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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Reliability analysis of single crystal NiAl turbine blades

As part of a co-operative agreement with General Electric Aircraft Engines (GEAE), NASA LeRC is modifying and validating the Ceramic Analysis and Reliability Evaluation of Structures algorithm for use in design of components made of high strength NiAl based intermetallic materials. NiAl single crystal alloys are being actively investigated by GEAE as a replacement for Ni-based single crystal superalloys for use in high pressure turbine blades and vanes. The driving force for this research lies in the numerous property advantages offered by NiAl alloys over their superalloy counterparts. These include a reduction of density by as much as a third without significantly sacrificing strength, higher melting point, greater thermal conductivity, better oxidation resistance, and a better response to thermal barrier coatings. The current drawback to high strength NiAl single crystals is their limited ductility. Consequently, significant efforts including the work agreement with GEAE are underway to develop testing and design methodologies for these materials. The approach to validation and component analysis involves the following steps: determination of the statistical nature and source of fracture in a high strength, NiAl single crystal turbine blade material; measurement of the failure strength envelope of the material; coding of statistically based reliability models; verification of the code and model; and modeling of turbine blades and vanes for rig testing.

Salem, Jonathan↗
NASA NTRS1980

Thermal fatigue performance of integrally cast automotive turbine wheels

Fluidized bed thermal fatigue testing was conducted on 16 integrally cast automotive turbine wheels for 1000-10,000 (600 sec total) thermal cycles at 935/50 C. The 16 wheels consisted of 14 IN-792 + 1% Hf and 2 gatorized AF2-1DA wheels; 6 of the IN-792 + Hf wheels contained crack arrest pockets inside the blade root flange. Temperature transients during the thermal cycling were measured in three calibration tests using either 18 or 30 thermocouples per wheel. Thermal cracking based on crack length versus accumulated cycles was greatest for unpocketed wheels developing cracks in 8-13 cycles compared to 75-250 cycles for unpocketed wheels. However, pocketed wheels survived up to 10,000 cycles with crack lengths less than 20 mm, whereas two unpocketed wheels developed 45 mm long cracks in 1000-2000 cycles.

Humphreys, V. E.↗
NASA NTRS1979

Wind tunnel performance of four energy efficient propellers designed for Mach 0.8 cruise

For the advanced turboprop to be competitive with proposed advanced turbofan-powered aircraft, it must have high propulsive efficiency at Mach 0.8 cruise above 9.144-km altitude with an acceptable cabin noise environment. Four 8-bladed propeller models are designed employing various concepts to reduce compressibility losses. Wind tunnel tests are conducted at zero model incidence to the free-stream flow. Aerodynamic and acoustic test results are presented and discussed. It is shown that the aeroacoustically designed configuration (SR-3) with 45 deg of tip sweep and an area-ruled spinner yields the highest propulsive efficiency (78.7% at Mach 0.8, 3.06 advance ratio, and 1.7 power coefficient), with an improvement of about 3% over the straight bladed configuration (SR-2, with zero-degree sweep). The phase-interference concept for noise reduction used in SR-3 yields about 5-6 dB reduction as compared to SR-2.

Jeracki, R. J.↗
DOE OSTI2014

Manufacturing process modeling for composite materials and structures, Sandia blade reliability collaborative

The increased use and interest in wind energy over the last few years has necessitated an increase in the manufacturing of wind turbine blades. This increase in manufacturing has in many ways out stepped the current understanding of not only the materials used but also the manufacturing methods used to construct composite laminates. The goal of this study is to develop a list of process parameters which influence the quality of composite laminates manufactured using vacuum assisted resin transfer molding and to evaluate how they influence laminate quality. Known to be primary factors for the manufacturing process are resin flow rate and vacuum pressure. An incorrect balance of these parameters will often cause porosity or voids in laminates that ultimately degrade the strength of the composite. Fiber waviness has also been seen as a major contributor to failures in wind turbine blades and is often the effect of mishandling during the lay-up process. Based on laboratory tests conducted, a relationship between these parameters and laminate quality has been established which will be a valuable tool in developing best practices and standard procedures for the manufacture of wind turbine blade composites.

Guest, Daniel A.↗
NASA NTRS1982

A simple system for helicopter Individual-Blade-Control and its application to lag damping augmentation

A new, advanced type of active control for helicopters and its application to a system for blade lag damping augmentation is described. The system, based on previously developed M.I.T. Individual-Blade-Control hardware, employs blade-mounted accelerometers to sense blade lag motion and feeds back rate information to increase the damping of the first lag mode. A linear model of the blade and control system dynamics is used to give guidance in the design process as well as to aid in analysis of experimental results. System performance in wind tunnel tests is described, and evidence is given of the system's ability to provide substantial additional damping to blade lag motion.

Ham, N. D.↗
NASA NTRS1991

Helicopter local blade circulation calculations for a model rotor in forward flight using laser velocimeter measurements

A program is described whose purpose was to develop the measurement and data processing techniques necessary to accurately compute the local rotor blade circulation at any azimuth and radius in a wind tunnel environment at representative forward speeds. With these techniques, further tests using a complex rotor system with local surface pressure measurements should help to determine the accuracy of the technique for general applications to rotor blade span-load measurement programs in wind tunnel forward flight conditions. Preliminary calculations are reported.

Hoad, Danny R.↗
NASA NTRS1997

Investigation of Boundary Layer Development in Multi-Stage Low Pressure

A review of recent literature has been made in the areas of unsteady measurement in turbomachinery and LP turbine design. This has included a detailed review of methods for extracting quantitative shear stress data from surface mounted hot-film arrays. Research goals were identified on the basis of the literature survey and following interaction with the GE and NASA contracts. Progress has also been made in the detailed planning of the research program. An array of hot-film sensors has been mounted at mid-span on a second stage nozzle blade ready for installation in the current turbine buildup. A new technique of applying the hot-film array using double sided adhesive is being tested. The temperature in the vicinity of the hot-films will be monitored using a thermocouple attached to the blade pressure surface. This will increase the accuracy of the data reduction process compared with the methods applied by Halstead et at. (1995) and others. Data obtained from this first set of sensors, along with data from the hot-wire investigation will help to determine the best locations for surface hot-film instrumentation for subsequent builds of the turbine. Other LSRT instrumentation issues which have been addressed include calibration of the torque measurement system and procurement of custom design hot-wire sensors required to compensate for the slope flow path. Preliminary attempts at modeling the boundary layer transition process have been completed. A steady, coupled viscous-inviscid flow solver (the MISES code of Drela and Youngren) was used to calculate the steady-flow boundary layer transition location.

Source record↗
DOE OSTI2016

Characterizing the Influence of Abstraction in Full-Scale Wind Turbine Nacelle Testing

In recent years, there has been a growing interest in full-scale wind turbine nacelle testing to complement individual component testing. As a result, several wind turbine nacelle test benches have been built to perform such testing with the intent of loading the integrated components as they are in the field. However, when mounted on a test bench the nacelle is not on the top of a tower and does not have blades attached to it - this is a form of abstraction. This paper aims to quantify the influence of such an abstraction on the dynamic response of the nacelle through a series of simulation case studies. The responses of several nacelle components are studied including the main bearing, main shaft, gearbox supports, generator, and yaw bearing interface. Results are presented to highlight the differences in the dynamic response of the nacelle caused by the abstraction. Additionally, the authors provide recommendations for mitigating the effects of the abstraction.

17 WIND ENERGY↗
NASA NTRS1985

Analysis of the free-tip rotor wind-tunnel test results

The results from a wind tunnel test of a small scale free-tip rotor are analyzed. The free-tip rotor has blade tips that are free to weathervane into the tip's relative wind, thus producing a more uniform lift around the azimuth. The free-tip assembly, which includes the controller, functioned flawlessly throughout the test. In a test of the free-tip's response after passing through a vertical air jet, the tip pitched freely and in a controlled manner. Analysis of the tip's response characteristics showed the free-tip system's damped natural frequency to be 5.2 per rev. Tip pitch angle responses to the local airstream are presented for an advance-ratio range of 0.1 to 0.397 and for a solidity weighted rotor lift coefficient range of 0.038 to 0.092. Harmonic analysis of the responses showed a dominance by the first harmonic. As a result of the tip being free, forward flight power requirements were reduced by 8% or more. More power reduction was recorded for high thrust conditions. In addition to the power reduction, flatwise blade bending moments were reduced by as much as 30% at the inboard blade stations.

Stroub, Robert H.↗
NASA NTRS1979

Evaluation of miniature single-wire sheathed thermocouples for turbine blade temperature measurement

Chromel Alumel thermocouples were used, with sheath diameters of 0.15 and 0.25 mm. Tests were conducted at temperatures ranging from 750 to 1250 K. Both steady state and thermal cycling tests were performed for times up to 200 hours. Initial testing was performed in a low velocity gas stream for long time periods using a Meker-type burner. Additional testing was done in a high velocity gas stream for short time periods using a hot gas tunnel and also in a J75 jet engine. A total of eleven 0.15 mm diameter thermocouples and six 0.25 mm diameter thermocouples were tested. Drift rates up to 2.5% in 10 hours were observed. Photomicrographs show that this design is near the limit of miniaturization based on present manufacturing capabilities. Results indicate that the effects of miniaturization on reliability and accuracy must be considered when choosing thermocouples for a particular application.

Hollanda, R.↗
NASA NTRS1982

Experimental study of turbulence in blade end wall corner region

Corner flows and wall pressure fluctuations, design and fabrication of the test model, preliminary resuls on boundary layer, flow visualization, turbulence intensity and spectra measurements are presented. The design consideration and fabrication report on the newly built wind tunnel to be used for subsequent continuation of the research effort is also presented.

Raj, R.↗
NASA NTRS2014

Aerodynamic Effects of Turbulence Intensity on a Variable-Speed Power-Turbine Blade with Large Incidence and Reynolds Number Variations

The effects of inlet turbulence intensity on the aerodynamic performance of a variable speed power turbine blade are examined over large incidence and Reynolds number ranges. Both high and low turbulence studies were conducted in the NASA Glenn Research Center Transonic Turbine Blade Cascade Facility. The purpose of the low inlet turbulence study was to examine the transitional flow effects that are anticipated at cruise Reynolds numbers. The high turbulence study extends this to LPT-relevant turbulence levels while perhaps sacrificing transitional flow effects. Downstream total pressure and exit angle data were acquired for ten incidence angles ranging from +15.8 to 51.0. For each incidence angle, data were obtained at five flow conditions with the exit Reynolds number ranging from 2.12105 to 2.12106 and at a design exit Mach number of 0.72. In order to achieve the lowest Reynolds number, the exit Mach number was reduced to 0.35 due to facility constraints. The inlet turbulence intensity, Tu, was measured using a single-wire hotwire located 0.415 axial-chord upstream of the blade row. The inlet turbulence levels ranged from 0.25 - 0.4 for the low Tu tests and 8- 15 for the high Tu study. Tu measurements were also made farther upstream so that turbulence decay rates could be calculated as needed for computational inlet boundary conditions. Downstream flow field measurements were obtained using a pneumatic five-hole pitchyaw probe located in a survey plane 7 axial chord aft of the blade trailing edge and covering three blade passages. Blade and endwall static pressures were acquired for each flow condition as well. The blade loading data show that the suction surface separation that was evident at many of the low Tu conditions has been eliminated. At the extreme positive and negative incidence angles, the data show substantial differences in the exit flow field. These differences are attributable to both the higher inlet Tu directly and to the thinner inlet endwall boundary layer that the turbulence grid imposes.

Turbines↗
DOE OSTI2016

Fractal-Like Materials Design with Optimized Radiative Properties for High-Efficiency Solar Energy Conversion

Novel designs to increase light trapping and thermal efficiency of concentrating solar receivers at multiple length scales have been conceived, designed, and tested. The fractal-like geometries and features are introduced at both macro (meters) and meso (millimeters to centimeters) scales. Advantages include increased solar absorptance, reduced thermal emittance, and increased thermal efficiency. Radial and linear structures at the meso (tube shape and geometry) and macro (total receiver geometry and configuration) scales redirect reflected solar radiation toward the interior of the receiver for increased absorptance. Hotter regions within the interior of the receiver can reduce thermal emittance due to reduced local view factors to the environment, and higher concentration ratios can be employed with similar surface irradiances to reduce the effective optical aperture, footprint, and thermal losses. Coupled optical/fluid/thermal models have been developed to evaluate the performance of these designs relative to conventional designs. Modeling results showed that fractal-like structures and geometries can increase the effective solar absorptance by 5 – 20% and the thermal efficiency by several percentage points at both the meso and macro scales, depending on factors such as intrinsic absorptance. Meso-scale prototypes were fabricated using additive manufacturing techniques, and a macro-scale bladed receiver design was fabricated using Inconel 625 tubes. On-sun tests were performed using the solar furnace and solar tower at the National Solar Thermal Test facility. The test results demonstrated enhanced solar absorptance and thermal efficiency of the fractal-like designs.

14 SOLAR ENERGY↗
NASA NTRS1999

Recent Development in the Analytical Investigation of Shipboard Rotorcraft Engage and Disengage Operations

This paper presents an overview of recent developments in an effort to predict transient aeroelastic rotor response during shipboard engage and disengage sequences. The blade is modeled as an elastic beam undergoing in flap, lag, extension and torsion. The blade equations of motion are formulated using Hamilton's principle and they are spatially discretized using the finite element method. The discretized blade equations of motion are integrated for a specified rotor speed run-up or run-down profile. Blade element theory is used to calculate quasi-steady or unsteady aerodynamic loads in linear and nonlinear regimes. The analysis is capable of simulating both articulated, hingeless, and gimballed rotor systems. Validation of the rotor code is discussed, including correlation with droop stop impact tests and wind tunnel experiments. Predictions of safe engagement and disengagement envelopes, limited by excessive blade tip deflections or hub moments, are presented. Future directions of study are also discussed.

Smith, Edward C.↗
NASA NTRS1977

Inlet turbulence and fan noise measured in an anechoic wind tunnel and statically with an inlet flow control device

Turbulence and acoustic measurements were taken in the NASA-Lewis anechoic wind tunnel - a facility which has demonstrated the blade passage tone cutoff phenomena with forward velocity. Turbulence data were taken in a subsonic inlet at various fan speeds under static and forward velocity conditions. A honeycomb/screen flow control device was placed over the inlet during static tests to modify the inflow in an attempt to simulate flight conditions. Acoustic levels of the blade passage tone along with transverse turbulence intensities were reduced with forward velocity. The flow control device reduced the blade passage tone to an intermediate level between those levels associated with static and forward velocity operation.

Shaw, L. M.↗
NASA NTRS1995

Flow structure generated by perpendicular blade vortex interaction and implications for helicopter noise predictions

This report summarizes accomplishments and progress for the period ending April 1995. Much of the work during this period has concentrated on preparation for an analysis of data produced by an extensive wind tunnel test. Time has also been spent further developing an empirical theory to account for the effects of blade-vortex interaction upon the circulation distribution of the vortex and on preliminary measurements aimed at controlling the vortex core size.

Devenport, William J.↗