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At least 91 records · Page 5

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NASA NTRS1986

The noncavitating performance and life of a small vane-type positive displacement pump in liquid hydrogen

The low flow rate and high head rise requirements of hydrogen/oxygen auxiliary propulsion systems make the application of centrifugal pumps difficult. Positive displacement pumps are well-suited for these flow conditions, but little is known about their performance and life characteristics in liquid hydrogen. An experimental and analytical investigation was conducted to determine the performance and life characteristics of a vane-type, positive displacement pump. In the experimental part of this effort, mass flow rate and shaft torque were determined as functions of shaft speed and pump pressure rise. Since liquid hydrogen offers little lubrication in a rubbing situation, pump life is an issue. During the life test, the pump was operated intermittently for 10 hr at the steady-state point of 0.074 lbm/sec (0.03 kg/sec) flow rate, 3000 psid (2.07 MPa) pressure rise, and 9000 rpm (938 rad/sec) shaft speed. Pump performance was monitored during the life test series and the results indicated no loss in performance. Material loss from the vanes was recorded and wear of the other components was documented. In the analytical part of this effort, a comprehensive pump performance analysis computer code, developed in-house, was used to predict pump performance. The results of the experimental investigation are presented and compared with the results of the analysis. Results of the life test are also presented.

Ulbricht, T. E.↗

NASA NTRS1988

Optimization of helicopter airframe structures for vibration reduction considerations, formulations and applications

Several key issues involved in the application of formal optimization technique to helicopter airframe structures for vibration reduction are addressed. Considerations which are important in the optimization of real airframe structures are discussed. Considerations necessary to establish relevant set of design variables, constraints and objectives which are appropriate to conceptual, preliminary, detailed design, ground and flight test phases of airframe design are discussed. A methodology is suggested for optimization of airframes in various phases of design. Optimization formulations that are unique to helicopter airframes are described and expressions for vibration related functions are derived. Using a recently developed computer code, the optimization of a Bell AH-1G helicopter airframe is demonstrated.

Murthy, T. Sreekanta↗

NASA NTRS1989

Tracing Rays In Laser-Fringe Anemometers

"OPTMAIN" is simple ray-tracing computer code developed to quantify refractive effects that result when laser-fringe anemometer used to observe flows through window. Code calculates changes for four different types of windows: flat-plate windows, simple cylindrical windows, "general" axisymmetric windows, and smooth general-surface windows. Written in FORTRAN IV.

Owen, Karl↗

NASA NTRS1988

Focal region fields of distorted reflectors

The problem of the focal region fields scattered by an arbitrary surface reflector under uniform plane wave illumination is solved. The physical optics (PO) approximation is used to calculate the current induced on the reflector. The surface of the reflector is described by a number of triangular domain-wise 5th degree bivariate polynomials. A 2-dimensional Gaussian quadrature is employed to numerically evaluate the integral expressions of the scattered fields. No Freshnel or Fraunhofer zone approximations are made. The relation of the focal fields problem to surface compensation techniques and other applications are mentioned. Several examples of distorted parabolic reflectors are presented. The computer code developed is included, together with instructions on its usage.

Buris, N. E.↗

NASA NTRS1988

Leakage predictions for Rayleigh-step, helium-purge seals

Rayleigh-step, helium purge, annular shaft seals, studied for use in liquid oxygen turbopumps, generate a hydrodynamic force that enables the seal to follow shaft perturbations. Hence, smaller clearances can be used to reduce seal leakage. FLOWCAL, a computer code developed by Mechanical Technology Incorporated, predicts gas flow rate through an annular seal with an axial pressure gradient. Analysis of a 50-mm Rayleigh-step, helium-purge, annular seal showed the flow rate increased axial pressure gradient, downstream pressure, and eccentricity ratio. Increased inlet temperature reduced leakage. Predictions made at maximum and minimum clearances (due to centrifugal and thermal growths, machining tolerances and + or - 2 percent uncertainty in the clearance measurement) placed wide boundaries on expected flow rates. The widest boundaries were set by thermal growth conditions. Predicted flow rates for a 50-mm Rayleigh-step, helium-purge, annular seal underestimated measured flow rates by three to seven times. However, the analysis did accurately predict flow rates for choked gas flow through annular seals when compared to flow rates measured in two other independent studies.

Proctor, Margaret P.↗

NASA NTRS1988

Computational design of an experimental laser-powered thruster

An extensive numerical experiment, using the developed computer code, was conducted to design an optimized laser-sustained hydrogen plasma thruster. The plasma was sustained using a 30 kW CO2 laser beam operated at 10.6 micrometers focused inside the thruster. The adopted physical model considers two-dimensional compressible Navier-Stokes equations coupled with the laser power absorption process, geometric ray tracing for the laser beam, and the thermodynamically equilibrium (LTE) assumption for the plasma thermophysical and optical properties. A pressure based Navier-Stokes solver using body-fitted coordinate was used to calculate the laser-supported rocket flow which consists of both recirculating and transonic flow regions. The computer code was used to study the behavior of laser-sustained plasmas within a pipe over a wide range of forced convection and optical arrangements before it was applied to the thruster design, and these theoretical calculations agree well with existing experimental results. Several different throat size thrusters operated at 150 and 300 kPa chamber pressure were evaluated in the numerical experiment. It is found that the thruster performance (vacuum specific impulse) is highly dependent on the operating conditions, and that an adequately designed laser-supported thruster can have a specific impulse around 1500 sec. The heat loading on the wall of the calculated thrusters were also estimated, and it is comparable to heat loading on the conventional chemical rocket. It was also found that the specific impulse of the calculated thrusters can be reduced by 200 secs due to the finite chemical reaction rate.

Jeng, San-Mou↗

NASA NTRS1988

Solar water heater for NASA's Space Station

The feasibility of using a solar water heater for NASA's Space Station is investigated using computer codes developed to model the Space Station configuration, orbit, and heating systems. Numerous orbit variations, system options, and geometries for the collector were analyzed. Results show that a solar water heater, which would provide 100 percent of the design heating load and would not impose a significant impact on the Space Station overall design is feasible. A heat pipe or pumped fluid radial plate collector of about 10-sq m, placed on top of the habitat module was found to be well suited for satisfying water demand of the Space Station. Due to the relatively small area required by a radial plate, a concentrator is unnecessary. The system would use only 7 to 10 percent as much electricity as an electric water-heating system.

Somers, Richard E.↗

NASA NTRS1990

Parametric studies to determine the effect of compliant layers on metal matrix composite systems

Computational simulation studies are conducted to identify compliant layers to reduce matrix stresses which result from the coefficient of thermal expansion mismatch and the large temperature range over which the current metal matrix composites will be used. The present study includes variations of compliant layers and their properties to determine their influence on unidirectional composite and constituent response. Two simulation methods are used for these studies. The first approach is based on a three-dimensional linear finite element analysis of a 9 fiber unidirectional composite system. The second approach is a micromechanics based nonlinear computer code developed to determine the behavior of metal matrix composite system for thermal and mechanical loads. The results show that an effective compliant layer for the SCS 6 (SiC)/Ti-24Al-11Nb (Ti3Al + Nb) and SCS 6 (SiC)/Ti-15V-3Cr-3Sn-3Al (Ti-15-3) composite systems should have modulus 15 percent that of the matrix and a coefficient of thermal expansion of the compliant layer roughly equal to that of the composite system without the CL. The matrix stress in the longitudinal and the transverse tangent (loop) direction are tensile for the Ti3Al + Nb and Ti-15-3 composite systems upon cool down from fabrication. The fiber longitudinal stress is compressive from fabrication cool down. Addition of a recommended compliant layer will result in a reduction in the composite modulus.

Caruso, J. J.↗

NASA NTRS1990

Radiation protection effectiveness of a proposed magnetic shielding concept for manned Mars missions

The effectiveness of a proposed concept for shielding a manned Mars vehicle using a confined magnetic field configuration is evaluated by computing estimated crew radiation exposures resulting from galactic cosmic rays and a large solar flare event. In the study the incident radiation spectra are transported through the spacecraft structure/magnetic shield using the deterministic space radiation transport computer codes developed at Langley Research Center. The calculated exposures unequivocally demonstrate that magnetic shielding could provide an effective barrier against solar flare protons but is virtually transparent to the more energetic galactic cosmic rays. It is then demonstrated that through proper selection of materials and shield configuration, adequate and reliable bulk material shielding can be provided for the same total mass as needed to generate and support the more risky magnetic field configuration.

Townsend, Lawrence W.↗

NASA NTRS1990

Parametric studies to determine the effect of compliant layers on metal matrix composite systems

Caruso, J. J.↗

NASA NTRS1990

ICAN sensitivity analysis

A computer program called Integrated Composite Analyzer (ICAN) was used to predict the properties of high-temperature polymer matrix composites. ICAN is a collection of NASA Lewis Research Center-developed computer codes designed to carry out analysis of multilayered fiber composites. The material properties used as input to the program were those of the thermoset polyimide resin PMR-15 and the carbon fiber Celion 6000. The sensitivity of the predicted composite properties to variations in the resin and fiber properties was examined. In addition, the predicted results were compared with experimental data. In most cases, the effect of changes in resin and fiber properties on composite properties was reasonable. However, the variations in the composite strengths with the moisture content of the PMR-15 resin were inconsistent. The ICAN-predicted composite moduli agreed fairly well with experimental values, but the predicted composite strengths were generally lower than experimental values.

Frimpong, Stephen↗

NASA NTRS1991

Computational simulation of hot composites structures

Three different computer codes developed in-house are described for application to hot composite structures. These codes include capabilities for: (1) laminate behavior (METCAN); (2) thermal/structural analysis of hot structures made from high temperature metal matrix composites (HITCAN); and (3) laminate tailoring (MMLT). Results for select sample cases are described to demonstrate the versatility as well as the application of these codes to specific situations. The sample case results show that METCAN can be used to simulate cyclic life in high temperature metal matrix composites; HITCAN can be used to evaluate the structural performance of curved panels as well as respective sensitivities of various nonlinearities, and MMLT can be used to tailor the fabrication process in order to reduce residual stresses in the matrix upon cool-down.

Chamis, Christos C.↗

NASA NTRS1991

ASTROP3 user's guide

ASTROP3 (Aeroelastic Stability and Response of Propulsion Systems) is a FORTRAN computer code developed for calculating the performance and dynamic stability (classical flutter) of single rotation propfans. Three-dimensional, subsonic aerodynamics with constant pressure panel discretization and MSC/NASTRAN finite element analysis of the blade are used to calculate the steady and unsteady aerodynamic forces. The flutter analysis is a modal based technique using motion dependent aerodynamic forces based on in-vacuum frequencies and normal modes of the individual propfan blades. The execution of ASTROP3 is illustrated through the calculation of blade performance and blade aeroelastic stability for the SR7L rotor. These calculations are representative of applications for ASTROP3. All input and output files necessary for program execution are discussed, as well as other appropriate information to aid the user in applying the program.

August, Richard↗

NASA NTRS1992

Metal matrix composite analyzer (METCAN) user's manual, version 4.0

The Metal Matrix Composite Analyzer (METCAN) is a computer code developed at Lewis Research Center to simulate the high temperature nonlinear behavior of metal matrix composites. An updated version of the METCAN User's Manual is presented. The manual provides the user with a step by step outline of the procedure necessary to run METCAN. The preparation of the input file is demonstrated, and the output files are explained. The sample problems are presented to highlight various features of METCAN. An overview of the geometric conventions, micromechanical unit cell, and the nonlinear constitutive relationships is also provided.

Lee, H.-J.↗

NASA NTRS1992

Design tradeoffs on engine-integrated hypersonic vehicles

Two classes of airbreathing hypersonic vehicle concepts, one for primarily cruise missions and the other for accelerator type missions, are presented. Both are designed with waverider airframes and hydrogen-fueled scramjet engine modules. Cruise configurations are optimized for the product of I(sp) and L/D while matching lift to weight and thrust to drag at some equivalence ratio. Accelerator configurations are optimized for effective specific impulse while matching lift to weight at an equivalence ratio of one. The method and computer code developed to optimize the configurations are discussed. The features and design tradeoffs for each class of vehicles are described. Recently available weight estimates for all-body waveriders have had a significant impact on the integrated configurations. Mach 8 vehicles at 40 km altitude optimized with the cruise objective function have L/Ds of 2.55 to 2.92 and I(sp)s of 2850 to 2940 sec. A Mach 14 vehicle at 40-km altitude optimized with the accelerator objective function has an I(sp) sub eff of 189 sec, and a Mach 10 vehicle an I(sp) sub eff of 880 sec.

O'Neill, Mary Kae L.↗

NASA NTRS1992

PAYCOS, a multidisciplinary sizing code for hypersonic vehicles

PAYCOS is a computer code developed to rapidly perform concept sizing, concept evaluation, and associated trade studies for supersonic and hypersonic maneuvering vehicles. PAYCOS is a multidisciplinary analysis code that allows the engineer to determine the best geometric configuration for each design through parametric studies and mathematical optimization. This paper presents a general overview of the code, including a brief discussion of the approach used to develop it. The modular structure of the code is reviewed, and a brief discussion of each module is presented. Input data needed to run the code and output data supplied by it are discussed. The role of mathematical optimization in the solution process is discussed in some detail and examples of this process are presented. Finally, current modifications to the code are described along with potential future modifications and applications.

Edington, Larry↗

NASA NTRS1993

Computing Flow Transition On Parallel Processors

Parallel algorithm developed on multiple-microprocessor computer. Program initiated to develop computer codes capable of directly simulating and mathematically modeling transition process at mach numbers ranging from subsonic to hypersonic. Parallel computers potentially offer reduction of processing time; processing time inversely proportional to number of available processors.

Bokhari, S.↗

NASA NTRS1993

Double-diffusive fingering convection in a porous medium

The characteristics of nonlinear two-dimensional horizontally periodic double-diffusive fingering convection in a saturated porous medium is investigated, using the Darcy equation including Brinkman and Forchheimer terms for the momentum equation. To solve the equations and the corresponding initial and boundary conditions, a Galerkin method is applied in the horizontal direction, and a hybrid finite difference method is used in the vertical direction. The developed computer code was used to compute the thermal convection case, and the results were found to be in good agreement with existing results.

Chen, Falin↗