Spectral Volume Method: application to Euler equations and performance appraisal

The compact high-order "Spectral Volume Method" designed for conservation laws on unstructured grids is presented. Its spectral reconstruction is exposed briefly and its applications to the Euler equations are presented through several test cases to assess its accuracy and stability. Comparisons with usual methods such as MUSCL show the superiority of SVM. The SVM method arises as a high-order accurate scheme, geometrically flexible and computationally efficient

Assessment of the Spectral Volume Method on inviscid and viscous flows

The compact high-order "Spectral Volume Method" designed for conservation laws on unstructured grids is presented. Its spectral reconstruction is exposed briefly and its applications to the Euler equations are presented through several test cases to assess its accuracy and stability. Comparisons with classical methods such as MUSCL show the superiority of SVM. The SVM method arises as a high-order accurate scheme, geometrically flexible and computationally efficient

Numerical study on parametrical design of long shrouded contra-rotating propulsion system in hovering

The parametrical study of Shrouded Contra-rotating Rotor was done in this paper based on 2D axisymmetric simulations. The calculations were made with an actuator disk as double rotor model. It objects to explore and quantify the effects of different shroud geometry parameters mainly using the performance of power loading (PL), which could evaluate the whole propulsion system capability as 5 Newton total thrust generation for hover demand. The numerical results show that: The increase of nozzle radius is desired but limited by the flow separation, its optimal design is around 1.15 times rotor radius, the viscosity effects greatly constraint the influence of nozzle shape, the divergent angle around 10.5° performs best for any chosen nozzle length; The parameters of inlet such as leading edge curvature, radius and internal shape do not affect thrust greatly but play an important role in pressure distribution which could produce most part of shroud thrust, they should be chosen according to the reduction of adverse pressure gradients to avoid the risk of boundary separation

Design of Optimum Torsionally Flexible PropRotors for Tilt-Body MAVs

This paper presents a methodology to design the optimum proprotor for tilt-body microair-vehicles (TB-MAV) with efficient global propulsion system and long flight endurance in both cruise and hover modes. The TB-MAV developed at ISAE, which is called MAVion, was used as a baseline in the design process. To acquire maximum performance of TB-MAV’s global propulsion system, an efficient optimization process of the proprotor propulsion system was carried out. The optimization process consists of two-step inverse design methods. The first step determines the optimal operating conditions in terms of power and rotational speed of proprotor and the second step designs the optimal blade geometry in terms of twist angle distribution. The optimal blade twist distribution along the blade was computed using the Glauert’s strip theory for minimum energy loss condition. Meanwhile, the optimal operating conditions were determined by the motor outputs corresponding to high motor efficiency. A comparison of performance in terms of total efficiency and flight endurance between the optimized flexible proprotor, the optimized rigid proprotor, optimized propeller and optimized rotor is presented

Marcel Pepin, l’homme du contre-pouvoir

Cette recherche sur la pensée de Marcel Pepin présente cet important leader syndical et montre sa contribution comme acteur du système de relations industrielles dans la deuxième moitié du XXe siècle. Inspirée des travaux de Fernand Dumont et de Louis-Marie Tremblay, portant notamment sur les idéologies et la philosophie du syndicalisme québécois, cette recherche permet d’examiner la pensée de Marcel Pepin selon les trois dimensions suivantes : la définition de soi, la définition du milieu et la définition du rapport entre soi et les autres. Une cinquantaine d’indicateurs regroupés à l’intérieur de treize composantes permettent de raffiner cette analyse de contenu. Les documents analysés sont principalement les écrits produits par Marcel Pepin, notamment ses rapports moraux produits alors qu’il préside la CSN, ainsi que les nombreux textes présentés comme conférencier, professeur d’université ou comme président du Mouvement socialiste. Ardent syndicaliste, ses actions visaient une plus grande justice sociale et économique. Homme d’une grande rigueur, il savait lier l’aspect intellectuel de sa pensée à des gestes concrets sur le terrain. Pour lui, le syndicalisme, par le biais de la CSN, était le moyen tout désigné pour apporter de nouvelles idées et des méthodes pour changer le système en place. Appelé à endosser un rôle de leader pendant toute sa carrière, Marcel Pepin a su exercer avec doigté une direction axée sur l’intelligence et le respect afin de créer ce contre-pouvoir essentiel à l’atteinte de ses idéaux. Cette recherche nous permet aussi de voir l’interrelation entre un leader et l’organisation qu’il représente.This research on the thought of Marcel Pepin presents this important labor-union leader and shows his contribution as a player in the industrial relations system in the second half of the twentieth century. Inspired by the work of Fernand Dumont and Louis-Marie Tremblay, which focused namely on ideology and philosophy of Quebec’s unionism movement, this research examines the thought of Marcel Pepin in the following three dimensions: self-definition, the definition of the environment and the definition of the relationship between self and others. Some fifty indicators grouped within thirteen components allow to refine this content analysis. The documents analysed here are mainly writings by Marcel Pepin, including the moral reports that he produced while presiding the CSN, as well as numerous texts presented as a speaker, university professor and as president of the Mouvement socialiste. Ardent unionist, his actions aimed at greater social and economic justice. Man of great rigor, he knew how to bind the intellectual aspect of his thought to concrete actions on the ground. He believed that unionism, through the CSN, was the most appropriate vehicle to bring new ideas and methods to change the system in place. Called upon to exercise a leader’s role throughout his career, he has skillfully exerted a management focused on intelligence and respect in order to create the against-power essential to the achievement of this ideals. This research also allows us to see the interrelationship between a leader and his organization

Revisiting Froude’s Theory for Hovering Shrouded Rotor

This paper extends Froude’s momentum theory for free propellers to the analysis of shrouded rotors. A one-dimensional analytical approach is provided, and a homokinetic normal inlet surface model is proposed. Formulations of thrusts and power for each system component are derived, leading to the definition of optimum design criteria and providing insight into the global aerodynamics of shrouded rotors. In the context of micro-air vehicles applications, assessment of the model is conducted with respect to numerical data. Overall, comparison between numerical and analytical results shows good agreement and highlights the sensitivity of the model to viscous effects

A High-Order Compact Limiter Based on Spatially Weighted Projections for the Spectral Volume and the Spectral Differences Method

This paper exposes the theoretical developments needed to design a class of spatially weighted polynomial projections used in the definition of a compact limiter dedicated to high-order methods. The spectral volume framework and its integral representation of the solution is used to introduce the degree reduction of the polynomial interpolation. The degree reduction is conducted through a linear projection onto a smaller polynomial space. A particular care is taken regarding the conservativity property and results in a parametric framework where projections can be monitored with spatial weights. These projections are used to define a simple and compact high-order limiting procedure, the SWeP limiter. Then, numerical evaluations are performed using the spectral differences method for the mono-dimensional Euler equations and demonstrate the high-order behavior of the SWeP limiter

The Mixed Lineage Kinase Leucine-Zipper Protein Kinase Exhibits a Differentiation-Associated Localization in Normal Human Skin and Induces Keratinocyte Differentiation upon Overexpression

Leucine-zipper protein kinase/dual leucine zipper bearing kinase/mitogen-activated protein kinase-upstream kinase is a recently described protein serine/threonine kinase which belongs to the mixed lineage kinase family. The overall pattern of expression of the leucine-zipper protein kinase/dual leucine zipper bearing kinase/mitogen-activated protein kinase-upstream kinase gene in embryonic and adult mouse tissues suggested that this kinase could be involved in the regulation of epithelial cell proliferation and differentiation. In order to get more insights into the potential role of leucine-zipper protein kinase in these cellular processes, we characterized its expression in normal human skin, both at the mRNA and protein levels. In situ hybridization, western blotting, and indirect immunofluorescence studies were conducted to localize leucine-zipper protein kinase on various human skin tissues. This is one of the first reports that leucine-zipper protein kinase has a very precise pattern of expression in human skin epithelia, as both mRNA and protein are restricted to the granular layer of the epidermis and inner root sheath of hair follicles. Detection of leucine-zipper protein kinase protein on skin from various body sites, donors of different ages as well as on reconstructed human skin always reveals that leucine-zipper protein kinase is present only in the very differentiated keratinocytes of epidermis and hair follicles. To determine directly whether leucine-zipper protein kinase exhibits any effect on cell growth and differentiation, keratinocytes were transfected with an expression vector harboring the leucine-zipper protein kinase cDNA. The presence of this construct in keratinocytes results in growth arrest together with a concomitant increase in filaggrin expression. Collectively, our results indicate that leucine-zipper protein kinase plays an active part in cellular processes related to terminal differentiation of epidermal keratinocytes

A conservative multirate explicit time integration method for computation of compressible flows

In the context of high fidelity simulation of compressible flows (LES and DNS) at extreme scale (small time steps) on massively parallel supercomputers, explicit time integration methods are widely used since they both have a good computational cost trade-off at small time scales and require a small number of parallel communications, thus having little impact on the parallel strategy compared to their implicit counterpart. However, the synchronous nature of the time integration of the governing equations can be a severe constraint when the stability condition is applied globally since the time scales are related to the flow properties and the mesh resolution, which may show strong variations throughout the computational domain. We propose to further improve the efficiency (CPU wall-time reduction) of explicit Runge-Kutta methods by developing a multirate explicit time integration method, by means of flux interpolation at the boundary between cells evolving with different time-steps, which enforces the conservation properties. In terms of computational efficiency, the presented multirate time integration method is easy to implement in pre-existing Eulerian compressible Navier-Stokes codes, requires less additional memory storage, and provides a considerable speed-up while being robust and preserving the order of accuracy of the legacy explicit Runge-Kutta time integration method. The multirate time integration method is implemented in the massively parallel finite volume and high-order (spectral difference) \IC3 code \cite{Bodart2016ECCOMAS} (fork of the solver \CharlesX), but it can also be applied to any flux-based spatial method such as discontinuous Galerkin or others. For a targeted $y^+=0.2$ on the developed turbulent channel flow test case at $Re_{\tau} = 392$, a 2.48 effective speedup is obtained versus an expected theoretical speedup of 2.53

On the properties of high-order least-squares finite-volume schemes

High-order finite-volume schemes based on polynomial least-squares methods are an active research topic for the discretization of hyperbolic equations as they allow to obtain high-order spatial discretization schemes in arbitrary meshes. However, few studies have analyzed their performance in good-quality/near-to-uniform meshes, which are commonly used as a meshing strategy in zones where turbulent effects are important. In this paper, the theoretical numerical properties of commonly used least-squares (LSQ) k-exact high-order finite volume schemes are studied in one-dimensional and in several two- dimensional meshes (with some remarks regarding their properties in three-dimensional meshes). These results are compared to those obtained using fully-constrained polynomial reconstructions only compatible with structured meshes. The numerical properties of the schemes are investigated through the von Neumann analysis methodology applied to the one-dimensional and two-dimensional finite volume formulation, including temporal discretization errors. This analysis is also extended to non-uniform and unstructured two- dimensional meshes. At last, the schemes are tested with several numerical experiments using the linear advection, the Euler equations and the Navier-Stokes equations. The analysis of both studies yields similar conclusions regarding the numerical errors and stability of the different studied schemes showing that the high-order least-squares finite volume schemes yield stable and robust results across different uniform and non-uniform unstructured meshes. However, their performance is heavily degraded in simulations with low mesh resolution compared to schemes specially catered to structured meshes. On the other hand, the latter schemes lack stability and robustness in general structured meshes and its formulation cannot be straightforwardly extended to unstructured meshes. Moreover, this work shows that the use of weighted-LSQ can drastically improve the results of LSQ schemes in under-resolved simulations