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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Analysis of open loop higher harmonic control at high airspeeds on a modern four-bladed articulated rotor

The effects of open loop higher harmonic control (HHC) on rotor hub loads, performance, and push rod loads of a Sikorsky S-76 helicopter rotor at high airspeeds (up to 200 knots) and moderate lift (10,000 lbs) were studied analytically. The analysis was performed as part of a wind tunnel pre-test prediction and preparation procedure, as well as to provide analytical results for post-test correlation efforts. The test associated with this study is to be concluded in the 40- by 80-Foot Wind Tunnel of the National Full-Scale Aerodynamics Complex (NFAC) at the NASA Ames Research Center. The results from this analytical study show that benefits from HHC can be achieved at high airspeeds. These results clear the way for conducting (with the requirement of safe pushrod loads) an open loop HHC test a high airspeeds in the 40- by 80-Foot Wind Tunnel using an S-76 rotor as the test article.

Kottapalli, Sesi↗
NASA NTRS1992

Analysis of open loop higher harmonic control at high airspeeds on a modern four-bladed articulated rotor

The effects of open loop higher harmonic control (HHC) on rotor hub loads, performance, and push rod loads of a Sikorsky S-76 helicopter rotor at high airspeeds (up to 200 knots) and moderate lift (10,000 lbs) were studied analytically. The present analysis was performed as a part of a wind tunnel pre-test prediction and preparation procedure, as well as to provide analytical results for post-test correlation efforts. The test associated with this study is to be concluded in the 40- by 80-Foot Wind Tunnel of the National Full-Scale Aerodynamics Complex (NFAC) at the NASA Ames Research Center. The results from this analytical study show that benefits from HHC can be achieved at high airspeeds. These results clear the way for conducting (with the requirement of safe pushrod loads) an open loop HHC test at high airspeeds in the 40- by 80-Foot Wind Tunnel using an S-76 rotor as the test article.

Kottapalli, Sesi↗
NASA NTRS1979

Analysis and correlation with theory of rotor lift-limit test data

A wind tunnel test program to define the cruise performance and determine any limitations to lift and propulsive force of a conventional helicopter rotor is described. A 2.96 foot radius model rotor was used. The maximum lift and propulsive force obtainable from an articulated rotor for advance ratios of 0.4 to 0.67, and the blade load growth as the lift approaches the limit are determined. Cruise rotor performance for advance ratios of 0.4 to 0.67 and the sensitivity of the rotor forces and moments to rotor control inputs as the lift limit is approached are established.

Sheffler, M.↗
NASA NTRS2012

An Assessment of Open Rotor Noise Prediction Tools

Assess the current capability for predicting the aerodynamic and acoustic performance of open rotors. The testbed is a GE blade set called F31/A31 for which significant amount of aerodynamic and acoustic data was acquired in model scale tests. F31/A31 is a vintage 1990s design with a 12-bladed front rotor and a 10-bladed aft rotor. This blade set was tested in both low-speed regime (representative of approach and takeoff conditions) and high-speed regime (representative of climb and cruise conditions). Uninstalled as well as installed configurations were tested. The focus of this interim presentation is on a subset of the low-speed tests for which the tip speed was varied, but the blade setting angles and tunnel Mach number were held fixed.

Envia, Ed↗
NASA NTRS1999

International Space Station Attitude Motion Associated With Flywheel Energy Storage

Flywheels can exert torque that alters the Station's attitude motion, either intentionally or unintentionally. A design is presented for a once planned experiment to contribute torque for Station attitude control, while storing or discharging energy. Two contingencies are studied: the abrupt stop of one rotor while another rotor continues to spin at high speed, and energy storage performed with one rotor instead of a counter rotating pair. Finally, the possible advantages to attitude control offered by a system of ninety-six flywheels are discussed.

Roithmayr, Carlos M.↗
NASA NTRS2016

Isolated Open Rotor Noise Prediction Assessment Using the F31A31 Historical Blade Set

In an effort to mitigate next-generation fuel efficiency and environmental impact concerns for aviation, open rotor propulsion systems have received renewed interest. However, maintaining the high propulsive efficiency while simultaneously meeting noise goals has been one of the challenges in making open rotor propulsion a viable option. Improvements in prediction tools and design methodologies have opened the design space for next generation open rotor designs that satisfy these challenging objectives. As such, validation of aerodynamic and acoustic prediction tools has been an important aspect of open rotor research efforts. This paper describes validation efforts of a combined computational fluid dynamics and Ffowcs Williams and Hawkings equation methodology for open rotor aeroacoustic modeling. Performance and acoustic predictions were made for a benchmark open rotor blade set and compared with measurements over a range of rotor speeds and observer angles. Overall, the results indicate that the computational approach is acceptable for assessing low-noise open rotor designs. Additionally, this approach may be used to provide realistic incident source fields for acoustic shielding/scattering studies on various aircraft configurations.

Nark, Douglas M.↗
NASA NTRS1980

Aerodynamic performances of three fan stator designs operating with rotor having tip speed of 337 meters per second and pressure ratio of 1.54. Relation of analytical code calculations to experimental performance

A hub-to-shroud and a blade-to-blade internal-flow analysis code, both inviscid and basically subsonic, were used to calculate the flow parameters within four stator-blade rows. The produced ratios of maximum suction-surface velocity to trailing-edge velocity correlated well in the midspan region, with the measured total-parameters over the minimum-loss to near stall operating range for all stators and speeds studied. The potential benefits of a blade designed with the aid of these flow analysis codes are illustrated by a proposed redesign of one of the four stators studied. An overall efficiency improvement of 1.6 points above the peak measured for that stator is predicted for the redesign.

Gelder, T. F.↗
NASA NTRS1980

Performance of a steel spar wind turbine blade on the Mod-0 100 kW experimental wind turbine

The performance and loading of a large wind rotor, 38.4 m in diameter and composed of two low-cost steel spar blades were examined. Two blades were fabricated at Lewis Research Center and successfully operated on the Mod-0 wind turbine at Plum Brook. The blades were operated on a tower on which the natural bending frequency were altered by placing the tower on a leaf-spring apparatus. It was found that neither blade performance nor loading were affected significantly by this tower softening technique. Rotor performance exceeded prediction while blade loads were found to be in reasonable agreement with those predicted. Seventy-five hours of operation over a five month period resulted in no deterioration in the blade.

Keith, T. G., Jr.↗
NASA NTRS2023

Performance, Inflow, and Tip Loss Characteristics of Rotors with Discontinuous Steps in Twist and Lift at the Blade-Tips

This paper examines the inflow and tip-loss characteristics of rotors incorporating indexed blade-tips that have discontinuous steps in twist or lift distribution. An extension of the classic two-dimensional Prandtl tip loss analysis is derived for indexed-tip rotors and proprotors. Additionally, parametric analysis of tip span and indexed-tip twist-steps was performed using computational fluid dynamics for hover and high-speed axial-flow conditions for proprotors. The intent of this work is to define a new class of active-rotor-twist-control designs for proprotors that avoids unnecessary aeroperformance compromises for rotor twist distributions for proprotors in all phases of flight.

rotors↗
NASA NTRS1985

Development and testing of tip devices for horizontal axis wind turbines

A theoretical and field experimental program has been carried out to investigate the use of tip devices on horizontal axis wind turbine rotors. The objective was to improve performance by the reduction of tip losses. While power output can always be increased by a simple radial tip extension, such a modification also results in an increased gale load both because of the extra projected area and longer moment arm. Tip devices have the potential to increase power output without such a structural penalty. A vortex lattice computer model was used to optimize three basic tip configuration types for a 25 kW stall limited commercial wind turbine. The types were a change in tip planform, and a single-element and double-element nonplanar tip extension (winglets). A complete data acquisition system was developed which recorded three wind speed components, ambient pressure, temperature, and turbine output. The system operated unattended and could perform real-time processing of the data, displaying the measured power curve as data accumulated in either a bin sort mode or polynomial curve fit. Approximately 270 hr of perormance data were collected over a three-month period. The sampling interval was 2.4 sec; thrus over 400,000 raw data points were logged. Results for each of the three new tip devices, compared with the original tip, showed a small decrease (of the order of 1 kW) in power output over the measured range of wind speeds from cut-in at about 4 m/s to over 20 m/s, well into the stall limiting region. Changes in orientation and angle-of-attack of the winglets were not made. For aircraft wing tip devices, favorable tip shapes have been reported and it is likely that the tip devices tested in this program did not improve rotor performance because they were not optimally adjusted.

Gyatt, G. W.↗
NASA NTRS1951

Calculated effects of turbine rotor-blade cooling-air flow, altitude, and compressor bleed point on performance of a turbojet engine

Effects of air-cooling turbine rotor blades on performance of a turbojet engine were calculated for a range of altitudes from sea level to 40,000 feet and a range of coolant flows up to 3 percent of compressor air flow, for two conditions of coolant bleed from the compressor. Bleeding at required coolant pressure resulted in a sea-level thrust reduction approximately twice the percentage coolant flow and in an increase in specific fuel consumption approximately equal to percentage coolant flow. For any fixed value of coolant flow ratio the percentage thrust reduction and percentage increase in specific fuel consumption decreased with altitude. Bleeding coolant at the compressor discharge resulted in an additional 1 percent loss in performance at sea level and in smaller increase in loss of performance at higher altitudes.

TURBINE COOLING↗
NASA NTRS1982

The effect of rotor blade thickness and surface finish on the performance of a small axial flow turbine

An experimental investigation was conducted to determine the effect of blade profile inaccuracies and surface finish on the aerodynamic performance of a 11.13 cm tip diameter turbine. The as-received cast rotor blades had a significantly thicker profile than the design intent and a fairly rough surface finish. Stage test results showed an increase of one point in efficieny by smoothing the surface finish and another three points by thinning the blade profiles to near the design profile. Most of the performance gain between the as-cast thick and the thinned rotor blades both with the same surface finish, was attributed to reduced trailing edge losses of the recontoured blades.

Roelke, R. J.↗
NASA NTRS1979

Effect of rotor tip clearance and configuration on overall performance of a 12.77-centimeter tip diameter axial-flow turbine

An extensive experimental investigation was made to determine the effect of varying the rotor tip clearance of a 12.77-cm-tip diameter, single-stage, axial-flow reaction turbine. In this investigation, the rotor tip clearance was obtained by use of a recess in the casing above the rotor blades and also by use of a reduced blade height. For the recessed casing configuration, the optimum rotor blade height was found to be the one where the rotor tip diameter was equal to the stator tip diameter. The tip clearance loss associated with this optimum recessed casing configuration was less than that for the reduced blade height configuration.

Haas, J. E.↗
NASA NTRS1988

Effect of advanced rotorcraft airfoil sections on the hover performance of a small-scale rotor model

A hover test was conducted on a small scale rotor model for two sets of tapered rotor blades. The baseline rotor blade set used a NACA 0012 airfoil section, whereas the second rotor blade set had advanced rotorcraft airfoils distributed along the radius. The experiment was conducted for a range of thrust coefficients and tip speeds, and the data were compared to the predictions of three analytical methods. The data show the advantage of the advanced airfoils at the higher rotor thrust levels; two of the analyses predicted the correct data trends.

Althoff, Susan L.↗