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1.
Several studies of jets impinging on a plane surface have already been made. This paper suggests a new approach to studying
impingements of jets. Comparisons have been made between visualisation results and wall pressure measurements. It is shown
that only one of these two techniques is sufficient for characterising the flow nature near the wall. Visualisations can be
sufficient for determining the location of wall pressure maxima and minima. Detachments and reattachments of the flow are
thus located, and the main characteristics of a jet impinging on a plane wall can be shown by simpler experiments such as
the spreading over method.
Received: 15 October 1998/Accepted: 27 July 1999 相似文献
2.
Topological concepts provide highly comprehensible representations of the main features of a flow with a limited number of
elements. This paper presents an automated classification method of instantaneous velocity fields based on the analysis of
their critical points distribution and feature flow fields. It uses the fact that topological changes of a velocity field
are continuous in time to extract large scale periodic phenomena from insufficiently time-resolved datasets. This method is
applied to two test-cases : an analytical flow field and PIV planes acquired downstream a wall-mounted cube. 相似文献
3.
F. Niro G. Brizzi M. Carlotti E. Papandrea M. Ridolfi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,103(1):14-26
In this paper, we present an improvement of the retrieval of pressure and temperature from the observations of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board of the environmental satellite (ENVISAT). The improvement has been obtained by integrating a state-of-the-art CO2 line-mixing model in a two-dimensional inversion system (Geo-fit). We describe the implementation of this model in the Geo-fit system and we show its capability to reproduce the CO2 spectral features affected by line-mixing. The upgraded analysis algorithm provides a better fit of the set of MIPAS observations analyzed by the European Space Agency (ESA) ground segment although these observations have been selected with criteria that should avoid line-mixing effects. Moreover, we show that this set of observations can be extended improving the precision of the retrieved pressure and temperature fields without increasing the computing demands. Since the CO2Q branches are very sensitive to pressure and temperature, the capability to model accurately the line-mixing effects opens the possibility to exploit at best these spectral regions to infer pressure and temperature distributions. According to this idea, we propose a new set of spectral intervals, including the most intense CO2Q branches. It is shown that the analysis of these intervals provides a significant improvement (up to 70%) in the precision of the retrieved pressure and temperature profiles, while using a smaller number of observations with respect to the ESA ground segment analysis. Since the knowledge of pressure and temperature is necessary for the retrieval of the altitude distribution of all the atmospheric constituents, the benefits of more precise pressure and temperature fields obtained in this work propagate into the quality of all the MIPAS products. 相似文献
4.
A hybrid sequential niche algorithm is used for the automated identification of critical points of velocity fields. This method combines an adaptive sequential niche technique with deterministic local optimization to detect critical points: focus, node and saddle points. A particle swarm algorithm performs a global search whereas vortex core identification functions compute the precise location as the extremum of the corresponding function. Once a critical point is found, a rectangular niche is constructed around the point. The particle swarm then proceeds to explore different regions of the velocity field. The process advances sequentially, avoiding areas near previously found critical points by blocking niches obtained from previous steps. The niche size is automatically adjusted each time a search enters inside an existing niche. Vortex core functions are used for critical point identification and calculating its precise location inside each niche. The procedure is validated on particle image velocimetry data obtained with two types of flows, an impinging jet flow and a flow downstream of a model building. The hybrid algorithm proved to be very efficient and robust for automated detection and identification of critical points. It can be used as a first step for studying the time‐dependent dynamic behavior of instantaneous velocity fields by tracking topological critical points. This is the first study that uses a multi‐modal particle swarm algorithm for critical point identification. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
A combined wall pressure/velocity analysis of the wake of a disk located in the vicinity of a flat wall is presented in this
paper. One gap ratio only is selected. In this situation, the footprint of the flow unsteadiness on the magnitude of the wall
fluctuating pressure is significant while the natural vortex shedding properties of the wake are only slightly altered. Spatio-temporal
velocity and pressure/velocity correlations are analyzed. They carry the signature of the large-scale coherence and periodicity
associated with vortex shedding and exhibit characteristic phase relations. Advanced statistical analysis techniques are adapted
and developed. A conditional phase averaging of the pressure and velocity fields is obtained. The proper orthogonal decomposition
of a spatio-temporal pressure data set on the axis of the near wake is shown to be efficient (1) to determine the phase of
the spatio-temporal pressure field projected on the two first modes and (2) to distinguish between quiescent random signatures
and more energetic phases. Conditional statistics show very clearly that the large-scale structures interact with the flat
wall. Finally, a linear stochastic estimation (LSE) of the velocity field is computed from the fluctuating pressure data.
We show the superiority of the spatio-temporal LSE over the spatial LSE in predicting the kinetic energy and the coherent
spectral properties of the fluctuating velocity field. Moreover, the linear stochastic estimation is very good in predicting
the phase-averaged conditional velocity field. 相似文献
6.
Frederic Dehoux Yannick Lecocq Sofiane Benhamadouche Remi Manceau Laurent-Emmanuel Brizzi 《Flow, Turbulence and Combustion》2012,88(1-2):77-100
The present paper focuses on the application of the elliptic blending approach to the modeling of turbulent heat fluxes, in order to account for the influence of solid boundaries. The analytical justification of the extension to the temperature–pressure gradient correlation term of this approach, originally applied to the velocity–pressure gradient, is given. The assumption of weak equilibrium enables the derivation of two new algebraic flux models valid down to the wall. It is shown, with both a priori tests and computations in forced and mixed convection regimes, that the predictions of the streamwise heat-flux and the temperature variance are significantly improved by the use of elliptic blending. A particular attention is devoted to the issue of the modeling of the correlation length scale involved in the elliptic blending for the heat fluxes, which is shown to have a significant influence on the predictions. 相似文献
7.
C. Bonechi A. Brizzi V. Brizzi M. Francioli A. Donati C. Rossi 《Magnetic resonance in chemistry : MRC》2001,39(8):432-437
The conformational properties of cis-5,8,11,14-eicosatetraenoylethanolamide (anandamide) were analysed by the combined use of NMR experimental results plus molecular simulations. The structure of anandamide was found to be a predominantly linear with a seven-atom ring of the ethanolamine group having a hydrogen bond which stabilizes the molecule. The vinylic group present has a cis conformation in solution. The terminal chain has a linear conformation and undergoes isotropic fast motion typical of this structure. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
8.
The aerodynamic study of a row of axisymmetric jets impinging a concave wall is carried out from velocity measurements obtained by the standard and stereoscopic Particle Image Velocimetry. The principle and the specific aspects of the stereoscopic PIV set up, a recent technique of three-dimensional velocimetry, are explained. After a statistical data processing, the three-dimensional structure and the characteristics of multiple jets impinging a concave wall are described with the mean velocity fields and the turbulent values in several planes of the flow. To cite this article: V. Gilard, L.-E. Brizzi, C. R. Mecanique 334 (2006). 相似文献
9.
B. Sapoval M. Filoche K. Karamanos R. Brizzi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):739-753
The concept of active zone in the Laplacian transport to and across irregular interfaces is rigorously introduced. It applies
to arbitrary geometries and uses the coarse-graining method proposed by Sapoval to compute the flux across an irregular interface
from its geometry without solving the general Laplace problem. Such transport play a dominant role in electrochemistry, heterogeneous
catalysis and physiological diffusion processes. In the field of electrochemistry, the method permits one to predict the impedance
of an electrode of arbitrary geometry for any value of the frequency. It shows that, for systems with aspect ratios of the
order of a few times unity or less, impedance spectroscopy yields in principle a reliable approximate measure of the length
of the chord corresponding to a perimeter length inversely proportional to the interface capacitance and frequency. For these
cases, impedance spectroscopy can determine the shape of an electrode to the extent that the knowledge of the average chord
length as a function of the perimeter determines the shape. For systems of arbitrary geometry, it is shown that impedance
spectroscopy permits a measure of the size of the active zone. These results can be transposed to several problems related
to Laplacian transfer, such as etching of irregular solids and catalysis in the Eley-Rideal regime.
Received 3 November 1998 and Received in final form 8 December 1998 相似文献
10.
Regioselective functionalization of quinolin-4(1H)-ones via sequential palladium-catalyzed reactions
Claudia MugnainiChiara Falciani Maria De RosaAntonella Brizzi Serena PasquiniFederico Corelli 《Tetrahedron》2011,67(32):5776-5783
A practical and general synthesis of 1,3,6-trisubstituted quinolin-4(1H)-ones starting from 1-alkyl-6-bromo-3-iodoquinolin-4(1H)-one is described, based on regioselective sequential palladium-catalyzed cross-coupling reactions, namely Suzuki-Miyaura, Sonogashira and aminocarbonylation reactions, under microwave irradiation. Good substrate generality, ease of execution and practicability make this method exploitable for the generation of libraries of chemically diverse 4-quinolones. 相似文献