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NASA NTRS2006

Development and Testing of a Radial Halbach Magnetic Bearing

The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Radial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Radial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical applications, manufacturing equipment, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Radial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

Eichenberg, Dennis J.↗

NASA NTRSDate not supplied

Comparison of Orion Flywheel to Commercially Available Flywheel Device

INTRODUCTION: The chosen exercise device for the Orion Multi-purpose Crew Vehicle (MPCV) for Artemis missions is the Orion Flywheel (OFW), which was selected in 2017 from a pool of exercise devices. The Orion Flywheel is to be installed in the MPCV for its first use during the Artemis II mission and will be utilized for subsequent Artemis missions. The OFW provides the capability to perform both resistive and aerobic exercises while taking up a small volume and not requiring power. Aerobic exercise consists of rowing while resistive exercise includes the deadlift, harness squat, and deadlift high pull among others. The efficacy of the OFW as an exercise countermeasure to spaceflight deconditioning has not yet been fully evaluated. A future HRP-funded study using head-down tilt bed rest is planned to evaluate the efficacy of the OFW to mitigate aerobic and muscular deconditioning. The OFW, made by KBR, is a specialized device that poses high costs for purchase and maintenance. The aim of the study is to determine if a commercially available alternative could be used as a backup for the OFW during the bed rest study or as an alternative in other studies. This study seeks to compare the loading profile and mechanics of a commercial flywheel device (kBox Pro) with the three resistance settings of the OFW using a controlled, instrumented setup to validate its acceptability as a backup. METHODS: An experimental setup was designed to simulate human use of the OFW. Flywheel devices can have varied actuated inertial mass and strap length. The inertial mass refers to the flywheel itself or the object that spins as the result of the movement of the strap. The OFW has three gears actuated with a lever, with the low gear used for aerobic rowing and the medium and high gears used for resistance exercises. These gears correspond to increasing flywheel inertia, which corresponds to a certain number and sizes of inertial plates on a commercial flywheel. The kBox Pro has varied sizes of inertial discs that are installed to the external shaft of the device and can be configured to roughly match the inertia seen in the OFW per gear setting. The strap length can be adjusted to allow for different ranges of motion. The experimental setup allows for the simulation of rowing, harness squats, and deadlift high pulls with corresponding exercise strap lengths. All three OFW gears are to be tested, as well as multiple combinations of kBox discs. The setup was created using a system of pulleys and cables to minimize friction loss. The system is actuated through the dropping of a connected mass which, through the pulley system, pulls the strap of the exercise device upwards as if a human was exercising. A string potentiometer and tensile force transducer are used to measure strap displacement and strap force, respectively. The masses dropped are exercise chains that simulate the decrease in force observed throughout a typical exercise. As the chains are lowered to the ground, they begin to spool and therefore are no longer subjecting the exercise device’s strap to their load. This setup was designed to provide realistic loads and protect the OFW from damage, an important precaution because it’s the only available unit for research and ground operations. Data is to be collected across simulated exercises and with different strap lengths, with the same conditions collected on both the OFW and the kBox Pro. RESULTS: Data collection is ongoing for the kBox and the Orion Flywheel. CONCLUSIONS: Study results will inform if the OFW and a kBox Pro device can be deemed mechanically similar. Depending on the results, additional data collection may be required to assess the user experience between the devices. A key result of this study is a mechanical characterization of the OFW device, demonstrating the load and force profile using a repeatable test method. This data will guide next steps on potential kBox Pro modifications needed to produce a comparable exercise experience to the OFW.

Exercise↗

NASA NTRS1973

Solar tidal friction and satellite loss

This paper treats the dynamical evolution of a satellite orbiting a primary that is being despun by solar tidal friction. The results are then applied to Mercury and Venus. It is concluded that a wide variety of satellites would not have survived the solar tidal braking of these planets. Hence, the absence of satellites around Mercury and Venus is not a compelling reason for thinking that this has always been the situation. Satellites are lost by orbital decay and impact with the primary. It is likely that Mercury would retain a record of such an event on its surface.

Ward, W. R.↗

NASA NTRS1984

Comparison between measured turbine stage performance and the predicted performance using quasi-3D flow and boundary layer analyses

A method for calculating turbine stage performance is described. The usefulness of the method is demonstrated by comparing measured and predicted efficiencies for nine different stages. Comparisons are made over a range of turbine pressure ratios and rotor speeds. A quasi-3D flow analysis is used to account for complex passage geometries. Boundary layer analyses are done to account for losses due to friction. Empirical loss models are used to account for incidence, secondary flow, disc windage, and clearance losses.

Boyle, R. J.↗

NASA NTRS1984

Comparison between measured turbine stage performance and the predicted performance using quasi-3D flow and boundary layer analyses

Boyle, R. J.↗

NASA NTRS2005

Experimental Investigation of Oscillatory Flow Pressure and Pressure Drop Through Complex Geometries

A series of experiments have been performed to investigate the oscillatory flow pressure and pressure drop through complex geometries. These experiments were conducted at the CSU-SLRE facility which is a horizontally opposed, two-piston, single-acting engine with a split crankshaft driving mechanism. Flow through a rectangular duct, with no insert (obstruction), was studied first. Then four different inserts were examined: Abrupt, Manifold, Diverging Short and Diverging Long. The inserts were mounted in the center of the rectangular duct to represent different type of geometries that could be encountered in Stirling machines. The pressure and pressure drop of the oscillating flow was studied for: 1) different inserts, 2) different phase angle between the two pistons of the engine (zero, 90 lead, 180, and 90 lag), and 3) for different piston frequencies (5, 10, 15, and 20 Hz). It was found that the pressure drop of the oscillatory flow increases with increasing Reynolds number. The pressure drop was shown to be mainly due to the gas inertia for the case of oscillatory flow through a rectangular duct with no insert. On the other hand, for the cases with different inserts into the rectangular duct, the pressure drop has three sources: inertia, friction, and local losses. The friction pressure drop is only a small fraction of the total pressure drop. It was also shown that the dimensionless pressure drop decreases with increasing kinetic Reynolds number.

Ibrahim, Mounir B.↗

NASA NTRSDate not supplied

Dynamical self-friction: how mass loss slows you down

Explore the source record for details and available documents.

Tim B Miller↗

NASA NTRS1993

On the Accuracy of CFD-Based Pressure Drop Predictions for Right-Angle Ducts

The predictive capability of computational fluid dynamics (CFD) codes for turbulent flow through curved ducts is of significant importance to the design and performance analysis of modern rocket engine flowpaths. Code calibration and validation studies for this class of flow are desireable to estimate the performance margin and operating range of components designed using Navier-Stokes methods. Parametric experimental studies such as that of Weske (NACA ARR W-39) provided a wealth of performance data for the design of single- and compound elbow configurations with various cross-sections, curvature and aspect ratios at varying Reynolds numbers. In that work, the majority of data is presented in the form of loss coefficients, characterizing pressure losses due to duct curvature, and including losses due to wall friction. Using measured friction coefficients, losses of equivalent straight lengths of duct are subtracted, resulting in performance curves useful for design computations. These data are currently used in a CFD-based parametric study covering a broad range of operating conditions. Of particular interest for the accuracy of CFD predictions are the effects on pressure loss due to inlet boundary layer thickness (dependent on upstream development length), and the wall treatment for the turbulence equations (conventional wall functions vs. wall integration using a two-layer model). The experimental data are reassessed in the form of an error analysis, and are compared with CFD predictions for 18 computational cases. Grid-independence, grid spacing, and convergence requirements of the cases are discussed. Conclusions regarding the relative importance of the parametric variables will be presented.

Brankovic, Andreja↗

NASA NTRSDate not supplied

Heat Pipe Heat Exchanger for Nuclear Electric Propulsion Power Conversion System

Heat pipe reactors have been considered by the Space Nuclear Propulsion program for Nuclear Electric Propulsion (NEP) power conversion systems and will require the use of heat exchangers to transfer heat via heat pipes to the Brayton working fluid from the reactor. Sodium (Na) and lithium (Li) were considered as viable working fluids inside the heat pipes which were assumed to have the same geometry based on studies and information from the Los Alamos National Laboratory. The heat exchanger was assumed to be a rectangular duct with heat pipes serving as tubes from previous NEP work and recommendations. Based on this geometry, Zukauskas correlations were used to model the convective heat transfer and pressure losses. Parametric sizing of the reactor component involved operational limits-based heat pipe thermal hydraulic modeling in cohesion with required user input geometry for the in-core lattice and various subcomponents. This work considered various power conversion inlet temperatures (PCIT) of 1100 K, 1150 K, and 1200 K for Na heat pipes and 1100 K, 1150 K, 1200 K, and 1400 K for Li heat pipes based on recommendations from prior work. Using these different PCITs, the subsystem masses and pressure losses were determined and analyzed. Na showed a lower overall operating temperature and about a fifth of the maximum heat throughput capability than that of Li for the same geometry. Due to this, the entire Na-based subsystem ended up being three times more massive than the Li-based subsystem given five times the required number of heat pipes. At the low PCIT of 1100 K, the Na-based subsystem exhibited the lowest pressure losses given the large overall cross sectional flow area and relatively low frictional pressure losses. However, as the PCIT increased, the frictional pressure losses increased resulting in higher pressure losses at the 1200 K PCIT than Li-based subsystem. However, the Li-based subsystem exhibited the largest pressure losses of all analyzed cases at the 1400 K PCIT due to the low density of the Brayton working fluid at this temperature.

electric↗

NASA NTRS1996

Ultralow Friction in a Superconducting Magnetic Bearing

Passive levitation by superconducting magnetic bearings can be utilized in flywheels for energy storage. Basic design criteria of such a bearing are high levitation force, sufficient vertical and horizontal stability and low friction. A test facility was built for the measurement and evaluation of friction in a superconducting magnetic bearing as a function of operating temperature and pressure in the vacuum vessel. The bearing consists of a commercial disk shaped magnet levitated above single grain, melt-textured YBCO high-temperature superconductor material. The superconductor was conduction cooled by an integrated AEG tactical cryocooler. The temperature could be varied from 50 K to 80 K. The pressure in the vacuum chamber was varied from 1 bar to 10(exp -5) mbar. At the lowest pressure setting, the drag torque shows a linear frequency dependence over the entire range investigated (0 less than f less than 40 Hz). Magnetic friction, the frequency independent contribution, is very low. The frequency dependent drag torque is generated by molecular friction from molecule-surface collisions and by eddy currents. Given the specific geometry of the set-up and gas pressure, the molecular drag torque can be estimated. At a speed of 40 Hz, the coefficient of friction (drag-to-lift ratio) was measured to be mu = 1.6 x 10(exp -7) at 10(exp -5) mbar and T = 60 K. This is equivalent to a drag torque of 7.6 x 10(exp -10) Nm. Magnetic friction causes approx. 1% of the total losses. Molecular friction accounts for about 13% of the frequency dependent drag torque, the remaining 87% being due to eddy currents and losses from rotor unbalance. The specific energy loss is only 0.3% per hour.

Bornemann, Hans J.↗

NASA NTRS1986

Measuring Gearbox Torque Loss

Accuracy increased by measuring small torque differences directly. Input and output torques are balanced by mechanical linkage in transmission-testing apparatus. Force applied to load cell proportional to frictional torque loss in transmission. Apparatus measures portion of input torque lost to friction in automotive transmissions or other gearbox. Apparatus more sensitive than previous measuring systems.

Schmidt, L. F.↗

NASA NTRS1972

Momentum flux in two phase two component low quality flow

In two phase flow systems line losses comprise frictional and momentum pressure drops. For design purposes, it would be desirable to estimate the line losses employing a one-dimensional calculation. Two methods for computing one-dimensional momentum flux at a test section discharge station are compared to the experimental value for a range of two-phase flow conditions. The one-dimensional homogeneous model appears to be more accurate generally in predicting the momentum than the variable slip model.

Baumeister, K. J.↗

NASA NTRS1973

Monitor for physical property changes in solid propellants

Specially designed sensor is attached to or imbedded in propellant. When sensor is driven into vibration, it moves with a phase lag directly proportional to internal friction or loss coefficent. Resonance frequency of the system is related to Young's modulus. Modulus or internal friction can be monitored over long period of time.

Black, R. E., Jr.↗

NASA NTRS1998

Tribometer for Lubrication Studies in Vacuum

The NASA Lewis Research Center has developed a new way to evaluate the liquid lubricants used in ball bearings in space mechanisms. For this evaluation, a liquid lubricant is exercised in the rolling contact vacuum tribometer shown in the photo. This tribometer, which is essentially a thrust bearing with three balls and flat races, has contact stresses similar to those in a typical preloaded, angular contact ball bearing. The rotating top plate drives the balls in an outward-winding spiral orbit instead of a circular path. Upon contact with the "guide plate," the balls are forced back to their initial smaller orbit radius; they then repeat this spiral orbit thousands of times. The orbit rate of the balls is low enough, 2 to 5 rpm, to allow the system to operate in the boundary lubrication regime that is most stressful to the liquid lubricant. This system can determine the friction coefficient, lubricant lifetime, and species evolved from the liquid lubricant by tribodegradation. The lifetime of the lubricant charge is only few micrograms, which is "used up" by degradation during rolling. The friction increases when the lubricant is exhausted. The species evolved by the degrading lubricant are determined by a quadrupole residual gas analyzer that directly views the rotating elements. The flat races (plates) and 0.5-in.-diameter balls are of a configuration and size that permit easy post-test examination by optical and electron microscopy and the full suite of modern surface and thin-film chemical analytical techniques, including infrared and Raman microspectroscopy and x-ray photoelectron spectroscopy. In addition, the simple sphere-on-a-flat-plate geometry allows an easy analysis of the contact stresses at all parts of the ball orbit and an understanding of the frictional energy losses to the lubricant. The analysis showed that when the ball contacts the guide plate, gross sliding occurs between the ball and rotating upper plate as the ball forced back to a smaller orbit radius. The friction force due to gross sliding is sensed by the piezoelectric force transducer behind the guide plate and furnishes the coefficient of friction for the system. This tribometer has been used to determine the relative lifetimes of Fomblin Z-25, a lubricant often used in space mechanisms, as a function of the material of the plates against which it was run. The balls were 440C steel in all cases; the plate materials were aluminum, chromium (Cr), 440C steel (17 wt % Cr), and 4150 steel (1 wt % Cr). As shown in the bar graph, the lifetime is greatest for the plate material with least chromium, thus implicating chromium as a tribochemically active element attacking Fomblin Z-25.

Pepper, Stephen V.↗

NASA NTRS1971

Dynamic behavior of the mercury damper

The dynamic behavior of the mercury nutation damper is investigated. Particular attention is paid to the eccentric annular mercury configuration, which is the final continuous ring phase that occurs in the operation of all mercury dampers. In this phase, damping is poorest, and the system is closely linear. During the investigation, the hydrodynamic problem is treated as three dimensional, and extensive use is made of a variational principle of least-viscous frictional power loss. A variational principle of least-constraint is also used to advantage. Formulas for calculating the behavior of the mercury damper are obtained. Some confirmatory experiments were performed with transparent ring channels on a laboratory gyroscope. Selected movie frames taken during wobble damping are shown along with the results of film measurements.

Crout, P. D.↗

NASA NTRS1972

Analysis of oil lubricated, fluid film, thrust bearings with allowance for temperature dependent viscosity

A preliminary design study was performed to seek a fluid-film thrust bearing design intended to be part of a high-speed, hybrid (rolling element/fluid film) bearing configuration. The base line used is a design previously tested. To improve the accuracy of theoretical predictions of load capacity, flow rate, and friction power loss, an analytical procedure was developed to include curvature effects inherent in thrust bearings and to allow for the temperature rise in the fluid due to viscous heating. Also, a narrow-groove approximation in the treatment of the temperature field was formulated to apply the procedure to the Whipple thrust bearing. A comparative trade-off study was carried out assuming isothermal films; its results showed the shrouded-step design to be superior to the Whipple design for the intended application. An extensive parametric study was performed, employing isoviscous calculations, to determine the optimized design, which was subsequently recalculated allowing for temperature effects.

Pan, C. H. T.↗

NASA NTRS1973

An electric motor with magnetic bearings: A concept

Because same magnetic flux is used to control rotor as to drive it, size, weight, and power required are minimized. Constant total current keeps motor torque invarient, and absence of mechanical bearings eliminates wear and reduces frictional power loss.

Studer, P. A.↗

NASA NTRS1973

Aluminum runway surface as possible aid to aircraft braking

Several concepts are described for use singly or in combination to improve aircraft braking. All involve a thin layer of aluminum covering all or part of the runway. Advantage would derive from faster heat conduction from the tire-runway interface. Heating of tread surface with consequent softening and loss of friction coefficient should be reduced. Equations are developed indicating that at least 99 percent of friction heat should flow into the aluminum. Preliminary test results indicate a coefficient of sliding friction of 1.4, with predictably slight heating of tread. Elimination of conventional brakes is at least a remote possibility.

Miller, C. D.↗