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At least 1,549 records · Page 86

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NASA NTRS1981

Unsteady fan blade pressure and acoustic radiation from a JT15D-1 turbofan engine at simulated forward speed

Tests have been conducted on a JT15D-1 turbofan engine both statically and at simulated forward speed in the Ames 12 x 24 Meter Wind Tunnel. Both far-field acoustic data and unsteady pressure data from transducers mounted on the fan blades were acquired. Results showed a sound power reduction of about 10 dB in the far-field acoustic levels with simulated forward speed over those measured without forward speed. Blade mounted transducer results showed rotor-turbulence interaction dominated the noise field at very low speeds while an interaction between the rotor and internal struts dominated at higher speeds. Results are presented to show the effects of varying engine rpm, changing the angle-of-attack of the engine inlet to tunnel flow and mounting an aircraft wing to simulate an installation condition on an actual aircraft.

Preisser, J. S.↗

NASA NTRS1981

Effects of mistuning on blade torsional flutter

An analytical model for the prediction of fan blade flutter is presented and evaluated using data from NASA tests on an advanced high performance engine. For the cascade conditions appropriate to the test points studied, the aerodynamic theory cannot predict subcritical flutter. Under the assumptions of a tuned assembly, the imaginary part of the aerodynamic coefficients does indicate flutter for a limited number of interblade phase angles, but these interblade phase angles are close to those at which the acoustic resonance is predicted. Upon using the individual blade frequencies and solving the mistuned system with aerodynamic coupling only, the results show a stable system. Eigenvectors calculated for the mistuned system demonstrate the presence of several harmonics in each mistuned mode. Inclusion of both mechanical and aerodynamic coupling in the solution of the eigenproblem influences not only the frequencies but also damping in the system with a trend toward stability.

Srinivasan, A. V.↗

NASA NTRS1981

Analysis of turbulent boundary layer on cascade and rotor blades of turbomachinery

The momentum integral technique for predicting the boundary layer growth in three-dimensional flow has been extended to include the entrainment equation as the closure model. The numerical solution is compared with the cascade, inducer, compressor, and fan rotor blade data from various sources. The agreement is found to be excellent in all cases, with the exception of the separated flow. Both the momentum thickness and the limiting streamline angle predicted from this analysis compare well with the measured data for a rotor blade. The technique is extremely useful in engineering design, analysis, and performance prediction.

Lakshminarayana, B.↗

NASA NTRS1980

Rotor blade aeroelastic stability and response in forward flight

The aeroelastic stability and response problem of the coupled flap-lag-torsional dynamics of a hingeless rotor blade in forward flight is treated in a comprehensive manner. The spatial dependence of the partial differential, nonlinear, equations of motion is discretized using a multimodal Galerkin method. The aeroelastic problem is coupled with the trim state of the helicopter obtained from improved, representative, trim procedures. The nonlinear time dependent equilibrium position, or response, about which the equations are linearized is obtained by solving a sequence of linear periodic response problems, using quasi-linearization. Numerous results illustrating blade behavior in forward flight are presented.

Friedmann, P. P.↗

NASA NTRS1980

Influence of rotor blade tip shape on tip vortex shedding - An unsteady, inviscid analysis

An unsteady potential flow panel method is described based on a time-stepping procedure and using planar quadrilateral panels to represent the surface of thick blades. Each panel has a constant source and doublet distribution and a central control point where an internal Dirichlet boundary condition is applied. The method includes detail paneling around the tip edge and offers the facility of prescribing a tip-edge separation. Preliminary results are shown for four blade tip shapes which are treated as semi-span wings oscillating in pitch about a mean angle of attack of 6 deg. Further work is planned for the wake model before proceeding to higher angles of attack.

Maskew, B.↗

NASA NTRS1980

Design and fabrication of a composite wind turbine blade

The design considerations are described which led to the combination of materials used for the MOD-I wind turbine generator rotor and to the fabrication processes which were required to accomplish it. It is noted that the design problem was to create a rotor for a 2500 kW wind turbine generator. The rotor was to consist of two blades, each with a length of 97.5 feet and a weight of less than 21,000 pounds. The spanwise frequency is 1.17-1.45 Hz, and the chordwise frequency 2.80-2.98 Hz. The design life of the blade is 30 years, or 4.35 x 10 to the 8th cycles. The structures of the spars and trailing edges are described, and the adhesive bonding system is discussed.

Brown, R. A.↗

NASA NTRS1981

The structure of trailing vortices generated by model rotor blades

Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described.

Tung, C.↗

NASA NTRS1981

A flight investigation of blade-section aerodynamics for a helicopter main rotor having 10-64C airfoil sections

Pressure data at 90 percent blade radius were obtained for a helicopter main rotor with 10-64C blade sections during flight. Concurrent measurements ere made of vehicle flight state, performance and some rotor loads. The test envelope included hover, level flight from about 65 to 162 knots, climb and descent, and collective fixed maneuvers. Good agreement is shown between some sets of airfoil pressure distributions obtained in flight and those from two-dimensional wind-tunnel tests or theoretical calculations.

Morris, C. E. K., Jr.↗

NASA NTRS1981

Aluminum blade development for the Mod-OA 200-kilowatt wind turbine

The rotor blade configuration, fabrication methods, analyses, operating experience, design modifications, and cost are described. Each 60-ft.-(18.3-m-) long aluminum blade used current aircraft fixed wing and rotary wing design and fabrication technologies. Structural damage, repairs, and modifications that occurred during 6500 hours of operation are summarized.

Linscott, B. S.↗

NASA NTRS1982

Three dimensional flow field inside compressor rotor, including blade boundary layers

The flow in a turbomachinery blade passage has a predominant flow direction. The viscous diffusion in the streamwise direction is usually small and the elliptic influence is transmitted upstream through the pressure field. Starting with a guessed pressure field, it is possible to converge on the full elliptic solution by iterating between a parabolic solution and an iteration of the pressure field. The main steps of the calculation are given. The blade boundary layers which are three dimensional with laminar, transitional, turbulent, and separation zones are investigated. The kinetic energy is analyzed, and the dissipation equation is presented. Measurements were made of the three dimensional flow inside an axial flow compressor passage.

Pouagare, M.↗

NASA NTRS1982

A flight investigation of blade-section aerodynamics for a helicopter main rotor having RC-SC2 airfoil sections

Pressure data at 90 percent blade radius for a helicopter main rotor with RC-SC2 blade sections was obtained. Concurrent measurements were made of vehicle flight state, performance and some rotor loads. The test envelope included hover, level flight from about 65 to 144 knots, climb and descent, and collective fixed maneuvers. Airfoil pressure distributions obtained in flight agree with those theoretical calculations for two dimensional, steady flow.

Morris, C. E. K., Jr.↗

NASA NTRS1982

Wire blade development for Fixed Abrasive Slicing Technique (FAST) slicing

A low cost, effective slicing method is essential to make ingot technology viable for photovoltaics in terrestrial applications. The fixed abrasive slicing technique (FAST) combines the advantages of the three commercially developed techniques. In its development stage FAST demonstrated cutting effectiveness of 10 cm and 15 cm diameter workpieces. Wire blade development is still the critical element for commercialization of FAST technology. Both impregnated and electroplated wire blades have been developed; techniques have been developed to fix diamonds only in the cutting edge of the wire. Electroplated wires show the most near term promise and this approach is emphasized. With plated wires it has been possible to control the size and shape of the electroplating, it is expected that this feature reduces kerf and prolongs the life of the wirepack.

Khattak, C. P.↗

NASA NTRS1982

Design and use of multiple blade slurry sawing in a production atmosphere

The technique and uses of the multiple blade slurry (MBS) saw are considered. Multiple bands of steel are arranged in a frame and the frame is reciprocated with the steel bands to a workpiece, while simultaneously applying abrasive at the point of contact. The blades wear slots in the workpiece and progress through the piece resulting in several parts of wafers. The transition to MBA from diamond slicing is justified by savings resulting from minimized kerf losses, minimized subsurface damage, and improved surface quality off the saw. This allows wafering much closer to finished thickness specifications. The current state of the art MBS technology must be significantly improved if the low cost solar array (LSA) goals are to be attained. It is concluded that although MBS will never be the answer to every wafering requirement, the economical production of wafers to LSA project specifications will be achieved.

Lynah, F. P., Jr.↗

NASA NTRS1982

Three dimensional flow field inside compressor rotor, including blade boundary layers

The Reynolds stress equation, pressure strain correlation, and dissipative terms and diffusion are discussed in relation to turbulence modelling using the Reynolds stress model. Algebraic modeling of Reynolds stresses and calculation of the boundary layer over an axial cylinder are examined with regards to the kinetic energy model for turbulence modelling. The numerical analysis of blade and hub wall boundary layers, and an experimental study of rotor blade boundary layer in an axial flow compressor rotor are discussed. The Patankar-Spalding numerical method for two dimensional boundary layers is included.

Galmes, J. M.↗

NASA NTRS1982

Helicopter vibration suppression using simple pendulum absorbers on the rotor blade

A comprehensive anaytical design procedure for the installation of simple pendulums on the blades of a helicopter rotor to suppress the root reactions is presented. A frequency response anaysis is conducted of typical rotor blades excited by a harmonic variation of spanwise airload distributions as well as a concentrated load at the tip. The results presented included the effect of pendulum tuning on the minimization of the hub reactions. It is found that a properly designed flapping pendulum attenuates the root out-of-plane force and moment whereas the optimum designed lead-lag pendulum attenuates the root in-plane reactions. For optimum pendulum tuning the parameters to be determined are the pendulum uncoupled natural frequency, the pendulum spanwise location and its mass. It is found that the optimum pendulum frequency is in the vicinity of the excitation frequency. For the optimum pendulum a parametric study is conducted. The parameters varied include prepitch, pretwist, precone and pendulum hinge offset.

Pierce, G. A.↗

NASA NTRS1982

Three dimensional turbulent boundary layer development on a fan rotor blade

This paper is concerned with an experimental study undertaken to measure the boundary layer growth on a fan rotor blade. The measurements were carried out using a miniature 'X' configuration hot wire probe at various chordwise and radial locations on both surfaces of the blade. The streamwise and radial velocity profiles as well as the corresponding intensity components are interpreted and correlated. The validity of conventional velocity profiles such as the 'law of the wall' for the streamwise profile and the hodograph plot for the cross flow profile are examined. The measured values of boundary-layer gross properties are compared with the predictions based on a momentum-integral technique.

Lakshminarayana, B.↗

NASA NTRS1982

Turbine blade nonlinear structural and life analysis

The utility of advanced structural analysis and life prediction techniques was evaluated for the life assessment of a commercial air-cooled turbine blade with a history of tip cracking. Three dimensional, nonlinear finite element structural analyses were performed for the blade tip region. The computed strain-temperature history of the critical location was imposed on a uniaxial strain controlled test specimen to evaluate the validity of the structural analysis method. Experimental results indicated higher peak stresses and greater stress relaxation than the analytical predictions. Life predictions using the Strainrange Partitioning and Frequency Modified approaches predicted 1200 to 4420 cycles and 2700 cycles to crack initiation, respectively, compared to an observed life of 3000 cycles.

Mcknight, R. L.↗

NASA NTRS1982

Noise of the 10-bladed, 40 deg swept SR-6 propeller in a wind tunnel

The noise generated by supersonic helical-tip-speed propellers is a likely cabin environment problem for future airplanes powered by these propellers. Three propeller models with different tip sweeps. SR-1M, SR-2, and SR-3, designed for 244 m/sec (800 ft/sec) tip speed at a flight Mach number of 0.8 were previously tested in the NASA Lewis 8- by 6-Foot Wind Tunnel. In order to investigated another design point condition, the SR-6 propeller was designed for 213 m-sec (700 ft/sec) tip speed at a flight Mach number of 0.8. The noise data from this propeller are reported herein. Curves of blade passing frequency noise versus tip Mach number (at constant advance ratio) showed that the SR-6 propeller behaved similarly to the SR-1M propeller. The noise of the SR-6 propeller at its design condition, helical tip Mach number of 1.07, is approximately 3 dB quieter than the SR-2 propeller at its higher design helical tip Mach number of 1.15, but about 2.5 dB noisier than SR-3 at its design condition. The helical tip Mach number shift of the steep noise rise followed the same progression as the blade sweep angle for all of the propellers. When operated at the SR-3 design point, the SR-6 propeller was approximately 1.5 dB quieter than SR-2 and 4 dB noisier than SR-3.

Dittmar, J. H.↗