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At least 1,171 records · Page 65

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NASA NTRS1973

Experimental and analytical determination of stability parameters for a balloon tethered in a wind

Experimental and analytical techniques for determining stability parameters for a balloon tethered in a steady wind are described. These techniques are applied to a particular 7.64-meter-long balloon, and the results are presented. The stability parameters of interest appear as coefficients in linearized stability equations and are derived from the various forces and moments acting on the balloon. In several cases the results from the experimental and analytical techniques are compared and suggestions are given as to which techniques are the most practical means of determining values for the stability parameters.

Redd, L. T.↗

NASA NTRS1973

Experimental investigation of boundary layers in an axisymmetric, Mach 2.5, mixed-compression inlet

An experimental investigation has been made of the boundary layer flow in a supersonic axisymmetric inlet. The inlet was designed for Mach 2.5 and had a 60 percent internal supersonic area contraction. Porous bleed regions were incorporated into both the cowl and centerbody for boundary-layer control. Five bleed configurations were studied; these included bleed regions upstream of, across, and downstream of the experimentally determined shock-impingement points. The tests were conducted at tunnel unit Reynolds numbers of 8.2 million and 2.7 million per meter. Static-pressure measurements were made along the internal inlet surfaces. In addition to locating the position of the shocks, these measurements also showed local regions of expansion resulting from the suction bleed. Boundary-layer profiles were measured with translating pitot pressure probes located on both sides of the shock-impingement points on the cowl and centerbody. These measurements showed that the boundary-layer profiles were distorted in the vicinity of the terminal shock.

Hingst, W. R.↗

NASA NTRS1973

An experimental investigation of two-phase liquid oxygen pumping

The results of an experimental program to explore the feasibility of pumping two-phase oxygen (liquid and gas) at the pump inlet are reported. Twenty-one cavitation tests were run on a standard J-2 oxygen pump at the MSFC Components Test Laboratory. All tests were run with liquid oxygen 5 to 10 K above the normal boiling point temperature. During ten tests run at approximately at the pump inlet were noted before complete pump performance 50 percent of the nominal operating speed, two phase conditions were achieved. Vapor volumes of 40 to 50 percent at the pump inlet were noted before complete pump performance loss. The experimental results compared to predictions. Nine cavitation tests run at the nominal pump speed over a 5 K temperature range showed progressively lower net positive suction head (NPSH) requirements as temperature was increased. Two-phase operation was not achieved. The temperature varying NPSH data were used to calculate thermodynamic effects on NPSH, and the results were compared to existing data.

Gross, L. A.↗

NASA NTRS1972

Experimental evaluation of a 600 lbf spacecraft rocket engine.

Experimental results are presented for a long-duration-capability (1000-sec), space-storable, bipropellant liquid rocket motor burning fluorine/hydrazine or FLOX/monomethylhydrazine. The interrelationship between injected mixture ratio and the per cent film cooling on vacuum specific impulse performance and chamber heat transfer is given. Experimental sea level measurements are used to predict space vacuum performance based upon simplified JANNAF reference procedures. Dynamic combustion stability is demonstrated over a wide range of operating conditions. Analytical results of char penetration, erosion, and ablative wall temperature distributions are presented for prototype chamber designs.

Hoehn, F. W.↗

NASA NTRS1973

Experimental verification of the energy dissipation mechanism in acoustic dampers.

An experimental program is described which verifies the theoretical model that acoustic damping devices undergoing high intensity oscillations dissipate energy via jet kinetic losses. Pressure measurements within the damping devices and flow duct together with detailed surveys of the jet velocities provide the experimental confirmation. The theory accounts for duct flow effects, both steady and unsteady, as well as the jet dissipation. Discrepancies between theory and experiment can be traced to neglect of higher order terms or ignoring the difficult wall friction term in the case of the quarter-wave tube.

Tang, P. K.↗

NASA NTRS1973

Experimental evaluation of remote manipulator systems.

The objectives of the experimental studies described include an evaluation of existing anthropomorphic manipulators and several controller/display combinations. Inherent limitations of the 12-M type manipulator are identified and recommendations are made concerning manipulator and work site designs that will permit servicing and maintenance tasks to be performed by manipulators. Regions needing additional analytical and experimental investigations are identified. The experiments conducted are concerned with thruster replacement, battery replacement, compartment inspection, antenna installation, fluid coupling, and maneuvering and docking.

Fornoff, H.↗

NASA NTRS1973

Theoretical and experimental investigation of the performance of a fan-in-wing VTOL configuration

The incompressible-flow momentum theory is extended to the case of lifting fans. The resulting theory includes many of the known experimentally determined characteristics of fan-in-wing aircraft. These characteristics include the negligible effect of forward speed on fan thrust, the large momentum drag, and the generally inefficient performance throughout the transition speed range. Although mutual interference between the fans and the wing was totally neglected, the theory is confirmed by experimental results for the configuration tested. Examination of the results of an investigation of wall interference leads to the conclusion that the large fan-induced lift reported in many earlier investigations was largely the result of neglecting wall interference in the reduction of wind-tunnel data.

Heyson, H. H.↗

NASA NTRS1973

Experimental hingeless rotor characteristics at low advance ratio with thrust

An experimental investigation to determine the dynamic characteristics of a hingeless rotor operating at moderate to high lift was conducted on a small scale, 7.5-foot diameter, four-bladed hingeless rotor model in a 7 x 10-foot wind tunnel. The primary objective of this research program was the empirical determination of the rotor steady-state and frequency responses to swashplate and body excitations. Collective pitch was set from 0 to 20 degrees, with the setting at a particular advance ratio limited by the cyclic pitch available for hub moment trim. Advance ratio varied from 0.00 to 0.36 for blades with nondimensional first-flap frequencies at 1.15, 1.28 and 1.33 times the rotor rotation frequency. Several conditions were run with the rotor operating in the transition regime. Rotor response at high lift is shown to be generally nonlinear in this region. As a secondary objective an experimental investigation of the rotor response to 4/revolution swashplate excitations at advance ratios of 0.2 to 0.85 and at a nondimensional, first-flap modal frequency of 1.34 was also conducted, using the 7 x 10-foot wind tunnel. It is shown that 4/revolution swashplate inputs are a method for substantially reducing rotor-induced, shafttransmitted vibratory forces.

London, R. J.↗

NASA NTRS1973

Experimental and data analysis techniques for deducing collision-induced forces from photographic histories of engine rotor fragment impact/interaction with a containment ring

An analysis method termed TEJ-JET is described whereby measured transient elastic and inelastic deformations of an engine-rotor fragment-impacted structural ring are analyzed to deduce the transient external forces experienced by that ring as a result of fragment impact and interaction with the ring. Although the theoretical feasibility of the TEJ-JET concept was established, its practical feasibility when utilizing experimental measurements of limited precision and accuracy remains to be established. The experimental equipment and the techniques (high-speed motion photography) employed to measure the transient deformations of fragment-impacted rings are described. Sources of error and data uncertainties are identified. Techniques employed to reduce data reading uncertainties and to correct the data for optical-distortion effects are discussed. These procedures, including spatial smoothing of the deformed ring shape by Fourier series and timewise smoothing by Gram polynomials, are applied illustratively to recent measurements involving the impact of a single T58 turbine rotor blade against an aluminum containment ring. Plausible predictions of the fragment-ring impact/interaction forces are obtained by one branch of this TEJ-JET method; however, a second branch of this method, which provides an independent estimate of these forces, remains to be evaluated.

Yeghiayan, R. P.↗

NASA NTRS1974

Diagnostics of seeded RF plasmas: An experimental study related to the gaseous core reactor

Measurements of the temperature profiles in an RF argon plasma were made over magnetic field intensities ranging from 20 amp turns/cm to 80 amp turns/cm. The results were compared with a one-dimensional numerical treatment of the governing equations and with an approximate closed form analytical solution that neglected radiation losses. The average measured temperatures in the plasma compared well with the numerical treatment, though the experimental profile showed less of an off center temperature peak than predicted by theory. This may be a result of the complex turbulent flow pattern present in the experimental torch and not modeled in the numerical treatment. The radiation term cannot be neglected for argon at the power levels investigated. The closed form analytical approximation that neglected radiation led to temperature predictions on the order of 1000 K to 2000 K higher than measured or predicted by the numerical treatment which considered radiation losses.

Thompson, S. D.↗

NASA NTRS1974

Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

Hingst, W. R.↗

NASA NTRS1974

An experimental investigation of wall boundary layer transition Reynolds numbers in an expansion tube

Experimental measurements of boundary-layer transition in an expansion-tube test-gas flow are presented along with radial distributions of pitot pressure. An integral method for calculating constant Reynolds number lines for an expansion-tube flow is introduced. Comparison of experimental data and constant Reynolds number calculations has shown that for given conditions, wall boundary-layer transition occurs at a constant Reynolds number in an expansion-tube flow. Operating conditions in the expansion tube were chosen so that the effects of test-gas nonequilibrium on boundary-layer transition could be studied.

Weilmuenster, K. J.↗

NASA NTRS1974

Model wall and recovery temperature effects on experimental heat transfer data analysis

Basic analytical procedures are used to illustrate, both qualitatively and quantitatively, the relative impact upon heat transfer data analysis of certain factors which may affect the accuracy of experimental heat transfer data. Inaccurate knowledge of adiabatic wall conditions results in a corresponding inaccuracy in the measured heat transfer coefficient. The magnitude of the resulting error is extreme for data obtained at wall temperatures approaching the adiabatic condition. High model wall temperatures and wall temperature gradients affect the level and distribution of heat transfer to an experimental model. The significance of each of these factors is examined and its impact upon heat transfer data analysis is assessed.

Throckmorton, D. A.↗

NASA NTRS1974

Comparisons of two-dimensional shock-expansion theory with experimental aerodynamic data for delta-planform wings at high supersonic speeds

An investigation has been conducted to explore the potential for optimizing airfoil shape at high supersonic speeds by utilizing the two-dimensional shock-expansion method. Theoretical and experimental force and moment coefficients are compared for four delta-planform semispan wings having a leading-edge sweep angle of 65 deg and incorporating modified diamond airfoils with a thickness-chord ratio of 0.06. The wings differ only in airfoil maximum-thickness position and camber. The experimental data are obtained at Mach numbers of 3.95 and 4.63 and at a Reynolds number of 9.84 million per meter. A relatively simple method is developed for predicting, in terms of lift-drag ratio, the optimum modified diamond airfoil at high supersonic and hypersonic speeds.

Jernell, L. S.↗

NASA NTRS1974

A Monte Carlo investigation of experimental data requirements for fitting polynomial functions

This report examines the extent to which sample size affects the accuracy of a low order polynomial approximation of an experimentally observed quantity and establishes a trend toward improvement in the accuracy of the approximation as a function of sample size. The task is made possible through a simulated analysis carried out by the Monte Carlo method, in which data are generated by using several transcendental or algebraic functions as models. Contaminated data of varying amounts are fitted to linear quadratic or cubic polynomials, and the behavior of the mean-squared error of the residual variance is determined as a function of sample size. Results indicate that the effect of the size of the sample is significant only for relatively small sample sizes and diminishes drastically for moderate and large amounts of experimental data.

Canavos, G. C.↗

NASA NTRS1974

Analytic and experimental evaluation of shadow shields and their support members for thermal control of space vehicles

The thermal performance of shadow shields, and their support struts, for the thermal protection of cryogenic propellants in a simulated deep-space environment was investigated analytically and experimentally. Very low overall heat-transfer rates were obtained when highly reflective aluminized Mylar shadow shields were used. The thermal interactions between the shields and support struts were investigated with fair to good agreement between the analysis and experimental data. The exterior surface of both fiberglass and titanium struts was coated to reduce the heat input into the test tank. The vacuum level inside the test facility strongly influenced the heat-transfer rates.

Boyle, R. J.↗

NASA NTRS1974

Analytical and experimental study of mean flow and turbulence characteristics inside the passages of an axial flow inducer

The effort conducted to gather additional understanding of the complex inviscid and viscid effects existing within the passages of a three-bladed axial flow inducer operating at a flow coefficient of 0.065 is summarized. The experimental investigations included determination of the blade static pressure and blade limiting streamline angle distributions, and measurement of the three components of mean velocity, turbulence intensities and turbulence stresses at locations inside the inducer blade passage utilizing a rotating three-sensor hotwire probe. Applicable equations were derived for the hotwire data reduction analysis and solved numerically to obtain the appropriate flow parameters. Analytical investigations were conducted to predict the three-dimensional inviscid flow in the inducer by numerically solving the exact equations of motion, and to approximately predict the three-dimensional viscid flow by incorporating the dominant viscous terms into the exact equations. The analytical results are compared with the experimental measurements and design values where appropriate.

Gorton, C. A.↗

NASA NTRS1974

Experimental and analytical sonic nozzle discharge coefficients for Reynolds numbers up to 8 x 10 to the 6th power

Sonic discharge coefficients are presented for two different geometry flow nozzles using nitrogen gas at high pressures where real gas corrections are significant. Throat Reynolds number range extended up to 8 million. Experimentally obtained coefficients for a nozzle with a continuous and finite radius of curvature agreed with those obtained analytically to within 0.2 percent. Experimental coefficients for a long radius ASME nozzle agreed to within 1/4 percent to an empirical equation representing the most probable subsonic discharge coefficient.

Szaniszlo, A. J.↗