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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

An analytical and experimental evaluation of a Fresnel lens solar concentrator

An analytical and experimental evaluation of line focusing Fresnel lenses with application potential in the 200 to 370 C range was studied. Analytical techniques were formulated to assess the solar transmission and imaging properties of a grooves down lens. Experimentation was based on a 56 cm wide, f/1.0 lens. A Sun tracking heliostat provided a nonmoving solar source. Measured data indicated more spreading at the profile base than analytically predicted, resulting in a peak concentration 18 percent lower than the computed peak of 57. The measured and computed transmittances were 85 and 87 percent, respectively. Preliminary testing with a subsequent lens indicated that modified manufacturing techniques corrected the profile spreading problem and should enable improved analytical experimental correlation.

Hastings, L. J.↗
NASA NTRS1977

Experimental studies of trailing-edge conditions on an oscillating airfoil at frequency parameters of up to one

This paper describes an investigation to find the range of reduced frequencies over which the classical Kutta-Joukowsky condition is valid and the nature of deviations beyond this range. An NACA 64A010 airfoil with a 15-cm chord is supported between the side walls of a 25-cm x 35-cm low-speed wind tunnel and oscillated over reduced frequencies ranging from 0.05 to 1.2. The experimentally determined loading near the trailing edge is measured and compared with unsteady incompressible small-disturbance theory. Experimental data are obtained both with and without a boundary-layer trip. It is observed that application of the Kutta-Joukowsky condition in the theoretical analysis is valid below a reduced frequency of about 0.6 in predicting the loading in the trailing-edge region. At reduced frequencies beyond 0.8, the predicted results underestimate the measured loading near the trailing edge, and the deviations increase further with reduced frequency. Similarly, the experimental phase angle of the loading in the trailing-edge region agrees reasonably with the linear theory up to k = 0.8 but lags the predicted value beyond k = 0.8.

Satyanarayana, B.↗
NASA NTRS1977

NASA/Pratt and Whitney experimental clean combustor program: Engine test results

A two-stage vorbix (vortex burning and mixing) combustor and associated fuel system components were successfully tested in an experimental JT9D engine at steady-state and transient operating conditions, using ASTM Jet-A fuel. Full-scale JT9D experimental engine tests were conducted in a phase three aircraft experimental clean combustor program. The low-pollution combustor, fuel system, and fuel control concepts were derived from phase one and phase two programs in which several combustor concepts were evaluated, refined, and optimized in a component test rig. Significant pollution reductions were achieved with the combustor which meets the performance, operating, and installation requirements of the engine.

Roberts, R.↗
NASA NTRS1978

A parametric experimental study of the interference effects and the boundary-condition coefficient of slotted wind-tunnel walls

An experimental study of slotted upper and lower walls in a two-dimensional transonic wind tunnel with solid sidewalls is reported. Results are presented for several slot spacings and slot openness ratios. The experimental data are pressure measurements which were made on an airfoil model and on a sidewall near one of the slotted walls. The slotted-wall boundary-condition coefficient, which relates the pressure and streamline curvature near the wall, is determined from the wall pressure measurements. The measured wall-induced interference is correlated with the experimental values for the boundary-condition coefficient. This correlation is compared with theory.

Everhart, J. L.↗
NASA NTRS1978

A parametric experimental study of the slotted-wall boundary condition

An experimental study of slotted upper and lower walls in a two dimensional transonic wind tunnel with solid sidewalls is reported. Results are presented for several slot spacings and slot openness ratios. The experimental data were pressure measurements which were made on an airfoil model and on a sidewall near one of the slotted walls. The slotted-wall boundary condition coefficient, which related the pressure and streamline curvature near the wall, was determined from the wall pressure measurements. The measured wall-induced interference was correlated with the experimental values for the boundary condition coefficient. This correlation was compared with theory.

Everhart, J. L.↗
NASA NTRS1978

An analytical and experimental study of sound propagation and attenuation in variable-area ducts

The performance of sound suppression techniques in ducts that produce refraction effects due to axial velocity gradients was evaluated. A computer code based on the method of multiple scales was used to calculate the influence of axial variations due to slow changes in the cross-sectional area as well as transverse gradients due to the wall boundary layers. An attempt was made to verify the analytical model through direct comparison of experimental and computational results and the analytical determination of the influence of axial gradients on optimum liner properties. However, the analytical studies were unable to examine the influence of non-parallel ducts on the optimum linear conditions. For liner properties not close to optimum, the analytical predictions and the experimental measurements were compared. The circumferential variations of pressure amplitudes and phases at several axial positions were examined in straight and variable-area ducts, hard-wall and lined sections with and without a mean flow. Reasonable agreement between the theoretical and experimental results was obtained.

Nayfeh, A. H.↗
NASA NTRS1979

A comparison of simulated and experimental wave spectra in the nearshore region

The results of comparing the experimental spectra measured over the shelf with spectra measured in deepwater conditions indicated that statistically significant changes occurred over the shelf region that could be attributed to shoaling and refraction effects. The comparison of the simulated spectra with the experimental agreed well at the 80% confidence level for all but the most inshore data segment. The total energy also showed similar agreement. However, the theoretical frequency at which peak spectral density occurred did not follow the decreasing trend seen in the experimental data. Guidelines are proposed for determining the type wavefield to which the modeling technique can best be applied, and caution is given on the selection of the digitization rate necessary to ensure sufficient detail for analysis of wave data.

Morris, W. D.↗
NASA NTRS1978

Antecedents and analogues - Experimental aircraft

The paper reviews the development of experimental aircraft from 1953 to the present. Consideration is given to the X-series experimental aircraft, to X-15 (the first aerospace plane), to the transition of experimental aircraft to high-speed flight, to XB-70 research, to lifting body research aircraft, and to current high-speed flight research.

Smith, R. H.↗
NASA NTRS1980

The effect of hypodynamia on mineral and protein metabolism in calcified tissues of the maxillodental system (experimental radioisotope study)

Mineral and protein metabolism was studied in experiments on 60 white rats, using P-32 and Ca-45 uptake in the mineral fractions, 2C-14-glycine in the protein fractions, and P-32 in both fractions of calcified tissues as indices over a 100 day period of experimental hypodynamia. Combined alterations in mineral and protein metabolism occurred in the calcified tissues of the experimental animals. The most pronounced changes were found in P-32 and 2C-14-glycine metabolism. In the incisors and femoral bones, these alterations occurred in two phases: P-32 and 2C-14-glycine uptake first increased, then decreased. Changes in Ca-45 metabolism were less pronounced, particularly in the initial period of the experiment. A marked reduction in P-32, Ca-45, and 2C-14-glycine uptake was found in various fractions of the calcified tissues on the 100th day of experimental hypodynamia.

Prokhonchukov, A. A.↗
NASA NTRS1981

A validation of LTRAN2 with high frequency extensions by comparisons with experimental measurements of unsteady transonic flows

A high frequency extension of the unsteady, transonic code LTRAN2 was created and is evaluated by comparisons with experimental results. The experimental test case is a NACA 64A010 airfoil in pitching motion at a Mach number of 0.8 over a range of reduced frequencies. Comparisons indicate that the modified code is an improvement of the original LTRAN2 and provides closer agreement with experimental lift and moment coefficients. A discussion of the code modifications, which involve the addition of high frequency terms of the boundary conditions of the numerical algorithm, is included.

Hessenius, K. A.↗
NASA NTRS1981

Combustion experimentation aboard the space transportation system

A description is presented of the preliminary concept, specifications, and general requirements of a proposed Combustion Facility (CF) for the Spacelab payload of the Space Transportation System. The CF will permit an experimenter to use suitably contained liquid, gas, or solid fuels. He can specify and establish the composition and pressure level of the atmosphere in which the combustion will take place. It will be possible to characterize the experiment with common types of instrumentation as well as selected specialized equipment, to study the combustion process visually by direct observation and by motion picture coverage, and to obtain time histories of pertinent experimental parameters. During an experimental period, the CF will depend on Spacelab resources for power, heat rejection, and vacuum. Activating the CF and preparing it for the various experiments, performing the experiments, and shutting down the facility will be largely manual operations performed by flight personnel.

Dewitt, R. L.↗
NASA NTRS1956

Experimental Droplet Impingement on Several Two-Dimensional Airfoils with Thickness Ratios of 6 to 16 Percent

The rate and area of cloud droplet impingement on several two-dimensional swept and unswept airfoils were obtained experimentally in the NACA Lewis icing tunnel with a dye-tracer technique. Airfoil thickness ratios of 6 to 16 percent; angles of attack from 0 deg to 12 deg, and chord sizes from 13 to 96 inches were included in the study. The data were obtained at 152 knots and are extended to other conditions by dimensionless impingement parameters. In general, the data show that the total and local collection efficiencies and impingement limits are primary functions of the modified inertia parameter (in which airspeed, droplet size, and body size are the most significant variables) and the airfoil thickness ratio. Local collection efficiencies and impingement limits also depend on angle of attack. Secondary factors affecting impingement characteristics are airfoil shape, camber, and sweep angle. The impingement characteristics obtained experimentally for the airfoils were within +/-10 percent on the average of the characteristics calculated from theoretical trajectories. Over the range of conditions studied, the experimental data demonstrate that a specific method can be used to predict the impingement characteristics of swept airfoils with large aspect ratios from the data for unswept airfoils of the same series.

Gelder, Thomas F.↗
NASA NTRS1957

Experimental Droplet Impingement on Four Bodies of Revolution

The rate and. area of cloud droplet impingement on four bodies of revolution were obtained experimentally in the NACA Lewis icing tunnel with a dye-tracer technique. The study included spheres, ellipsoidal forebodies of fineness ratios of 2.5 and 3.0, and a conical forebody of 300 included angle and covered a range of angles of attack from 0? to 60 and rotational speeds up to 1200 rpm. The data were obtained at an airspeed of 157 knots and are correlated by dimensionless impingement parameters. In general, the experimental data show that the local and total impingement rates and impingement limits of bodies of revolution are primarily functions of the modified inertia parameters, the body shape, and fineness ratio. Both the local impingement rate and impingement limits depend upon the angle of attack. Rotation of the bodies had a negligible effect on the impingement characteristics except for an averaging effect at angle of attack. For comparable diameters the bluffer bodies had the largest total impingement efficiency, but the finer and sharper bodies had the largest values of maximum local impingement efficiency and, in most cases, the largest limits of impingement. In most cases, the impingement characteristics were less than those calculated from theoretical trajectories; in general, however, fairly good agreement was obtained between the experimental and theoretical impingement characteristics.

Lewis, James P.↗
NASA NTRS1981

Experimental validation of a numerical model predicting the charging characteristics of Teflon and Kapton under electron beam irradiation

The effect differential charging of spacecraft thermal control surfaces is assessed by studying the dynamics of the charging process. A program to experimentally validate a computer model of the charging process was established. Time resolved measurements of the surface potential were obtained for samples of Kapton and Teflon irradiated with a monoenergetic electron beam. Results indicate that the computer model and experimental measurements agree well and that for Teflon, secondary emission is the governing factor. Experimental data indicate that bulk conductivities play a significant role in the charging of Kapton.

Hazelton, R. C.↗
NASA NTRS1982

Comparison between computations and experimental data in unsteady three-dimensional transonic aerodynamics, including aeroelastic applications

Comparisons were made of computed and experimental data in three-dimensional unsteady transonic aerodynamics, including aeroelastic applications. The computer code LTRAN3, which is based on small-disturbance aerodynamic theory, was used to obtain the aerodynamic data. A procedure based on the U-g method was developed to compute flutter boundaries by using the unsteady aerodynamic coefficients obtained from LTRAN3. The experimental data were obtained from available NASA publications. All the studies were conducted for thin, unswept, rectangular wings with circular-arc cross sections. Numerical and experimental steady and unsteady aerodynamic data were compared for a wing with an aspect ratio of 3 and a thickness ratio of 5% at Mach numbers of 0.7 and 0.9. Flutter data were compared for a wing with an aspect ratio of 5. Two thickness ratios, 6% at Mach numbers of 0.715, 0.851, and 0.913, and 4% at Mach number of 0.904, were considered. Based on the unsteady aerodynamic data obtained from LTRAN3, flutter boundaries were computed; they were compared with those obtained from experiments and the code NASTRAN, which uses linear aerodynamics.

Guruswamy, P.↗
NASA NTRS1982

Comparison of analytical and experimental subsonic steady and unsteady pressure distributions for a high-aspect-ratio-supercritical wing model with oscillating control surfaces

The results of a comparative study using the unsteady aerodynamic lifting surface theory, known as the Doublet Lattice method, and experimental subsonic steady- and unsteady-pressure measurements, are presented for a high-aspect-ratio supercritical wing model. Comparisons of pressure distributions due to wing angle of attack and control-surface deflections were made. In general, good correlation existed between experimental and theoretical data over most of the wing planform. The more significant deviations found between experimental and theoretical data were in the vicinity of control surfaces for both static and oscillatory control-surface deflections.

Mccain, W. E.↗
NASA NTRS1983

Comparison of predicted and experimental external heat transfer around a film cooled cylinder in crossflow

Calculations were made of the film cooling provided by rows of holes around the circumference of a cylinder in crossflow and the results were compared to experimental data. The calculations and experimental data were for conditions that simulate most of those that are typical of air cooled turbine vane leading edges. Injection was from a single and multiple rows of holes located at different angular locations from the stagnation line. The holes in the rows were angled normal to the flow direction and at a 25 degree angle to the cylinder wall. The calculations and experimental data were for several constant values of blowing ratios for all rows and for different blowing ratios for each row, representing a simulation of a common coolant plenum supply to multiple rows of holes. The calculations were made using a finite difference boundary layer code, STAN5. Contrary to initial expectations that injection would trip the boundary layer flow into the turbulent regime, the results indicated that the high free stream acceleration apparently kept the flow laminar for holes in the first 45 degrees past stagnation. The trend in Stanton number reduction due to coolant injection was predicted with generally good agreement at the lower blowing rates, but for multile rows of holes, agreement was poor beyond the first row.

Stepka, F. S.↗
NASA NTRS1982

Survey of engineering computational methods and experimental programs for estimating supersonic missile aerodynamic characteristics

This paper presents a survey of engineering computational methods and experimental programs used for estimating the aerodynamic characteristics of missile configurations. Emphasis is placed on those methods which are suitable for preliminary design of conventional and advanced concepts. An analysis of the technical approaches of the various methods is made in order to assess their suitability to estimate longitudinal and/or lateral-directional characteristics for different classes of missile configurations. Some comparisons between the predicted characteristics and experimental data are presented. These comparisons are made for a large variation in flow conditions and model attitude parameters. The paper also presents known experimental research programs developed for the specific purpose of validating analytical methods and extending the capability of data-base programs.

Sawyer, W. C.↗