Hover Performance using Influence Coefficients), uses a quasi-linear wake relaxation to solve for the rotor performance. The coupling was accomplished by expanding of the matrix of linearized influence coefficients in EHPIC to accommodate design variables and deriving new coefficients for linearized equations governing perturbations in power and thrust. These coefficients formed the input to a linear optimization analysis, which used the flow tangency conditions on the blade and in the wake to impose equality constraints on the expanded system of equations; user-specified inequality contraints were also employed to bound the changes in the design. It was found that this locally linearized analysis could be invoked to predict a design change that would produce a reduction in the power required by the rotor at constant thrust. Thus, an efficient search for improved versions of the baseline design can be carried out while retaining the accuracy inherent in a free wake/lifting surface performance analysis.

Quackenbush, T. R.↗
NASA NTRS1988

Comparisons of predicted and measured rotor performance in hover using a new free wake analysis

A new free-wake analysis has been developed to predict the performance of rotors in hover and axial flight. The analysis finds the rotor wake geometry using a novel influence coefficient/relaxation scheme. In this paper, the features of the analysis are reviewed, and the accuracy of the analysis is assessed for a wide range of rotor configurations in hover and vertical climb. The effects of variations in the analysis parameters are addressed, and recommendations for future development are presented. Generally good results were obtained for the predicted performance of a wide range of rotor geometries and operating conditions without any special 'tuning' of the analysis. The analysis also provides predictions of rotor performance in vertical climb that are substantially more accurate than momentum theory.

Felker, Fort F.↗
NASA NTRS1989

Reduction of sound transmission through fuselage walls by alternate resonance tuning (A.R.T.)

The ability of alternate resonance tuning (ART) to block sound transmission through light-weight flexible paneled walls by controlling the dynamics of the wall panels is considered. Analytical results for sound transmission through an idealized panel wall illustrate the effect of varying system parameters and show that one or more harmonics of the incident sound field can be cancelled by the present method. Experimental results demonstrate that very large transmission losses with reasonable bandwidths can be achieved by a simple ART panel barrier in a duct.

Bliss, Donald B.↗