4,856 research outputs found
Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone
Transition and fluctuating surface pressure data were acquired on a 10 deg included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot-pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number RE(T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M(e) = 1.2. Above M(e) = 1.2, however, this correlation deteriorates, with the flight Re(T) being 25 to 30% higher than the wind tunnel Re(T) at M(e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations, according to the equation used. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels
TAIR: A transonic airfoil analysis computer code
The operation of the TAIR (Transonic AIRfoil) computer code, which uses a fast, fully implicit algorithm to solve the conservative full-potential equation for transonic flow fields about arbitrary airfoils, is described on two levels of sophistication: simplified operation and detailed operation. The program organization and theory are elaborated to simplify modification of TAIR for new applications. Examples with input and output are given for a wide range of cases, including incompressible, subcritical compressible, and transonic calculations
An X-Ray Jet from a White Dwarf - Detection of the Collimated Outflow from CH Cygni with Chandra
Most symbiotic stars consist of a white dwarf accreting material from the
wind of a red giant. An increasing number of these objects have been found to
produce jets. Analysis of archival Chandra data of the symbiotic system CH
Cygni reveals faint extended emission to the south, aligned with the optical
and radio jets seen in earlier HST and VLA observations. CH Cygni thus contains
only the second known white dwarf with an X-ray jet, after R Aquarii. The
X-rays from symbiotic-star jets appear to be produced when jet material is
shock-heated following collision with surrounding gas, as with the outflows
from some protostellar objects and bipolar planetary nebulae.Comment: 4 & a bit pages, 4 figures, accepted by ApJL; uses emulateapj.cls and
revtex4. Minor changes following referees report, & shortened to meet page
limi
Paper Session I-B - Computational Fluid Dynamics Analysis of Space Shuttle Vehicle and Exhaust Plume Flows at High Altitude Flight Conditions
Computational fluid dynamics (CFD) analysis has provided verification of Space Shuttle flight performance details and is being applied to performance predictions with Advanced Solid Rocket Motors (ASRM\u27s) scheduled to begin operation in 1997. Advancements in CFD methodology described herein have allowed definition of exhaust plume flow details completing the capability for \u27nose-to-plume\u27 simulation. CFD predictions of the Space Shuttle vehicle aerodynamic performance at Mach 3.5 and 107,000 ft with ASRM\u27s confirm no adverse effects for high-altitude flight conditions
Techniques development for whale migration tracking
Effort leading to the completion of development and fabrication of expansible whale harnesses and whale-carried instrument pods is described, along with details of the gear. Early preparative effort for a January-February 1974 field expedition is reported
Origin of the transient unpulsed radio emission from the PSR B1259-63 binary system
We discuss the interpretation of transient, unpulsed radio emission detected
from the unique pulsar/Be-star binary system PSR B1259-63. Extensive monitoring
of the 1994 and 1997 periastron passages has shown that the source flares over
a 100-day interval around periastron, varying on time-scales as short as a day
and peaking at 60 mJy (~100 times the apastron flux density) at 1.4 GHz.
Interpreting the emission as synchrotron radiation, we show that (i) the
observed variations in flux density are too large to be caused by the shock
interaction between the pulsar wind and an isotropic, radiatively driven,
Be-star wind, and (ii) the radio emitting electrons do not originate from the
pulsar wind. We argue instead that the radio electrons originate from the
circumstellar disk of the Be star and are accelerated at two epochs, one before
and one after periastron, when the pulsar passes through the disk. A simple
model incorporating two epochs of impulsive acceleration followed by
synchrotron cooling reproduces the essential features of the radio light curve
and spectrum and is consistent with the system geometry inferred from pulsed
radio data.Comment: To be published in Astrophysical Journal Letters 7 pages, 1
postscript figur
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
Precipitation Event Size Controls on Long-Term Abundance of \u3ci\u3eOpuntia Polyacantha\u3c/i\u3e (Plains Prickly-Pear) in Great Plains Grasslands
Opuntia polyacantha Haw. (plains prickly-pear) is a common cactus in the Great Plains of North America. We used two data sets, from Montana and Colorado, to test the hypothesis that there is a range of precipitation event sizes upon which O. polyacantha specializes. Events smaller than this range (\u3e2 to ≤6 mm) do not moisten sufficient soil to be utilized, and larger events have negative effects on the status of O. polyacantha because they favor the development of taller and denser grass canopies. Multiple regressions of either green cladode density (northern mixed prairie) or O. polyacantha frequency (shortgrass steppe) with precipitation event sizes indicated negative effects of large precipitation events on the yearly changes in the either density or frequency of O. polyacantha. We suggest that weather conditions in the Great Plains may cause O. polyacantha to be controlled almost entirely by light competition from grasses and other negative biotic effects
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