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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 NTRS1989

Annular honeycomb seals: Test results for leakage and rotordynamic coefficients; comparisons to labyrinth and smooth configurations

Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals show the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluid entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.

Childs, Dara W.↗
NASA NTRS1989

Annular honeycomb seals: Test results for leakage and rotordynamic coefficients - Comparisons to labyrinth and smooth configurations

Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals shows the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluids entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.

Childs, D.↗
NASA NTRS1997

Angled Injection: Turbulent Flow Hybrid Bearings Comparison to Test Results

Hydrostatic/hydrodynamic (hybrid) journal bearings handling process liquids have limited dynamic stability characteristics and their application as support elements to high speed flexible rotating systems is severely restricted. Measurements on water hybrid bearings with angled orifice injection have demonstrated improved rotordynamic performance with virtual elimination of cross-coupled stiffness coefficients and null or negative whirl frequency ratios. A bulk-flow model for prediction of the static performance and force coefficients of hybrid bearings with angled orifice injection is advanced. The analysis reveals that the fluid momentum exchange at the orifice discharge produces a pressure rise in the hydrostatic recess retards the shear flow induced by journal rotation, and thus, reduces cross-coupling forces. The predictions from the model are compared with experimental measurements for a 45 deg. angled orifice injection, 5 recess water hybrid bearing operating at 10.2, 17.4, and 24.6 krpm and with supply pressures of 4, 5.5, and 7 MPa. The correlations include recess pressures, flow rates, and rotordynamic force coefficients at the journal centered position.

SanAndres, Luis↗
NASA NTRS2013

Coupled Vortex-Lattice Flight Dynamic Model with Aeroelastic Finite-Element Model of Flexible Wing Transport Aircraft with Variable Camber Continuous Trailing Edge Flap for Drag Reduction

This paper presents a coupled vortex-lattice flight dynamic model with an aeroelastic finite-element model to predict dynamic characteristics of a flexible wing transport aircraft. The aircraft model is based on NASA Generic Transport Model (GTM) with representative mass and stiffness properties to achieve a wing tip deflection about twice that of a conventional transport aircraft (10% versus 5%). This flexible wing transport aircraft is referred to as an Elastically Shaped Aircraft Concept (ESAC) which is equipped with a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for active wing shaping control for drag reduction. A vortex-lattice aerodynamic model of the ESAC is developed and is coupled with an aeroelastic finite-element model via an automated geometry modeler. This coupled model is used to compute static and dynamic aeroelastic solutions. The deflection information from the finite-element model and the vortex-lattice model is used to compute unsteady contributions to the aerodynamic force and moment coefficients. A coupled aeroelastic-longitudinal flight dynamic model is developed by coupling the finite-element model with the rigid-body flight dynamic model of the GTM.

Flexible Aicraft↗
NASA NTRS1991

Growth and characterization of high-performance photorefractive BaTiO3 crystals

Barium titanate has been used for many nonlinear optical applications primarily because it has high grain and high self-pumped phase conjugate reflectivities. However, barium titanate has had a relatively slow response time, and thus low sensitivity. Therefore, it has not been suited to real-time operations. In this report we will describe the modifications in crystal growth, doping, reduction, and poling that have produced barium titanate crystals with the fastest photorefractive response time reported to date, approximately 21 microseconds with a beam-coupling gain coefficient of 38.7 cm(exp -1) and the highest sensitivity reported to date of 3.44 cm(exp 3)/kJ. The sensitivity of these barium titanate crystals is comparable to or greater than other photorefractive oxides. We will show, for the first time, beam-coupling in barium titanate at video frame rates. We infer from response time measurements that barium titanate has a phonon limited mobility. Also, photorefractive response time measurements as a function of the crystallographic orientation and grating wave vector for our cobalt-doped oxygen reduced crystals indicate that their faster response time arise because of an increase in the free carrier lifetime.

Warde, C.↗
NASA NTRS1987

Rotordynamic coefficients and leakage flow of parallel grooved seals and smooth seals

Based on Childs finite length solution for annular plain seals an extension of the bulk flow theory is derived to calculate the rotordynamic coefficients and the leakage flow of seals with parallel grooves in the stator. Hirs turbulent lubricant equations are modified to account for the different friction factors in circumferential and axial direction. Furthermore an average groove depth is introduced to consider the additional circumferential flow in the grooves. Theoretical and experimental results are compared for the smooth constant clearance seal and the corresponding seal with parallel grooves. Compared to the smooth seal the direct and cross-coupled stiffness coefficients as well as the direct damping coefficients are lower in the grooved seal configuration. Leakage is reduced by the grooving pattern.

Nordmann, R.↗
NASA NTRS1982

Finite-length solutions for rotodynamic coefficients of turbulent annular seals

A finite-length solution procedure is developed for perturbation equations which are based on Hirs' (1973) turbulent lubrication model. The equations apply to small motions about a centered position and include the influence of swirl and changes in Reynolds number due to perturbations in clearances. Numerical results are presented for a range of L/D ratios, with and without swirl. For zero swirl, changes in the L/D ratios show results which are similar to those obtained by Black and Jenssen (1970), but when L/D = 1, differences of about 15 percent appear. The results including swirl give physically insupportable results at small L/D ratios, such as a negative cross-coupled stiffness coefficient at L/D = 0.2. This result demonstrates that the complete Hirs turbulence model is not suitable for short seals with significant swirling flow.

Childs, D. W.↗
NASA NTRS1967

High transients suppressed in electromagnetic devices

A bifilar winding around the magnetic core of electromagnetic devices suppresses high transient voltages. The winding is alternately spaced vertically and radially from the core to achieve a high coefficient of coupling.

Marion, C. W.↗
NASA NTRS1979

Squeeze effects in radial face seals

Squeeze effects in a liquid lubricated radial face seal are analyzed. The analysis considers face misalignment with both axial and angular vibrations of the primary seal ring. Translational, rotational, and cross-coupled damping coefficients of the fluid film are derived analytically from a solution of the Reynolds equation utilizing the narrow seal approximation. Results are given for a wide range of practical radius ratios. At each radius ratio, the complete range of angular misalignment - from parallel faces to touch down - is covered. It is shown that squeeze effects in face seals are usually larger than the more familiar hydrodynamic effects. These effects play an important role in the seal's mechanism of operation and therefore have to be considered in any realistic seal model.

Etsion, I.↗
NASA NTRS1984

Hydraulic forces on a centrifugal impeller undergoing synchronous whirl

High speed centrifugal rotating machinery with large vibrations caused by aerodynamic forces on impellers was examined. A method to calculate forces in a two dimensional orbiting impeller in an unbounded fluid with nonuniform entering flow was developed. A finite element model of the full impeller is employed to solve the inviscid flow equations. Five forces acting on the impeller are: Coriolis forces, centripetal forces, changes in linear momentum, changes in pressure due to rotation and pressure changes due to linear momentum. Both principal and cross coupled stiffness coefficients are calculated for the impeller.

Allaire, P. E.↗
NASA NTRS1987

Effect of flow oscillations on axial energy transport in a porous material

The effects of flow oscillations on axial energy diffusion in a porous medium, in which the flow is continuously disrupted by the irregularities of the porous structure, are analyzed. The formulation employs an internal heat transfer coefficient that couples the fluid and solid temperatures. The final relationship shows that the axial energy transport per unit cross-sectional area and time is directly proportional to the axial temperature gradient and the square of the maximum fluid displacement.

Siegel, R.↗
NASA NTRS1987

Spatial light modulation by beam coupling in GaAs crystals

The first demonstration of spatial light modulation in GaAs using the photorefractive effect is reported. A special configuration was employed in which polarization rotation created by beam coupling was utilized. The ability to obtain these results despite a small coupling gain coefficient demonstrates the usefulness of the polarization technique presented here for optical processing with GaAs crystals.

Cheng, Li-Jen↗
NASA NTRS1987

The importance of aerodynamics on dynamics

The effects of aerodynamic phenomena on helicopter structural dynamics are examined, reviewing the results of recent theoretical and experimental investigations. A schematic diagram of a dynamic analysis is presented and discussed, noting the numerous aerodynamic inputs, and numerical data are presented in graphs. Consideration is given to forcing functions, aerodynamic damping, aeroelastic coupling, negative damping, apparent coriolis coupling, periodic coefficients, inverse damping, additional degrees of freedom, flap-lag stability, and dynamic inflow. The need for theoretical models which account for the dynamic loop between blade lift and induced flow (permitting blade motion to dynamically alter the flowfield during transients) is indicated.

Peters, David A.↗
NASA NTRS1994

Turbomachinery Laboratory Texas A and M University research progress on annular gas seals

Three helically-grooved seals were tested and the results were compared to the MTI code SPIRALG. A smooth annular seal was tested at six eccentricity ratios from 0 to 0.5. The following are concluded in this viewgraph presentation: (1) Helical-grooved seals provide a substantial reduction in cross-coupled stiffness coefficients. Negative k(sub xy) values are obtained for no-swirl or low-swirl cases. (2) SPIRALG is completely unsuitable for the type of seal tested, namely, turbulent flow, wide grooves and lands, etc. (3) A good analysis code is needed to guide the design of helically-grooved annular seals including groove and smooth sections.

Childs, Dara W.↗
NASA NTRS1993

The Influence of Swirl Brakes and a Tip Discharge Orifice on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Shrouded Centrifugal Pumps

Recent experiments conducted in the Rotor Force Test Facility at the California Institute of Technology have examined the effects of a tip leakage restriction and swirl brakes on the rotordynamic forces due to leakage flows on an impeller undergoing a prescribed circular whirl. The experiments simulate the leakage flow conditions and geometry of the Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump and are critical to evaluating the pump's rotordynamic instability problems. Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces. Also, previous experiments have shown that leakage inlet (pump discharge) swirl can increase the cross-coupled stiffness coefficient and hence increase the range of positive whirl for which the tangential force is destabilizing. In recent experimental work, the present authors demonstrated that when the swirl velocity within the leakage path is reduced by the introduction of ribs or swirl brakes, then a substantial decrease in both the destabilizing normal and tangential forces could be achieved. Motivation for the present research is that previous experiments have shown that restrictions such as wear rings or orifices at pump inlets affect the leakage forces. Recent pump designs such as the Space Shuttle Alternate Turbopump Design (ATD) utilize tip orifices at discharge for the purpose of establishing axial thrust balance. The ATD has experienced rotordynamic instability problems and one may surmise that these tip discharge orifices may also have an important effect on the normal and tangential forces in the plane of impeller rotation. The present study determines if such tip leakage restrictions contribute to undesirable rotordynamic forces. Additional motivation for the present study is that the widening of the leakage path annular clearance and the installation of swirl brakes in the ATD has been proposed to solve its instability problems. The present study assesses the effect of such a design modification on the rotordynamic forces. The experimental apparatus consists of a solid or dummy impeller, a housing instrumented for pressure measurements, a rotating dynamometer and an eccentric whirl mechanism. The solid impeller is used so that leakage flow contributions to the forces are measured, but the main throughflow contributions are not experienced. The inner surface of the housing has been modified to accommodate meridional ribs or swirl brakes within the leakage annulus. In addition, the housing has been modified to accommodate a discharge orifice that qualitatively simulates one side of the balance piston orifice of the Space Shuttle ATD. Results indicate the detrimental effects of a discharge orifice and the beneficial effects of brakes. Plots of the tangential and normal forces versus whirl ratio show a substantial increase in these forces along with destabilizing resonances at some positive whirl ratios when a discharge orifice is added. When brakes are added, some of the detrimental effects of the orifice are reduced. For the tangential force, a plot versus whirl ratio shows a significant reduction and a destabilizing resonance appears to be eliminated. For the normal force, although the overall force is not reduced, again a destabilizing resonance appears to be eliminated.

Sivo, Joseph M.↗
NASA NTRS1996

Ice Detector and Deicing Fluid Effectiveness Monitoring System

An ice detector and deicing fluid effectiveness monitoring system for an aircraft is disclosed. The ice detection portion is particularly suited for use in flight to notify the flight crew of an accumulation of ice on an aircraft lifting and control surfaces, or helicopter rotors, whereas the deicing fluid effectiveness monitoring portion is particularly suited for use on the ground to notify the flight crew of the possible loss of the effectiveness of the deicing fluid. The ice detection portion comprises a temperature sensor and a parallel arrangement of electrodes whose coefficient of coupling is indicative of the formation of the ice, as well as the thickness of the formed ice. The fluid effectiveness monitoring portion comprises a temperature sensor and an ionic-conduction cell array that measures the conductivity of the deicing fluid which is indicative of its concentration and, thus, its freezing point. By measuring the temperature and having knowledge of the freezing point of the deicing fluid, the fluid effectiveness monitoring portion predicts when the deicing fluid may lose its effectiveness because its freezing point may correspond to the temperature of the ambient.

Seegmiller, H. Lee B.↗
NASA NTRS2003

The computation of the k factor for lossy materials around resonance

An important property of a piezoelectric material for practical applications is its ability to generate and to detect stress waves, i.e. to convert electrical energy into mechanical energy and vice versa. As it is well known, the electromechanical coupling factor k fully characterize this energy conversion under static conditions. In this work we show that the definition of kw as ratio of energies can also be extended to lossy materials (kw); the losses are accounted by considering comlex quantities for the elastic, dielectric and piezoelectric material constants.

coupling coefficients↗
NASA NTRS2009

Skill Assessment of a Spectral Ocean-Atmosphere Radiative Model

Ocean phytoplankton, detrital material, and water absorb and scatter light spectrally. The Ocean- Atmosphere Spectral Irradiance Model (OASIM) is intended to provide surface irradiance over the oceans with sufficient spectral resolution to support ocean ecology, biogeochemistry, and heat exchange investigations, and of sufficient duration to support inter-annual and decadal investigations. OASIM total surface irradiance (integrated 200 nm to 4 microns) was compared to in situ data and three publicly available global data products at monthly 1-degree resolution. OASIM spectrally-integrated surface irradiance had root mean square (RMS) difference= 20.1 W/sq m (about 11%), bias=1.6 W/sq m (about 0.8%), regression slope= 1.01 and correlation coefficient= 0.89, when compared to 2322 in situ observations. OASIM had the lowest bias of any of the global data products evaluated (ISCCP-FD, NCEP, and ISLSCP 11), and the best slope (nearest to unity). It had the second best RMS, and the third best correlation coefficient. OASIM total surface irradiance compared well with ISCCP-FD (RMS= 20.7 W/sq m; bias=-11.4 W/sq m, r=0.98) and ISLSCP II (RMS =25.2 W/sq m; bias= -13.8 W/sq m; r=0.97), but less well with NCEP (RMS =43.0 W/sq m ;bias=-22.6 W/sq m; x=0.91). Comparisons of OASIM photosynthetically available radiation (PAR) with PAR derived from SeaWiFS showed low bias (-1.8 mol photons /sq m/d, or about 5%), RMS (4.25 mol photons /sq m/d ' or about 12%), near unity slope (1.03) and high correlation coefficient (0.97). Coupled with previous estimates of clear sky spectral irradiance in OASIM (6.6% RMS at 1 nm resolution), these results suggest that OASIM provides reasonable estimates of surface broadband and spectral irradiance in the oceans, and can support studies on ocean ecosystems, carbon cycling, and heat exchange.

Gregg, Watson, W.↗