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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Comparison of propeller cruise noise data taken in the NASA Lewis 8- by 6-foot wind tunnel with other tunnel and flight data

The noise of advanced high speed propeller models measured in the NASA 8- by 6-foot wind tunnel has been compared with model propeller noise measured in another tunnel and with full-scale propeller noise measured in flight. Good agreement was obtained for the noise of a model counterrotation propeller tested in the 8- by 6-foot wind tunnel and in the acoustically treated test section of the Boeing Transonic Wind Tunnel. This good agreement indicates the relative validity of taking cruise noise data on a plate in the 8- by 6-foot wind tunnel compared with the free-field method in the Boeing tunnel. Good agreement was also obtained for both single rotation and counter-rotation model noise comparisons with full-scale propeller noise in flight. The good scale model to full-scale comparisons indicate both the validity of the 8- by 6-foot wind tunnel data and the ability to scale to full size. Boundary layer refraction on the plate provides a limitation to the measurement of forward arc noise in the 8- by 6-foot wind tunnel at the higher harmonics of the blade passing tone. The use of a validated boundary layer refraction model to adjust the data could remove this limitation.

Dittmar, James H.↗
NASA NTRS1989

A comparison of radar measurements of atmospheric turbulence intensities by both C sub n sup 2 and spectral width methods

There are two main techniques by which turbulence intensities in the atmosphere can be measured by radars. One is to utilize the absolute backscattered power received by the radar, and use this to deduce C sub n sup 2 (refractivity turbulence structure constant). With appropriate assumptions, this parameter can then be converted to an energy dissipation rate. The second method utilizes the width of the spectrum of the signal received by the radar. Neither of these techniques have been used a great deal, and they have never been properly compared. Thus it was not possible to determine the validity of the assumptions made in applying each technique, nor was it possible to determine the limitations of each method. The first comparisons of the two techniques are presented. Measurements were made with the Adelaide VHF ST radar, and the results of the comparison are discussed.

Hocking, W. K.↗
NASA NTRS1989

On ice shape prediction methodologies and comparison with experimental data

Comparisons are made between the analysis of Wilder (1969), Bragg (1982), and the ice shape predictions of LEWICE given a specific airfoil geometry and set of meteorological conditions. Also, comparisons are made between the actual ice shapes as found in flight tests of the NASA Lewic RC Twin Otter and that predicted by the approximate methods noted earlier and LEWICE. Further, an investigation of two important parameters in the analysis of LEWICE has been made. Time stepping and initial surface roughness has been varied to identify any trends in the results. Guidelines have been identified for the correlation of these two parameters with the results in terms of atmospheric conditions. The range of meteorological conditions chosen, such as droplet diameter, free air temperature, and liquid water content has allowed rime, mixed, and glaze ice shapes at the leading edge of an airfoil to be investigated.

Korkan, K. D.↗
NASA NTRS1989

Comparison of propeller cruise noise data taken in the NASA Lewis 8- by 6-foot wind tunnel with other tunnel and flight data

The noise of advanced high speed propeller models measured in the NASA 8- by 6-foot wind tunnel has been compared with model propeller noise measured in another tunnel and with full-scale propeller noise measured in flight. Good agreement was obtained for the noise of a model counterrotation propeller tested in the 8- by 6-foot wind tunnel and in the acoustically treated test section of the Boeing Transonic Wind Tunnel. This good agreement indicates the relative validity of taking cruise noise data on a plate in the 8- by 6-foot wind tunnel compared with the free-field method in the Boeing tunnel. Good agreement was also obtained for both single rotation and counter-rotation model noise comparisons with full-scale propeller noise in flight. The good scale model to full-scale comparisons indicate both the validity of the 8- by 6-foot wind tunnel data and the ability to scale to full size. Boundary layer refraction on the plate provides a limitation to the measurement of forward arc noise in the 8- by 6-foot wind tunnel at the higher harmonics of the blade passing tone. The sue of a validated boundary layer refraction model to adjust the data could remove this limitation.

Dittmar, James↗
NASA NTRS1989

Comparison of conventional and adaptive wall wind tunnel results with regard to Reynolds number effects

A comparison of results from conventional and adaptive wall wind tunnels with regard to Reynolds number effects was carried out. The special objective of this comparison was to confirm or reject earlier conclusions, soley based on conventional wind tunnel results, concerning the influence of viscous effects on the characteristics of partially open wind tunnel walls, hence wall interference. The following postulations could be confirmed: (1) certain classes of supercritical airfoils exhibit a non-linear increase in lift which is, at least in part, related to viscous-inviscid interactions on the airfoil. This non-linear lift characteristic can erroneously be suppressed by sidewall interference effects in addition to being affected by changes in Reynolds number. Adaptive walls seem to relieve the influence of sidewall interference; (2) the degree of (horizontal) wall interference effects can be significantly affected by changes in Reynolds number, thus appearing as true Reynolds number effects; (3) perforated wall characteristics seem much more susceptible to viscous changes than the characteristics of slotted walls; here, blockage interference may be most severely influenced by viscous changes; and (4) real Reynolds number effects are present on the CAST 10-2/DOA 2 airfoil; they were shown to be appreciable also by the adaptive wall wind tunnel tests.

Stanewsky, E.↗
NASA NTRS1989

Comparison of satellite derived dynamical quantities in the stratosphere of the Southern Hemisphere

The proceedings are summarized from a pre-MASH planning workshop on the intercomparison of Southern Hemisphere observations, analyses and derived dynamical quantities held in Williamsburg, Virginia during April 1986. The aims of this workshop were primarily twofold: (1) comparison of Southern Hemisphere dynamical quantities derived from various satellite data archives (e.g., from limb scanners and nadir sounders); and (2) assessing the impact of different base-level height information on such derived quantities. These tasks are viewed as especially important in the Southern Hemisphere because of the paucity of conventional measurements. A further strong impetus for the MASH program comes from the recent discovery of the springtime ozone hold over Antarctica. Insight gained from validation studies such as the one reported here will contribute to an improved understanding of the role of meteorology in the development and evolution of the hold, in its interannual variability, and in its interhemispheric differences. The dynamical quantities examined in this workshop included geopotential height, zonal wind, potential vorticity, eddy heat and momentum fluxes, and Eliassen-Palm fluxes. The time periods and data sources constituting the MASH comparisons are summarized.

Miles, Thomas↗
NASA NTRS1989

A day-to-day comparison study of Seasat scatterometer winds with winds observed from islands in the tropical Pacific

The winds derived from the Seasat-A Satellite Scatterometer (SASS) measurements have been the subject of great interest since the 1978 mission, because of the promise of radically improved wind observations over the world ocean. Due to the early end of the mission, only a few of the planned ground truth validation experiments could be made, and the subsequent lack of sufficient high quality independent wind data for comparison has limited the ability to resolve critical issues regarding the scatterometer's performance and the correct interpretation of its signal. Operational weather observations were made of ocean winds independent of Seasat mission plans during the Seasat mission period; the results are reported of a comparison study using such observations. Previous verification with in situ winds has been primarily in middle latitudes (GOASEX, JASIN, and NDBO buoys); winds observed from nine tropical Pacific islands are compared with nearly contemporaneous measurements taken by SASS during overpasses of the islands.

Davison, Jerry↗
NASA NTRS1989

The consistent comparison problem in N-version software

The authors have identified a difficulty in the implementation of N-version programming. The problem, called the consistent comparison problem, arises for applications in which decisions are based on the results of comparing finite-precision numbers. It is shown that when versions make comparisons involving the results of finite-precision calculations, it is impossible to guarantee the consistency of their results. It is therefore possible that correct versions may arrive at completely different outputs for an application that does not apparently have multiple correct solutions. If this problem is not dealt with explicitly, an N-version system may be unable to reach consensus even when none of its component versions falls.

Brilliant, Susan S.↗
NASA NTRS1990

Comparison of three-dimensional nonequilibrium PNS codes

A comparison study has been conducted using four recently developed parabolized Navier-Stokes (PNS) codes which have the capability of predicting finite-rate, chemically reacting flows over three-dimensional bodies. These are the (1) UPS code, (2) the STUFF code, (3) the TONIC code, and (4) the VRA-PNS code. All of the codes use the same seven-species, single-temperature air chemistry model, but otherwise they are unique, with different capabilities and characteristics. The differences include upwinding vs central differencing, strongly-coupled vs weakly-coupled chemistry, shock capturing vs shock fitting, finite volume vs finite difference, and full PNS vs thin-layer PNS equations. Three test cases were utilized to compare the codes. The comparisons presented indicate a good agreement among the codes tested.

Buelow, Philip E.↗
NASA NTRS1989

A comparison of various micromechanics models for metal matrix composites

Four micromechanics models currently used in the analysis of metal matrix composites are reviewed. The four models are the vanishing fiber diameter model, the Aboudi model, the multicell model, and discrete fiber-matrix model. Results predicted by computer programs based on each of the models are compared. Comparisons are made for the laminate properties and laminate stress-strain behavior for boron/aluminum and silicon-carbide/titanium composites. The predictions of constituent stresses are also compared. The predictions are compared to experimental data. Each of the models did a reasonably good job predicting laminate properties and stress-strain behavior. Thus, the discriminator between the models is a question of what type of results are required, the capabilities of the model and program, or the ease of operation. The choice of a model and program depends on several factors and the same program may not be the best choice for all analysis needs. The descriptions and comparisons made in this paper should aid in the choice of a model and program.

Bigelow, C. A.↗
NASA NTRS1990

The ROTONET prediction system and initial comparisons with far-field acoustics measurements for the XV-15 tilt-rotor aircraft

The NASA Langley Research Center is developing the ROTONET prediction system, a comprehensive computer program for the prediction of full system rotorcraft noise, to provide an analytical tool for estimating the total noise signature of rotorcraft. It contains models of many rotorcraft noise generating mechanisms. NASA is also performing a series of flight tests to provide comprehensive validation data bases for the ROTONET System. A joint NASA/Bell Helicopter Textron Incorporated test of an XV-15 tilt-rotor aircraft is one of several flight test which has been performed. A data base consisting of spectra, noise level time histories, and effective perceived noise levels, incorporating actual meteorological conditions, and tilt-order aircraft flight dynamics, is being produced from this test. The ROTONET prediction system is described, the flight test methodology is explained, and initial comparisons are shown of ROTONET predictions with data from the flight test. EPNL, noise level time history, and narrowband noise spectra comparisons demonstrate the overall capabilities of the prediction system.

Golub, Robert A.↗
NASA NTRS1990

Comparison of equivalent plate and finite element analysis of a realistic aircraft structural configuration

This paper presents a comparison study to assess how well a realistic aircraft structure can be represented with an equivalent plate model. A wing box and full wing structure of a high-speed civil transport aircraft configuration are analyzed. Static and vibration results from the equivalent plate analysis are compared with results from a finite element model. The results from these comparisons show that, for the simpler wing box models, the static displacements and first vibration frequency agree to within 1.5 percent. The full wing models only agree to within 10 percent, for both models, the higher frequencies vary by as much as 26 percent. These differences are due to inadequate refinement of the equivalent plate model.

Kao, Pi-Jen↗
NASA NTRS1990

A comparison of UV surface brightness and HI surface densities for spiral galaxies

Shaya and Federman (1987) suggested that the ambient ultraviolet flux at 1000 A permeating a spiral galaxy controls the neutral hydrogen (HI) surface density in the galaxy. They found that the atomic envelopes surrounding small molecular clouds, because of their great number, provide the major contribution to the HI surface density over the stellar disk. The increase in HI surface density with later Hubble types was ascribed to the stronger UV fields from more high-mass stars in later Hubble types. These hypotheses are based on the observations of nearby diffuse interstellar clouds, which show a sharp atomic-to-molecular transition (Savage et al. 1977), and on the theoretical framework introduced by Federman, Glassgold, and Kwan (1979). Atomic envelopes around interstellar clouds in the solar neighborhood arise when a steady state is reached between photodissociation of H2 and the formation of H2 on grains. The photodissociation process involves photons with wavelengths between 912 A and 1108 A. Shaya and Federman used H-alpha flux as an approximate measure for the far UV flux and made their comparisons based on averages over Hubble type. Here, researchers compare, on an individual basis, UV data obtained with space-borne and balloon-borne instruments for galaxies with measurements of HI surface density (Warmels 1988a, b). The comparisons substantiate the conclusion of Shaya and Federman that the far UV field controls the HI content of spiral galaxies.

Federman, S. R.↗
NASA NTRS1990

Comparison of digital controllers used in magnetic suspension and balance systems

Dynamic systems that were once controlled by analog circuits are now controlled by digital computers. Presented is a comparison of the digital controllers presently used with magnetic suspension and balance systems. The overall responses of the systems are compared using a computer simulation of the magnetic suspension and balance system and the digital controllers. The comparisons include responses to both simulated force and position inputs. A preferred digital controller is determined from the simulated responses.

Kilgore, William A.↗
NASA NTRS1991

Comparison of several system identification methods for flexible structures

In the last few years various methods of identifying structural dynamics models from modal testing data have appeared. A comparison is presented of four of these algorithms: the Eigensystem Realization Algorithm (ERA), the modified version ERA/DC where DC indicated that it makes use of data correlation, the Q-Markov Cover algorithm, and an algorithm due to Moonen, DeMoor, Vandenberghe, and Vandewalle. The comparison is made using a five mode computer module of the 20 meter Mini-Mast truss structure at NASA Langley Research Center, and various noise levels are superimposed to produced simulated data. The results show that for the example considered ERA/DC generally gives the best results; that ERA/DC is always at least as good as ERA which is shown to be a special case of ERA/DC; that Q-Markov requires the use of significantly more data than ERA/DC to produce comparable results; and that is some situations Q-Markov cannot produce comparable results.

Lew, J.-S.↗
NASA NTRS1991

Model comparison of July 7, 1990 microburst

Model comparison of July 7, 1990 microburst is presented in the form of view-graphs. The following topics are covered: 7 July 1990 Orlando, FL simulations; model input sounding for 7 July 1990 Orlando case; 7 July 1990 Orlando microburst; and comparison of simulated and observed characteristics of microburst event.

Proctor, Fred↗
NASA NTRS1991

Comparison of a quasi-3D analysis and experimental performance for three compact radial turbines

An experimental aerodynamic evaluation of three compact radial turbine builds was performed. Two rotors which were 40 to 50 percent shorter in axial length than conventional state of the art radial rotors were tested. A single nozzle design was used. One rotor was tested with the nozzle at two stagger angle settings. A second rotor was tested with the nozzle in only the closed down setting. Experimental results were compared to predict results from a quasi-3D inviscid and boundary layer analysis, called Meridl/Tsonic/Blayer (MTSB). This analysis was used to predict turbine performance. It has previously been calibrated only for axial, not radial, turbomachinery. The predicted and measured efficiencies were compared at the design point for the three turbines. At the design points the analysis overpredicted the efficiency by less than 1.7 points. Comparisons were also made at off-design operating points. The results of these comparisons showed the importance of an accurate clearance model for efficiency predictions and also that there are deficiencies in the incidence loss model used.

Simonyi, P. S.↗
NASA NTRS1991

Comparisons of elastic and rigid blade-element rotor models using parallel processing technology for piloted simulations

A piloted comparison of rigid and aeroelastic blade-element rotor models was conducted at the Crew Station Research and Development Facility (CSRDF) at Ames Research Center. A simulation development and analysis tool, FLIGHTLAB, was used to implement these models in real time using parallel processing technology. Pilot comments and quantitative analysis performed both on-line and off-line confirmed that elastic degrees of freedom significantly affect perceived handling qualities. Trim comparisons show improved correlation with flight test data when elastic modes are modeled. The results demonstrate the efficiency with which the mathematical modeling sophistication of existing simulation facilities can be upgraded using parallel processing, and the importance of these upgrades to simulation fidelity.

Hill, Gary↗