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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Internal rotor friction instability

The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.

Walton, J.↗
NASA NTRS1985

Energy and momentum management of the Space Station using magnetically suspended composite rotors

The research addresses the feasibility of using magnetically suspended composite rotors to jointly perform the energy and momentum management functions of an advanced manned Space Station. Recent advancements in composite materials, magnetic suspensions, and power conversion electronics have given flywheel concepts the potential to simultaneously perform these functions for large, long duration spacecraft, while offering significant weight, volume, and cost savings over conventional approaches. The Space Station flywheel concept arising out of this study consists of a composite-material rotor, a large-angle magnetic suspension (LAMS) system, an ironless armature motor/generator, and high-efficiency power conversion electronics. The LAMS design permits the application of appropriate spacecraft control torques without the use of conventional mechanical gimbals. In addition, flywheel systems have the growth potential and modularity needed to play a key role in many future system developments.

Eisenhaure, D. B.↗
NASA NTRS1978

Analytical design of a high performance stability and control augmentation system for a hingeless rotor helicopter

A stability and control augmentation system (SCAS) was designed based on a set of comprehensive performance criteria. Linear optimal control theory was applied to determine appropriate feedback gains for the stability augmentation system (SAS). The helicopter was represented by six-degree-of-freedom rigid body equations of motion and constant factors were used as weightings for state and control variables. The ratio of these factors was employed as a parameter for SAS analysis and values of the feedback gains were selected on this basis to satisfy three of the performance criteria for full and partial state feedback systems. A least squares design method was then applied to determine control augmentation system (CAS) cross feed gains to satisfy the remaining seven performance criteria. The SCAS gains were then evaluated by nine degree-of-freedom equations which include flapping motion and conclusions drawn concerning the necessity of including the pitch/regressing and roll/regressing modes in SCAS analyses.

Miyajima, K.↗
NASA NTRS1994

Navier-Stokes Calculations for a Highly-Twisted Rotor Near Stall

The viscous flow field near the surface of a hovering rotor blade was studied for blade twist distributions typical of a till rotor blade and a conventional helicopter rotor blade. Three blade geometries were studied, including a tilt rotor blade twist distribution (baseline), conventional helicopter rotor blade twist distribution, and the baseline twist distribution with 2 deg of precone. The results give insight into the delayed stall phenomenon often observed for highly twisted rotors. Calculations were performed for a high thrust condition near stall using the thin-layer Navier-Stokes CFD code TURNS. Effects of built-in twist on section force coefficients, skin friction, velocities, surface pressures, and boundary layer shape factor are discussed. Although the rotor thrust coefficient was nominally the same for the cases using the two twist distributions, large differences were found in the section in-plane and normal force coefficients. These preliminary results imply that the blade outboard region, rather than the inboard region, provides the majority of the performance advantage of the baseline case over the low twist case. Skin friction, velocities near the blade, and surface pressures for the two twist distributions reveal significant differences in the blade outboard region.

Yamauchi, Gloria K.↗
NASA NTRS1991

Fundamental studies of rotor wakes in low speed forward flight using wide-field shadowgraphy

Experiments were conducted using the wide-field shadowgraph method to visualize the wake geometry from a helicopter rotor in low speed forward flight. The experiments were performed with an isolated rotor and with a body representing a helicopter fuselage. Particular attention was paid to documenting the isolated rotor wake geometry, blade vortex interaction phenomena near the rotor plane, the distortion made to the wake due to the presence of the body, and detailing the interaction of the tip vortices with the body surface. Quantitative measurements were made of the wake trajectories as functions of wake age, as well as estimates of the tip vortex core radius. The results have provided many details of the rotor wake structure that are useful for validating rotor wake and rotor/body interactional models in forward flight. The use of the wide-field shadowgraph method offers an important tool for visualizing rotor wake vortices, and helping to understand the complex three-dimensional nature of rotor wakes in forward flight.

Leishman, J. G.↗
NASA NTRS1993

A comparison between numerically modelled and experimentally measured loss mechanisms in wave rotors

A numerical model has been developed which is capable of predicting the performance of a wave rotor (pressure exchanger) of specified geometry over a wide range of operating conditions. The model can account for the major loss mechanisms of leakage from the tube ends, fluid viscosity, heat transfer to the tube wails, finite tube opening time, shock waves, and non-uniform port flows. It is a one dimensional flow model which follows a single tube as it rotates past the various stationary ports. Since the model is relatively simple (i.e., one dimensional) it uses little computer time. This makes it suitable for design as well as analytical purposes. This paper will present a brief description of the model then discuss a comparison between the model predictions and several wave rotor experiments.

Paxson, Daniel E.↗
NASA NTRS1993

A Comparison Between Numerically Modelled and Experimentally Measured Loss Mechanisms in Wave Rotors

A numerical model has been developed which is capable of predicting the performance of a wave rotor (pressure exchanger) of specified geometry over a wide range of operating conditions. The model can account for the major loss mechanisms of leakage from the tube ends, fluid viscosity, heat transfer to the tube walls, finite tube opening time, shock waves, and non-uniform port flows. It is a one dimensional flow model which follows a single tube as it rotates past the various stationary ports. Since the model is relatively simple (i.e. one dimensional) it uses little computer time. This makes it suitable for design as well as analytical purposes. This paper will present a brief description of the model then discuss a comparison between the model predictions and several wave rotor experiments.

Paxson, Daniel E.↗
NASA NTRS1996

An aeroelastic analysis of helicopter rotor blades incorporating piezoelectric fiber composite twist actuation

A simple aeroelastic analysis of a helicopter rotor blade incorporating embedded piezoelectric fiber composite, interdigitated electrode blade twist actuators is described. The analysis consist of a linear torsion and flapwise bending model coupled with a nonlinear ONERA based unsteady aerodynamics model. A modified Galerkin procedure is performed upon the rotor blade partial differential equations of motion to develop a system of ordinary differential equations suitable for numerical integration. The twist actuation responses for three conceptual full-scale blade designs with realistic constraints on blade mass are numerically evaluated using the analysis. Numerical results indicate that useful amplitudes of nonresonant elastic twist, on the order of one to two degrees, are achievable under one-g hovering flight conditions for interdigitated electrode poling configurations. Twist actuation for the interdigitated electrode blades is also compared with the twist actuation of a conventionally poled piezoelectric fiber composite blade. Elastic twist produced using the interdigitated electrode actuators was found to be four to five times larger than that obtained with the conventionally poled actuators.

Wilkie, W. Keats↗
NASA NTRS1996

Aeroelastic Analysis of Helicopter Rotor Blades Incorporating Anisotropic Piezoelectric Twist Actuation

A simple aeroelastic analysis of a helicopter rotor blade incorporating embedded piezoelectric fiber composite, interdigitated electrode blade twist actuators is described. The analysis consists of a linear torsion and flapwise bending model coupled with a nonlinear ONERA based unsteady aerodynamics model. A modified Galerkin procedure is performed upon the rotor blade partial differential equations of motion to develop a system of ordinary differential equations suitable for dynamics simulation using numerical integration. The twist actuation responses for three conceptual fullscale blade designs with realistic constraints on blade mass are numerically evaluated using the analysis. Numerical results indicate that useful amplitudes of nonresonant elastic twist, on the order of one to two degrees, are achievable under one-g hovering flight conditions for interdigitated electrode poling configurations. Twist actuation for the interdigitated electrode blades is also compared with the twist actuation of a conventionally poled piezoelectric fiber composite blade. Elastic twist produced using the interdigitated electrode actuators was found to be four to five times larger than that obtained with the conventionally poled actuators.

Wilkie, W. Keats↗
NASA NTRS2019

Towards Urban Air Mobility: NASA’s Quadcopter Air Taxi Concept

Urban Air Mobility (UAM) is envisioned to be the future air transportation system over populated areas, where everything from small package delivery drones to passenger-carrying air taxis are able to interact safely and efficiently. The capacity of multi-rotor vehicles to perform vertical takeoff and landing (VTOL), together with their great maneuverability, make them an excellent choice for UAM aircraft. The accurate prediction of multirotor vehicles performance and acoustics is very challenging due to the unsteady and complex flows, as well as the aerodynamic interactions. By running high-fidelity computational fluid dynamics simulations on NASA supercomputers, researchers model the complex aerodynamics of multi-rotor flows, getting us closer to making UAM a reality.

Ventura Diaz, Patricia↗
NASA NTRS1972

High-loading low-speed fan study. 4: Data and performance with redesign stator and including a rotor tip casing treatment

A single stage fan with a rotor tip speed of 1000 ft/sec(304.8 m/sec) and a hub-to-tip ratio of 0.392 was retested with a redesigned stator. Tests were conducted with uniform inlet, tip-radial, hub-radial, and circumferential inlet distortions. With uniform inlet flow, stall margin was improved 12 percentage points above that with the original stator. The fan demonstrated an efficiency of 0.883 and a stall margin of 15 percent at a pressure ratio of 1.488 and a specific flow of 41.17 lb/sec/sq ft. Tests were also made with a redesigned casing treatment consisting of skewed slots over the rotor blade tips. This casing treatment gave a 7 percentage point improvement in stall margin when tested with tip radial distortion (when the rotor tip initiated stall). Noise measurements at the fan inlet and exit indicate no effect from closing the stator 10 degrees, nor were there measurable effects from adding skewed slots over the blade tips.

Harley, K. G.↗