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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Comparison of experimental and computational techniques for plane mixing layers

In this paper, results from two experimental and two computational investigations of plane turbulent mixing layers are presented and compared. The experimental results include flow visualization data using the smoke laser technique and mean flow and turbulence measurements obtained with hot X-wires and a two-component LDV. Reasonably good agreement is found among these techniques, at least for turbulence quantities up to second order. Reynolds-averaged computations are successful at capturing the complete evolution of the mixing layer, including wake effects in the near field and approach to self-preservation in the far field. The two-dimensional vortex method shows excellent qualitative and quantitative agreement with measured data for the forced mixing layer. For the unforced layer, the results seem to indicate that a three-dimensional computation may be necessary.

Mehta, R. D.↗
NASA NTRS1988

A comparison of experimental and theoretical results for labyrinth gas seals with honeycomb stators

Experimental results for the rotordynamic stiffness and damping coefficients of a labyrinth -rotor honeycomb-stator seal are presented. The coefficients are compared to the coefficients of a labyrinth-rotor smooth-stator seal having the same geometry. The coefficients are compared to analytical results 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 rotor speeds. At high rotor speeds and low clearance, the smooth stator seal is more stable. 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. Overall, the model does not perform as well for low clearance seals as for high clearance seals.

Hawkins, Lawrence Allen↗
NASA NTRS1988

A comparison of experimental and calculated thin-shell leading-edge buckling due to thermal stresses

High-temperature thin-shell leading-edge buckling test data are analyzed using NASA structural analysis (NASTRAN) as a finite element tool for predicting thermal buckling characteristics. Buckling points are predicted for several combinations of edge boundary conditions. The problem of relating the appropriate plate area to the edge stress distribution and the stress gradient is addressed in terms of analysis assumptions. Local plasticity was found to occur on the specimen analyzed, and this tended to simplify the basic problem since it effectively equalized the stress gradient from loaded edge to loaded edge. The initial loading was found to be difficult to select for the buckling analysis because of the transient nature of thermal stress. Multiple initial model loadings are likely required for complicated thermal stress time histories before a pertinent finite element buckling analysis can be achieved. The basic mode shapes determined from experimentation were correctly identified from computation.

Jenkins, Jerald M.↗
NASA NTRS1988

Comparison of experimental rotor damping data-reduction techniques

The ability of existing data reduction techniques to determine frequency and damping from transient time-history records was evaluated. Analog data records representative of small-scale helicopter aeroelastic stability tests were analyzed. The data records were selected to provide information on the accuracy of reduced frequency and decay coefficients as a function of modal damping level, modal frequency, number of modes present in the time history record, proximity to other modes with different frequencies, steady offset in time history, and signal-to-noise ratio. The study utilized the results from each of the major U.S. helicopter manufacturers, the U.S. Army Aeroflightdynamics Directorate, and NASA Ames Research Center using their inhouse data reduction and analysis techniques. Consequently, the accuracy of different data analysis techniques and the manner in which they were implemented were also evaluated. It was found that modal frequencies can be accurately determined even in the presence of significant random and periodic noise. Identified decay coefficients do, however, show considerable variation, particularly for highly damped modes. The manner in which the data are reduced and the role of the data analyst was shown to be important. Although several different damping determination methods were used, no clear trends were evident for the observed differences between the individual analysis techniques. It is concluded that the data reduction of modal-damping characteristics from transient time histories results in a range of damping values.

Warmbrodt, William↗
NASA NTRS1988

Comparison of experimental coupled helicopter rotor/body stability results with a simple analytical model

The results of an analytical study aimed at predicting the aeromechanical stability of a helicopter in ground resonance, with the inclusion of aerodynamic forces are presented. The theoretical results are found to be in good agreement with the experimental results, available in literature, indicating that the coupled rotor/fuselage system can be represented by a reasonably simple mathematical model.

Friedmann, P. P.↗
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 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 NTRS1990

A study of ice shape prediction methodologies and comparison with experimental data

Current analytical ice shape prediction methods are described and evaluated. The analyses of Gray (1958), Wilder (1969), and Bragg (1982) are compared with the prediction of the LEWICE computer analysis. The effects of time stepping and initial surface roughness on analysis predictions are studied utilizing the prediction methods and flight data. Rime, mixed, and glazed ice shapes at the leading edge of an airfoil are analyzed. It is observed that there is no change in ice shape prediction if ice accumulation is less than 0.01, a minimum of 2 time steps is need to incorporate time dependent behavior into the analysis, and the LEWICE analysis provided the most accurate predictions.

Korkan, K. D.↗
NASA NTRS1990

Modeling of the SiC chemical vapor deposition process and comparison with experimental results

A model of the NASA Lewis SiC CVD process is described, and the results presented. A key feature of the model is the direct coupling of gas-phase chemical kinetics with diffusion. A deposition chemistry model using reactive sticking coefficients for each gas-phase species provides the diffusion boundary conditions. SiC deposition rates predicted by the model agree reasonably well with experimentally observed rates.

Annen, K. D.↗
NASA NTRS1990

Numerical simulation of fluid flow and heat transfer in a thin liquid film over a stationary and rotating disk and comparison with experimental data

In the first section, improvements in the theoretical model and computational procedure for the prediction of film height and heat-transfer coefficient of the free surface flow of a radially-spreading thin liquid film adjacent to a flat horizontal surface of finite extent are presented. Flows in the presence and absence of gravity are considered. Theoretical results are compared to available experimental data with good agreement. In the presence of gravity, a hydraulic jump is present, isolating the flow into two regimes: supercritical upstream from the jump and subcritical downstream of it. In this situation, the effects of surface tension are important near the outer edge of the disk where the fluid experiences a free fall. A region of flow separation is present just downstream of the jump. In the absence of gravity, no hydraulic jump or separated flow region is present. The variation of the heat-transfer coefficient for flows in the presence and absence of gravity are also presented. In the second section, the results of a numerical simulation of the flow field and associated heat transfer coefficients are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation was performed for different flow rates and rotational velocities using a 3-D boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an iterative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow is found to be dominated by inertia near the entrance and close to the free surface and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhances the heat transfer coefficient by a significant amount.

Faghri, Amir↗
NASA NTRS1991

A comparison of experimental observations and numerical predictions for the initiation of fiber microbuckling in notched composite laminates

The results of the present experimental study of fiber microbuckling indicates that free surfaces, ply orientations, and resin-rich regions affect the strain level for the initiation of in-plane fiber microbuckling. Nonlinear matrix constitutive behavior, in conjunction with initial fiber waviness, cause significant reductions of fiber microbuckling initiation strain level; these two factors generate nonlinear global stress-strain responses in the models. The fiber microbuckling initiation strains correlate well with the applied strain associated with asymptotic local shear strains.

Guynn, E. G.↗
NASA NTRS1992

Beam-waveguide antenna performance predictions with comparisons to experimental results

An overview of a NASA/JPL antenna project is presented, with specific focus on the methodology used to predict the microwave performance of a 34-m-diameter beam-waveguide (BWG) reflector antenna, designated DSS 13 (Deep Space Station 13). DSS 13 is the R&D facility serving the NASA/JPL Deep Space Network. Microwave performance predictions as well as a summary of test results for the antenna are given. The antenna has Cassegrain and centerline BWG operating modes at X-band (8.450-GHz) and Ka-band (32-GHz) frequencies. The performance predictions regarding antenna area efficiencies, corresponding beampeak gains, and for several (but not all) operating noise temperatures are found to agree reasonably well with the corresponding experimental results.

Bathker, Dan A.↗
NASA NTRS1992

A comparison of experimental data with CFD for the NSWC Hypervelocity Wind Tunnel No. 9 Mach 14 Nozzle

An experimental and numerical study has been performed of the flow physics occurring in the Naval Surface Warfare Center Hypervelocity Wind Tunnel No.9 Mach 14 Nozzle. Mach 8, 10, 14, and 18 test section conditions are obtained utilizing various axisymmetric contoured wind tunnel nozzles. Numerical and experimental results are presented for the Mach 14 configuration.

Korte, John J.↗