159,014 research outputs found
A survey of the turbulence statistics of a model-scale installed jet at low and moderate mach numbers
No full textIn modern high-bypass ratio engine configurations, the exhausted jet is deflected and modified by the wing and high lift devices. The present paper reports a survey on a model-scale jet in the presence of a flat plate installed at two height (h) and two length (l) positions from the center of the nozzle. The aim of this work is to evaluate the one-point statistics of isolated and installed jets. Experimental data of the axial component of the velocity is acquired for a 1½” nozzle via hot-wire anemometry. The investigation is made for several jet velocities, ranging from acoustical Mach numbers 0.2 to 0.8. Mean velocity profile results show a slight acceleration of the jet in regions close to the plate. This effect is notorious for plate locations in which the jet wets the plate close to the nozzle exit. It also seems to have a weak velocity dependency. This acceleration of the jet is consistent with the conservation of mass and changes in the entrainment at that region. As a direct result of the local jet acceleration, locations close to the plate present lower levels of turbulence intensity. Other factor that may contribute to this effect is the break-down of the eddies at the rigid surface. Turbulence intensity profiles have also shown a spike immediately downstream of the trailing edge. This is possibly an effect of the boundary layer separation, or a wake-type of flow originated at the trailing edge. Results for low and higher-order statistics of the shear layer opposite to the plate are exactly the same as results measured for the isolated jet configuration. Boundary layer development along the plate in both streamwise and spanwise direction is presented. It is shown that, even though the present problem consists of a non-uniform flow interacting with a surface, boundary layer properties could be defined for close-coupled, long surfaces. Finally, the spectra information from hot-wire sensors are analysed and qualitatively compared to the spectra measured by near-field surface pressure transducers located streamwise along the plate. The power spectral density of the velocity signal has a -5/3 decay, which is not seen in the pressure spectra.</p
Blockage effects on the pressure field of 3D-printed small-scale jet nozzles
No full textThis paper presents a preliminary investigation into the pressure fields of jets exhausting from partially blocked nozzles. Measurements are performed for a series of asymmetric, smallscale, single stream nozzles mimicking the bypass flow from an engine-pylon-wing configuration. The hydrodynamic and acoustic pressure fields of the pylon nozzles are compared to data from an axisymmetric, annular jet baseline nozzle. For the good aerodynamic pylon designs, the isolated jet mixing noise source is slightly modified at azimuthal angles near the blockage. The blockage effects on the installed jet-wing interaction noise source are also small, even when corrections for thrust are applied. In-flight data suggest that a significant increase in the pressure levels exist at relatively high flight-to-jet-velocity ratios for the blocked configurations. For the poorly aerodynamically designed blockages, flow separation occurs close to the nozzle exit. This flow separation induces an augmentation of the jet noise sources. The near-field pressure data shows that the main effects of the pylon are, firstly, an increase in the strength of the hydrodynamic pressure field perpendicular to the pylon surface due to vortex shedding and, secondly, a fast recovery of symmetry downstream of the pylon trailing edge
Wall pressure fluctuations induced by a single stream jet over a semi-finite plate
No full textThis work provides an experimental investigation into the interaction between a jet flow and a semi-finite plate parallel to the jet. Wall pressure fluctuations have been measured in a high compressible subsonic regime and for different distances between the jet and the plate trailing edge. The experiment has been carried out in the ISVR anechoic Doak Laboratory at the University of Southampton, using wall pressure transducers flush mounted on the plate surface. Signals were acquired in the stream-wise direction along the jet centreline and in the span-wise direction in a region close to the trailing edge. The radial position of the flat plate was fixed very close to the jet axis to simulate a realistic jet–wing configuration. The plate was moved axially in order to investigate four different jet-trailing edge distances and to include measurements upstream of the nozzle exhaust. The acquired database was analyzed in both the frequency and the time domains providing an extensive statistical characterization in terms of spectral uni– and multi–variate quantities as well as high order statistical moments. A wavelet analysis was performed as well to investigate the time evolution of the wall pressure events
Seismic assessment and base isolation retrofit of a modern heritage R/C swimming pool
No full textA modern heritage reinforced concrete (R/C) swimming pool building designed by Pier Luigi Nervi is examined in this paper. The distinguishing feature of the structure is represented by the barrel vault-shaped roof, constituted by prefab R/C curved beams with smoothed-V wavy section, typical of the internationally recognized Nervi’s style. The R/C columns and beams supporting the roof and the lateral aisles — originally designed for gravitational loads only and pursuing a minimal size philosophy with respect to the calculated stress states — have very small cross sections. As a consequence, the seismic performance assessment analysis carried out in this study shows general unsafe response conditions of these members. In order to substantially improve the seismic response capacity of the building, as well as to avoid any intrusive intervention on the exposed structural elements, an advanced retrofit strategy is proposed, which consists in the installation of a base isolation system incorporating double curved surface slider devices at the feet of all columns and below the pool tank
An experimental investigation into model-scale installed jet-pylon-wing noise
No full textA model-scale experimental investigation of an installed jet-pylon-wing configuration was conducted at the University of Southampton, with the scope to study the effect a pylon has on noise generation and to clarify its impact on the fluctuating wall-pressure load. The set-up consisted of two single-stream nozzles, a baseline axisymmetric annular nozzle and a partially blocked annular pylon nozzle. The nozzles were tested first isolated and then installed next to a NACA4415 aerofoil 'wing' at a single nozzle-wing position. The jet Mach number was varied between and measurements were performed both under static and in-flight ambient flow conditions up to. The jet flow-field qualification was carried out using a single-velocity-component hot-wire anemometer probe. The pressure field on the wing surface was investigated using two miniature wall-pressure transducers that were flush-mounted in the streamwise and spanwise directions within the pressure side of the wing. A linear 'flyover' microphone array was used to record the noise radiated to the far field. The unsteady pressure data were analysed in both time and frequency domains using multi-variate statistics, highlighting a far-field noise reduction provided by the presence of the pylon only in the installed case. Furthermore, the wake field generated behind the pylon is seen to significantly modify the wall-pressure fluctuations, particularly at streamwise locations close to the pylon trailing edge
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
An experimental investigation into model-scale installed jet-pylon-wing noise
No full textA model-scale experimental investigation of an installed jet-pylon-wing configuration was conducted at the University of Southampton, with the scope to study the effect a pylon has on noise generation and to clarify its impact on the fluctuating wall-pressure load. The set-up consisted of two single-stream nozzles, a baseline axisymmetric annular nozzle and a partially blocked annular pylon nozzle. The nozzles were tested first isolated and then installed next to a NACA4415 aerofoil 'wing' at a single nozzle-wing position. The jet Mach number was varied between 0.5 <= M-j <= 0.8 and measurements were performed both under static and in-flight ambient flow conditions up to M-f = 0.2. The jet flow-field qualification was carried out using a single-velocity-component hot-wire anemometer probe. The pressure field on the wing surface was investigated using two miniature wall-pressure transducers that were flush-mounted in the streamwise and spanwise directions within the pressure side of the wing. A linear 'flyover' microphone array was used to record the noise radiated to the far field. The unsteady pressure data were analysed in both time and frequency domains using multi-variate statistics, highlighting a far-field noise reduction provided by the presence of the pylon only in the installed case. Furthermore, the wake field generated behind the pylon is seen to significantly modify the wall-pressure fluctuations, particularly at streamwise locations close to the pylon trailing edge
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
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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