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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 199 records · Page 11

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NASA NTRS1971

Extended ion pumped vacuum friction test

Boundary layer friction data under ion pumped vacuum was taken for sixteen material couples. The test series was an extension of a previous study of the effects of modified ion pumped environments. Sliding distances imposed in the present effort greatly exceeded any studied in the previous contiguous, flight or ground tests. Wear out of specific couples, in particular, thin film lubricants was noted. The behavior of the test hardware including wear out of the mechanisms was noted. As a result, the impact of test interruption was observed for several test couples. Recovery of the friction upon re-establishing sliding in vacuum was generally rapid. The results of the extended sliding study reinforce the previous conclusion that sliding distance (mechanical history) is the primary factor in establishing the force limiting boundary layer friction. General friction value under the extended sliding confirm those observed in previous orbital and the related ground test studies.

Hammel, R. L.↗

NASA NTRSDate not supplied

Gimbal Bearing Friction in the SLS Core Stage Thrust Vector Control System

The Space Launch System (SLS) Core Stage Thrust Vector Control (TVC) system is comprised of eight mechanical feedback Shuttle heritage Type III TVC actuators that vector the four Shuttle heritage RS-25 engines about a Shuttle heritage gimbal block/bearing. The MSFC Controls community has long regarded gimbal friction to be a negligible effect on the overall control of gimbaled RS-25 engines. This is corroborated by Space Shuttle test and flight data that does not appear to show degraded effects, nor limit cycling at the end of the shuttle flight. For this reason, friction was not expected to be a driving factor of performance and control of the reused RS-25 engines aboard the SLS. However, after test data showed a large shift in frequency behavior and a highly damped step-response in the time series, there was further investigation into what could have caused this behavior. Heritage friction models used in previous gimbal and ball bearings were evaluated such as Coulomb, Dahl and LuGre, but the single degree of freedom friction models alone were not enough to explain the behavior and shifts seen in the test data. This paper presents the additional findings and modeling efforts regarding friction on the RS-25 engines. Using the Two Actuator Operational Simulation (TAOS), the difference from modeling separate friction degrees of freedom to coupled degrees of freedom was investigated to deduce the effects of one axis’s movement on the other. Next, due to the vibration environment, a modified LuGre model has been proposed that adds an additional term to decrease the friction coefficient at low engine velocity amplitudes. Lastly, the addition of the stiffness in each half of the gimbal bearing has increased modeling fidelity by also adding the effect on the gimbal bearing bending in compliance to both the friction torque on the surface of the gimbal bearing and the actuator force that is forcing the engine in a specified direction. Through these effects, the time and frequency domain behavior seen in test can be characterized accurately.

Friction↗

NASA NTRSDate not supplied

Gimbal Bearing Friction in the SLS Core Stage Thrust Vector Control System

Friction↗

NASA NTRS1980

In-flight boundary-layer measurements on a hollow cylinder at a Mach number of 3.0

Skin temperatures, shear forces, surface static pressures, boundary layer pitot pressures, and boundary layer total temperatures were measured on the external surface of a hollow cylinder that was 3.04 meters long and 0.437 meter in diameter and was mounted beneath the fuselage of the YF-12A airplane. The data were obtained at a nominal free stream Mach number of 3.0 (a local Mach number of 2.9) and at wall to recovery temperature ratios of 0.66 to 0.91. The local Reynolds number had a nominal value of 4,300,000 per meter. Heat transfer coefficients and skin friction coefficients were derived from skin temperature time histories and shear force measurements, respectively. In addition, boundary layer velocity profiles were derived from pitot pressure measurements, and a Reynolds analogy factor was obtained from the heat transfer and skin friction measurements. The measured data are compared with several boundary layer prediction methods.

Quinn, R. D.↗

NASA NTRS1974

Effect of frictional heating on brake materials

An exploratory study of the properties of aircraft brake materials was made to determine ways of improving friction and wear behavior while minimizing surface temperatures. It is found that frictional variation at high temperature involves material softening and metal transfer, formation of oxides, and surface melting. The choice of proper materials to combat these effects is discussed. Minimum surface temperatures are found to result from use of materials with large density-specific heat and density-specific heat-conductivity factors, use of a higher load-lower friction system, and maximization of the contact area. Some useful trade-off criteria for the size of brake disks against weight considerations are suggested. Additional information on material behavior and peak braking temperatures was gathered from an inspection of used brake pads and rotor disks.

Ho, T.-L.↗

NASA NTRS1995

HINCOF-1: a Code for Hail Ingestion in Engine Inlets

One of the major concerns during hail ingestion into an engine is the resulting amount and space- and time-wise distribution of hail at the engine face for a given geometry of inlet and set of atmospheric and flight conditions. The appearance of hail in the capture streamtube is invariably random in space and time, with respect to size and momentum. During the motion of a hailstone through an inlet, a hailstone undergoes several processes, namely impact with other hailstones and material surfaces of the inlet and spinner, rolling and rebound following impact; heat and mass transfer; phase change; and shattering, the latter three due to friction and impact. Taking all of these factors into account, a numerical code, designated HINCOF-I, has been developed for determining the motion hailstones from the atmosphere, through an inlet, and up to the engine face. The numerical procedure is based on the Monte-Carlo method. The report presents a description of the code, along with several illustrative cases. The code can be utilized to relate the spinner geometry - conical or, more effective, elliptical - to the possible diversion of hail at the engine face into the bypass stream. The code is also useful for assessing the influence of various hail characteristics on the ingestion and distribution of hailstones over the engine face.

Gopalaswamy, N.↗

NASA NTRS2008

Numerical Analysis of Rocket Exhaust Cratering

Supersonic jet exhaust impinging onto a flat surface is a fundamental flow encountered in space or with a missile launch vehicle system. The flow is important because it can endanger launch operations. The purpose of this study is to evaluate the effect of a landing rocket s exhaust on soils. From numerical simulations and analysis, we developed characteristic expressions and curves, which we can use, along with rocket nozzle performance, to predict cratering effects during a soft-soil landing. We conducted a series of multiphase flow simulations with two phases: exhaust gas and sand particles. The main objective of the simulation was to obtain the numerical results as close to the experimental results as possible. After several simulating test runs, the results showed that packing limit and the angle of internal friction are the two critical and dominant factors in the simulations.

Source record↗

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 NTRS2022

Controlling Palm-Object Interactions via Friction for Enhanced In-Hand Manipulation

In-hand manipulation is necessary, yet challenging for robotic hands as robots begin to interact with real-world objects and environments. The intentional incorporation of an active palm can lead to improved dexterity. In this work, we demonstrate how controlling the palm-object interaction enables access to different sets of motion primitives. We first discuss how various properties of the palm affect in-hand manipulation, as well as grasping. Here, we focus on varying the friction force between the object and the palm by either changing the coefficient of friction or the normal load. We explore how these two design factors can be actively controlled to enable 5-degree-of-freedom object motion within the hand. We present variable-friction and variable-preload palms that enable on-the-fly switching between in-plane and out-of-plane manipulation modes. Additionally, we discuss their impact on grasp stability. Finally, we demonstrate how an object can be translated and pivoted within the hand by sequentially performing synchronized palm and finger actions.

Clark B Teeple↗

NASA NTRS1994

Physical and Tribological Characteristics of Ion-Implanted Diamond Films

Unidirectional sliding friction experiments were conducted with a natural, polished diamond pin in contact with both as-deposited and carbon-ion-implanted diamond films in ultrahigh vacuum. Diamond films were deposited on silicon, silicon carbide, and silicon nitride by microwave-plasma-assisted chemical vapor deposition. The as-deposited diamond films were impacted with carbon ions at an accelerating energy of 60 keV and a current density of 50 micron A/cm(exp 2) for approximately 6 min, resulting in a dose of 1.2 x 10(exp 17) carbon ions/cm(exp 2). The results indicate that the carbon ion implantation produced a thin surface layer of amorphous, nondiamond carbon. The nondiamond carbon greatly decreased both friction and wear of the diamond films. The coefficients of friction for the carbon-ion-implanted, fine-grain diamond films were less than 0.1, factors of 20 to 30 lower than those for the as-deposited, fine-grain diamond films. The coefficients of friction for the carbon-ion-implanted, coarse-grain diamond films were approximately 0.35, a factor of five lower than those for the as-deposited, coarse-grain diamond films. The wear rates for the carbon-ion-implanted, diamond films were on the order of 10(exp -6) mm(exp 3)/Nm, factors of 30 to 80 lower than that for the as-deposited diamond films, regardless of grain size. The friction of the carbon-ion-implanted diamond films was greatly reduced because the amorphous, nondiamond carbon, which had a low shear strength, was restricted to the surface layers (less than 0.1 micron thick) and because the underlying diamond materials retained their high hardness. In conclusion, the carbon-ion-implanted, fine-grain diamond films can be used effectively as wear resistant, self-lubricating coatings for ceramics, such as silicon nitride and silicon carbide, in ultrahigh vacuum.

Miyoshi, K.↗

NASA NTRS1975

Analysis of effect of internal and operating variables on performance of SVDS constraint model (ABIND)

An examination of the factors which modify the simulation of a constraint in the motion of the aft attach points of the orbiter and external tank during separation has been made. The factors considered were both internal (spring and damper constants) and external (friction coefficient and dynamic pressure). The results show that an acceptable choice of spring/damper constant combinations exist over the expected range of the external factors and that the choice is consistent with a practical integration interval. The constraint model is shown to produce about a 10 percent increase in the relative body pitch angles over the unconstrained case whereas the MDC-STL constraint model is shown to produce about a 38 percent increase.

Pendergrass, J. R.↗

NASA NTRS2018

Friction and Wear of Unlubricated NiTiHf with Nitriding Surface Treatments

The unlubricated friction and wear properties of the superelastic materials NiTi and NiTiHf, treated by either gas nitriding or plasma nitriding, have been investigated. Pin on disk testing of the studied materials was performed at sliding speeds from 0.01 to 1m/s at normal loads of 1, 5 or 10N. For all of the studied friction pairs (NiTiHf pins vs. NiTi and NiTiHf disks) over the given parameters, the steady-state coefficients of friction varied from 0.22 to 1.6. Pin wear factors ranged from approximately 1E-6 against the NiTiHf and plasma nitrided disks to approximately 1E-4 for the gas nitrided disks. The plasma nitrided disks provided wear protection in several cases and tended to wear by adhesion. The gas nitrided treatment generated the most pin wear but had essentially no disk wear except at the most severe of the studied conditions (1N load and 1m/s sliding speed). The results of this study are expected to provide guidance for design of components such as gears and fasteners.

friction↗

NASA NTRS2002

Educational Brief: Using Space for a Better Foundation on Earth Mechanics of Granular Materials

Soils are three-phase composite materials that consist of soil, solid particles, and voids filled with water and/or air. Based on the particle-size distribution, they are generally classified as fine-grained (clays and plastic silts) and coarse-grained soils (nonplastic silts, sand, and gravel). Soil's resistance to external loadings is mainly derived from friction between particles and cohesion. Friction resistance is due to particles' surface-to-surface friction, interlocking, crushing, rearrangement, and dilation (or expansion) during shearing. Cohesion can be due to chemical cementation between particles, electrostatic and electromagnetic forces, and soil-water reaction and equilibrium. The basic factor responsible for the strength of coarse-grained soils is friction. Cohesion can be ignored. This educational brief focuses on measuring shear strength of sands (typical example of coarse-grained soils) where, for the same material, packing density is a main factor to be considered when one asks about the shear strength value. As the external load is applied, the soil's resistance is attained through shearing resistance, which causes the soil volume to increase (expand) or decrease (compress) depending on the initial packing density.

Dooling, Dave↗

NASA NTRS1976

Effect of design factors on surface temperature and wear in disk brakes

The temperatures, friction, wear and contact conditions that occur in high energy disk brakes are studied. Surface and near surface temperatures were monitored at various locations in a caliper disk brake during drag type testing, with friction coefficient and wear rates also being determined. The recorded transient temperature distributions in the friction pads and infrared photographs of the rotor disk surface both showed that contact at the friction surface was not uniform, with contact areas constantly shifting due to nonuniform thermal expansion and wear. The effect of external cooling and of design modifications on friction, wear and temperatures was also investigated. It was found that significant decreases in surface temperature and in wear rate can be achieved without a reduction in friction either by slotting the contacting face of the brake pad or by modifying the design of the pad support to improve pad compliance. Both design changes result in more uniform contact conditions on the friction surface.

Santini, J. J.↗

NASA NTRS1978

A simplified gross thrust computing technique for an afterburning turbofan engine

A simplified gross thrust computing technique extended to the F100-PW-100 afterburning turbofan engine is described. The technique uses measured total and static pressures in the engine tailpipe and ambient static pressure to compute gross thrust. Empirically evaluated calibration factors account for three-dimensional effects, the effects of friction and mass transfer, and the effects of simplifying assumptions for solving the equations. Instrumentation requirements and the sensitivity of computed thrust to transducer errors are presented. NASA altitude facility tests on F100 engines (computed thrust versus measured thrust) are presented, and calibration factors obtained on one engine are shown to be applicable to the second engine by comparing the computed gross thrust. It is concluded that this thrust method is potentially suitable for flight test application and engine maintenance on production engines with a minimum amount of instrumentation.

Hamer, M. J.↗

NASA NTRS1978

In-flight Compressible Turbulent Boundary Layer Measurements on a Hollow Cylinder at a Mach Number of 3.0

Skin temperatures, shearing forces, surface static pressures, and boundary layer pitot pressures and total temperatures were measured on a hollow cylinder 3.04 meters long and 0.437 meter in diameter mounted beneath the fuselage of the YF-12A airplane. The data were obtained at a nominal free stream Mach number of 3.0 and at wall-to-recovery temperature ratios of 0.66 to 0.91. The free stream Reynolds number had a minimal value of 4.2 million per meter. Heat transfer coefficients and skin friction coefficients were derived from skin temperature time histories and shear force measurements, respectively. Boundary layer velocity profiles were derived from pitot pressure measurements, and a Reynolds analogy factor of 1.11 was obtained from the measured heat transfer and skin friction data. The skin friction coefficients predicted by the theory of van Driest were in excellent agreement with the measurements. Theoretical heat transfer coefficients, in the form of Stanton numbers calculated by using a modified Reynolds analogy between skin friction and heat transfer, were compared with measured values. The measured velocity profiles were compared to Coles' incompressible law-of-the-wall profile.

Quinn, R. D.↗

NASA NTRS1996

A Proof of Concept Experiment for Reducing Skin Friction by Using a Micro-Blowing Technique

A proof of concept experiment for reducing skin friction has been conducted in the Advanced Nozzle and Engine Components Test Facility at the NASA Lewis Research Center. In this unique concept, called the micro-blowing technique (MBT), an extremely small amount of air was blown vertically through very small holes to reduce the surface roughness and to control the gradient of the flow velocity profile on the surface thereby reducing skin friction. Research revealed that the skin was the most important factor to make this concept achievable. The proposed skin consisted of two layers. The inner layer was a low permeable porous skin for distributing the blowing air evenly while the outer layer with small holes controlled the vertical or nearly vertical blowing air. Preliminary experimental results showed that the MBT has the potential of a very large reduction in skin friction below the skin friction of a nonporous plain flat plate. Of the skins tested, three have been identified as the MBT skins. They provided very low unblown skin friction such that a large skin friction reduction, below a flat plate value, was achieved with very small amounts of blowing air. The reduction in skin friction of 55 percent was achieved at the Mach number of 0.3 for the exhaust pressure of 0.85 atm, and 60 percent reduction was obtained for the exhaust pressure of 0.24 atm (corresponding to 10 700-m altitude) at the same Mach number. A significant reduction in skin friction of over 25 percent was achieved for the exhaust pressure of 0.24 atm at the Mach number of 0.7. This implied that the MBT could be applied to a wide range of flight conditions. It is also believed that additional 10 percent reduction could be obtained by eliminating the gap between the inner layer and the outer layer. The aspect ratio of the vertical small holes for the outer layer of the MBT skin should be larger than 4 based on the preliminary conclusion from this test. Many experiments are needed to find out the optimal MBT skin. The penalty associated with the MBT needs to be assessed. However, preliminary results indicated that the MBT could provide a 25 to 35 percent reduction for real-world application. The concept can be applied to not only an airplane, but also a missile, a submarine (micro-blow water instead of air), and an ocean liner.

Hwang, Danny P.↗

NASA NTRS1943

Experimental Investigation of a Model of a Two-Stage Turboblower

In the present paper an investigation is made of two stages of a multistage turboblower having a vaneless diffuser behind the impeller and guide vanes at the inlet to the nest stage. The method employed was that of investigating the performance of the successive elements of the blower (the impeller, vaneless diffuser, ets.) whereby the kinematics of the flow through the blower could be followed and the pressure at the different points computed. The character of the flow and the physical significance of the loss coefficients could thereby be determined so as to secure the best agreement of the computed with the actual performance of the blower. Since the tests were carried out for various delivery volumes, the dependence of the coefficients on a number of factors (angle of attack, velocities, etc.) could be obtained. The distribution of the losses that occur during the transformation of dynamic pressure at the impeller exit into static pressure could be found and likewise the range within which the friction coefficient varies in the vaneless diffuser. With the aid of factors having a certain physical significance, the centrifugal blower could be computed on the basis of a more or less schematical consideration of the phenomena occuring during the air flow through it, and the use of arbitrary factors and recourse to the geometrical similtude law thus avoided. The present investigation largely summarizes all the previous work af the CHI Blower Section on the different elements of a centrifugal blower. Some considerations on the analysis of model test data for application to full-scale are presented in the appendix.

Dovjik, s.↗