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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Experimental aerodynamic characteristics of an NACA 0012 airfoil with simulated glaze ice

The effect of a simulated glaze-ice accretion on the aerodynamic performance of a NACA 0012 airfoil was studied experimentally. Two ice shapes were tested: one from an experimentally measured accretion, and one from an accretion predicted using a computer model given the same icing conditions. Lift, drag, and pitching moment were measured for the airfoil with both smooth and rough ice shapes. The ice shapes caused large lift and drag penalties, primarily due to large separation bubbles. Surface pressure distributions clearly showed the regions of separated flow. The aerodynamic performance of the two shapes compared well at positive, but not negative, angles of attack.

Bragg, M. B.↗
NASA NTRS1988

An experimental adaptive array to suppress weak interfering signals

An experimental adaptive antenna system to suppress weak interfering signals is described. It is a sidelobe canceller with two auxiliary elements. Modified feedback loops are used to control the array weights. The received signals are simulated in hardware for parameter control. Digital processing is used for algorithm implementation and performance evaluation. The experimental results are presented. They show that interfering signals as much as 10 dB below the thermal noise level in the main channel are suppressed by 20-30 dB. Such a system has potential application in suppressing the interference encountered in direct broadcast satellite communication systems.

Walton, Eric K.↗
NASA NTRS1989

Experimental results for labyrinth gas seals with honeycomb stators - Comparisons to smooth-stator seals and theoretical predictions

Experimental measurements are presented for the rotordynamic stiffness and damping coefficients of a teeth-on-rotor labyrinth seal with a honeycomb stator. Inlet circumferential velocity, inlet pressure, rotor speed, and seal clearance are primary variables. Results are compared to data for teeth-on-rotor labyrinth seals with smooth stators and to analytical predictions from a two-control-volume compressible flow model. The experimental results show that the honeycomb-stator configuration is more stable than the smooth-stator configuration at low rator speeds. At high rotor speeds, the stator surface does not affect stability. The theoretical model predicts the cross-coupled stiffness of the honeycomb-stator seal correctly within 25 percent of measured values. The model provides accurate predictions of direct damping for large clearance seals; however, the model predictions and test results diverge with increasing running speed. Overall, the model does not perform as well for low clearance seals as for high clearance seals.

Hawkins, Larry↗
NASA NTRS1989

TranAir and Euler computations of a generic fighter including comparisons with experimental data

The TranAir full-potential code and the FLO57 Euler code were used to calculate transonic flow solutions over two configurations of a generic fighter model. The results were computed at Mach numbers of 0.60 and 0.80 for angles of attack between 0 and 12 deg for TranAir and between 4 and 20 deg for FLO57. Due to the fact that TranAir solves the full-potential equations for transonic flow, TranAir is only accurate to about alpha = 8 deg, at which point the experimental results show the formation of a vortex at the leading edge. Euler results show good agreement with experimental results until vortex breakdown occurs in the solutions.

Goodsell, Aga M.↗
NASA NTRS1988

Results from NASA Langley experimental studies of multiaxis thrust vectoring nozzles

Multiaxis thrust-vectoring nozzles can furnish substantial combat performance gains for military aircraft; in pursuit of these gains, NASA-Langley has conducted an extensive experimental research program encompassing both static and freestream performance evaluations for numerous multiaxis thrust-vectoring nozzle concepts using air-powered simulation models. An evaluation is presently made of a selection of these experimental results. Two-dimensional and axisymmetric convergent-divergent configurations and hybrid configurations, with and without postexit vanes, have been studied.

Berrier, Bobby L.↗
NASA NTRS1989

Experimental studies of adaptive structures for precision performance

An experimental study was made of the adaptive structure concept. Experimental data were obtained for a three-longeron, thirteen-bay truss-type test structure. This test structure can be softly suspended as well as rigidly clamped at the central bay. The load-carrying active member consists of a stack of concentric piezoelectric wafers, an eddy current displacement sensor, and a strain gage force sensor. A bridge (or compound) feedback technique developed in communication engineering is applied to the problem of active damping augmentation in adaptive structures. Using collocated force and velocity feedback around the active member, a desired output mechanical impedance can be implemented to maximize energy absorption by the active members. In addition, large gains can be implemented to linearize the active member's nonlinear behavior. Good agreements with linear finite element analysis was found for both static and dynamic structural responses. An 11 percent damping in the first bending mode was demonstrated in the closed-loop damping experiment.

Chen, G.-S.↗
NASA NTRS1989

The nature and barium partitioning between immiscible melts - A comparison of experimental and natural systems with reference to lunar granite petrogenesis

Elemental partitioning between immiscible melts has been studied using experimental liquid-liquid Kds and those determined by analysis of immiscible glasses in basalt mesostases in order to investigate lunar granite petrogenesis. Experimental data show that Ba is partitioned into the basic immiscible melt, while probe analysis results show that Ba is partitioned into the granitic immiscible melt. It is concluded that lunar granite of significant size can only occur in a plutonic or deep hypabyssal environment.

Neal, C. R.↗
NASA NTRS1989

Comparison of experimental and calculated attachment rate constants for CFCl3 and CCl4 in the temperature range 294-500 K

Electron-attachment cross sections and rate constants have been measured and calculated for the dissociative attachment processes e + CFCl3 - Cl(-) + CFCl2 and e + CCl4 - Cl(-) + CCl3. Good agreement over the electron-energy range 1-200 meV is found in energy dependence between present calculated cross sections and experimental cross sections at 300 K. The same calculation, with suitable adjustment of thermal populations, was used to calculate electron-attachment rate constants in the range 50-600 K. Experimental rate constants for CFCl3 and CCl4 were measured at temperatures of 294, 404, and 496 K (CFCl3) and 294, 400, and 500 K (CCl4) using the Cavalleri electron-density sampling method. Good agreement is found between present measurements and calculations, poor agreement with flowing-afterglow Langmuir-probe (FALP) data in CFCl3 at the higher temperatures, and reasonable agreement with FALP data for CCl4.

Orient, O. J.↗
NASA NTRS1989

An approach to experimental evaluation of real-time fault-tolerant distributed computing schemes

A testbed-based approach to the evaluation of fault-tolerant distributed computing schemes is discussed. The approach is based on experimental incorporation of system structuring and design techniques into real-time distributed-computing testbeds centered around tightly coupled microcomputer networks. The effectiveness of this approach has been experimentally confirmed. Primary advantages of this approach include the accuracy of the timing and logical-complexity data and the degree of assurance of the practical effectiveness of the scheme evaluated. Various design issues encountered in the course of establishing the network testbed facilities are discussed, along with their augmentation to support some experiments. The shortcomings of the testbeds are also discussed together with the desired extensions of the testbeds.

Kim, K. H.↗
NASA NTRS1989

Mach 5 inlet CFD and experimental results

An experimental research program was conducted in the NASA Lewis Research Center 10 ft. by 10 ft. supersonic wind tunnel. The two-dimensional inlet model was designed to study the Mach 3.0 to 5.0 speed range for an 'over-under' turbojet plus ramjet propulsion system. The model was extensively instrumented to provide both analytical code validation data as well as inlet performance information. Support studies for the program include flow field predictions with both three-dimensional parabolized Navier-Stokes (PNS) and three-dimensional full Navier-Stokes (FNS) analytical codes. Analytical predictions and experimental results are compared.

Weir, Lois J.↗
NASA NTRS1989

Experimental and computational results for 5 degree blunt cones with shock generators at high velocity

Experiments and computations have been performed under laminar conditions in air on 5-deg blunt cones at velocities of 5 km/s and 6 km/s and at Reynolds numbers of 100,000 and 1 million. The computations were performed using ideal-, equilibrium- and nonequilibrium-chemistry models for air. At the conditions of the tests, the aerodynamic coefficients are sensitive to the real-gas effects present, and both experimental and computational aerodynamic coefficients show real-gas and nonlinear effects. The nonequilibrium computations show that a large amount of oxygen is dissociated in the blunt nose region of the flow and much of the oxygen remains dissociated over the entire length of the body, providing an insight into the source of the observed effects in the aerodynamic coefficients. The experimental and computational shock-shapes are in good agreement.

Strawa, A. W.↗
NASA NTRS1989

A numerical and experimental study of coaxial jets

An algebraic stress model and the standard k-epsilon model is applied to predict the mean and turbulence quantities for axisymmetric, nonswirling coaxial jets without confinement. To investigate the effects of numerical (false) diffusion on the predicted results, three different discretization schemes, namely, hybrid, power-law, and the flux-spline, are employed. In addition, an experimental study is conducted to provide data of good quality, especially near the inlet, for model assessment. The results show that the use of the algebraic stress model leads to better agreement between the numerical results and experimental data.

Nikjooy, M.↗
NASA NTRS1989

Experimental validation of flexible robot arm modeling and control

Flexibility is important for high speed, high precision operation of lightweight manipulators. Accurate dynamic modeling of flexible robot arms is needed. Previous work has mostly been based on linear elasticity with prescribed rigid body motions (i.e., no effect of flexible motion on rigid body motion). Little or no experimental validation of dynamic models for flexible arms is available. Experimental results are also limited for flexible arm control. Researchers include the effects of prismatic as well as revolute joints. They investigate the effect of full coupling between the rigid and flexible motions, and of axial shortening, and consider the control of flexible arms using only additional sensors.

Ulsoy, A. Galip↗
NASA NTRS1988

An experimental investigation of the aerodynamic characteristics of slanted base ogive cylinders using magnetic suspension technology

An experimental investigation is reported on slanted base ogive cylinders at zero incidence. The Mach number range is 0.05 to 0.3. All flow disturbances associated with wind tunnel supports are eliminated in this investigation by magnetically suspending the wind tunnel models. The sudden and drastic changes in the lift, pitching moment, and drag for a slight change in base slant angle are reported. Flow visualization with liquid crystals and oil is used to observe base flow patterns, which are responsible for the sudden changes in aerodynamic characteristics. Hysteretic effects in base flow pattern changes are present in this investigation and are reported. The effect of a wire support attachment on the 0 deg slanted base model is studied. Computational drag and transition location results using VSAERO and SANDRAG are presented and compared with experimental results. Base pressure measurements over the slanted bases are made with an onboard pressure transducer using remote data telemetry.

Alcorn, Charles W.↗
NASA NTRS1987

Experimental studies on Goertler vortices

Goertler vortices arise in laminar boundary layers along concave walls due to an imbalance between pressure and centrifugal forces. In advanced laminar-flow control (LFC) supercritical airfoil designs, boundary-layer suction is primarily used to control Tollmien-Schlichting instability and cross-flow vortices in the concave region near the leading edge of the airfoil lower surface. The concave region itself is comprised of a number of linear segments positioned to limit the total growth of Goertler vortices. Such an approach is based on physical reasonings but rigorous theoretical justification or experimental evidence to support such an approach does not exist. An experimental project was initiated at NASA Langley to verify this concept. In the first phase of the project an experiment was conducted on an airfoil whose concave region has a continuous curvature distribution. Some results of this experiment were previously reported and significant features are summarized.

Mangalam, Siva M.↗
NASA NTRS1987

Experimental and theoretical investigation of boundary-layer instability mechanisms on a swept leading edge at Mach 3.5

A brief outline of the experimental and theoretical investigation of boundary layer instability mechanisms on a swept leading edge at Mach 3.5 is presented. Transition is affected by wind tunnel noise only when roughness is present. Local bar-R sub * Reynolds number and k/eta sub * are useful correlation parameters for a wide range of free stream Mach numbers. Stability theory is in good agreement with the experimental cross flow vortex wavelength. These conclusions are briefly discussed.

Creel, Theodore R., Jr.↗
NASA NTRS1990

Experimental measurements of the laminar separation bubble on an Eppler 387 airfoil at low Reynolds numbers

An experimental investigation was conducted to measure the flow velocity in the boundary layer of an Eppler 387 airfoil. In particular, the laminar separation bubble that this airfoil exhibits at low Reynolds numbers was the focus. Single component laser Doppler velocimetry data were obtained at a Reynolds number of 100,000 at an angle of attack of 2.0 degree. Static Pressure and flow visualization data for the Eppler 387 airfoil were also obtained. The difficulty in obtaining accurate experimental measurements at low Reynolds numbers is addressed. Laser Doppler velocimetry boundary layer data for the NACA 663-018 airfoil at a Reynolds number of 160,000 and angle of attack of 12 degree is also presented.

Cole, Gregory M.↗
NASA NTRS1990

Experimental and theoretical aerodynamic characteristics of a high-lift semispan wing model

Experimental and theoretical aerodynamic characteristics were compared for a high-lift, semispan wing configuration that incorporated a slightly modified version of the NASA Advanced Laminar Flow Control airfoil section. The experimental investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel at chord Reynolds numbers of 2.36 and 3.33 million. A two-dimensional airfoil code and a three-dimensional panel code were used to obtain aerodynamic predictions. Two-dimensional data were corrected for three-dimensional effects. Comparisons between predicted and measured values were made for the cruise configuration and for various high-lift configurations. Both codes predicted lift and pitching moment coefficients that agreed well with experiment for the cruise configuration. These parameters were overpredicted for all high-lift configurations. Drag coefficient was underpredicted for all cases. Corrected two-dimensional pressure distributions typically agreed well with experiment, while the panel code overpredicted the leading-edge suction peak on the wing. One important feature missing from both of these codes was a capability for separated flow analysis. The major cause of disparity between the measured data and predictions presented herein was attributed to separated flow conditions.

Applin, Zachary T.↗