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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

An aeroacoustic model for high-speed, unsteady blade-vortex interaction

A three-dimensional aeroacoustic model is developed to predict the sound pulse radiated by the passage of a helicopter blade over a potential vortex. The linearized analysis assumes that either the blade-vortex separation is small or that the blade-tip Mach number is close to 1, or both, so that an acoustically noncompact situation exists. The three-dimensional blade loading due to blade-vortex interaction is constructed through a spanwise superposition of two-dimensional solutions with strength linearly increasing from hub to tip. Such a loading overestimates somewhat the strength of tip region dipoles in the acoustic calculation that follows. The final expression for the predicted far-field signature is obtained in closed form, and thus permits a relatively inexpensive calculation of the directivity of peak acoustic pressures in three dimensions.

Martinez, R.↗
NASA NTRS1994

Reduction of Helicopter BVI Noise, Vibration, and Power Consumption Through Individual Blade Control

A wind tunnel test was conducted with a full-scale BO 105 helicopter rotor to evaluate the potential of open-loop individual blade control (IBC) to improve rotor performance, to reduce blade vortex interaction (BVI) noise, and to alleviate helicopter vibrations. The wind tunnel test was an international collaborative effort between NASA/U.S. Army AFDD, ZF Luftfahrttechnik, Eurocopter Deutschland, and the German Aerospace Laboratory (DLR) and was conducted under the auspices of the U.S./German MOU on Rotorcraft Aeromechanics. In this test the normal blade pitch links of the rotor were replaced by servo-actuators so that the pitch of each blade could be controlled independently of the other blades. The specially designed servoactuators and IBC control system were designed and manufactured by ZF Luftfahrttechnik, GmbH. The wind tunnel test was conducted in the 40- by 80-Foot Wind Tunnel at the NASA Ames Research Center. An extensive amount of measurement information was acquired for each IBC data point. These data include rotor performance, static and dynamic hub forces and moments, rotor loads, control loads, inboard and outboard blade pitch motion, and BVI noise data. The data indicated very significant (80 percent) simultaneous reductions in both BVI noise and hub vibrations could be obtained using multi-harmonic input at the critical descent (terminal approach) condition. The data also showed that performance improvements of up to 7 percent could be obtained using 2P input at high-speed forward flight conditions.

Jacklin, Stephen A.↗
NASA NTRS1986

Large-scale Advanced Prop-fan (LAP) hub/blade retention design report

The Large-scale Advanced Prop-fan (LAP) hub assembly forms a semi-rigid link between the blades, which provide the thrust, and the engine shaft, which provides the torque. The hub and tailshaft is a one piece partially forged part which is carburized, heat treated and machined. A single row ball bearing restrains each of the eight blades in the hub, while the tailshaft secures the propeller to the engine shaft with two cone seats that are preloaded against each other by the Prop-fan retaining nut. The hub also forms the support for the pitch change actuator system, the control and the spinner. The retention transmits the loads from the blades to the hub while allowing the changes in blade pitch. The single row ball bearing retention provides ease of maintenance by allowing individual blade replacement without dissassembly of the hub. It has a through hardened inner race which seats against the aluminum blade shank and an outer race which is integral with the barrel. The outer race area is carburized to achieve the hardness necessary to support the ball loads. The balls are kept from contact with each other by a separator. The rotational speed of the propeller keeps the retention submerged in the oil which is contained in the hub by a seal. Stress and strain analysis, material hardness requirements, weight predictions, and stiffness characteristics are discussed.

Soule, Matthew↗
NASA NTRS1987

High speed propeller performance and noise predictions at takeoff/landing conditions

The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.

Nallasamy, M.↗
NASA NTRS1988

High speed propeller performance and noise predictions at takeoff/landing conditions

The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.

Nallasamy, M.↗
NASA NTRS1982

Effects of blade loading and rotation on compressor rotor wake in end wall regions

This study was carried out to understand the effects of blade loading and rotation on the rotor end wall flow structure, including the wake. The measurements were taken with a stationary three sensor hot wire located at the exit of a compressor rotor. The signal was ensemble averaged to derive all the three components of velocity and six components of stresses at the exit. Measurements were made at two different rotational speeds (1753 and 1010 rpm) and at two differing blade loadings at several radii near the hub and the annulus wall. The wake decay in the annulus wall region is found to be much more rapid than the mid span regions. Furthermore, both the loading and rotation of the blade have appreciable influence on the end wall flow and wake structure. Interaction of the annulus and hub wall boundary layers (and secondary flow resulting from these) have appreciable influence on the wake structure in the endwall regions.

Lakshminarayana, B.↗
NASA NTRS1984

Design of an Advanced Wood Composite Rotor and Development of Wood Composite Blade Technology

In support of a program to advance wood composite wind turbine blade technology, a design was completed for a prototype, 90-foot diameter, two-bladed, one-piece rotor, with all wood/epoxy composite structure. The rotor was sized for compatibility with a generator having a maximum power rating of 4000 kilowatts. Innovative features of the rotor include: a teetering hub to minimize the effects of gust loads, untwisted blades to promote rotor power control through stall, joining of blades to the hub structure via an adhesive bonded structural joint, and a blade structural design which was simplified relative to earlier efforts. The prototype rotor was designed to allow flexibility for configuring the rotor upwind or downwind of the tower, for evaluating various types of teeter dampers and/or elastomeric stops, and with variable delta-three angle settings of the teeter shaft axis. The prototype rotor was also designed with provisions for installing pressure tap and angle of attack instrumentation in one blade. A production version rotor cost analysis was conducted. Included in the program were efforts directed at developing advanced load take-off stud designs for subsequent evaluation testing by NASA, development of aerodynamic tip brake concepts, exploratory testing of a wood/epoxy/graphite concept, and compression testing of wood/epoxy laminate, with scarf-jointed plies.

Stroebel, Thomas↗
NASA NTRS1978

Preliminary analysis of hub and spoke air freight distribution system

A brief analysis is made of the hub and spoke air freight distribution system which would employ less than 15 hub centers world wide with very large advanced distributed-load freighters providing the line-haul delivery between hubs. This system is compared to a more conventional network using conventionally-designed long-haul freighters which travel between numerous major airports. The analysis calculates all of the transportation costs, including handling charges and pickup and delivery costs. The results show that the economics of the hub/spoke system are severely compromised by the extensive use of feeder aircraft to deliver cargo into and from the large freighter terminals. Not only are the higher costs for the smaller feeder airplanes disadvantageous, but their use implies an additional exchange of cargo between modes compared to truck delivery. The conventional system uses far fewer feeder airplanes, and in many cases, none at all. When feeder aircraft are eliminated from the hub/spoke system, however, that system is universally more economical than any conventional system employing smaller line-haul aircraft.

Whitehead, A. H., Jr.↗
NASA NTRS1974

Swashplate feedback control for tilt-rotor aircraft

Changes in angle of attack in system were sensed indirectly by gages which responded to strains induced in wing structure. Output signals were amplified, filtered, and used to activate swashplate actuators. System provided significant reduction in blade loads and desirable changes in hub forces and moments.

Alexander, H. R.↗
NASA NTRS1989

Prediction of unsteady blade surface pressures on an advanced propeller at an angle of attack

The paper considers the numerical solution of the unsteady, three-dimensional, Euler equations to obtain the blade surface pressures of an advanced propeller at an angle of attack. The specific configuration considered is the SR7L propeller at cruise conditions with a 4.6 deg inflow angle corresponding to the +2 deg nacelle tilt of the Propeller Test Assessment (PTA) flight test condition. The results indicate nearly sinusoidal response of the blade loading, with angle of attack. For the first time, detailed variations of the chordwise loading as a function of azimuthal angle are presented. It is observed that the blade is lightly loaded for part of the revolution and shocks appear from hub to about 80 percent radial station for the highly loaded portion of the revolution.

Nallasamy, M.↗
NASA NTRS1989

Prediction of Unsteady Blade Surface Pressures on an Advanced Propeller at an Angle of Attack

The numerical solution of the unsteady, three-dimensional, Euler equations is considered in order to obtain the blade surface pressures of an advanced propeller at an angle of attack. The specific configuration considered is the SR7L propeller at cruise conditions with a 4.6 deg inflow angle corresponding to the plus 2 deg nacelle tilt of the Propeller Test Assessment (PTA) flight test condition. The results indicate nearly sinusoidal response of the blade loading, with angle of attack. For the first time, detailed variations of the chordwise loading as a function of azimuthal angle are presented. It is observed that the blade is lightly loaded for part of the revolution and shocks appear from hub to about 80 percent radial station for the highly loaded portion of the revolution.

Nallasamy, M.↗
NASA NTRS2009

Reduced In-Plane, Low Frequency Helicopter Noise of an Active Flap Rotor

Results from a recent joint DARPA/Boeing/NASA/Army wind tunnel test demonstrated the ability to reduce in-plane, low frequency noise of the full-scale Boeing-SMART rotor using active flaps. Test data reported in this paper illustrated that acoustic energy in the first six blade-passing harmonics could be reduced by up to 6 decibels at a moderate airspeed, level flight condition corresponding to advance ratio of 0.30. Reduced noise levels were attributed to selective active flap schedules that modified in-plane blade airloads on the advancing side of the rotor, in a manner, which generated counteracting acoustic pulses that partially offset the negative pressure peaks associated with in-plane, steady thickness noise. These favorable reduced-noise operating states are a strong function of the active flap actuation amplitude, frequency and phase. The associated noise reductions resulted in reduced aural detection distance by up to 18%, but incurred significant vibratory load penalties due to increased hub shear forces. Small reductions in rotor lift-to-drag ratios, of no more than 3%, were also measured

Sim, Ben W.↗
NASA NTRS1976

The effect of circumferential distortion on fan performance at two levels of blade loading

Single stage fans designed for two levels of pressure ratio or blade loading were subjected to screen induced circumferential distortions of 90 degree extent. Both fan rotors were designed for a blade tip speed of 425 m/sec, blade solidity of 1.3 and a hub-to-tip radius ratio of 0.5. Circumferential measurements of total pressure, temperature, static pressure, and flow angle were obtained at the hub, mean and tip radii at five axial stations. Rotor loading level did not appear to have a significant influence on rotor response to distorted flow. Losses in overall pressure ratio due to distortion were most severe in the stator hub region of the more highly loaded stage. At the near stall operating condition tip and hub regions of (either) rotor demonstrated different response characteristics to the distorted flow. No effect of loading was apparent on interactions between rotor and upstream distorted flow fields.

Hartmann, M. J.↗
NASA NTRS1975

The effect of circumferential distortion on fan performance at two levels of blade loading

Single stage fans designed for two levels of pressure ratio or blade loading were subjected to screen-induced circumferential distortions of 90-degree extent. Both fan rotors were designed for a blade tip speed of 425 m/sec, blade solidity of 1.3 and a hub-to-tip radius ratio of 0.5. Circumferential measurements of total pressure, temperature, static pressure, and flow angle were obtained at the hub, mean and tip radii at five axial stations. Rotor loading level did not appear to have a significant influence on rotor response to distorted flow. Losses in overall pressure ratio due to distortion were most severe in the stator hub region of the more highly loaded stage. At the near stall operating condition tip and hub regions of (either) rotor demonstrated different response characteristics to the distorted flow. No effect of loading was apparent on interactions between rotor and upstream distorted flow fields.

Hartmann, M. J.↗
NASA NTRS1986

Experimental investigation of rotorcraft hub and shaft fairing drag reduction

A wind-tunnel test was conducted to obtain data on several rotorcraft hub and shaft fairing drag reduction configurations. Aerodynamic loads and moments were acquired for each test configuration. Limited wake pressure measurements and flow visualization (tuft) photographs were obtained for some configurations. All hub and shaft fairing configurations were tested on a 1/5-scale XH-59A model fuselage. Both coaxial and single rotor configurations were tested. All rotor assemblies were modeled with nonrotating hardware. The drag reduction methods tested included cambered elliptical hub fairings, several different shaft fairings, and strakes. Test data show that significant drag reductions can be attained with certain fairing configurations. The lowest drag values for the single rotor configurations were obtained for a cambered elliptical hub fairing with a large thickness airfoil shaft fairing. The lowest coaxial configuration drag values were obtained with cambered elliptical hub fairings and a long chord intermediate shaft fairing.

Young, L. A.↗
NASA NTRS2009

Floating wind turbine system

A floating wind turbine system with a tower structure that includes at least one stability arm extending therefrom and that is anchored to the sea floor with a rotatable position retention device that facilitates deep water installations. Variable buoyancy for the wind turbine system is provided by buoyancy chambers that are integral to the tower itself as well as the stability arm. Pumps are included for adjusting the buoyancy as an aid in system transport, installation, repair and removal. The wind turbine rotor is located downwind of the tower structure to allow the wind turbine to follow the wind direction without an active yaw drive system. The support tower and stability arm structure is designed to balance tension in the tether with buoyancy, gravity and wind forces in such a way that the top of the support tower leans downwind, providing a large clearance between the support tower and the rotor blade tips. This large clearance facilitates the use of articulated rotor hubs to reduced damaging structural dynamic loads. Major components of the turbine can be assembled at the shore and transported to an offshore installation site.

Viterna, Larry A.↗
NASA NTRS1981

A multi-purpose method for analysis of spur gear tooth loading

A large digitized approach was developed for the static and dynamic load analysis of spur gearing. An iterative procedure was used to calculate directly the "variable-variable" gear mesh stiffness as a function of transmitted load, gear tooth profile errors, gear tooth deflections and gear hub torsional deformation, and position of contacting profile points. The developed approach can be used to analyze the loads, Hertz stresses, and PV for the normal and high contrast ratio gearing, presently the modeling is limited to the condition that for a given gear all teeth have identical spacing and profiles (with or without surface imperfections). Certain types of simulated sinusoidal profile errors and pitting can cause interruptions of the gear mesh stiffness function and, thus, increase the dynamic loads in spur gearing. In addition, a finite element stress and mesh subprogram was developed for future introduction into the main program for calculating the gear tooth bending stresses under dynamic loads.

Kasuba, R.↗