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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

An Experimental Study of Small-Scale Variability of Raindrop Size Distribution

An experimental study of small-scale variability of raindrop size distributions (DSDs) has been carried out at Wallops Island, Virginia. Three Joss-Waldvogel disdrometers were operated at a distance of 0.65, 1.05, and 1.70 km in a nearly straight line. The main purpose of the study was to examine the variability of DSDs and its integral parameters of liquid water content, rainfall, and reflectivity within a 2-km array: a typical size of Cartesian radar pixel. The composite DSD of rain events showed very good agreement among the disdrometers except where there were noticeable differences in midsize and large drops in a few events. For consideration of partial beam filling where the radar pixel was not completely covered by rain, a single disdrometer reported just over 10% more rainy minutes than the rainy minutes when all three disdrometers reported rainfall. Similarly two out of three disdrometers reported5%more rainy minutes than when all three were reporting rainfall. These percentages were based on a 1-min average, and were less for longer averaging periods. Considering only the minutes when all three disdrometers were reporting rainfall, just over one quarter of the observations showed an increase in the difference in rainfall with distance. This finding was based on a 15-min average and was even less for shorter averaging periods. The probability and cumulative distributions of a gamma-fitted DSD and integral rain parameters between the three disdrometers had a very good agreement and no major variability. This was mainly due to the high percentage of light stratiform rain and to the number of storms that traveled along the track of the disdrometers. At a fixed time step, however, both DSDs and integral rain parameters showed substantial variability. The standard deviation (SD) of rain rate was near 3 mm/h, while the SD of reflectivity exceeded 3 dBZ at the longest separation distance. These standard deviations were at 6-min average and were higher at shorter averaging periods. The correlations decreased with increasing separation distance. For rain rate, the correlations were higher than previous gauge-based studies. This was attributed to the differences in data processing and the difference in rainfall characteristics in different climate regions. It was also considered that the gauge sampling errors could be a factor. In this regard, gauge measurements were simulated employing existing disdrometer dataset. While a difference was noticed in cumulative distribution of rain occurrence between the simulated gauge and disdrometer observations, the correlations in simulated gauge measurements did not differ from the disdrometer measurements.

Tokay, Ali↗
NASA NTRS1995

Study of Structure and Small-Scale Fragmentation in TMC-1

Large-scale C(sup 18)O maps show that the Taurus molecular cloud 1 (TMC-1) has numerous cores located along a ridge which extends about 12 minutes by at least 35 minutes. The cores traced by C(sup 18)O are about a few arcminutes (0.1-0.2 pc) in extent, typically contain about 0.5-3 solar mass, and are probably gravitationally bound. We present a detailed study of the small-scale fragmentary structure of one of these cores, called core D, within TMC-1 using very high spectral and spatial resolution maps of CCS and CS. The CCS lines are excellent tracers for investigating the density, temperature, and velocity structure in dense cores. The high spectral resolution, 0.008 km /s, data consist mainly of single-dish, Nyquist-sampled maps of CCS at 22 GHz with 45 sec spatial resolution taken with NASA's 70 m DSN antenna at Goldstone. The high spatial resolution spectral line maps were made with the Very Large Array (9 sec resolution) at 22 GHz and with the OVRO millimeter array in CCS and CS at 93 GHz and 98 GHz, respectively, with 6 sec resolution. These maps are supplemented with single-dish observations of CCS and CC(sup 34)S spectra at 33 GHz using a NASA 34 m DSN antenna, CCS 93 GHz, C(sup 34)S (2-1), and C(sup 18)O (1-0) single-dish observations made with the AT&T Bell Laboratories 7 m antenna. Our high spectral and spatial CCS and CS maps show that core D is highly fragmented. The single-dish CCS observations map out several clumps which range in size from approx. 45 sec to 90 sec (0.03-0.06 pc). These clumps have very narrow intrinsic line widths, 0.11-0.25 km/s, slightly larger than the thermal line width for CCS at 10 K, and masses about 0.03-0.2 solar mass. Interferometer observations of some of these clumps show that they have considerable additional internal structure, consisting of several condensations ranging in size from approx. 10 sec- 30 sec (0.007-0.021 pc), also with narrow line widths. The mass of these smallest fragments is of order 0.01 solar mass. These small-scale structures traced by CCS appear to be gravitationally unbound by a large factor. Most of these objects have masses that fall below those of the putative proto-brown dwarfs (approx. less than 0.1 solar mass). The presence of many small gravitationally unbound clumps suggests that fragmentation mechanisms other than a purely Jeans gravitational instability may be important for the dynamics of these cold dense cores.

Langer, W. D.↗
NASA NTRS2003

Small-Scale Interstellar Structure Toward the Open Cluster CHI Persei-Fuse II

The purpose of this study was to measure the physical conditions of gas along sight lines toward 6 stars in the core Chi Persei open cluster. These sight lines traverse gas in both the Orion and Perseus spiral arms of the Galaxy, at distances of 500 and 2000 pc, respectively. The stars have angular separations ranging from 45 to 280 arcsec; 60 arcsec corresponds to linear distances of 0.15 and 0.6 pc in the two arms. Thus, abundance variations in these observations would constitute evidence for small-scale variations in the properties of the interstellar medium. Ground-based Na I observations at high resolution (approx. 15 km/sec) toward 172 stars (including the 6 in this study) in the double open cluster h and Chi Persei have revealed complex spatial variation. These variations are especially evident in the gas at velocities of -40 and -55 km/sec, corresponding to the Perseus spiral arm. 21 cm observations of HI emission using the Low Resolution DRAO Survey, with a 12-arcmin beam, also show variations. Averaging the Na I apparent optical depth profiles of neighboring sight lines in order to mimic such a beam size reduces the variation, as compared to the individual Na I measurements, but still show variations larger than seen in the 21 cm profiles. Na I is not the dominant ionization state of Na in the interstellar medium. Thus, it is possible that the variations seen really trace physical structures in the interstellar medium, or they may simply result from variations in the radiation field seen by the gas, or be due to some other environmental circumstance. To distinguish among these possibilities in the present study we obtained FUSE spectra toward the 6 targets in order to measure the molecular hydrogen absorption profiles along these sight lines. The higher J states of H2 are populated by the ambient W radiation field, and thus can provide insight into the environment affecting the gas. If both the high and low J states reveal absorption line profiles with variations similar to that observed in Na I, this would indicate that the variations are due to real structures in the interstellar medium. On the other hand, if the only the high J profiles mimicked the Na I profiles, then the variations may be attributable to environmental effects. We found that the H2 profiles showed considerable variation over the 6 sight lines, and that the profiles, despite having somewhat lower velocity resolution, resemble the Na I profiles. Thus, it appears that the gas really does exhibit variations in physical structures along these sight lines. Useful follow-up work would be to obtain higher signal-to-noise FUSE observations of H2, since the present data are of only moderate quality, and to obtain data on additional targets in this double cluster, in order to map out in more detail the extent and magnitude of the small-scale variations.

Sonneborn, George↗
NASA NTRS1976

Small-scale test program to develop a more efficient swivel nozzle thrust deflector for V/STOL lift/cruise engines

The installed performance degradation of a swivel nozzle thrust deflector system obtained during increased vectoring angles of a large-scale test program was investigated and improved. Small-scale models were used to generate performance data for analyzing selected swivel nozzle configurations. A single-swivel nozzle design model with five different nozzle configurations and a twin-swivel nozzle design model, scaled to 0.15 size of the large-scale test hardware, were statically tested at low exhaust pressure ratios of 1.4, 1.3, 1.2, and 1.1 and vectored at four nozzle positions from 0 deg cruise through 90 deg vertical used for the VTOL mode.

Schlundt, D. W.↗
NASA NTRS1990

IAPSA 2 small-scale system specification

The details of a hardware implementation of a representative small scale flight critical system is described using Advanced Information Processing System (AIPS) building block components and simulated sensor/actuator interfaces. The system was used to study application performance and reliability issues during both normal and faulted operation.

Cohen, Gerald C.↗
NASA NTRS1994

Study of noise on a small-scale hovering tilt rotor

A study of the noise from a small-scale, semi-span test of a hovering tilt rotor is presented. The effect on noise of the tilt rotor fountain and of several tilt rotor configuration changes is examined. Measurments were made of an isolated rotor; rotor and wing; rotor and image plane; and rotor, wing and image plane. This last configuration models a tilt rotor. With a tilt rotor, the wing turns some of the rotor downwash inboard. When the flows meet, some of the flow is forced upward creating a fountain. Some of the fountain is ingested into the rotor disc. Rotor fountain interactions produce very unsteady impulsive noise to the rear of the aircraft. Configuration changes to investigate download reduction included increasing the rotor/wing separation, deflecting the flap, adding the nacelle, adding vortex trapping plates and blowing on the upper surface. These configuration changes produced little or no effect on the noise, although they changed the net download. Increasing the wing span, however, reduced the annoying content of this impulse noise about 2dB.

Mosher, Marianne↗
NASA NTRS2007

Small Scale Response and Modeling of Periodically Forced Turbulence

The response of the small scales of isotropic turbulence to periodic large scale forcing is studied using two-point closures. The frequency response of the turbulent kinetic energy and dissipation rate, and the phase shifts between production, energy and dissipation are determined as functions of Reynolds number. It is observed that the amplitude and phase of the dissipation exhibit nontrivial frequency and Reynolds number dependence that reveals a filtering effect of the energy cascade. Perturbation analysis is applied to understand this behavior which is shown to depend on distant interactions between widely separated scales of motion. Finally, the extent to which finite dimensional models (standard two-equation models and various generalizations) can reproduce the observed behavior is discussed.

Bos, Wouter↗
NASA NTRS1986

Small-scale motions observed by aircraft in the tropical lower stratosphere - Evidence for mixing and its relationship to large-scale flows

Measurements of temperature and ozone from instrumented aircraft in the tropical lower stratosphere show the presence of small-scale disturbances generated by underlying cumulus convection and Kelvin-Helmholtz instability. The disturbances associated with underlying convection have peak-to-peak vertical parcel excursions of about 300 m. Flying conditions were smooth, suggesting an ensemble of gravity waves and little or no turbulent mixing. It is nevertheless possible that these waves break at other altitudes, leading to turbulent mixing and net fluxes of vertically stratified tracers. Disturbances attributed to KH instability implied vertical parcel excursions of 300-400 m. The disturbances coincided with rough flying conditions, suggesting turbulent mixing. A linear stability analysis of the atmospheric basic state defined by high-resolution radiosondes shows fastest growing waves with horizontal wavelengths of 1.4-1.8 km, consistent with the aircraft observations. The strong shears responsible for the KH instability are due to large-scale waves propagating into a region of small intrinsic frequency. Radiosonde observations show that the zonal length scale of these waves is about 1000 km.

Pfister, Leonhard↗
NASA NTRS1974

Limitations to the small scale yielding approximation for crack tip plasticity

Recent finite-element results by S. G. Larsson and A. J. Carlsson suggest a limited range of validity to the 'small scale yielding approximation,' whereby small crack tip plastic zones are correlated in terms of the elastic stress intensity factor. It is shown with the help of a model for plane strain yielding that their results may be explained by considering the non-singular stress, acting parallel to the crack at its tip, which accompanies the inverse square-root elastic singularity. Further implications of the non-singular stress term for crack tip deformations and fracturing are examined. It is suggested that its effect on crack tip parameters, such as the opening displacement and J-integral, is less pronounced than its effect on the yield zone size.

Rice, J. R.↗
NASA NTRS1970

A semi-operational agricultural inventory using small scale aerial photography

The feasibility of performing inventories of agricultural resources using very small scale aerial or space photography was studied. The results were encouraging on two counts: (1) The very practical problems of an operational survey are being faced and solutions are being found. (2) It seems that a fully operational agricultural inventory using space photography is not beyond the scope of present technology.

Draeger, W. C.↗
NASA NTRS1974

Observations of small-scale turbulence in the atmosphere of Venus by Mariner 5

Information regarding small-scale turbulence in the Venus atmosphere is important and desirable because it contributes to understanding of the atmosphere's circulation. It is demonstrated that the radio occultation data of a flyby spacecraft such as Mariner 5 can provide valuable information on turbulence in the Venus atmosphere. Unlike previous studies of the Mariner 5 data, this paper is based on the frequency spectrum rather than the variance of the log-amplitude fluctuations. The excellent agreement between the processed and previously derived theoretical spectra furnishes strong evidence that the Mariner 5 fluctuations are primarily turbulence-induced. It is seen that, above 35 km, turbulence is strongest in the vicinity of 45 and 60 km, and that the outer scale of turbulence is of the order of 100 m. Comparison with the results obtained from the Venera missions is also discussed.

Woo, R.↗
NASA NTRS1974

Small-scale yielding analysis of mixed mode plane-strain crack problems

The small-scale yielding analysis of an elastic-plastic body with a line crack under plane-strain conditions subject to combinations of Mode I and II loadings is examined. The analysis of the near-tip field follows the works of Hutchinson and Rice and Rosengren. Dominant singularity solutions governing the asymptotic behavior of the stresses and strains at the crack tip are obtained for the complete range of loadings between Mode I and II. The results of an accurate finite element technique, which imbeds the dominant singularity solutions, directly relates the near-tip behavior to the elastic stress intensity factors K(I) and K(II). Implications of this study to mixed mode fracture mechanics is also discussed, particularly with respect to the direction of crack initiation and the relation of fracture toughness under mixed modes to that in Mode I. Details of the mixed mode plastic zone sizes and shapes are also given.

Shih, C. F.↗
NASA NTRS1976

Effect of simulated forward airspeed on small-scale-model externally blown flap noise

Noise tests were conducted on a small-scale model of an externally blown flap lift augmentation system. The nozzle/wing model was subjected to external flow that simulated takeoff and landing flight velocities by placing it in a 33-centimeter-diameter free jet. The results showed that external flow attenuated the noise associated with the various configurations tested. The amount of attenuation depended on flap setting. More attenuation occurred with a trailing-flap setting of 20 deg than with one of 60 deg. Noise varied with relative velocity as a function of the trailing-flap setting and the angle from the nozzle inlet.

Goodykoontz, J. H.↗
NASA NTRS1996

Comparison of the Aeroacoustics of Two Small-Scale Supersonic Inlets

An aerodynamic and acoustic investigation was performed on two small-scale supersonic inlets to determine which inlet would be more suitable for a High Speed Civil Transport (HSCT) aircraft during approach and takeoff flight conditions. The comparison was made between an axisymmetric supersonic P inlet and a bifurcated two-dimensional supersonic inlet. The 1/14 scale model supersonic inlets were used in conjunction with a 4.1 in (10.4 cm) turbofan engine simulator. A bellmouth was utilized on each inlet to eliminate lip separation commonly associated with airplane engine inlets that are tested under static conditions. Steady state measurements of the aerodynamic flowfield and acoustic farfield were made in order to evaluate the aeroacoustic performance of the inlets. The aerodynamic results show the total pressure recovery of the two inlets to be nearly identical, 99% at the approach condition and 98% at the takeoff condition. At the approach fan speed (60% design speed), there was no appreciable difference in the acoustic performance of either inlet over the entire 0 deg to 110 deg farfield measurement sector. The inlet flow field results at the takeoff fan speed (88% design speed), show the average inlet throat Mach number for the P inlet (Mach 0.52) to be approximately 2 times that of the 2D inlet (Mach 0.26). The difference in the throat Mach number is a result of the smaller throughflow area of the P inlet. This reduced area resulted in a 'soft choking' of the P inlet which lowered the tone and overall sound pressure levels of the simulator in the forward sector by an average of 9 dB and 3 dB, respectively, when compared to the 2D inlet.

Ng, Wing↗
NASA NTRS1985

Small-scale cyclones on the periphery of a Gulf Stream warm-core ring

Small-scale cyclones found around Gulf Stream warm-core ring 82B are investigated by using infrared satellite images and current information obtained with an acoustic-Doppler velocimeter. Currents in these cyclones reveal speeds ranging from 20 to 80 cm/s. One small cyclone or 'ringlet' found in June 1982 was studied extensively by removing the basic rotational velocities of 82B. The azimuthal velocity field for this ringlet was used with the gradient current equation to calculate the absolute dynamic topography at 100 dbar. It was found that the ringlet was 13 dyn-cm lower than its surroundings. In addition, neglect of the centrifugal term would have changed the dynamic topography of the ringlet by 30 percent. From a comparison with CTD data the absolute reference level was determined, and a vertical profile of horizontal currents was calculated for the ringlet. Other cyclones were found throughout the slope water region around warm-core ring 82B with observable lifetimes of 1 to 2 weeks. The northeast quadrant of 82B was a favored generation site for ringlets. Two cyclones were observed to form in this region and were advected anticyclonically around 82B. Typically, at any one time, six cyclones with diameters of approximately 40 to 50 km can be detected north of the Gulf Stream by using satellite images.

Kennelly, M. A.↗
NASA NTRSDate not supplied

Observations and 3D MHD Modeling of Small-scale Solar Prominence Oscillations

Small scaleoscillations were recently observed in prominences with high resolution Hinode/SOT and IRIS SJI in unprecedented detailand identified as fast magnetosonic waves. The high-resolution observations provide evidence of flows of cool material, fluid instabilities such as Kelvin-Helmholtz and Rayleigh-Taylor, and the spectroscopic information provides evidence of Doppler shifts, heating, and cooling of the prominence material. Recently nonlinear fast magnetosonic waves were observed withperiods in the range of 5–11 minutes and wavelengths in the plane of the sky (POS) of ~2000kmand flows, and the flows in narrow threads withPOS speed ∼16–46 km/s. Thenonlinear fast magnetosonic waves and flows were modeled using 2.5D MHD (Ofman & Kucera 2020). Here, we extend the studyof the nonlinear fast magnetosonic waves using more realistic 3D MHD model. The model includes the 3D structure of the density and the magnetic fieldas well as mode coupling anddemonstrate the propagating density compressions associated with the nonlinear fast magnetosonicwaves, as well as the guided modesin the pillar. The 3DMHD modelingimprove understanding ofthe POSeffects in limb prominence oscillations observations.The results of the modeling are useful for coronal seismology of the prominence structure.

Leon Ofman↗