Analyse numérique d'un décollement alterné dans un diffuseur radial transsonique

L'écoulement dans le diffuseur radial d'un compresseur centrifuge est analysé à régime partiel à partir de calculs RANS. Des calculs mono-canal, stationnaires et instationnaires, sont menés dans un premier temps. En dessous d'un certain débit, les calculs instationnaires chorochroniques ne convergent plus et une basse fréquence apparaît au cours du calcul. A la suite de ce constat, d'autres types de calculs instationnaires sont envisagés, incluant plusieurs canaux par roue. La structure observée dans le diffuseur est alors assez surprenante : à bas débit, l'écoulement s'organise sur un motif de deux canaux adjacents. Au sein d'une paire de canaux adjacents, une dissymétrie de fonctionnement est observée, d'où l'appellation de décollement alterné. Ce schéma à deux canaux alternés est stable et les décollements associés (sur la face en pression dans un canal, sur la face en dépression dans le voisin) sont stationnaires

Improvement of the Parallel Compressor Model and Application to Inlet Flow Distortion

This paper introduces a semi-analytical approach which enables one to deal with distorted inflow in axial fans or compressors. It is inspired by the classical parallel compressor (PC) theory but relies on a local flow-loading coefficient formalism. It is applied to non-uniform flow conditions to study the aerodynamic behavior of a low-speed fan in response to upstream flow distortion. Experimental measurements and 3D RANS simulations are used to evaluate the prediction of fan performance obtained with the local PC method. The comparison proves that, despite its simplicity, the present approach enables to correctly capture first order phenomena, offering interesting perspectives for an early design phase if different fan geometries are to be tested and if the upstream distortion maps are available

Body-Force Modelling of Multiple Distributed Propulsors with Boundary Layer Ingestion

A coupled wing-propulsor configuration is modelled in order to extract the coupled lift, drag or thrust coefficients and to investigate a methodology for in-flight energy recovery via loaded windmilling. The baseline wing geometry and flight conditions of the configuration are representative of the Daher TBM900 aeroplane. The propulsors are modelled using RANS Body Force Modelling (BFM) in order to analyse the non-homogenous incoming flow at computation cost somewhat coherent with preliminary design. The main coupled phenomena such as Boundary Layer Ingestion (BLI), suction-side flow acceleration, propulsor-to-propulsor influence, lateral loads and increased operability are discussed; numerical modifications to the baseline Hall-Thollet model are introduced, providing control-by-power of the propulsor. In continuiation of previous in-house efforts, the simulations were carried out for a typical takeoff case. The obtained results provide preliminary evidence for the possibility of energy recovery by loaded windmilling, which lays groundwork for further investigations at other flight conditions and more complex configurations

Generalised Methodology for Sizing of Air Vehicles with Hybrid-Electric Propulsion

In the context of increasing attention given to aircraft propulsive system electrification by the aeronautical community, Department of Aerodynamics, Energetics and Propulsion at ISAE-SUPAERO is undertaking an effort to develop a preliminary sizing tool for aeroplanes with propulsive architectures ranging between conventional gas turbine and different hybrid-electric solutions. The baseline used to initiate this work is semi-empirical handbook sizing method by Jan Roskam. The method is firstly extended by introducing a generic propulsive power architecture space, described parametrically by an array of power hybridisation parameters. Furthermore, a proposal of modified Breguet range equation is given for fuel weight iterations including batteries. With these upgrades, a trial sizing run was performed on a Pilatus PC-12 test case to verify the functioning of the developed tool. A more comprehensive study of an equivalent aeroplane powered with various hybrid-electric solutions is then presented, along with an associated parametric study. Mission performance results of all the hybrid architectures are inferior to the ones for the fuel-based baseline, with the most promising solutions indicated by the results being series and parallel hybrid architectures. While the tool produces qualitatively coherent results, the quantitative validity thereof is yet to be ascertained. Notably, the hybrid range equation needs to be further placed under scrutiny and its applicability for mission sizing of all the hybrid architectures of interest is to be validated. In the long run, the work will look into other current limitations such as lack of possibility to consider battery recharge in the mission calculations or lack of capability to perform sensitivity studies

Nonlinear Refraction and Absorption of Ag 29 Nanoclusters: Evidence for Two-Photon Absorption Saturation

International audienc

Body Force Modeling of the Aerodynamics of a Low-Speed Fan under Distorted Inflow

New propulsive concepts, such as boundary layer ingestion, involve stronger interactions between the engine and its environment, and are thus more complex flows compared to classical architectures. Usual turbomachinery design tools are inadequate, and new numerical methodologies are needed to accurately predict the engine performance with affordable CPU resources. The present paper examines the relevance of a reduced-order modeling approach—the body force modeling (BFM) method—for a low-speed cooling fan with inflow distortion. The formulation itself accounts for the blade metal blockage and compressibility effects, and it relies on a semiempirical loss model, independent of computational fluid dynamics (CFD) calibration. The BFM results obtained in the present work are assessed against full-annulus unsteady Reynolds-averaged Navier-Stokes (URANS) results and experiments. The comparison shows that the BFM approach successfully quantifies the fan stage performance. Furthermore, the distortion transfer across the stage is examined and the flow patterns observed are found to be the same as in the URANS results and in the measurements. Hence, this methodology, coming at a low CPU cost, is well-adapted to the early design phase of an innovative propulsion system

Body force modeling of the aerodynamics of a low-speed fan under distorted inflow

New propulsive concepts such as Boundary Layer Ingestion involve stronger interactions between the engine and its environment, and thus more complex flows compared to classical architectures. Usual turbomachinery design tools are inadequate, and new numerical methodologies are needed to accurately predict the engine performance with affordable CPU resources. The present paper examines the relevance of a reduced-order modeling approach, the body force modeling (BFM) method, for a low-speed cooling fan with inflow distortion. The formulation itself accounts for the blade metal blockage, compressible effects and it relies on a physics-based loss model, independent of CFD calibration. The BFM results obtained in the present work are assessed against full-annulus URANS results and experiments. The comparison shows that the BFM approach successfully quantifies the fan stage performance. Furthermore, the distortion transfer across the stage is examined and the flow patterns observed are found to be the same as in the URANS results and in the measurements. Hence, this methodology, coming at a low CPU cost, is well-adapted to the early design phase of an innovative propulsion system

Universal scaling of plasmon coupling in metal nanostructures: Checking the validity for higher plasmonic modes using second harmonic generation

The universal scaling of plasmon coupling in metallic nanostructures is now a well-established feature. However, if the interaction between dipolar plasmon modes has been intensively studied, this is not the case of the coupling between higher order ones. Using Mie theory extended to second harmonic generation, we investigate the coupling between quadrupolar plasmon modes in metallic nanoshells. Like in the case of dipolar plasmon modes, a universal scaling behavior is observed in agreement with the plasmon hybridization model

Functional characterization of SlscADH1, a fruit-ripening associated short-chain alcohol dehydrogenase of tomato

A tomato short-chain dehydrogenase-reductase (SlscADH1) is preferentially expressed in fruit with a maximum expression at the breaker stage while expression in roots, stems, leaves and flowers is very weak. It represents a potential candidate for the formation of aroma volatiles by interconverting alcohols and aldehydes. The SlscADH1 recombinant protein produced in Escherichia coli exhibited dehydrogenase-reductase activity towards several volatile compounds present in tomato flavour with a strong preference for the NAD/NADH co-factors. The strongest activity was observed for the reduction of hexanal (Km = 0.175 mM) and phenylacetaldehyde (Km = 0.375 mM) in the presence of NADH. The oxidation process of hexanol and 1-phenylethanol was much less efficient (Kms of 2.9 and 23.0 mM, respectively), indicating that the enzyme preferentially acts as a reductase. However activity was observed only for hexanal, phenylacetaldehyde, (E)-2-hexenal and acetaldehyde and the corresponding alcohols. No activity could be detected for other aroma volatiles important for tomato flavour, such as methyl-butanol/methyl-butanal, 5-methyl-6-hepten-2-one/5-methyl-6-hepten-2-ol, citronellal/citronellol, neral/nerol, geraniol. In order to assess the function of the SlscADH1 gene, transgenic plants have been generated using the technique of RNA interference (RNAi). Constitutive down-regulation using the 35S promoter resulted in the generation of dwarf plants, indicating that the SlscADH1 gene, although weakly expressed in vegetative tissues, had a function in regulating plant development. Fruitspecific down-regulation using the 2A11 promoter had no morphogenetic effect and did not alter the aldehyde/alcohol balance of the volatiles compounds produced by the fruit. Nevertheless, SlscADH1-inhibited fruit unexpectedly accumulated higher concentrations of C5 and C6 volatile compounds of the lipoxygenase pathway, possibly as an indirect effect of the suppression of SlscADH1 on the catabolism of phospholipids and/or integrity of membranes

Second harmonic scattering from silver nanocubes

The second harmonic light scattered from silver nanocubes dispersed in an aqueous suspension is investigated. The first hyperpolarizability is determined and corrected for resonance enhancement. It is shown to be similar to that of silver nanospheres with a comparable volume. The polarization-resolved analysis of the scattered harmonic intensity exhibits a surface response strongly modulated by the different multipolar field contributions. As a result, the shape does not play a leading role anymore for nanoparticles with a centrosymmetric shape when retardation must be considered. Comparing the right angle and forward-scattered polarized intensity responses, the unequal balance of the eight nanocube corners' contribution to the total response is revealed despite the high degree of centrosymmetry of the cubic shape. It is then demonstrated with a simple model that the nanocubes' first hyperpolarizability exhibits an octupolar tensorial symmetry. The surface integral equation method calculations are finally provided to investigate further the role of the corners’ and edges’ rounding