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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1933

The Effect of Nozzle Design and Operating Conditions on the Atomization and Distribution of Fuel Sprays

The atomization and distribution characteristics of fuel sprays from automatic injection valves for compression-ignition engines were determined by catching the fuel drops on smoked-glass plates, and then measuring and counting the impressions made in the lampblack. The experiments were made in an air-tight chamber in which the air density was raised to values corresponding to engine conditions.

Lee, Dana W↗
NASA NTRS1961

Flight Investigation of Effects of Selected Operating Conditions on the Bending and Torsional Moments Encountered by a Helicopter Rotor Blade

Flight tests have been conducted with a single-rotor helicopter to determine the effects of partial-power descents with forward speed, high-speed level turns, pull-outs from autorotation, and high-forward-speed high-rotor-speed autorotation on the flapwise bending and torsional moments of the rotor blade. One blade of the helicopter was equipped at 14 percent and 40 percent of the blade radius with strain gages calibrated to measure moments rather than stresses. The results indicate that the maximum moments encountered in partial-power descents with forward speed tend to be generally reduced from the maximum moments encountered during partid-power descents at zero forward speed. High-speed level turns and pull-outs from auto-rotation caused retreating-blade stall which produced torsional moments (values up to 2,400 inch-pounds). at the 14-percent-radius station that were as large as those encountered during the previous investigations of retreating-blade stall (values up t o 2,500 inch-pounds). High-forward- speed high-rotor-speed autorotation produced flapwise bending moments (values up to 7,200 inch-pounds) at the 40-percent-radius station which were as large as the flapwise bending moments (values up to 7,800 inch-pounds) a t the 14-percent-radius station encountered during partial - power vertical descents. The results of the present investigation (tip-speed ratios up to 0.325 and an unaccelerated level-flight mean lift coefficient of about 0.6), in combination with the related results of at zero forward speed produce the largest rotor-blade vibratory moments. However, inasmuch as these large moments occur only during 1 percent of the cycles and 88 percent of the cycles are at moment values less than 70 percent of these maximum values in partial-power descents, other conditions, such as high-speed flight where the large moments are combined with large percentages of time spent,must not be neglected in any rotor-blade service-life assessment.

Ludi, LeRoy H.↗
NASA NTRS2007

Operational Condition and Superfinishing Effect on High-Speed Helical Gearing System Performance

An experimental effort has been conducted on an aerospace-quality helical gear train to investigate the thermal behavior of the gear system. Oil inlet temperature was varied from 160 to 250 F. Also, the test gears were run in both an as-ground condition and after isotropic superfinishing (ISF) condition. In-depth temperature measurements were made across the face width and at the axial end of the gear mesh. Supply power measurements were made at varying speeds and loads up to 5000 hp and 15000 rpm (pitch line velocity to 24000 feet per minute). Test results from the parametric studies and the superfinishing process are presented. The tests indicated that superfinishing offered no improvement in performance due to the high lubricant film thickness generated by the extremely high pitch line velocity that the majority of the tests were conducted. Increasing lubricant inlet temperature had the most dramatic effect on performance improvement.

Handschuh, R.↗
NASA NTRS2007

A Computational Fluid Dynamics Study of Transitional Flows in Low-Pressure Turbines under a Wide Range of Operating Conditions

A transport equation for the intermittency factor is employed to predict the transitional flows in low-pressure turbines. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mu(sub p) with the intermittency factor, gamma. Turbulent quantities are predicted using Menter's two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The model had been previously validated against low-pressure turbine experiments with success. In this paper, the model is applied to predictions of three sets of recent low-pressure turbine experiments on the Pack B blade to further validate its predicting capabilities under various flow conditions. Comparisons of computational results with experimental data are provided. Overall, good agreement between the experimental data and computational results is obtained. The new model has been shown to have the capability of accurately predicting transitional flows under a wide range of low-pressure turbine conditions.

Suzen, Y. B.↗
NASA NTRS1947

Cooling Characteristics of the V-1650-7 Engine: Coolant-Flow Distribution, Cylinder Temperatures, and Heat Rejections at Typical Operating Conditions - 1

An investigation was conducted to determine the coolant-flow distribu tion, the cylinder temperatures, and the heat rejections of the V-165 0-7 engine . The tests were run a t several power levels varying from minimum fuel consumption to war emergency power and at each power l evel the coolant flows corresponded to the extremes of those likely t o be encountered in typical airplane installations, A mixture of 30-p ercent ethylene glycol and 70-percent water was used as the coolant. The temperature of each cylinder was measured between the exhaust val ves, between the intake valves, in the center of the head, on the exh aust-valve guide, at the top of the barrel on the exhaust side, and o n each exhaust spark-plug gasket. For an increase in engine power fro m 628 to approximately 1700 brake horsepower the average temperature for the cylinder heads between the exhaust valves increased from 437 deg to 517 deg F, the engine coolant heat rejection increased from 12 ,600 to 22,700 Btu. per minute, the oil heat rejection increased from 1030 to 4600 Btu per minute, and the aftercooler-coolant heat reject ion increased from 450 to 3500 Btu -per minute.

Povolny, John H.↗
NASA NTRS2013

Assessment of tbe Performance of Ablative Insulators Under Realistic Solid Rocket Motor Operating Conditions (a Doctoral Dissertation)

Ablative insulators are used in the interior surfaces of solid rocket motors to prevent the mechanical structure of the rocket from failing due to intense heating by the high-temperature solid-propellant combustion products. The complexity of the ablation process underscores the need for ablative material response data procured from a realistic solid rocket motor environment, where all of the potential contributions to material degradation are present and in their appropriate proportions. For this purpose, the present study examines ablative material behavior in a laboratory-scale solid rocket motor. The test apparatus includes a planar, two-dimensional flow channel in which flat ablative material samples are installed downstream of an aluminized solid propellant grain and imaged via real-time X-ray radiography. In this way, the in-situ transient thermal response of an ablator to all of the thermal, chemical, and mechanical erosion mechanisms present in a solid rocket environment can be observed and recorded. The ablative material is instrumented with multiple micro-thermocouples, so that in-depth temperature histories are known. Both total heat flux and thermal radiation flux gauges have been designed, fabricated, and tested to characterize the thermal environment to which the ablative material samples are exposed. These tests not only allow different ablative materials to be compared in a realistic solid rocket motor environment but also improve the understanding of the mechanisms that influence the erosion behavior of a given ablative material.

Martin, Heath Thomas↗
NASA NTRS2016

Optimizing Facility Configurations and Operating Conditions for Improved Performance in the NASA Ames 24 Inch Shock Tube

The Ames Electric Arc Shock Tube (EAST) is a shock tube wherein the driver gas can be heated by an electric arc discharge. The electrical energy is stored in a 1.2 MJ capacitor bank. Four inch and 24 inch diameter driven tubes are available. The facility is described and the need for testing in the 24 inch tube to better simulate low density NASA mission profiles is discussed. Three test entries, 53, 53B and 59, are discussed. Tests are done with air or Mars gas (95.7% CO2/2.7% N2/1.6% Ar) at pressures of 0.01 to 0.14 Torr. Velocities spanned 6.3-9.2 km/s, with a nominal center of 7 km/s. Many facility configurations are studied in an effort to improve data quality. Various driver and driven tube configurations and the use of a buffer section between the driver and the driven tube are studied. Diagnostics include test times, time histories of the shock light pulses and tilts of the shock wave off the plane normal to the tube axis. The report will detail the results of the various trials, give the best configuration/operating conditions found to date and provide recommendations for further improvements. Finally, diaphragm performance is discussed.

Shock Tube↗
NASA NTRS2015

Numerical Simulations of the XR-5 Hall Thruster for Life Assessment at Different Operating Conditions

NASA's Jet Propulsion Laboratory has been investigating the applicability of Aerojet Rocketdyne's XR-5 thruster, a 4.5 kW class Hall thruster, for deep-space missions. Major considerations for qualifying the XR-5 for deep-space missions are demonstration of a wide throttling envelope and a usable life capability in excess of 10,000 h. Numerical simulations with the 2-D axisymmetric code Hall2De are employed to inform the qualification process by assessing erosion rates at the thruster surfaces in a wide range of throttling conditions without the need for conducting costly endurance testing. In previous work at JPL by Jorns et al., the anomalous collision frequency distribution for 11 different throttling conditions of the XR-5 spanning 0.3-4.5 kW were identified based on probe measurements of the electron temperature in the near plume region. In this paper, we provide estimates for the erosion rates at the channel walls and pole covers for the same 11 conditions. Uncertainties in the plasma measurements and in the anomalous collision frequency distribution are addressed by determining upper and lower bounds of the erosion rates. Results suggest that erosion of the walls only occurs in the last 5% of the acceleration channel and the rate of such erosion decreases as the geometry of the thruster changes in time due to magnetic shielding. A quasi-zero-erosion state is eventually achieved in all the examined throttling conditions. Examination of the results for pole surface erosion and estimated cathode life indicates that the XR-5 propellant throughput capability will exceed 700 kg, which provides 50% margin over the usable throughput capability of 466 kg as already demonstrated in wear testing.

Lopez Ortega, Alejandro↗
DOE OSTI2021

Preventing Voltage Divergence in Series-Stacked Bidirectional Battery Energy Storage DC-DC Converter under Asymmetrical Operating Conditions

DC stacked topologies have gained popularity for interfacing individual photovoltaic panels to a high-voltage DC bus. A similar approach can be used to interface individual battery packs to the same DC bus, which allows active balancing of battery substrings and the use of lower voltage switches. Any imbalance in battery current, however, can cause the converter output voltages to diverge. This paper describes the source of voltage divergence and demonstrates a solution that allows seamless stacking of multiple battery packs to be interfaced to a high voltage DC bus. To prevent the voltage divergence phenomenon and allow asymmetrical battery charging for efficient battery state of charge management, the PI-based decentralized voltage control enabling both capacitor voltage sharing and asymmetrical capacitor voltage control is proposed. The effectiveness of the decentralized voltage control strategy is demonstrated through controller hardware-in-the-loop test results.

Kim, Namwon↗
DOE OSTI2021

Radial Compressor Design and Off-Design for Trans-critical CO2 Operating Conditions

Presentation for the The 7th International Supercritical CO2 Power Cycles Symposium, February 21 – 24, 2022, San Antonio, Texas. A multi-staged intercooled centrifugal compressor design is performed for an indirect-fired sCO2 cycle and the design point data are used to generate the performance maps using a 2D mean-line analysis code. Fluid and turbomachinery similarity laws are applied to find an appropriate surrogate ideal gas fluid to be used in the design and performance map generation codes. The performance maps are then scaled back for the sCO2 fluid case using the affinity laws.

Uysal, Selcuk Can↗