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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1940

Photographic Observations of Blade Motion of the YG-1B Autogiro Equipped with Tapered Rotor Blades

This report presents the results of photographic observations in flight of the flapping, the motion about the vertical pin, and the dynamic twist of a new type tapered rotor blade on the Kellett YG-1B autogiro. The blades, which were designed by the Kellett Autogiro Corporation, made use of the NACA 230 series airfoil section, for the purpose of eliminating undesirable dynamic blade twist present in the original blades. The results reported herein show that in actual operation the new blades very closely approach the desired condition of no dynamic twist.

Bailey, F. J., Jr.↗
NASA NTRS1953

Aerodynamic Characteristics of a Two-blade NACA 10-(3)(062)-045 Propeller and of a Two-blade NACA 10-(3)(08)-045 Propeller

Characteristics are given for the two-blade NACA 10-(3)(062)-045 propeller and for the two-blade NACA 10-(3)(08)-045 propeller over a range of advance ratio from 0.5 to 3.8, through a blade-angle range from 20 degrees to 55 degrees measured at the 0.75 radius. Maximum efficiencies of the order of 91.5 to 92 percent were obtained for the propellers. The propeller with the thinner airfoil sections over the outboard portion of the blades, the NACA 10-(3)(062)-045 propeller, had lower losses at high tip speeds, the difference amounting to about 5 percent at a helical tip Mach number of 1.10.

BLADE SECTIONS-PROPELLERS↗
NASA NTRS1981

Improved method for calculating transonic velocities on blade-to-blade stream surfaces of a turbomachine

A method was developed to improve the accuracy of an existing computer program used to calculate transonic velocities on a blade-to-blade surface of a turbomachine. The method eliminates problems encountered in obtaining solutions with the velocity gradient equation when large gradients in velocity occur through the blade row. With the improved method, results indicate that the transonic solution can be obtained by scaling the velocities obtained at the reduced mass flow rate where all velocities are subsonic thereby eliminating the need for a solution of the velocity gradient equation. Solutions obtained with the scaling method on a two dimensional compressor cascade and an axial turbine stator show good agreement with experimental data. The results obtained for the stationary blade rows and comparison of analytical results obtained with and without the present method suggest that the method will yield an improved solution for centrifugal compressor impellers.

Wood, J. R.↗
NASA NTRS1983

Blade loss transient dynamics analysis with flexible bladed disk

The transient dynamic response of a flexible bladed disk on a flexible rotor in a two rotor system is formulated by modal synthesis and a Lagrangian approach. Only the nonequilibrated one diameter flexible mode is considered for the flexible bladed disk, while the two flexible rotors are represented by their normal modes. The flexible bladed disk motion is modeled as a combination of two one diameter standing waves, and is coupled inertially and gyroscopically to the flexible rotors. Application to a two rotor model shows that a flexible bladed disk on one rotor can be driven into resonance by an unbalance in the other rotor, and at a frequency equal to the difference in the rotor speeds.

Gallardo, V. C.↗
NASA NTRS1986

Effects of blade-to-blade dissimilarities on rotor-body lead-lag dynamics

Small blade-to-blade property differences are investigated to determine their effects on the behavior of a simple rotor-body system. An analytical approach is used which emphasizes the significance of these effects from the experimental point of view. It is found that the primary effect of blade-to-blade dissimilarities is the appearance of additional peaks in the frequency spectrum which are separated from the convention response modes by multiples of the rotor speed. These additional responses are potential experimental problems because when they occur near a mode of interest they act as contaminant frequencies which can make damping measurements difficult. The effects of increased rotor-body coupling and a rotor shaft degree of freedom act to improve the situation by altering the frequency separation of the modes.

Mcnulty, M. J.↗
NASA NTRS1985

Vibrations of blades and bladed disk assemblies; Proceedings of the Tenth Biennial Conference on Mechanical Vibration and Noise, Cincinnati, OH, September 10-13, 1985

The papers presented in this volume provide an overview of recent theoretical and analytical research in bladed disk assemblies, with particular attention given to forced response, mistuning, and damping. Specific topics discussed include the response of mistuned bladed disk assemblies; forced response analysis of an aerodynamically detuned supersonic turbomachine rotor; dynamic analysis of blade groups using component mode synthesis; and pendulum dynamic vibration absorbers for reducing blade vibration in industrial fans.

Kielb, R. E.↗
NASA NTRS1985

Effects of blade-to-blade dissimilarities on rotor-body lead-lag dynamics

Small blade-to-blade property differences are investigated to determine their effects on the behavior of a simple rotor-body system. An analytical approach is used which emphasizes the significance of these effects from the experimental point of view. It is found that the primary effect of blade-to-blade dissimilarities is the appearance of additional peaks in the frequency spectrum which are separated from the conventional response modes by multiples of the rotor speed. These additional responses are potential experimental problems because when they occur near a mode of interest they act as contaminant frequencies which can make damping measurements difficult. The effects of increased rotor-body coupling and a rotor shaft degree of freedom act to improve the situation by altering the frequency separation of the modes.

Mcnulty, Michael J.↗
NASA NTRS1987

Blade-vortex interaction noise predictions using measured blade surface pressures

The generation of helicopter noise by blade-vortex interactions during descent under impulsive conditions is investigated analytically. A noise-prediction technique is developed on the basis of the dipole source term of the Ffowcs-Williams/Hawkings equation and applied to data from simultaneous blade-pressure and acoustic measurements obtained by Cowan et al. (1986) on a 10-ft-diameter 4-blade rotor model in a wind tunnel. Preliminary results show that input-blade-airload azimuth resolution of 1 deg or better and computational azimuth step size of 2 deg or less are required to achieve good agreement between predicted and recorded acoustic time histories. The need for more sophisticated methods to model chordwise input data and for a more extensive experimental data base is indicated.

Ziegenbein, Perry R.↗
NASA NTRS1959

A Dynamic Model Investigation of the Effect of a Sharp-Edge Vertical Gust on Blade Periodic Flapping Angles and Bending Moments of a Two-Blade Rotor

A two-blade rotor having a diameter of 4 feet and a solidity of 0.037 was subjected to sharp-edge vertical gusts while being operated at various forward speeds to study the effect of the gusts on the blade periodic bending moments and flapping angles. Variables studied included gust velocity, collective pitch angle, flapping hinge offset, and tip-speed ratio. Dimensionless coefficients are derived for the periodic components of the incremental changes in blade flapping angles and bending moments which arise when a rotor blade penetrates a sharp-edge gust. Mental changes in both the flapping angles and bending moments are essentially proportional to gust velocity, and the coefficients express the ratio of these increments to gust velccity. The results show that the flapping coefficient usually increases with an increase in collective pitch angle, is generally dependent on tip-speed ratio, and is essentially independent of the amount of flapping hinge offset. The bending-moment coefficient is also dependent on collective pitch angle and tip-speed ratio. Expected reductions in bending moments are realized by the use of flapping hinges, and further reductions in bending moments are achieved as the amount of flapping hinge offset is increased. Comparison of the experimental results of this investigation with limited available theoretical results shows substantial agreement but indicates that the assumption that the response of the rotor to a sharp-edge gust is independent of the collective pitch angle prior to gust entry is probably inadequate.

McCarty, John Locke↗
NASA NTRS1985

Effects of Blade to Blade Dissimilarities on Rotor Body Lead Lag Dynamics

Small blade-to-blade property differences are investigated to determine how they affect the behavior of a simple rotor-body system. An analytical approach is used which emphasizes the significance of these effects from the experimental point of view. It is found that the primary effect of blade-to-blade dissimilarities is the appearance of additional peaks in the frequency spectrum which are separated from the conventional response peaks by multiples of the rotor speed. These additional responses are potential experimental problems because when they occur near a mode of interest they act as contaminant frequencies which can make damping measurements difficult. Increased rotor-body coupling and a rotor shaft degree of freedom act to improve the situation by altering the frequency separation of the modes.

McNulty, Michael J.↗
NASA NTRS1946

Altitude-Wind-Tunnel Investigation of Performance of Several Propellers on YP-47M Airplane at High Blade Loading: Curtiss 838-1C2-18R1 Four-Blade Propeller - 2

An investigation was conducted in the Cleveland altitude wind tunnel to determine the performance of a Curtiss propeller with four 838-lC2-lSRl blades on a YP-47M airplane at high blade loadings and engine powers. The study was made for a range of power coefficients between 0.30 and 1.00 at free-stream Mach numbers of 0.40 and 0.50. The results of the force measurements indicate primarily the trend of propeller efficiency for changes in power coefficient or advance-diameter ratio, inasmuch as corrections for the effects of tunnel-wall constriction on the installation have not been applied. Slip-stream pressure surveys across the propeller disk are presented to illustrate blade thrust load distribution for several operating conditions. At a free-stream Mach number of 0.40, nearly constant peak efficiencies were obtained at power coefficients from 0.30 to 0.70. A change in power coefficient from 0.70 to 0.90 reduced the peak efficiency about 5 percent. Blade stall at the tip sections became evident for a power coefficient of 0.91 when the advance-diameter ratio was reduced to 1.87. At a free-stream Mach number of 0.50, the highest propeller efficiencies were obtained for power coefficients from 0.80 to 1.00 at advance-diameter ratios above 2.90. At advance-diameter ratios below 2.90, the highest efficiencies were obtained for power coefficients of 0.60 and 0.70. The envelope of the efficiency curves decreased about 12 percent between advance-diameter ratios of 2.60 and 4.20. Local compressibility effects became evident for a power coefficient of 0.40 when the advance-diameter ratio was decreased to 1.75.

Wallner, Lewis E.↗
NASA NTRS2000

Turbine Blade and Endwall Heat Transfer Measured in NASA Glenn's Transonic Turbine Blade Cascade

Higher operating temperatures increase the efficiency of aircraft gas turbine engines, but can also degrade internal components. High-pressure turbine blades just downstream of the combustor are particularly susceptible to overheating. Computational fluid dynamics (CFD) computer programs can predict the flow around the blades so that potential hot spots can be identified and appropriate cooling schemes can be designed. Various blade and cooling schemes can be examined computationally before any hardware is built, thus saving time and effort. Often though, the accuracy of these programs has been found to be inadequate for predicting heat transfer. Code and model developers need highly detailed aerodynamic and heat transfer data to validate and improve their analyses. The Transonic Turbine Blade Cascade was built at the NASA Glenn Research Center at Lewis Field to help satisfy the need for this type of data.

Giel, Paul W.↗
NASA NTRS1940

Observations in Flight of the Region of Stalled Flow Over the Blades of the Kellett YG-1B Tapered-Blade Autogiro Rotor

In conjunction with a series of tests requested by the Army Air corps on a new set of tapered rotor blades, of NACA 230 series section and built for the Kellett YG-1B autogiro, it was convenient to supplement previous studies of the region or stalled flow on rotors by making photographic observations of the flow over the blades in flight. These observations are described in this report. It is shown that the maximum radius stalled on the new rotor increases more rapidly with tip-speed ratio than was true on the rectangular-blade, Gottingen 606 section rotor previously tested on the same ship, though the increase in importance of the stalled region is not as decisive as consideration of the change in section would suggest. The increased loss in the stalled region is felt to be at least a contributing cause in the failure of the new blades to Increase the top speed of the machine.

Gustafson, Frederic B.↗
NASA NTRS2019

Estimating Inducer Blade Damping in Water with On-Blade Strain Measurements

This paper describes the testing, methodology, and results for estimating critical damping ratios of inducer blade structural natural frequencies. A sub-scale inducer water flow test was performed with on-blade strain gauge measurements. Data were acquired in quiescent air and water, and also at several shaft speeds and operating conditions. Two methods were used to provide active excitation to the blades. The first was to impart a mechanical impulse to the inducer shaft and observe the strain gauge response. The second was to install a stator plate upstream of the inducer to create a non-uniform but regular pressure field at the inducer inlet. There are challenges with using either approach, but damping information was extracted using both methods. Results showed that the critical damping ratio for a given blade mode increased from air to quiescent water, and also increased when the inducer was spinning.

Mulder, Andrew↗
NASA NTRS1971

Concepts for a theoretical and experimental study of lifting rotor random loads and vibrations. Phase 5A: Effects of torsional blade flexibility on single blade random gust response statistics

Quasi-steady aerodynamics were assumed, as well as a torsion mode where the amplitude is proportional to the distance from the rotor center. Aerodynamic torsional moment inputs are limited to the region of reverse flow where the aerodynamic center and the section center of gravity are separated by half the blade chord. Thus negligible effects of blade torsional flexibility are obtained for rotor conditions with negligible reverse flow effects. Numerical examples refer to conditions with 1.6 rotor advance ratio. It was found that the random flapping response is only moderately affected by torsional flexibility. However large random torsional loads and deflections occur even if flapping is completely suppressed. The coupling of the actual flapping motion into the blade torsional motion produces a substantial increase in the random torsional loads or deflections.

Hohenemser, K. H.↗