1,721,022 research outputs found
MODELLING AND SIMULATION OF LIQUID ROCKET ENGINE IGNITION TRANSIENTS
No full textEuropean Space Agency (ESA
Modelling of Stratification in Cooling Channels and its Implementation in a Transient System Analysis Tool
No full textThe use of system modelling tools for transient analysis of LRE is becoming more and more common since their accuracy is constantly improving. But the design and analysis of regeneratively cooled walls of cryogenic thrust chambers is still a challenging problem. Conventional one-dimensional calculation methods assume an ideal mixing of the thermal energy into the fluid cell, therefore in case of cooling channels with high aspect ratio a significant error will arise on the fluid to wall heat exchange because thermal stratification
effects are not taken into account in the fluid flow formulation.
EcosimPro is an object oriented tool capable of modelling various kinds of dynamic systems. The model described within this paper is implemented alongside ESPSS, the propulsion system library compatible with EcosimPro. This paper covers a new simplified “Quasi-2D” approach to study the coupled problem of coolant flow and wall structure heat transfer in the cooling channels of a liquid rocket engine from a system point of view. With this approach it is possible to have a fast prediction of the evolution in space and
time of both coolant and wall temperature distribution. Unlike the previous models used to evaluate thermal stratification, this one is based on 1D unsteady mass governing equation, and “Quasi-2D” momentum and energy conservation equations. For each longitudinal node, the channel is divided into slices. The governing equations take into account the shear stresses between the slices and the heat fluxes in vertical direction due to turbulent mixing.
The model hereafter described can be easily embedded in an unsteady propulsion system analysis for simulating the ignition transient. The code flexibility allows for using the same model also for performance analysis in steady-state, and for off-design studies. Numerical test cases from the University of Rome, and experimental test cases from the German Aerospace Center (DLR) will be simulated and their results will be compared with the simulation results of the model
Start-up transient simulation of a liquid rocket engine
No full textDuring the start-up of a liquid rocket engine most of the engine components are required to work at extreme operating conditions; this phase features very complex phenomena such as combustion instabilities, water hammer eFFects in feed lines, turbopumps operating far from design conditions and two-phase flows that cannot be neglected when design studies of an engine are to be performed or the assessment of the valve opening sequence has to be done. For these reasons simulations of the ignition transient phase become necessary in order to reduce the experimental tests and increase the engine safety and reliability. The subject of the present work is to develop an LRE transient model, to apply it to simulate the start-up transient and to validate the model with an existing liquid rocket engine (the RL-10). A system approach has been used, since it is necessary to take into account all the interactions between all the components of an engine. This choice is fundamental if a detailed estimation of the engine transient behaviour is the task. The system simulated by the code encompasses the complete feeding system from the tanks down to the the turbopump subsystems, the valves, the pipes, the thrust chamber's inlets, the flow ducts of the thrust chamber itself and the chemical reactions inside the combustion chamber. The engine model is built using ESPSS,5 the propulsion system library compatible with EcosimPro, an object oriented tool capable of modelling various kinds of dynamic systems. The engine model includes also original models developed by the authors and presented in previous works6 such as a new injector plate model, and more realistic heat transfer coefficient correlations. The transient phase of the Pratt and Whitney RL-10 engine has been taken as validation case. This engine has been chosen for several reasons, among which the good availability of engine construction data, performance and tests results in open literature.1-3 The main subsystem models of this engine will be described and their validation will be presented. Then the integrated model of the entire engine will be described alongside the comparison of the simulation with experimental data. © 2011 by F. Di Matteo
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
A methodology to study the possible occurrence of chugging in liquid rocket engines during transient start-up
No full textAn investigation on the low frequency combustion instabilities due to the interaction of combustion chamber and feed line dynamics in a liquid rocket engine is carried out implementing a specific module in the system analysis software EcosimPro. The properties of the selected double time lag model are identified according to the two classical assumptions of constant and variable time lag. Module capabilities are evaluated on a literature experimental set up consisting of a combustion chamber decoupled from the upstream feed lines. The computed stability map results to be in good agreement with both experimental data and analytical models. Moreover, the first characteristic frequency of the engine is correctly predicted, giving confidence on the use of the module for the analysis of chugging instabilities. As an example of application, a study is carried out on the influence of the feed lines on the system stability, correctly capturing that the lines extend the stable regime of the combustion chamber and that the propellant domes play a key role in coupling the dynamics of combustion chamber and feed lines. A further example is presented to discuss on the role of pressure growth rate and of the combustion chamber properties on the possible occurrence of chug instability during engine start-up and on the conditions that lead to its damping or growth. © 2017 IA
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
Fluorescence confocal microscopy for rapid evaluation of EUS fine-needle biopsy in pancreatic solid lesions
Full text link: Video 1EUS fine-needle biopsy of a pancreatic solid lesion evaluated with fluorescence confocal microscopy
A new tool for rapid evaluation of endoscopic ultrasound through the needle biopsy in pancreatic cystic neoplasm
No full textNo abstract availabl
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
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