A Parabolised Stability Equation based Broadband Shock-Associated Noise Model

International audienceWavepacket models have been used extensively to predict the noise produced from turbulent subsonic and supersonic jets. Such wavepackets, which represent the organised structures of the flow, are solutions to the linearised Navier-Stokes equations. Using a kinematic two-point model, Wong et al. [1] have indicated the importance of incorporating coherence decay in modelling broadband shock-associated noise (BBSAN) in supersonic jets. In this work, we aim to improve the model by using solutions from linear parabolised stability equations (PSE) to model the wavepacket part of the BBSAN source. The two-point coherence of the wavepackets is obtained from large-eddy simulation (LES) data of a M j = 1.5 fully-expanded isothermal supersonic jet [2]. The aim is to build a dynamic sound-source model for BBSAN that would improve on the simplified line-source model proposed by Wong et al. [3]. We find that a frequency dependent coherence decay length scale is important in order to suppress the higher-order harmonic peaks [4] and to obtain the correct BBSAN peak shape. Moderate agreement up to St = 1 was found between the current noise predictions and those from experimental data. I. Nomenclature ω = wavepacket frequency θ = azimuthal coordinate c s n = amplitude coefficient of the shock cells G = Green's function k s = shock-cell wavenumber k h = hydrodynamic wavenumber L = longitudinal extent of wavepacket L c = coherence length of wavepacket m = azimuthal mode number M j = ideally-expanded Mach number r = radial coordinate u s = shock cell velocity fluctuation u t = wavepacket fluctuationŝ u * ω = velocity fluctuations at a frequency ω x = axial coordinat

Two years of a pluralistic work: ASN published a white paper on tritium

Radioactive releases in the environment around civilian nuclear facilities have significantly decreased over the last few decades, with the exception of tritium. In late 2007, papers published in the UK (RIFE 11 report, study by the HPA’s Advisory Group on Ionising Radiation (AGIR)) raised questions as to the behaviour of tritium in the environment. Given this context, ASN wanted to get a clear analysis of the existing studies into the issue and in early 2008 decided to establish two independent pluralistic working groups. Two main points of the discussions are on the bioaccumulation and the biological effects

Colistin: alternative for the treatment of swine colibacillosis with the respect of human health protection

From suckling up to slaughter, pigs experience frequently enteritis outbreaks caused by various pathogens, most of them from bacterial origin. Preliminary epidemiological studies have shown that Escherichia coli are the most often isolated bacteria during diarrhoeas. Quinolones and penicillins are the most frequently used treatments when colibacillosis is suspected. Many reports have shown these bacteria became frequently resistant when these antibiotics were massively used. Moreover, many cross resistances were demonstrated in these antibiotic families, leading to a major zootechnical and zoonotic concern.</p

A complex-valued resonance model for axisymmetric screech tones in supersonic jets

We model the resonance mechanism underpinning generation of A1 and A2 screech tones in an under-expanded supersonic jet. Starting from the resonance model recently proposed by Mancinelli et al. (Exp. Fluids, vol. 60, 2019, p. 22), where the upstream-travelling wave is a neutrally stable guided-jet mode, we here present a more complete linear-stability-based model for screech prediction. We study temperature and shear-layer thickness effects and show that, in order to accurately describe the experimental data, the effect of the finite thickness of the shear layer must be incorporated in the jet-dynamics model. We then present an improved resonance model for screech-frequency predictions in which both downstream- A nd upstream-travelling waves may have a complex wavenumber and frequency. This resonance model requires knowledge of the reflection coefficients at the upstream and downstream locations of the resonance loop. We explore the effect of the reflection coefficients on the resonance model and propose an approach for their identification. The complex-mode model identifies limited regions of frequency-flow parameter space for which the resonance loop is amplified in time, a necessary condition for the resonance to be sustained. This model provides an improved description of the experimental measurements

Screech-tone prediction using upstream-travelling jet modes

Abstract: The purpose of this paper is to characterise and model the A1 and A2 screech modes in supersonic jets operating at off-design conditions. The usual screech-modelling scenario involves a feedback loop between a downstream-travelling Kelvin–Helmholtz instability wave and an upstream-travelling acoustic wave. We review state-of-the-art screech-frequency prediction models and associated limitations. Following the work of Edgington-Mitchell et al. (J Fluid Mech 855, 2018), a new prediction approach is proposed where the feedback loop is closed by the upstream-travelling jet modes first discussed in Tam and Hu (J Fluid Mech 201:447–483, 1989) in lieu of the free-stream sound waves. The Kelvin–Helmholtz and upstream-travelling jet modes are obtained using a cylindrical vortex-sheet model. The predictions provide a better agreement with experimental observations than does the classical screech-prediction approach. Screech dynamics associated with the staging process is explored through a wavelet analysis, highlighting that staging involves mutually exclusive switching that is underpinned by non-linear interactions. Graphical abstract: [Figure not available: see fulltext.]

Radioactivity, environment and the public: Building an index of environmental radioactivity

In the end of 2007, ASN launched an internal reflexion on the information of the public on the radioactivity levels in the environment. The aim was to develop a radioactivity environment scale or index, based on existing scales used for air pollution. After the presentation of a demonstration model by ASN in 2008 to HCTISN, a working group (WG) was constituted in the beginning of 2009 by ASN with stakeholders with the approval in March 2009 of the goals to be reached by this index: a communication instrument to qualify the information of the radioactivity levels in the environment, consistent with INES, particularly when sanitary consequences may occur, easy to elaborate from the available measured values of radioactivity and always usable for any location, independently of an incidental or accidental situation

Micromorphology and submicroscopy of isotropic and anisotropic Al/Si coatings in a quaternary Allier terrace, (France)

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