130,581 research outputs found
Head-on collision of shock wave induced vortices with solid and perforated walls
No full textAn experimental study has been conducted to examine the interaction of shock wave induced vortices with a flat plate and a perforated plate. The experiments were carried out using a internal diameter shock-tube at Mach numbers 1.31, 1.49, and 1.61 under critical driver conditions. Air was used both in the driver and driven sections. High-speed schlieren photography was employed to study the flow development and the resulting interactions with the plates. Wall pressure measurements on both plates were also carried out in order to study the flow interactions quantitatively. The experimental results indicated that a region of strong flow development is generated near the wall surface, due to the flow interactions of reflected waves and oncoming induced vortices. This flow behavior causes the generation of multiple pressure fluctuations on the wall. In the case of the perforated plate, a weaker initial reflected wave is produced, which is followed by compression waves, due to the internal reflections within the plate. The transmitted wave is reduced in strength, compared to the initial incident shock wave
Surface heat-transfer measurements inside a supersonic combustor by LIF
No full textA study has been conducted to measure surface temperatures inside a model rectangular supersonic combustor using a technique exploiting the fluorescence properties of Dy:YAG by LIF. The wind tunnel was a blown down type using vitiated air with nominal conditions at the entrance of the test section M∞=2.5, Po=5×105 N/m2, To=800 K and Re∞/m=9.6×106. Fuel was hydrogen gas in room temperature injected parallel to the tunnel through a fuel injector slit located along the backward surface of a step. The results under hot flow conditions were compared with numerical simulations performed using a 2-D Navier-Stokes code with full chemistry. © 2002 by K. Kontis. Published by the American Institute of Aeronautics and Astronautics, Inc
Surface heat-transfer measurements inside a supersonic combustor by LIF
No full textA study has been conducted to measure surface temperatures inside a model rectangular supersonic combustor using a technique exploiting the fluorescence properties of Dy:YAG by LIF. The wind tunnel was a blown down type using vitiated air with nominal conditions at the entrance of the test section M∞=2.5, Po=5×105 N/m2, To=800 K and Re∞/m=9.6×106. Fuel was hydrogen gas in room temperature injected parallel to the tunnel through a fuel injector slit located along the backward surface of a step. The results under hot flow conditions were compared with numerical simulations performed using a 2-D Navier-Stokes code with full chemistry. © 2002 by K. Kontis. Published by the American Institute of Aeronautics and Astronautics, Inc
Study of detonation interactions inside a 2-D ejector using detonation transmission tubing
No full textStudy of detonation interactions inside a two-dimensional ejector using detonation transmission tubing was reported. The main objective of the ejector assembly in the study is to make the flow-field as close to 2-D as possible. Optical-grade Perspex sheets with a thickness of 10 mm were used on both sides of the nozzle to allow visualization of the flow. Wall pressure measurements were conducted at the locations. The NONEL tube was flush with the entrance of the nozzle. The signal to begin pressure measurements and image acquisition was obtained through a Kulite XT-190 transducer. The detonation was initiate by an electronic blasting machine, DynoStart 2, with a capacitance of 0.2μF and an output voltage of 2500 V. High-speed shadowgraphy was employed to visualize the flow. The results show that the effects of 3-D flow at the initial stage of the detonation affect the incident shock front and the reflected shock wave system at the nozzle entrance
Shock wave interactions inside a complex geometry
No full textStudies of shocks expanding into confined regions lack detailed quantitative data of major flowfield features that evolve in time. The transient behaviour of shock waves and detonations has been the subject of study of many investigators. These include phenomena such as shock reflections, diffractions and shock/vortex interactions. The mentioned phenomena have been explored by various authors, for example shock wave reflections have been studied both phenomenon experimentally and analytically by Ben-Dor and Takayama [1], Ben-Dor et al. [2] and Henderson and Lozzi [3]. The shock diffraction pattern over corners at different Mach numbers has been studied experimentally by Skews ([4], [5]) and also by Griffith and Bricklet [6]. Shock diffraction from small areas to larger ones, have been studied by authors such as, Jiang et al. [7] and Chang and Kim [8]
Head-on collision of shock wave induced vortices with a cylinder and a sphere
No full textAn experimental study has been conducted to examine the interaction of shock wave induced vortices with a cylinder and a sphere. The experiments were carried out using a 30 mm internal diameter shock-tube, using air as both the driver and driven gas. High-speed schlieren photography was employed to study the development of the flow-field and the resulting interactions with the body configurations. Wall pressure measurements were also carried out to study the flow quantitatively along the leading edge of the cylinder. Three different diaphragm pressures ratios of 3.95, 7.89, and 11.84 were examined; the experimental shock Mach numbers were 1.28, 1.51 and 1.63, respectively. The experimental results indicate that as the incident shock wave impinges on the frontal surface of the cylinder or sphere, it undergoes transition from regular to Mach reflection. The induced flow-field due to the interaction of the vortex ring with the two models is highly three-dimensional and time dependent. The vortex ring attempts to engulf the sphere, whereas, in the case of the cylinder, part of the ring accelerates rapidly in the lateral direction along the leading edge of the body, whereas, the remaining flow moves around the cylinder. In both cases, the ring maintains its structure throughout the interactions
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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