Dropkin A.,Naval Undersea Warfare Center |
Custodio D.,Worcester Polytechnic Institute |
Henoch C.W.,Naval Undersea Warfare Center |
Henoch C.W.,Research Engineer |
And 2 more authors.
Journal of Aircraft | Year: 2012
The flowfield and the aerodynamic forces on a two-dimensional airfoil with sinusoidal leading-edge protuberances were computed numerically and compared with the baseline NACA 634-021 airfoil. The amplitude and wavelength of the sinusoidal leading edge were 12 and 50% of the mean chord length. The sinusoidal leading-edge airfoil is dominated by the flow around and over the protuberances at all angles of attack, resulting in significant spanwise variation in all flow properties, in contrast to the baseline airfoil. The surface-pressure distribution on the modified airfoil consists of low-pressure pockets in the troughs that are symmetric and periodic at low angles of attack, and evolve into complicated patterns at higher angles. The low-pressure pockets persist to high angles of attack, resulting in the continued increase of lift. The modified airfoil has lower lift and higher drag in the prestall regime. The lift and drag characteristics at high angles of attack, as well as the dependence on Reynolds number, are addressed in this study. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.
Viviani A.,The Second University of Naples |
Pezzella G.,Centro Italiano Ricerche Aerospaziali |
Pezzella G.,Research Engineer
Journal of Spacecraft and Rockets | Year: 2010
This paper deals with aerodynamic and aerothermodynamic studies carried out to design a capsule vehicle suitable for the recovery of crew members from the International Space Station and/or from exploration missions to the moon or Mars. An integrated design tool called ENTRY is used to support vehicle reentry analysis and computational fluid dynamics design activities. A possible low-Earth-orbit reentry scenario, with the associated aeroheating environment, is generated and then analyzed. Several Euler and Navier-Stokes computations are performed to simulate the flowfleld past the vehicle, for both perfect-gas and nonequilibrium reacting-gas models for the air. Numerical results and their comparison with flight data and wind-tunnel data are presented. An analysis of flowflelds, obtained from numerical computations, is provided by means of flight forces and moments coefficients. Experimentally measured surface pressure distributions and aerodynamic coefficients compare rather well with numerical results.
Reynier P.,Research Engineer
Acta Astronautica | Year: 2013
During a planetary entry, the decomposition of the thermal protection system material resin by the pyrolysis process produces strong blowing gases that are injected into the boundary layer. Induced by the blowing gas, the blockage phenomenon has a strong effect on the level of heat-fluxes. For some entries, such as Earth super-orbital re-entries characteristic of sample return missions, blockage is one of the key issues that have to be addressed. Additionally, this phenomenon is strongly linked to turbulence and to the porous aspects of the ablative material. Here, experimental, numerical and flight data available for different missions, involving high level of heat-.uxes, are gathered and discussed. The models for convective blockage found in the literature have been reviewed in order to select a generic way to estimate this phenomenon. It appears from this study that the convective blockage is still not fully understood and that there is no established approach for its accurate modelling since most of the existing correlations possess a high degree of empiricism. & 2012 Elsevier Ltd. All rights reserved.
Vukasinovic B.,Georgia Institute of Technology |
Vukasinovic B.,Research Engineer |
Glezer A.,Georgia Institute of Technology |
Gordeyev S.,University of Notre Dame |
And 2 more authors.
AIAA Journal | Year: 2011
Effects of hybrid flow control and its active and passive components on the aerodynamic characteristics of flow over a 0.254-m-diam conformal optical aperture embedded in the hemispherical cap of a cylinder turret model (D= 0:61 m) are investigated at M= 0:3-0:5 and Re D= 4:4-7:4× 10 6. Resulting mean flows are characterized by surface static pressure distributions and oil-flow visualizations, while the separated-flow dynamics are assessed by hot-film measurements. Active flow control is effected by arrays of piezoelectrically driven synthetic jet modules distributed in multiple arrays upstream from the aperture. Active flow control is further assisted by global flow alterations induced by a passive forward partition plate, and, when combined, constitute hybrid flow control. It is shown that the hybrid flow control combines the positive effects of its component control elements to yield superior results in any cumulative aerodynamic aspect of the separated flow. This cumulative effect of the actuation is manifested by concomitant delay of flow separation and active, dissipative suppression of turbulent motions downstream of separation. It is also demonstrated by means of direct two-dimensional wave-front measurements that the overall aerodynamic improvements correlate with substantial suppression of optical aberrations through the separated flow. Furthermore, estimated Strehl ratios for the laser beam indicate that nearly invariant Strehl ratio is established within the range of tested aperture elevation angles, yielding improvement of about50%for the highest elevation angle. © 2011 by B.Vukasinovic, A. Glezer, S. Gordeyev, E. Jumper, and V. Kibens.
A view from the Experimental Zone floor of the ALPHA-2 Cryostat and external solenoid assembly, with control and data acquisition electronics located on the overhead platform above the cryostat. Credit: Photo by Robert Thompson, ALPHA-2 member, University of Calgary Scientists of the international ALPHA Collaboration have once again pushed the boundaries of antimatter research with their latest breakthrough studying the properties of antihydrogen. Published today in the prestigious journal Nature, the collaboration's result improved the measurement of the charge of antihydrogen, essentially zero, by a factor of 20. Their work is the latest contribution in the quest to chase down the answer to the basic antimatter question, "If matter and antimatter were created in equal amounts during the Big Bang, where did all the antimatter go?" "That means the electrical charge of antihydrogen - the antimatter analogue of hydrogen - can be ruled out as the answer to the antimatter question," says York University Professor Scott Menary, an ALPHA member. "The point of the experiment was to search for a clue as to how or where our predictions of nature are wrong," continues Menary. "Something is missing in our understanding otherwise the matter and antimatter at the Big Bang would have annihilated each other and there would be no universe today. The interactions of matter and antimatter must somehow be different." Physics dictates that for every particle of matter there is an oppositely charged antiparticle with an equal mass. An antihydrogen atom should have the exact same charge as hydrogen (zero). That's because the antiproton and antielectron (positron), which make up antihydrogen, should have the exact opposite charge of the proton and electron that make up hydrogen. Dr. Andrea Capra, a former PhD student of Menary's (now at TRIUMF) who played a major role in the analysis behind this result, says, "We take the charge of matter and antimatter for granted, however, you cannot analyze data or make an experiment assuming it's true." This result showed that antihydrogen and hydrogen are indeed both electrically neutral at a level 20 times more precise than before. Since the antiproton charge is also known to a similar precision, the collaboration also has improved the previous best precision on the positron charge by a factor of 25. While both results uphold the Standard Model, they have constrained what possible extensions to it could be. Capra points out that this work addresses one piece of a larger puzzle. When comparing normal matter to antimatter, he says that "there is the piece comparing their charges, the piece comparing their light spectrums, and the piece comparing how they respond to gravity." The latter piece will be investigated by a dedicated experiment, ALPHA-g, spearheaded by the University of Calgary and including the Canadian members of the collaboration. The experiment was the first using the upgraded "ALPHA-2" system which began operation last year. The largest component, the cooling cryostat, was designed and built at TRIUMF and the University of Calgary by a team led by Mechanical Research Engineer Cam Marshall and Research Scientist (now Emeritus) Art Olin. Scientists at Simon Fraser University and the University of British Columbia also contributed to the construction and assembly of the ALPHA-2 apparatus, including the cryostat. Marshall explained that "the cryostat houses a unique octopole magnet with the antimatter trap, into which was fed the laser spectroscopy system, microwave system, liquid helium cooling, super-conducting current leads, diagnostic wiring, and thermal shielding. A lot going on in a small space!" According to Olin, the experiment's success was "facilitated by the stable cryogenic environment and higher trapping rate of this new atom trap." The experiment was tricky because the team had to isolate the antihydrogen within a sophisticated "magnetic bottle" without it coming into contact with matter as it would then annihilate and disappear. Having passed the first test of their upgraded apparatus with flying colours, the ALPHA Collobration is anxious to attack the other even more exciting pieces of the antimatter puzzle in the coming years. "We will now look at the other pieces of the puzzle, such as the colour of the light emitted by antihydrogen, and test whether hydrogen and antihydrogen emit light in the same way," says Capra. "We are also working on measuring the gravitational acceleration of antihydrogen and determining whether matter and antimatter have the same gravitational behaviour. The next several years are going to be very exciting." Explore further: How things break (and why scientists want to know) More information: M. Ahmadi et al. An improved limit on the charge of antihydrogen from stochastic acceleration, Nature (2016). DOI: 10.1038/nature16491