Linear stability analysis in rotating frames and its application to fan blade transition prediction

The in-house linear stability solver of ONERA has been extended to rotating frames. The theoretical details of linear stability theory in rotating frames are given. Validation is performed by comparing against the well-known Ekman layer case. Moreover, two new compressible validation cases are proposed for which very good agreement is as well obtained. Linear stability analysis is then performed on a flow around a rotating fan blade, obtained by means of RANS computation. By neglecting or taking into account rotation in the linear stability equations, the effect of rotation on transition mechanisms is investigated. Moreover, N-factors are computed for transition prediction. The present results show that rotation hardly modifies the growth-rate of Tollmien-Schlichting instabilities. However, rotation destabilizes stationary cross-flow waves but not enough to trigger transition

Linear stability analysis in rotating frames and its application to fan blade transition prediction

A linear stability solver has been extended to rotating frames. The theoretical details of the linear stability theory in rotating frames are given. Validation is performed by comparing against the well-known Ekman layer case. Moreover, two new compressible validation cases are proposed for which very good agreement is well obtained. Linear stability analysis is then performed on a rotating fan blade with incoming flow, which is obtained by means of a Reynolds-averaged Navier–Stokes computation. By neglecting or taking into account rotation in the linear stability equations, the effect of rotation on transition mechanisms is investigated. Moreover, N factors are computed for transition prediction. The present results show that rotation hardly modifies the growth rate of Tollmien–Schlichting instabilities. However, rotation destabilizes stationary crossflow waves, but not enough to trigger transition

Unsteady Body Force Methodology for Fan Operability Assessment under Clean and Distorted Inflow Conditions

With more complex aircraft architectures, fast and cost-effective design iterations are key to improve overall fuel efficiency. This paper proposes to revisit a low-order unsteady modeling approach to replace costly full annulus URANS simulation. Unsteady Body Force Methods (UBFM) could allow a significant cost reduction for fan distortion ingestion and operability assessment. In this approach, the bladed area in the computational domain is replaced by source terms in the Navier–Stokes equations, and the cost of the simulation is reduced by a factor of 26. The operability of the fan is evaluated with and without distortion in order to assess the accuracy of the model. Previously published results of URANS simulations performed on the same fan subject to an unsteady vortex ingestion are used as reference.1 The results show that our UBFM is able to predict rotating stall cells, with patterns and rotating speed similar to the URANS data

Future Aircraft and the Future of Aircraft Noise

In order to cope with increasing air traffic and the requirement to decrease the overall footprint of the aviation sector - making it more sustainably and acceptable for the whole society - drastic technology improvements are required beside all other measures. This includes also the development of novel aircraft configurations and associated technologies which are anticipated to bring significant improvements for fuel burn, gaseous and noise emissions compared to the current state and the current evolutionary development. Several research projects all over the world have been investigating specific technologies to address these goals individually, or novel - sometimes also called "disruptive" - aircraft concepts as a whole. The chapter provides a small glimpse on these activities - mainly from a point of view of recent European funded research activities like Horizon2020 projects ARTEM, PARSIFAL, and SENECA being by no-way complete or exhaustive. The focus of this collection is on noise implications of exemplary novel concepts as this is one of the most complicated and least addressed topics in the assessment of aircraft configurations in an early design stage. Beside the boundary layer ingestion concept, the design process for a blended wing body aircraft is described, a box-wing concept is presented and an outlook on emerging supersonic air transport is given

Quadrupole splitting and isomer shifts in Te oxides investigated using nuclear forward scattering

Nuclear forward scattering by 125Te is a viable alternative to conventional 125Te Mössbauer spectroscopy avoiding all source related issues. Using reference compounds with known hyperfine parameters and Te oxides exhibiting stereochemically active lone pairs, we show that nuclear forward scattering by 125Te can be reliably used to extract quadrupole splitting energy and relative isomer shift. The rough correlation between Te-Ocoordination and quadrupole splitting energy as put forward by Takeda and Greenwood (J. Chem. Soc. Dalton, 2207, 1975), is corroborated by the presented results

Subsidence de champ pétrolier suivie par le satellite Sentinel-1 : étude du champ de Patos-Marinza, Albanie

International audienc

Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion

On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells

Subsidence de champ pétrolier suivie par le satellite Sentinel-1 : étude du champ de Patos-Marinza, Albanie

International audienc

Chronologie et répartition spatiale des établissements fortifiés tardo-laténiens du Plateau et du Jura suisses

International audienceDer vorliegende Gemeinschaftsartikel diskutiert die spätlatènezeitliche Siedlungslandschaft im heutigen Schweizer Mittelland und Jura. Trotzteilweise lückenhaftem Forschungsstand können im Untersuchungsgebiet zwanzig befestigte Siedlungen lokalisiert und, dank einer aufReferenzfundkomplexen basierenden Regionalchronologie, datiert werden. Die Zeitstellung und Belegungsdauer der Siedlungen geben Einblickein die vorherrschende Siedlungsdynamik. Während sich im Umland Genfs und im Jura eine stabile Siedlungslandschaft abzeichnet, zeigt sich imMittelland am Übergang der Stufen LT D1b zu LT D2a bei der Art der befestigten Siedlungen ein grösserer Wechsel: Praktisch alle grossen befestigtenSiedlungen werden verlassen und es entstehen kleinere Neugründungen. Der Prozess setzt sich in der Stufe LT D2b fort mit der Entstehungneuer, stärker militärisch geprägter Siedlungen.Despite the sometimes incomplete nature of the archaeological record for the late Iron Age, it is still possible to date the twenty known fortifiedsites in the Swiss Plateau and Jura. The chronology is established from a corpus of settlements in these regions, which have been recentlyenriched with new find assemblages. Thanks to the site chronology, trajectories in their occupation can be identified. While a certain continuitycharacterizes the sites of Geneva and in the Jura, a rupture appears clearly in the sites in the Swiss Plateau at the time of transition from La TèneD1b and D2a, when almost all of the large fortified sites of the Plateau were abandoned in favour of smaller foundations. From La Tène D2bonwards, these were then complemented by new sites with an essentially military character (traduction Andrew Lawrence)