Stability and instability of hydromagnetic Taylor–Couette flows

Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor–Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm¯=√Re⋅Rm (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm≫1 while for Pm≪1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm≪1 the onset of the instability scales with Re while it scales with Rm¯ for Pm≫1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm=1. It scales with Re for Pm→0 and with Rm for Pm→∞. The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect

Far-Field Drag Extraction fromNumerical Solutions and Wake Surveys

The paper focuses on ONERA drag extraction methods from numerical simulations and flow field wake surveys. A new far-field drag extraction software allows, thanks to the face-based data structure, to extract drag as well from structured (elsA cell-centred) as from unstructured (TAU cell-vertex) RANS solutions

Aerodynamic design and preliminary optimization of a commercial PrandtlPlane aircraft

The paper aims to present the phases and the achievements of the aerodynamic design activities carried out on a box-wing aircraft, called PrandtlPlane, proposed as a sustainable solution for the fulfilment of the more and more demanding requirements of the fast-growing air transport. The activities here presented are included in the on-going Project PARSIFAL (“Prandtlplane ARchitecture for the Sustainable Improvement of Future AirpLanes”), funded by European Union under the Horizon2020 Program. Starting from the conceptual aerodynamic design of the PrandtlPlane architecture, the paper follows the development of the aerodynamic design, dealing with the preliminary definition of a reference configuration, which performances have been evaluated with both low and high fidelity tools, and the optimization procedure for the improvement of cruise performance

CONCEPTUAL DESIGN STUDIES OF UNCONVENTIONAL CONFIGURATIONS

The potential of unconventional configurations to reduce the fuel consumption of future aircraft is investigated in the European Clean Sky 2 (ITD Airframe) ONERA-DLR project NACOR (New Aircraft Concepts Research - Call for Core Partners Wave 1). Two design missions are considered: a short/medium range mission (SMR) based on the requirements of an Airbus A320, and a business jet (BJ) mission. In this paper, an overview of the activities considering the conceptual aircraft design phase including initial high fidelity studies is provided