United Technologies Research Center Research Articles

Role of fuel chemical properties on combustor radiative heat load

In an attempt to rigorously study the fuel chemical property influence on combustor radiative heat load, United Technologies Research Center (UTRC) has conducted an experimental program using 25 test fuels. The burner was a 12.7-cm dia cylindrical device fueled by a single pressure-atomizing injector. Fuel physical properties were de-emphasized by selecting injectors which produced high-atomized, and hence rapidly-vaporizing sprays. The fuels were specified to cover the following wide ranges of chemical properties; hydrogen, 9.1 to 15- (wt) pct; total aromatics, 0 to 100 (vol) pct; and naphthalene, 0 to 30 (vol) pct. They included standard fuels, specialty products and fuel blends. Fuel naphthalene content exhibited the strongest influence on radiation of the chemical properties investigated. Smoke point was a good global indicator of radiation severity.

Adhesive evaluation of LARC-TPI and a water-soluble version of LARC-TPI

A linear thermoplastic polyimide, LARC-TPI, developed several years ago at NASA Langley Research Center, showed promise as a high temperature adhesive for application in aircraft and spacecraft based on the material's toughness, flexibility, good thermal and thermo-oxidative stability, and other attractive properties. Since then, a commercial product manufactured and supplied by Mitsui Toatsu Chemicals, Inc, Tokyo, Japan, has become available. In addition, a water-soluble version containing N,N-dimethylethanol amine salt was supplied by United Technologies Research Center, East Hartford, CT, USA. The water-soluble version is highly attractive because of the safety requirements involved with organic solvents presently used for polyimide materials. This report details the results of a study to evaluate the two LARC-TPI materials as high temperature thermoplastic adhesives and primers for bonding titanium (6Al-4V) adherends. A limited characterization of the materials was performed using a diffuse reflectance-Fourier transform infrared spectroscopy technique. Thermomechanical analysis and torsional braid techniques were used to determine the glass transition temperature. The effects of long-term thermal exposure (up to 1000 h) at 204°C and 72 h water-boil on the strength of the adhesives was determined by simple lap shear tests.

Application of Thermal Plasma Arc Melting for Critical Alloy Ingot Preparation

Volatile foreign dependence, cyclic availability, and restricted critical material stockpiles have focused considerable attention on the feasibility of new and more efficient processing/ recycling schemes. Over the past several years United Technologies Research Center (UTRC) has been investigating plasma processing techniques for the reprocessing and upgrading of critical materials and alloys. As part of this effort, a laboratory scale dc thermal plasma reactor operating in the transferred mode was developed and successfully demonstrated. The reactor was originally developed for recycling MCrAlY and Ni alloy materials and more recently modified for processing titanium (Ti) alloys. The reactor demonstrated the ability to produce homogeneous void-free 5-cm-diameter ingots in an inert atmospheric pressure environment without loss of volatile alloy constituents and with no significant contamination introduction. Exploratory experiments were also conducted to investigate the effectiveness of this type of plasma reactor for reducing the surface oxygen contamination of the Ti alloy feed material, as generated during high-speed machining operations. The process is based on high-reactivity atomic hydrogen species generated in the plasma region for reducing the oxygenated titanium surface compounds (measured to be predominantly TiO2). Only modest oxygen reductions were achieved. Aspects of this research and development will be described in this paper.

Secondary Flows and Losses Downstream of a Turbine Cascade

The loss mechanisms and the behavior of secondary flows downstream of a large scale, linear turbine cascade have been investigated experimentally. A five-blade replica of the cascade used by Langston et al. at United Technologies Research Center was used for the present tests. Detailed flow measurements, using five-hole and three-hole probes, were made at four different planes, one just upstream of the trailing edge and the rest downstream. The secondary flow field at each measurement plane was found to be dominated by a single large passage vortex, which decayed in strength because of the mixing occurring in the flow. More than one-third of the losses were found to occur downstream of the trailing edge. This rise in total pressure loss in the present tests was almost entirely explained by a corresponding dissipation of the secondary kinetic energy of the flow. A mixing analysis of the flow was done to predict the additional losses due to “mixing” until the flow became completely uniform.

Further comparisons of wind tunnel and airplane acoustic data for advanced design high‐speed propeller models

The noise of high‐tip‐speed propellers at cruise has been identified as a possible cabin noise problem for advanced turboprop airplanes. Comparisons were made between the SR‐2 and SR‐3 model propeller noise data taken in the NASA 8×6 wind tunnel, in the United Technologies Research Center (UTRC) Anechoic Tunnel, and with boom and fuselage microphones on the NASA Jetstar airplane. Plots of peak blade passage tone noise versus helical tip Mach number generally showed good agreement. The curve shapes were similar except for the UTRC data, which was flatter than the other sets. This was attributed to the UTRC data being taken at constant power while the other data were at constant advance ratio. Directivity shape comparisons at the cruise condition were also similar. The generally good comparisons of the data from four configurations using three facilities indicates the ability to use any of these facilities for measuring the blade passage tone noise of these types of propellers.

Materials Research at United Technologies Research Center

Materials Research at United Technologies Research Center

Flow in a Turbine Cascade: Part 1—Losses and Leading-Edge Effects

An experimental investigation was conducted to study the effect of the leading-edge shape on the overall losses in a large-scale linear cascade of turbine blades. The leading-edge shapes used were a cylinder and a wedge. The cascade was designed to be geometrically similar to the cascade used by Langston et al. at United Technologies Research Center, with the same span/chord and pitch/chord ratios. Measurements of wall static pressure on the blades and of total pressure and flow direction downstream of the cascade showed only minor changes due to the alteration of the leading-edge shape. The measurements of the flow and loss distributions downstream of the cascade complement the results of Langston et al., which showed the flow development only within the cascade. The downstream flow is important, however, as apppoximately 50 percent of the losses occur downstream of the trailing edge. Regions of high loss were found near midspan at an axial location 40 percent of the axial chord downstream of the trailing edge. The sources of fluid in these regions are determined in Part 2.

Noise of a model helicopter rotor due to ingestion of isotropic turbulence

A theoretical and experimental investigation of the noise of a model helicopter rotor due to the ingestion of grid-generated, isotropic turbulence is described. Simulated forward flight and vertical ascent tests were performed with a 0·76 m diameter, articulated model rotor in the United Technologies Research Center Acoustic Research Tunnel. Far field noise spectra and directivity were measured in addition to inflow turbulence intensities, length scales and spectra. Measured inflow turbulence statistics and rotor operating parameters were employed in a theoretical procedure to predict turbulence ingestion noise spectra and directivity. This theoretical formulation represented an absolute level prediction method in that empirical or adjustable constants were not employed. From this study it is concluded that incident turbulence represents a potentially important source of rotor narrowband random (quasi-tonal) and broadband noise. With due regard to the absolute level nature of the prediction method, agreement between theory and experiment is reasonable: quasi-tonal noise at low frequency tends to be overpredicted whereas mid-frequency tonal noise and high frequency broadband noise are well predicted. This theory, therefore, provides a means to predict the contribution of turbulence ingestion noise to overall rotor noise spectra and directivity in cases where reasonable estimates of incident turbulence statistics can be made. Ingestion of main rotor wake turbulence by tail rotors in flight and ingestion of atmospheric turbulence by main and tail rotors in hover would be expected to be the most important sources of turbulence ingestion noise in full scale applications.

Shining blue light

While UV emitting gas mixtures (together with phosphor converters) and mercury-seeded gas mixtures have shown some promise, it has always been difficult to develop a display device that emits either blue or green light with the same efficiency as a neon glow discharge tube produces its red-orange emission. However, W L Nighan and C M Ferrar (United Technologies Research Center, East Hartford, Connecticut) have discovered that electrical excitation of high pressure (5–10 atm) mixtures containing xenon and chlorine donors gives rise to strong broadband Xe2CI emission in the 450–550 nm range (Appl. Phys. Lett. 1982 40 (3) 223).

Communications: Fiber-optic transducers: Sensing and control systems based on fiber-optic conversion of input variables into modulated light signals are in development

All fiber-optic transducers employ at least one light source for injecting a continuous signal into the fiber, a light detector for receiving the signal after the light has been modulated by a sensor, and electronics for converting the detected signal into a useful output. The two basic types of fiber-optic sensors are those in which the measured parameter causes a change in the transmission properties of the fiber itself and those in which the fiber acts merely as a conduit to carry light signals to and from the sensor. Development work is predominantly on transducers for military applications. For example, Sperry Research Center, Sudbury, Mass., is working on such systems for underwater sound and United Technologies Research Center, E. Hartford, Conn., for aircraft engine variables. Possible applications for fiber-optic transducers include sensing and control systems for farm equipment, industrial robots, commercial aircraft, ships, and buildings. Here qualities such as noise immunity, ruggedness, economy, and light weight give optical fibers a big advantage over electrical wiring.

UTRC 8-kW Wind-Turbine Tests

The United Technologies Research Center (UTRC) 8-kW prototype wind turbine became operational in July 1979 and underwent testing in East Hartford, Connecticut, until delivery to Rockwell International, the prime contractor, in February 1980. This project, funded under the DOE wind-energy program, began in October 1977, following two years of feasibility studies under contract to ERDA. The program will continue with the field evaluation by Rockwell at their Rocky Flats site beginning in 1980. The prototype testing demonstrated the basic operation of the unique control concept of the UTRC Composite Bearingless Wind Turbine which utilizes a hub-mounted pendulum employed to twist the graphite composite inboard region of the blade producing blade pitch variations. The tests also demonstrated the predicted performance of 9 kW at 20 mi/h = (9 m/s) and the high-speed-stall control feature.

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Scientists at United Technologies Research Center are using light beams as thermometers to get information for designing cleaner, more efficient jet engines.

Self-regulating composite bearingless wind turbine

The Composite Bearingless Rotor (CBR) concept has been shown to have characteristics ideally suited for wind turbine applications. Originally developed for helicopters to reduce weight, costs and complexity, the CBR eliminates blade bearings and hinges through the utilization of the unique structural characteristics of uniaxial composite materials. This rotor concept was further developed under an ERDA contract to provide a fully self-regulating and self-aligning wind turbine. Such a system was achieved without the need for auxiliary controls or sensors. These features allow self-starting for wind initiating from any direction and automatic pitch and yaw variations to optimize performance under all normal wind conditions. The work described in this report consists of the design and fabrication of a 4.5 ft dynamically scaled wind turbine model and the successful testing of this model in the United Technologies Research Center low speed wind tunnel.

Self‐consistent background gas density calculation in a multichambered neutral beam line

A model for calculating the self‐consistent background gas density in a multichamber beam‐line system is described. This model is applied to the design of the experiment chamber/beam‐line vacuum system for the laser‐initiated target experiment at the United Technologies Research Center.

Effect of Simulated Forward Flight on Subsonic Jet Exhaust Noise

A wind-tunnel model program was conducted to investigate the effect of aircraft forward speed on the jet noise characteristics of a single subsonic jet. The tests were performed in the United Technologies Research Center Acoustic Research Tunnel, a low-noise open-jet anechoic wind tunnel designed specifically for acoustic testing. Electrically heated air was supplied to a convergent nozzle located on the tunnel centerline. The nozzle diameter of 2.4 in. produced a tunnel to nozzle area ratio of 220. Microphones were located at a radius of 50 nozzle diameters in the anechoic chamber outside the tunnel flow. Nozzle operating conditions covered a range of velocities up to 1670 fps, and temperatures to 900°F. Wind-tunnel speeds ranged from near zero to 350 fps. Measured noise data were corrected for tunnel shear layer refraction and moving medium convection effects, thus simulating the effects on the jet noise sources of relative velocity during an aircraft flyover. Measured overall sound pressure level reductions due to relative velocity were correlated with relative velocity raised to an exponent that increased towards the aft angles. The results showed general agreement with recent National Gas Turbine Establishment (NGTE) test results obtained in a large wind tunnel.