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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1954

Aspects of internal-flow-system design for helicopter propulsive units

Pertinent items relating to the design of internal-flow systems for reciprocating engine, turbine engine, and pressure-jet installations in helicopters are discussed. The importance of the following items is emphasized: controllable exit and ram recovery for reciprocating-engine cooling; performance penalties possible in turbine-engine installations attributed to distortions in the flow distribution at the face of the axial compressor; the effects of high subsonic flow velocities on the performance of duct elements; and the effects of centrifugal forces on the flow in a ducted helicopter rotor. Data on the maximum flow capacities of bends are included.

John R Henry↗
NASA NTRS1953

A New Simple Interferometer for Obtaining Quantitatively Evaluable Flow Patterns

The method described in the present report makes it possible to obtain interferometer records with the aid of any one of the available Schlieren optics by the addition of very simple expedients, which fundamentally need not to be inferior to those obtained by other methods, such as the Mach-Zehnder interferometer, for example. The method is based on the fundamental concept of the phase-contrast process developed by Zernike, but which in principle has been enlarged to such an extent that it practically represents an independent interference method for general applications. Moreover, the method offers the possibility, in case of necessity, of superposing any apparent wedge field on the density field to be gauged. The theory is explained on a purely physical basis and illustrated and proved by experimental data. A number of typical cases are cited and some quantitative results reported.

INSTRUMENTS - INTERFEROMETERS↗
DOE OSTI2021

New Design Yields Robust Large-Area Framing Camera

Framing cameras provide a discrete series of images over a short period of time in a manner that mimics a high-speed movie camera, but with individual shutter times that must be extremely short in order to capture freeze-frame images of rapidly evolving phenomena such as high-explosive shock-driven ejecta, dynamic compression of metals, and high-velocity fluid flow. The NNSS has designed and fielded a new, large-area, gated framing camera called Kraken. The camera design emphasized manufacturability and flexibility by improving imager yield and creating a camera architecture to shorten design cycles. Design strategies and field data are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1995

Instantaneous 2D Velocity and Temperature Measurements in High Speed Flows Based on Spectrally Resolved Molecular Rayleigh Scattering

A Rayleigh scattering diagnostic for high speed flows is described for the simultaneous, instantaneous measurement of gas temperature and velocity at a number (up to about one hundred) of locations in a plane illuminated by an injection-seeded, frequency doubled Nd:YAG laser. Molecular Rayleigh scattered light is collected and passed through a planar mirror Fabry-Perot interferometer. The resulting image is analyzed to determine the gas temperature and bulk velocity at each of the regions. The Cramer Rao lower bound for measurement uncertainty is calculated. Experimental data is presented for a free jet and for preliminary measurements in the Lewis 4 inch by 10 inch supersonic wind tunnel.

Seasholtz, Richard G.↗
NASA NTRS1993

Nonintrusive, multipoint velocity measurements in high-pressure combustion flows

A combined experimental and analytical effort was conducted to demonstrate the applicability of OH Doppler-shifted fluorescence imaging of velocity distributions in supersonic combustion gases. The experiments were conducted in the underexpanded exhaust flow from a 6.8 atm, 2400 K, H2-O2-N2 burner exhausting into the atmosphere. In order to quantify the effects of in-plane variations of the gas thermodynamic properties on the measurement accuracy, a set of detailed measurements of the OH (1,0) band collisional broadening and shifting in H2-air gases was produced. The effect of pulse-to-pulse variations in the dye laser bandshape was also examined in detail and a modification was developed which increased in the single pulse bandwidth, thereby increasing the intraimage velocity dynamic range as well as reducing the sensitivity of the velocity measurement to the gas property variations. Single point and imaging measurements of the velocity field in the exhaust flowfield were compared with 2D, finite-rate kinetics simulations of the flowfield. Relative velocity accuracies of +/- 50 m/s out of 1600 m/s were achieved in time-averaged imaging measurements of the flow over an order of magnitude variation in pressure and a factor of two variation in temperature.

Allen, M.↗
NASA NTRS1988

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for high Reynolds number laminar flows

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.

Kim, Sang-Wook↗
NASA NTRS2003

Investigation of Critical Heat Flux in Reduced Gravity Using Photomicrographic Techniques

Experiments were performed to examine the effects of body force on flow boiling critical heat flux (CHF). FC-72 was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface just prior to CHF. High-speed video imaging techniques were used to identify dominant CHF mechanisms corresponding to different flow orientations and liquid velocities. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed significant sensitivity to orientation for flow velocities below 0.2 m/s, where extremely low CHF values where measured, especially with downward-facing heated wall and downflow orientations. High flow velocities dampened the effects of orientation considerably. The CHF data were used to assess the suitability of previous CHF models and correlations. It is shown the Interfacial Lift-off Model is very effective at predicting CHF for high velocities at all orientations. The flooding limit, on the other hand, is useful at estimating CHF at low velocities and for downflow orientations. A new method consisting of three dimensionless criteria is developed for determining the minimum flow velocity required to overcome body force effects on near-saturated flow boiling CHF. Vertical upflow boiling experiments were performed in pursuit of identifying the trigger mechanism for subcooled flow boiling CHF. While virtually all prior studies on flow boiling CHF concern the prediction or measurement of conditions that lead to CHF, this study was focused on events that take place during the CHF transient. High-speed video imaging and photomicrographic techniques were used to record the transient behavior of interfacial features from the last steady-state power level before CHF until the moment of power cut-off following CHF. The video records show the development of a wavy vapor layer which propagates along the heated wall, permitting cooling prior to CHF only in wetting fronts corresponding to the wave troughs. Image analysis software was developed to estimate void fraction from the individual video images. The void fraction records for subcooled flow boiling show the CHF transient is accompanied by gradual lift-off of wetting fronts culminating in some maximum vapor layer mean thickness, following which the vapor layer begins to thin down as the transition to film boiling ensues. This study proves the Interfacial Lift-off Model, which has been validated for near-saturated flow boiling CHF, is equally valid for subcooled conditions.

Mudawar, Issam↗
NASA NTRS1995

The Dynamics of Rapidly Emplaced Terrestrial Lava Flows and Implications for Planetary Volcanism

The Kaupulehu 1800-1801 lava flow of Hualalai volcano and the 1823 Keaiwa flow from the Great Crack of the Kilauea southwest rift zone had certain unusual and possibly unique properties for terrestrial basaltic lava flows. Both flows apparently had very low viscosities, high effusion rates, and uncommonly rapid rates of advance. Ultramafic xenolith nodules in the 1801 flow form stacks of cobbles with lava rinds of only millimeter thicknesses. The velocity of the lava stream in the 1801 flow was extremely high, at least 10 m/s (more than 40 km/h). Observations and geological evidence suggest similarly high velocities for the 1823 flow. The unusual eruption conditions that produced these lava flows suggest a floodlike mode of emplacement unlike that of most other present-day flows. Although considerable effort has gone into understanding the viscous fluid dynamics and thermal processes that often occur in basaltic flows, the unusual conditions prevalent for the Kaupulehu and Keaiwa flows necessitate different modeling considerations. We propose an elementary flood model for this type of lava emplacement and show that it produces consistent agreement with the overall dimensions of the flow, channel sizes, and other supporting field evidence. The reconstructed dynamics of these rapidly emplaced terrestrial lava flows provide significant insights about the nature of these eruptions and their analogs in planetary volcanism.

Baloga, Stephen↗
NASA NTRS2012

Multi-Component, Multi-Point Interferometric Rayleigh/Mie Doppler Velocimeter

An interferometric Rayleigh scattering system was developed to enable the measurement of multiple, orthogonal velocity components at several points within very-high-speed or high-temperature flows. The velocity of a gaseous flow can be optically measured by sending laser light into the gas flow, and then measuring the scattered light signal that is returned from matter within the flow. Scattering can arise from either gas molecules within the flow itself, known as Rayleigh scattering, or from particles within the flow, known as Mie scattering. Measuring Mie scattering is the basis of all commercial laser Doppler and particle imaging velocimetry systems, but particle seeding is problematic when measuring high-speed and high-temperature flows. The velocimeter is designed to measure the Doppler shift from only Rayleigh scattering, and does not require, but can also measure, particles within the flow. The system combines a direct-view, large-optic interferometric setup that calculates the Doppler shift from fringe patterns collected with a digital camera, and a subsystem to capture and re-circulate scattered light to maximize signal density. By measuring two orthogonal components of the velocity at multiple positions in the flow volume, the accuracy and usefulness of the flow measurement increase significantly over single or nonorthogonal component approaches.

Danehy, Paul M.↗
NASA NTRSDate not supplied

Velocity and Temperature Measurements in High-speed Flows with Naturally Present Dust Particles Using Rayleigh and Mie Scattering

Dust particles and occasional moisture condensations are unavoidable reality of all wind tunnels. On the path to pursue a goal of velocity and temperature measurements in high-speed wind tunnels we have created a tabletop, spectrally resolved, Rayleigh-Mie scattering setup around a small jet fed by ambient and air with different particle concentration to determine the accuracy of the technique. The other reality of a wind tunnel setup is the spurious reflection and scattering of the incident laser beam by solid surfaces (flare light), which contaminates the Rayleigh-Mie scattered light. This is simulated by backgrounds with different reflectivity towards the collection optics. Light from a CW laser is delivered via an optical fiber and the scattered light from a point on the laser path is spectrally resolved using a stabilized Fabry-Perot interferometer, followed by imaging on an EMCCD camera. A model of the combined background glare, Mie scattering, and the Rayleigh spectrum was fitted to the camera image using maximum likelihood estimation. It was observed that the present modeling approach can extract velocity and temperature with reasonable accuracy when the intensity of the Mie scattered light is less than or comparable to that of the Rayleigh scattered light; beyond that error in velocity measurement remains reasonable ±12m/s but the temperature measurement becomes progressively more inaccurate. Increasingly the flare light is found to cause a bias error in velocity. Similar trend is observed in the presence of both the flare light and the Mie scattered light. The setup has provided a set of data for the future improvement of the modeling procedure, and demonstrated that even in the case of large amount of dust particles and large flare light the present technique can provide measurement of velocity with reasonable accuracy.

Rayleigh scattering↗
NASA NTRS2001

Rayleigh Scattering Diagnostic for Dynamic Measurement of Velocity Fluctuations in High Speed Jets

A flow diagnostic technique based on the molecular Rayleigh scattering of laser light is used to obtain dynamic density and velocity data in a high speed flow. The technique is based on analyzing the Rayleigh scattered light with a Fabry-Perot interferometer used in the static, imaging mode. An analysis is presented that established a lower bound for measurement uncertainty of about 20 m/sec for individual velocity measurements obtained in a 100 microsecond time interval. Software and hardware interfaces were developed to allow computer control of all aspects of the experiment and data acquisition. The signals from three photomultiplier tubes were simultaneously recorded using photon counting at a 10 kHz sampling rate and 10 second recording periods. Density and velocity data, including distribution functions and power spectra, taken in a Mach 0.8 free jet, are presented.

Seasholtz, Richard G.↗