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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 613 records · Page 34

All sources NASA NTRS DOE OSTI

NASA NTRS1975

An analytical study of a multicycle controllable twist rotor

A rotor employing a servo-flap to effect blade torsional deflections (the Kaman Controllable Twist Rotor) has been used in a theoretical study to assess the potential of multicyclic flap control, (i.e., 1P, 2P, 3P, and 4P flap deflections). The results show that virtual elimination of pylon vibratory loads may be achieved with concurrent blade bending moments reduced by 50%. The amplitude requirements of the higher harmonic deflections are of the order of 3 or 4 deg. The study is in two parts; the calculation of rotor loads for specific combinations of multicyclic flap deflections by a typical rotor computer analysis, and an analysis of those results to determine optimum combinations of the multicyclic flap control. The paper discusses the analysis and indicates the potentials of a multicyclic controllable twist rotor.

Mccloud, J. L., III↗

NASA NTRS1976

Acoustic and aerodynamic effects of rotor pitch angle for a variable-pitch, 6-foot diameter fan stage

An externally driven, 1.2 pressure ratio full-scale fan stage with an adjustable pitch rotor was tested in an outdoor facility at the Lewis Research Center. Rotor pitch angles resulting in minimum sideline perceived noise levels are defined as a function of stage thrust. Thrust-corrected fan noise variations are examined for operation at constant thrust, rotor tip speed, and stage work coefficient. At constant stage thrust, reducing the rotor pitch angle below design values increased the fan noise with the greatest change occurring in the blade passing tone level. At constant fan speed the minimum noise occurred at a particular rotor pitch angle, which was not the minimum thrust condition. With constant stage work coefficient, rear quadrant noise increased at above-design speed conditions.

Woodward, R. P.↗

NASA NTRS1976

Three-dimensional flow calculation for a transonic compressor rotor

A numerical calculation of the steady, inviscid, three dimensional flow in a isolated transonic compressor rotor has been completed using MacCormack's second order accurate time-marching scheme. This rotor has a tip Mach number of 1.2, an overall diameter of 2 feet, and inlet hub/tip ratio of 0.5. The computed rotor total pressure ratio is 1.82. Comparisons between the numerical solution, measurements of the intra-blade static density field obtained by gas fluorescence, and time resolved exit flow measurements showed that the inviscid computation accurately models transonic rotor aerodynamics and rotor blade pressure distributions in the upstream portions of the blade passages, the viscous effects influencing mainly the downstream flow.

Thompkins, W. T., Jr.↗

NASA NTRS1977

Application of system identification to analytic rotor modeling from simulated and wind tunnel dynamic test data, part 2

An introduction to aircraft state and parameter identification methods is presented. A simplified form of the maximum likelihood method is selected to extract analytical aeroelastic rotor models from simulated and dynamic wind tunnel test results for accelerated cyclic pitch stirring excitation. The dynamic inflow characteristics for forward flight conditions from the blade flapping responses without direct inflow measurements were examined. The rotor blades are essentially rigid for inplane bending and for torsion within the frequency range of study, but flexible in out-of-plane bending. Reverse flow effects are considered for high rotor advance ratios. Two inflow models are studied; the first is based on an equivalent blade Lock number, the second is based on a time delayed momentum inflow. In addition to the inflow parameters, basic rotor parameters like the blade natural frequency and the actual blade Lock number are identified together with measurement bias values. The effect of the theoretical dynamic inflow on the rotor eigenvalues is evaluated.

Hohenemser, K. H.↗

NASA NTRS1977

An experimental investigation of helicopter rotor high frequency broadband noise

The paper describes experiments involving a 4.17 foot diameter model rotor operating in a 5 times 7.5 ft open jet wind tunnel enclosed in an anechoic chamber. The effects of rotor thrust, advance ratio, and the number of blades on the intensity and spectrum of high frequency broadband noise (HFBN) have been investigated. The effects of each parameter were determined by keeping the other two constant. The directivities of the two- and three-bladed rotors were measured in a direction perpendicular to the plane of the rotor disk. The effects of heading edge, pressure side, and suction side serrations on HFBN were measured under several operating conditions, and the effects of the serrations on the mean thrust generated by the rotor were studied. A scaling law is proposed to determine the location of the peak frequency and intensity of HFBN.

Lee, A.↗

NASA NTRS1977

Calculated Hovering Helicopter Flight Dynamics with a Circulation Controlled Rotor

The influence of the rotor blowing coefficient on the calculated roots of the longitudinal and lateral motion was examined for a range of values of the rotor lift and the blade flap frequency. The control characteristics of a helicopter with a circulation controlled rotor are discussed. The principal effect of the blowing is a reduction in the rotor speed stability derivative. Above a critical level of blowing coefficient, which depends on the flap frequency and rotor lift, negative speed stability is produced and the dynamic characteristics of the helicopter are radically altered.

Johnson, W.↗

NASA NTRS1977

Pilot evaluation of an advanced hingeless rotor XY-15 simulation

A piloted simulation of an advanced hingeless rotor XV-15 tilt-rotor aircraft was carried out. The evaluation was made by a pilot from NASA-Ames who had previous experience flying a simulation of the current gimballed rotor NASA/Army XV-15. It was pointed out that some modifications to the force feel system were needed in order to provide rapid force trimming during rapid maneuvers. Some additional tailoring of the SCAS system was required to achieve good nap-of-the-earth performance. Overall pilot opinion on the hingeless rotor XV-15 tilt rotor was favorable. Brief discussion on the mathematical models and the simulator configuration are presented. The maneuvers and pilot comments are given along with some engineering comments.

Mcveigh, M. A.↗

NASA NTRS1978

Effects of rotor location, coning, and tilt on critical loads in large wind turbines

Several large (1500 kW) horizontal rotor configurations were analyzed to determine the effects on dynamic loads of upwind downwind rotor locations, coned and radial blade positions, and tilted and horizontal rotor axis positions. Loads were calculated for a range of wind velocities at three locations in the structure: (1) the blade shank; (2) the hub shaft; and (3) the yaw drive. Blade axis coning and rotor axis tilt were found to have minor effects on loads. However, locating the rotor upwind of the tower significantly reduced loads at all locations analyzed.

Spera, D. A.↗

NASA NTRS1978

A rotor-mounted digital instrumentation system for helicopter blade flight research measurements

A rotor mounted flight instrumentation system developed for helicopter rotor blade research is described. The system utilizes high speed digital techniques to acquire research data from miniature pressure transducers on advanced rotor airfoils which are flight tested on an AH-1G helicopter. The system employs microelectronic pulse code modulation (PCM) multiplexer digitizer stations located remotely on the blade and in a hub mounted metal canister. As many as 25 sensors can be remotely digitized by a 2.5 mm thick electronics package mounted on the blade near the tip to reduce blade wiring. The electronics contained in the canister digitizes up to 16 sensors, formats these data with serial PCM data from the remote stations, and transmits the data from the canister which is above the plane of the rotor. Data are transmitted over an RF link to the ground for real time monitoring and to the helicopter fuselage for tape recording. The complete system is powered by batteries located in the canister and requires no slip rings on the rotor shaft.

Knight, V. H., Jr.↗

NASA NTRS1977

Flow in a transonic compressor rotor

Some results of a comprehensive study of the flow through a transonic compressor rotor are presented. The rotor produces a pressure ratio of 1.6 at a tip Mach number of 1.2, has a cylindrical casing, sloped hub, and MCA blade sections. The gas density has been measured in the rotor by gas fluorescence, which reveals details of the shock and boundary layer structure as well as density in the passages. Time resolved measurements of the flow just downstream of the rotor give the blade wake structure, which is related to the features shown by the fluorescence. Of particular interest is a complex three-dimensional separation near the sonic radius. The flow through the rotor has also been computed in three dimensions by a time-marching technique, and the results of this computation are compared to those found by flow visualization.

Kerrebrock, J. L.↗

NASA NTRS1977

Effects of rotor location, coning, and tilt on critical loads in large wind turbines

Three large (1500 kW) horizontal rotor configurations were analyzed to determine the effects on dynamic loads of upwind and downwind rotor locations, coned and radial blade positions, and tilted and horizontal rotor axis positions. Loads were calculated for a range of wind velocities at three locations in the structure: the blade shank, the hub shaft, and the yaw drive. Blade axis coning and rotor axis tilt were found to have little effect on loads. However, locating the rotor upwind of the tower significantly reduced loads at all locations analyzed.

Spera, D. A.↗

NASA NTRS1978

Apparatus and method for reducing thermal stress in a turbine rotor

A gas turbine is described wherein the thermal stresses in the turbine rotor are reduced. The rotor includes a central disc with a peripheral rim, and a plurality of blades extending radially outward from the rim. To reduce thermal stresses, a duct arrangement is provided which selectively directs hot gases from the turbine combustor to the rim during the turbine start up. The hot gases from the combustor serve to heat the rim, and decrease the start up period necessary to bring the temperature profile of the rotor into the operating temperature range. After the start up period, the duct arrangement is then used to direct cool gases from the turbine compressor to the rim of the rotor in order to maintain a lower rotor equilibrium temperature.

Heller, J. A.↗

NASA NTRS1979

T700 power turbine rotor multiplane/multispeed balancing demonstration

Research was conducted to demonstrate the ability of influence coefficient based multispeed balancing to control rotor vibration through bending criticals. Rotor dynamic analyses were conducted of the General Electric T700 power turbine rotor. The information was used to generate expected rotor behavior for optimal considerations in designing a balance rig and a balance technique. The rotor was successfully balanced 9500 rpm. Uncontrollable coupling behavior prevented observations through the 16,000 rpm service speed. The balance technique is practical and with additional refinement it can meet production standards.

Burgess, G.↗

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 NTRS1979

The effects of some design parameters of an isolated rotor on inlet flow distortions

A study of the effects of rotor-blade geometry, steady loading, and distortion wavelength on the distortion flow field upstream and downstream of an unstalled isolated rotor shows that the attenuation of the distortion as it passes through the rotor is a function of the blade stagger angle and the distortion-reduced frequency or the ratio of rotor blade spacing to the distortion wavelength. Maximum attenuation occurs when this ratio is 0.5 and increases with increasing stagger angle. Little influence of rotor incidence angle or steady loading was observed.

Yocum, A. M.↗

NASA NTRS1979

A flight investigation of performance and loads for a helicopter with NLR-1T main-rotor blade sections

Data on performance and rotor loads for a teetering-rotor, AH-1G helicopter flown with a main rotor that had the NLR-1T airfoil as the blade-section contour are presented. The test envelope included hover, forward-flight speed sweeps from 35 to 85 m/sec, and collective-fixed maneuvers at about 0.25 tip-speed ratio. The data set for each test point described vehicle flight state, control positions, rotor loads, power requirements, and blade motions. Rotor loads are reviewed primarily in terms of peak-to-peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor.

Morris, C. E. K., Jr.↗

NASA NTRS1979

Synthesis of rotor test data for real-time simulation

A mathematical model of a hingeless tilting rotor is presented. The model was obtained by a systematic curve fit procedure applied to an extensive set of model scale wind tunnel data. The math model equations were used in a real time flight simulation model of a hingeless tilt rotor XV-15 to assess changes in flying qualities compared to those obtained using a previous rotor model. Extensive plots of the rotor derivatives are given. Discussions of attempts to apply multivariable linear regression technqiues to the data and the use of an analytical rotor representation are included.

Mcveigh, M. A.↗

NASA NTRS1980

A flight investigation of performance and loads for a helicopter with 10-64C main rotor blade sections

A flight investigation produced data on performance and rotor loads for a teetering rotor, AH-1G helicopter flown with a main rotor that had the NLR-1T airfoil as the blade section contour. The test envelope included hover, forward flight speeds from 34 to 83 m/sec (65 to 162 knots), and collective fixed maneuvers at about 0.25 tip speed ratio. The data set for each test point describes vehicle flight state, control positions, rotor loads, power requirements, and blade motions. Rotor loads are reviewed primarily in terms of peak to peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor. Detailed data for an advanced airfoil on an AH-1G are presented.

Morris, C. E. K.↗