1,720,988 research outputs found
RANS simulations of a junction flow
No full textThe ERCOFTAC junction flow is numerically simulated with both a structured and an unstructured RANS solver for incompressible flows. The structured code adopts a finite volume, cell-centered formulation while the unstructured code uses residual distribution schemes and a vertex centered storage of the unknowns. Two differential eddy viscosity models, based on local quantities, are considered in the computations: the one-equation Spalart Allmaras model and the two equations k-e model proposed by Lam and Bremhorst. The grid dependence of the numerical solutions is evaluated by means of a convergence analysis based on computation of the GCI and a code-to-code comparison. The numerical results provided by both turbulence models are compared with the experimental measurements of the pressure and velocity fields
Truncation error analysis in turbulent boundary layers
No full textThe influence of turbulence model and numerical technique on RANS computations is discussed in the case of turbulent boundary layer flow on a flat plate. In particular, results are presented for a centered scheme with artificial dissipation and a ENO-type scheme with the Baldwin-Lomax and Spalart-Allmaras models. First, in an a priori analysis, the truncation errors are evaluated under the assumption of parallel Couette flow, and some conclusions about mesh optimization and scheme performance are drawn. Then, the a posteriori analysis for the numerical solution of turbulent boundary, layer on a flat plate is performed. Grid Convergence Index and convergence rate analysis confirm the a priori results
On the Aerodynamic Heating of VEGA Launcher: Compressible Chimera Navier-Stokes Simulation with Complex Surfaces
No full textThe results of accurate compressible Navier-Stokes simulations of aerodynamic heating of the Vega launcher are presented. Three selected steady conditions of the Vega mission profile are considered: the first corresponding to the altitude of 18 km, the second to 25 km and the last to 33 km. The numerical code is based on the Favre–Average Navier–Stokes equations; the turbulent model
chosen for closure is the one-equation model by Spalart–Allmaras. The equations are discretized by a finite volume approach, that can handle block-structured meshes with partial overlap (“Chimera” grid-overlapping technique). The isothermal boundary condition has been applied to the lancher wall.
Particular care was devoted to the construction of the discrete model; indeed, the launcher is equipped with many protrusions and geometrical peculiarities (as antennas, raceways, inter-stage connection flanges and retrorockets) that are expected to affect considerably the local thermal flow-field and the level of heat fluxes, because the flow have to undergo strong variation in space; consequently, special attention was devoted to the definition
of a tailored mesh, capable of catching local details of the aerothermal flow field (shocks, expansion fans, boundary layer, etc..).
The computed results are reported together with uncertainty and actual convergence order, that were estimated by the standard procedures suggested by AIAA
On the Effects of Supersonic Igniter Jets during Pre-Ignition Transient of SRMs
No full textThis paper presents and discusses the early phase of the ignition transient of the VEGA Launcher's third stage solid rocket motor, Zefiro 9A. Relevant experimental data coming from two different static ring tests (QM2 - VT1 and VT2) will be compared with numerical simulations performed with a Quasi-1D code, named Spit, as well as a 3D code named Xaer, both developed by DMA. During the last two ring tests of the Z9A SRM (QM2 and VT1) a peculiar unexpected negative force peak as well as a significant pressure unbalance in the motor chamber were measured during the very rst phase of the ignition transient. The Q-1D numerical simulation obtained by the Spit code for the prediction of the SRM behavior
underestimates this anomalous pressurization. Hence, 3D simulations were performed to reconstruct the flowfield features affecting the SRM behavior by the Xaer code, showing a much better agreement with the experimental measurements. 3D simulation, indeed,
can provide a good insight on the origin of this peculiar pressure distribution, clearly identifying a supersonic region spreading across the entire motor chamber section that temporally "blocks" the motor head section delaying its pressurization.
In order to x the unexpected negative force, out of the system specifications, a modification of the igniter design was decided for the Z9A SRM and a third static ring test was carried out (VT2), for which both the Q1D and the 3D models provided numerical predictions of the first phase of the SRM ignition transient.
Hence, the Q1D and the 3D models simulation will be compared with the experimental data and used for the reconstruction of the Z9A behavior for the QM2 and VT1 SFTs, for the investigation of the main cause of the negative force peak experienced. Whereas, the 3D tool will be used for the prediction of the flowfield pressure unbalance for the Z9-A VT2 and compared with the SFT experimental data
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
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