362 research outputs found
Multi-Scale Turbulence Injector: a new tool to generate intense homogeneous and isotropic turbulence for premixed combustion
Nearly homogeneous and isotropic, highly turbulent flow, generated by an
original multi-scale injector is experimentally studied. This multi-scale
injector is made of three perforated plates shifted in space such that the
diameter of their holes and their blockage ratio increase with the downstream
distance. The Multi-Scale Turbulence Injector (hereafter, MuSTI) is compared
with a Mono-Scale Turbulence Injector (MoSTI), the latter being constituted by
only the last plate of MuSTI. This comparison is done for both cold and
reactive flows. For the cold flow, it is shown that, in comparison with the
classical mono-scale injector, for the MuSTI injector: (i) the turbulent
kinetic energy is roughly twice larger, and the kinetic energy supply is
distributed over the whole range of scales. This is emphasized by second and
third order structure functions. (ii) the transverse fluxes of momentum and
energy are enhanced, (iii) the homogeneity and isotropy are reached earlier
(%), (iv) the jet merging distance is the relevant scaling
length-scale of the turbulent flow, (v) high turbulence intensity (%) is achieved in the homogeneous and isotropic region, although the
Reynolds number based on the Taylor microscale remains moderate (). In a second part, the interaction between the multi-scale
generated turbulence and the premixed flame front is investigated by laser
tomography. A lean V-shaped methane/air flame is stabilised on a heated rod in
the homogeneous and isotropic region of the turbulent flow. The main
observation is that the flame wrinkling is hugely amplified with the
multi-scale generated injector, as testified by the increase of the flame brush
thickness.Comment: 29 pages, 21 figures, submitted to Journal of Turbulenc
Wake of super-hydrophobic falling spheres: influence of the air layer deformation
We report an experimental investigation of the wake of free falling
super-hydrophobic spheres. The mutual interaction between the air layer
(plastron) encapsulating the super-hydrophobic spheres and the flow is
emphasised by studying the hydrodynamic performances. It is found that the air
plastron adapts its shape to the flow-induced stresses which compete with the
surface tension. This competition is characterised by introducing the Weber
number , whilst the plastron deformation is estimated via the
aspect ratio . While noticeable distortions are locally observed, the
plastron becomes more and more spherical in average (i.e. )
as far as increases. In comparison to the reference spheres,
high deformation of the air plastron plastron (oblate shape) leads to lift and
drag increase, whereas low deformation (spherical shape) yields lift and drag
mitigation. Accordingly, taking into account the plastron deformation provides
an attractive way to explain the somehow discordant results reported in other
studies at comparable Reynolds numbers. If confirmed by additional studies, our
findings would imply that plastron compliance and its feedback on the flow,
which are currently neglected in most theoretical works and numerical
simulations, must be accounted for to design super-hydrophobic surfaces and/or
predict their performances
Separation between coherent and turbulent fluctuations. What can we learn from the Empirical Mode Decomposition?
The performances of a new data processing technique, namely the Empirical
Mode Decomposition, are evaluated on a fully developed turbulent velocity
signal perturbed by a numerical forcing which mimics a long-period flapping.
First, we introduce a "resemblance" criterion to discriminate between the
polluted and the unpolluted modes extracted from the perturbed velocity signal
by means of the Empirical Mode Decomposition algorithm. A rejection procedure,
playing, somehow, the role of a high-pass filter, is then designed in order to
infer the original velocity signal from the perturbed one. The quality of this
recovering procedure is extensively evaluated in the case of a "mono-component"
perturbation (sine wave) by varying both the amplitude and the frequency of the
perturbation. An excellent agreement between the recovered and the reference
velocity signals is found, even though some discrepancies are observed when the
perturbation frequency overlaps the frequency range corresponding to the
energy-containing eddies as emphasized by both the energy spectrum and the
structure functions. Finally, our recovering procedure is successfully
performed on a time-dependent perturbation (linear chirp) covering a broad
range of frequencies.Comment: 23 pages, 13 figures, submitted to Experiments in Fluid
Photoinductive degradation of two pesticies by natural dissolved organic matter under simulated sunlight
This study focused on the photochemical degradation of two herbicides : isoproturon (IPU) and diuron (DIU), that are two of the most abundant phenylureas found in surface and ground waters in France and classified as prioritary substances by European Directive (DCE). Sunlight irradiation was performed by a solar simulator Atlas Suntest CPS+ (290 nm < λ < 700 nm, 250 W/m2). Pesticide concentrations used in the experiments were approximately 1 µM. Photodegradation efficiencies have been measured for aqueous solutions of IPU and DIU, in the presence of DOM (20 mg/L) isolated from surface waters. LC-MS analysis was performed in order to identify possible photoproducts
Nicole Colin, Deutsche Dramatik im französischen Theater nach 1945. Künstlerisches Selbstverständnis im Kulturtransfer
C’est une somme passionnante et novatrice qu’a publiée Nicole Colin aux Éditions transcript sous le titre Deutsche Dramatik im französischen Theater nach 1945.La découverte des auteurs dramatiques de langue allemande par les metteurs en scène français à partir de 1950 y est analysée à la lumière des mutations structurelles que connaît le système théâtral français dans la seconde moitié du xxe siècle. Cet ouvrage vient combler une lacune par son approche méthodologique : là où les études exist..
- …