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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Velocity profiles of high-excitation molecular hydrogen lines

Profiles of three lines of molecular hydrogen near 2.2 microns, originating from widely spaced energy levels, have been measured at a resolution of 32 km/s at Peak 1 in the Orion molecular outflow. The three lines, 1 - 0 S(1), 2 - 1 S(1), and 3 - 2 S(3), are found to have identical profiles. This result rules out any significant contribution to the population of the higher energy levels of molecular hydrogen at Peak 1 by fluorescence, and is generally consistent with emission from multiple J-type shocks.

Moorhouse, A.↗
NASA NTRS1991

Velocity profiles in a hot jet by simplified RELIEF

Raman Excitation + Laser Induced Electronic Fluorescence (RELIEF) is a double resonance velocimetry technique in which oxygen molecules are vibrationally excited via stimulated Raman scattering at a specific location within a flow field. After suitable time delay, typically 1-10 microseconds, the displacement of the tagged molecules is determined by laser induced fluorescence imaging. Providing support for the installation of simplified RELIEF flow tagging instrumentation at NASA LaRC was the principal goal of this research.

Source record↗
NASA NTRS2011

Comparisons of Crosswind Velocity Profile Estimates Used in Fast-Time Wake Vortex Prediction Models

Five methods for estimating crosswind profiles used in fast-time wake vortex prediction models are compared in this study. Previous investigations have shown that temporal and spatial variations in the crosswind vertical profile have a large impact on the transport and time evolution of the trailing vortex pair. The most important crosswind parameters are the magnitude of the crosswind and the gradient in the crosswind shear. It is known that pulsed and continuous wave lidar measurements can provide good estimates of the wind profile in the vicinity of airports. In this study comparisons are made between estimates of the crosswind profiles from a priori information on the trajectory of the vortex pair as well as crosswind profiles derived from different sensors and a regional numerical weather prediction model.

Pruis, Mathew J.↗
DOE OSTI2025

Small-scale validation tests for MFIX-Exa CFD-DEM

This report describes several bench-scale fluidization experiments that can be used to validate the CFD-DEM method as encapsulated in the MFIX-Exa code. The five cases considered are the cold-flow fluidized beds of Müller et al., Link et al. (spout-fluid), and Goldschmidt et al. (bi-disperse), the hot fluidized bed of Patil et al., and the adsorbing fluidized bed of Li et al. and Janssen. In most cases, MFIX-Exa with “standard” or “typical” CFD-DEM settings, the Gidaspow drag model, and the Gunn heat transfer provide a relatively good prediction of the quantities considered: mean void fraction profiles, mean velocity profiles, fluctuating velocity profiles, mean particle temperature and segregation index. These results, with other verification and validation tests reported elsewhere, contribute to a body of work providing confidence and credibility in CFD predictions from the MFIX-Exa code.

97 MATHEMATICS AND COMPUTING↗
NASA NTRSDate not supplied

Velocity Measurements in the Wake of the Swept Wing Flow Test Model at the National Transonic Facility

Femtosecond laser electronic excitation tagging (FLEET) was applied to obtain flowfield velocity data for the Swept Wing Flow Test (SWiFT) at the NASA Langley Research Center National Transonic Facility (NTF). Despite numerous challenges associated with performing flow velocimetry measurements within a large-scale cryogenic wind tunnel facility, the experimental campaign was conducted under various conditions, including dry air at 320 K, cool nitrogen at 240 K, and Mach numbers of 0.2 and 0.8. FLEET velocimetry measurements were performed in the downstream wake of the SWiFT model, providing a quantitative dataset. This dataset includes one-dimensional velocity profiles and two-dimensional velocity maps acquired at different angles of attack and Reynolds numbers. The two-dimensional single component velocity maps indicate relatively uniform flow across the 120-mm wide wake flow survey suggesting that the main flow features can be represented by single-position linear velocity profiles. The measured instantaneous velocity profiles at variable angles of attack are compared to model lift coefficient information obtained at Mach 0.2. At high Reynolds numbers, a sudden velocity decrease was observed in the FLEET measurements at the same time as stall in lift coefficient was observed. At a low Reynolds number, both the velocity profiles and the lift coefficient show a smoother transition, without a sudden stall. Furthermore, the two-dimensional, one component velocity map reveals a velocity deficit region at Mach 0.8 at various angles of attack. Both single shot and mean velocity measurements were acquired allowing assessment of flowfield fluctuations and measurement precisions. The uncertainties are within 4 m/s in mean measurements based on repeatability data and about 5 m/s in instantaneous single-shot measurements. Measurements are reported with ~4.8 mm spatial resolution with 32-pixel averaging used to reduce measurement errors.

femtosecond↗
NASA NTRSDate not supplied

Velocity Measurements in the Wake of the Swept Wing Flow Test (SWIFT) Model at the National Transonic Facility

Femtosecond laser electronic excitation tagging (FLEET) was applied to obtain flowfield velocity data for the Swept Wing Flow Test (SWiFT) at the NASA Langley Research Center National Transonic Facility (NTF). Despite numerous challenges associated with performing flow velocimetry measurements within a large-scale cryogenic wind tunnel facility, the experimental campaign was conducted under various conditions, including dry air at 320 K, cool nitrogen at 240 K, and Mach numbers of 0.2 and 0.8. FLEET velocimetry measurements were performed in the downstream wake of the SWiFT model, providing a quantitative dataset. This dataset includes one-dimensional velocity profiles and two-dimensional velocity maps acquired at different angles of attack and Reynolds numbers. The two-dimensional single component velocity maps indicate relatively uniform flow across the 120-mm wide wake flow survey suggesting that the main flow features can be represented by single-position linear velocity profiles. The measured instantaneous velocity profiles at variable angles of attack are compared to model lift coefficient information obtained at Mach 0.2. At high Reynolds numbers, a sudden velocity decrease was observed in the FLEET measurements at the same time as stall in lift coefficient was observed. At a low Reynolds number, both the velocity profiles and the lift coefficient show a smoother transition, without a sudden stall. Furthermore, the two-dimensional, one component velocity map reveals a velocity deficit region at Mach 0.8 at various angles of attack. Both single shot and mean velocity measurements were acquired allowing assessment of flowfield fluctuations and measurement precisions. The uncertainties are within 4 m/s in mean measurements based on repeatability data and about 5 m/s in instantaneous single-shot measurements. Measurements are reported with ~4.8 mm spatial resolution with 32-pixel averaging used to reduce measurement errors.

Transonic↗
NASA NTRS1991

Experimental study of a vortex subjected to imposed strain

An experimental project was undertaken to investigate the character of vortex breakdown with particular regard to the waveguide theories of vortex breakdown. A rectangular wing based on the NACA 0012 airfoil was used to produce a trailing vortex which convected downstream without undergoing breakdown. Dye marked the vortex location. A disturbance was then introduced onto the vortex using a small moving wire to 'cut' the vortex. The development of upstream and downstream propagating disturbance waves was observed and the propagation velocities measured. The downstream traveling wave produced a structure similar in appearance to a vortex breakdown. The upstream wave produced a moving, swirling, turbulent region that was not a vortex breakdown. The waves moving in either direction have the same swirl velocity profiles but quite different axial velocity profiles. The upstream disturbance (turbulence) moved into a flow with an axial velocity profile that had a wake-like defect in the core region. The downstream moving vortex breakdown moved into a flow with a jet-like overshoot in the core region. The fact that no breakdown was observed for the wake-like defect and breakdown was observed for the jet-like overshoot is not consistent with computational fluid dynamics (CFD) calculations. Although there are not a lot of examples, CFD results show breakdown for both types of profiles. The longitudinal and swirl velocity profiles were documented by Laser Doppler Velocimeter (LDV) measurement. Wave velocities, swirl angles, and swirl parameters are reported.

Panton, Ronald L.↗
NASA NTRS1994

The effects of profiles on supersonic jet noise

The effect of velocity profiles on supersonic jet noise are studied by using stability calculations made for a shock-free coannular jet, with both the inner and outer flows supersonic. The Mach wave emission process is modeled as the noise generated by the large scale turbulent structures or the instability waves in the mixing region. Both the vortex-sheet and the realistic finite thickness shear layer models are considered. The stability calculations were performed for both inverted and normal velocity profiles. Comparisons are made with the results for an equivalent single jet, based on equal thrust, mass flow rate and exit area to that of the coannular jet. The advantages and disadvantages of these velocity profiles as far as noise radiation is concerned are discussed. It is shown that the Rayleigh's model prediction of the merits and demerits of different velocity profiles are in good agreement with the experimental data.

Tiwari, S. N.↗
NASA NTRS1950

Laminar mixing of a compressible fluid

A theoretical investigation of the velocity profiles for laminar mixing of a high-velocity stream with a region of fluid at rest has been made assuming that the Prandtl number is unity. A method which involves only quadratures is presented for calculating the velocity profile in the mixing layer for an arbitrary value of the free-stream Mach number. Detailed velocity profiles have been calculated for free-stream Mach numbers of 0, 1, 2, 3, and 5. For each Mach number, velocity profiles are presented for both a linear and a 0.76-power variation of viscosity with absolute temperature. The calculations for a linear variation are much simpler than those for a 0.76-power variation. It is shown that by selecting the constant of proportionality in the liner approximation such that it gives the correct value for the viscosity in the high-temperature part of the mixing layer, the resulting velocity profiles are in excellent agreement with those calculated by a 0.76-power variation.

Chapman, Dean R↗
NASA NTRS1984

Swirl, confinement and nozzle effects on confined turbulent flow

Predictions of swirl, confinement and nozzle effects on confined turbulent flow are exhibited and compared with five-hole pitot-probe time-mean velocity measurements. Two sets of computations are given, one using the standard k-epsilon turbulence model and the other using a C sub mu formulation model deduced from recent six-orientation single-wire hot-wire measurements. Results confirm that the accuracy of the latter model is superior. To highlight the effects of confinement and exit nozzle area on this flow, three expansion ratios and two contraction ratios are used. Predictions are given for a full range of swirl strengths using measured inlet conditions for axial, radial and swirl velocity profiles. The predicted velocity profiles illustrate the large-scale effects of inlet swirl on flowfields. It appears that a strong contraction nozzle has a pronounced effect, on swirl flow cases, with discouragement of central recirculation zones, and forward flow in highly swirled vortex core regions. The expansion ratio value has large-scale effects on the size and location of the recirculation zones.

Abujelala, M. T.↗
NASA NTRS1984

Experimental investigation of turbulent flow in smooth and longitudinal grooved tubes

Turbulent flow in tubes with and without longitudinal grooves is examined. The discovery of fine grooves forming a sort of streamline pattern on the body of sharks led to the expectation that the grooves on a surface reduce the momentum change, and thus the drag. To test this thesis, drag law, velocity profile and the profile of the velocity fluctuation were determined. Results show that for moderate Reynolds numbers the drag coefficient for grooved tubes is about 3 percent smaller than that of the smooth tubes. At higher Reynolds numbers, however, the drag coefficient for grooved tubes becomes larger than that for smooth tubes. No significant differences in the velocity profiles between grooved tubes and smooth tubes are found.

Nitschke, P.↗
NASA NTRS2005

Time-Averaged Velocity, Temperature and Density Surveys of Supersonic Free Jets

A spectrally resolved molecular Rayleigh scattering technique was used to simultaneously measure axial component of velocity U, static temperature T, and density p in unheated free jets at Mach numbers M = 0.6,0.95, 1.4 and 1.8. The latter two conditions were achieved using contoured convergent-divergent nozzles. A narrow line-width continuous wave laser was passed through the jet plumes and molecular scattered light from a small region on the beam was collected and analyzed using a Fabry-Perot interferometer. The optical spectrum analysis air density at the probe volume was determined by monitoring the intensity variation of the scattered light using photo-multiplier tubes. The Fabry-Perot interferometer was operated in the imaging mode, whereby the fringe formed at the image plane was captured by a cooled CCD camera. Special attention was given to remove dust particles from the plume and to provide adequate vibration isolation to the optical components. The velocity profiles from various operating conditions were compared with that measured by a Pitot tube. An excellent comparison within 5m's demonstrated the maturity of the technique. Temperature was measured least accurately, within 10K, while density was measured within 1% uncertainty. The survey data consisted of centerline variations and radial profiles of time-averaged U, T and p. The static temperature and density values were used to determine static pressure variations inside the jet. The data provided a comparative study of jet growth rates with increasing Mach number. The current work is part of a data-base development project for Computational Fluid Dynamics and Aeroacoustics codes that endeavor to predict noise characteristics of high speed jets. A limited amount of far field noise spectra from the same jets are also presented. Finally, a direct experimental validation was obtained for the Crocco-Busemann equation which is commonly used to predict temperature and density profiles from known velocity profiles. Data presented in this paper are available in ASCII format upon request.

Panda, Jayanta↗