1,721,019 research outputs found
High altitude operations with piston engines powerplant design optimization part II: Turbo-charging, turbo matching, efficiency and serial arrangement optimization
No full textLow BSFC (Brake Specific Fuel Consumption) and flat-altitude-rating make piston engines ideal choice for altitudes up to 20,000m-65,000ft. These propulsion systems are more complex than traditional applications that are normally limited to 5,000-7,000m (16,000-23,000ft). In fact, the air propulsion (propeller or fan), the air intake, the fuel system, the turbocharging, the exhaust and the cooling system take part to the design optimization process. An integrated design is strictly necessary. At high altitudes, the intake air is taken from high-pressure areas into an alternate, extremely optimized, path. In propeller systems, a diffuser is usually positioned in the lower part of the aircraft. It converts kinetic energy into pressure. In fan systems, a little amount of "high pressure" air is taken from the high-pressure area of the fan. In lower power units, automotive-derived turbochargers can achieve the required pressure ratio. However, this option is limited by the maximum amount of volumetric flow rate. Moreover, automotive turbocharger housings have to be redesigned to use low-weight inconel alloys instead of heavier cast-iron. A complete redesign of the high pressure turbocharger (the unit closer to the engine manifold) can achieve pressure ratios from 8:1 to 10:1. This expensive process increases the power to mass ratio of the propulsion system. For higher power rating over about 200 kW axial compressorturbine assemblies derived from small turboshafts can be used as a turbocharging unit. In this case the burner is substituted by the piston engine. Especially for diesel engines, the advantage lies in the efficiency (BSFC). In fact, the maximum temperature reached in the diesel combustion chamber is about 4200K and the air flow is much lower than traditional turboshafts. Hybrid and turbocompound solutions are also possible. The exhaust and the intake of the piston engine have to be redesigned. However, the requirements of low weight, high reliability and long endurance HALE (High Altitude Long Endurance) UAVs (Unmanned Aerial Vehicle) requires further work on this specific subject
Electrothermal Simulation and Experimental Detection of the Hot Spot Onset in Power Bipolar Transistors
No full textHigh altitude operations with piston engines powerplant design optimization part III: The diffuser critical design
No full textLow BSFC (Brake Specific Fuel Consumption) and flat-altitude-rating make piston engines ideal choice for subsonic flight at altitudes up to 20, 000m-65, 000ft. These propulsion systems are more complex than traditional applications that are normally limited to 5, 000-7, 000m (16, 000-23, 000ft). In fact, the air propulsion (propeller or fan), the air intake and the cooling system take part have huge volumes. Therefore, their design influences vehicle aerodynamics as a whole. The cooling system is an integral part of aircraft design. As assessed from WWII design heritage, the cooling duct can be a static subsonic ramjet: the Meredith cooling duct. At high altitudes, the Meredith duct air is taken from highpressure areas into an alternate, extremely optimized, path. This path should end with a nozzle in a low pressure, high turbulence area of the aerial vehicle. In subsonic ramjet cooling ducts, the "static compressor" or diffuser is the most critical part. In fact the maximum compression ratio is below 1.5. Its efficiency highly influences the total thrust and the cooling efficacy of the duct. The Meredith duct should be embedded in the fuselage or in the wing to avoid excessive external drag. Only the air intake is positioned outside. In propeller systems, the intake is positioned in the lower part of the aircraft at about 2/3 of the wing chord, where the pressure reaches its maximum. In propeller systems, the high altitude engine intake can be positioned at the end of diffuser to increase the engine boost. In this way the turbomachinery mass and volume is reduced and the power to mass ratio of the propulsion system is increased. In fan systems, higher pressure is present inside the fan duct. In this paper, the preliminary design of the cooling duct is introduced. However, a CFD/wind tunnel optimization is strictly necessary to achieve a fully effective system. In any case, the requirements of low weight, high reliability and long endurance HALE (High Altitude Long Endurance) UAVs (Unmanned Aerial Vehicle) requires further work on this specific subject
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Optimal intercooler layout arrangement for Formula 1 racing engines
No full textThis paper demonstrates that efficiency and torque output of the actual Formula 1 power units depends mostly on the turbocharger (TC) efficiency. Compressor and turbine off-design efficiency and turbine energy recovery capability should be maximized to maximize the torque to fuel ratio. Since larger TCs increase turbolag, a new layout for the intercooler is proposed in this paper. This solution reduces turbolag and make it possible to focus on the TC efficiency as a thermal machine. In fact, not only the TC design choices can radically alter the efficiency of the TC itself, but also influence the efficiency of the ICE and of the MGU (Motor Generator Units). Energy evaluation of the TC readily exploits the concept. © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved
Direct comparison of fsi optimized theodorsen and larrabee propellers
No full textThe goal of this study is the analysis of the design process of aircraft propellers which are coupled to a piston engine, aiming to find the best design approach. The first design step is the calculation of the initial geometry. This phase is particularly critical since it will affect the following optimization. Several theories for blade design have been proposed during the years. The most popular are the Larrabee's procedure and the Theodorsen's theory. The Larrabee theory is the most used in recent years, while the Theodorsen was most popular in the WWII era. This work focuses on the differences on the results of the two approaches for a general aviation propeller for light aircrafts. For this aerial vehicle category both the strength and efficiency should be considered, since the production technology cannot be as refined as for larger propellers. As it will be seen, the subsonic nature of these aerial vehicles makes it possible to use both initial design approaches. In a second phase, the evaluation of the effect of aerodynamics and centrifugal loads requires the union of the results that come from CFD (Computational Fluid Dynamics) and the ones come from the CSM (Computational Structural Mechanics), through the execution of several one way FSI (Fluid Structure Interaction) analyses. However the starting point proved to be critical for the final result. The Larrabee procedure proves to be ideal for high speed aircraft propellers manufactured with up-to-date materials and procedures. The "old" Theodorsen theory leads to a stronger blade that can be easily manufactured with wood or simplified technologies. The Theodorsen blade is superior for the centrifugal load bearing capacity. This geometry leads to lighter blades. The efficiency of the Larrabee blade seems to be superior. However, experience proved that the CFD analysis can be tricky and unreliable for efficiency evaluation. The pressures are better distributed along the Larrabee's blade with better results at high airspeed. Eventually two geometrically optimized blades have been designed, which have a deformed shape (at cruise conditions) similar to the best aerodynamic geometry and comparable technological characteristics. The Larrabee and Theodorsen designs lead to different optimized blades even after the FSI simulation, demonstrating that the optimization procedure is largely influenced by the initial propeller blade design. © 2006-2015 Asian Research Publishing Network (ARPN)
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