Optimisation d'une aile d'avion par la méthode de décomposition de la traînée

RÉSUMÉ Le projet de recherche actuel évalue la capacité d’une méthode de décomposition de la traînée aérodynamique à mener un processus d’optimisation vers une aile d’avion plus efficace. La décomposition de la traînée est une méthode permettant d’isoler et de quantifier les différents types de traînées qui sont : la traînée d’onde, la traînée visqueuse, la traînée induite et la traînée numérique. Tous ces types de traînées proviennent de phénomènes physiques à l’exception de la traînée numérique. Cette dernière, inhérente à toutes solutions numériques de mécanique des fluides, se manifeste comme une fausse traînée aérodynamique et découle essentiellement d’erreurs de discrétisation, d’erreurs de troncature et de l’ajout de dissipation artificielle. L’intégration d’une méthode de décomposition à un processus d’optimisation permet théoriquement d’atténuer l’influence de la fausse traînée sur ce processus et de guider celui-ci vers une meilleure aile d’avion. Pour ce projet de recherche, la traînée aérodynamique du profil RAE2822 et de l’aile d’avion NASA CRM est minimisée en utilisant des processus avec et sans décomposition de traînée. Les résultats sont ensuite analysés et comparés. Pour tous ces processus d’optimisation, une méthode à base radiale est utilisée pour paramétriser les géométries et l’algorithme Pointer de Isight Simulia ® est employé comme algorithme d’optimisation----------ABSTRACT The current research project assesses the ability of a drag decomposition method in steering an optimization process towards a more efficient aircraft wing design. This method allows for aerodynamic drag to be broken down into different types of drag, which are namely: wave drag, viscous drag, induced drag, and spurious drag. Apart from spurious drag, all these types of aerodynamic drag are the result of physical phenomena. For its part, spurious drag is inherent to all numerical solutions and is mainly due to discretization errors, truncation errors and the use of artificial dissipation by most solvers to smooth large gradients. Joining a drag decomposition method to an optimization process may theoretically mitigate the detrimental influences spurious drag may have on an optimization process and may, therefore, lead it to a better wing design. For this research project, the aerodynamic drag of the RAE2822 airfoil and the NASA CRM wing have been minimized using optimization processes with and without a drag decomposition method. The results of these optimizations are then analyzed and compared. For these optimization processes, a radial basis function method has been used to parameterize the geometries. The optimization algorithm used was Pointer from Isight Simulia ®

Development and Validation of a New Boundary Condition for Intake Analysis with Distortion

The design of an intake for a gas turbine engine involves CFD-based investigation and experimental assessment in an intake test rig. In both cases, the engine is represented by a mass flux sink, usually positioned a few fan radii aft of the real fan face. In general, this approach is sufficient to analyze intake geometry for low distortion at the fan face, because in this case the interaction of the fan with the inlet flow can be neglected. Where there are higher levels of distortion at the fan face, the interaction could become more significant and a different approach would be preferable. One alternative that takes into account the interaction in such cases includes the fan in the analysis of the intake, using either a steady or unsteady flow model approach. However, this solution is expensive and too computationally intensive to be useful in design mode. The solution proposed in this paper is to implement a new boundary condition at the fan face which better represents the interaction of the fan with the flow in the air intake in the presence of distortion. This boundary condition includes a simplified fan model and a coupling strategy applied between the fan and the inlet. The results obtained with this new boundary condition are compared to full 3D unsteady CFD simulations that include the fan

Impact of Wind Direction, Wind Speed, and Particle Characteristics on the Collection Efficiency of the Double Fence Intercomparison Reference

The accurate measurement of snowfall is important in various fields of study such as climate variability, transportation, and water resources. A major concern is that snowfall measurements are difficult and can result in significant errors. For example, collection efficiency of most gauge–shield configurations generally decreases with increasing wind speed. In addition, much scatter is observed for a given wind speed, which is thought to be caused by the type of snowflake. Furthermore, the collection efficiency depends strongly on the reference used to correct the data, which is often the Double Fence Intercomparison Reference (DFIR) recommended by the World Meteorological Organization. The goal of this study is to assess the impact of weather conditions on the collection efficiency of the DFIR. Note that the DFIR is defined as a manual gauge placed in a double fence. In this study, however, only the double fence is being investigated while still being called DFIR. To address this issue, a detailed analysis of the flow field in the vicinity of the DFIR is conducted using computational fluid dynamics. Particle trajectories are obtained to compute the collection efficiency associated with different precipitation types for varying wind speed. The results show that the precipitation reaching the center of the DFIR can exceed 100% of the actual precipitation, and it depends on the snowflake type, wind speed, and direction. Overall, this study contributes to a better understanding of the sources of uncertainty associated with the use of the DFIR as a reference gauge to measure snowfall

Risk factors for Coronavirus disease 2019 (Covid-19) death in a population cohort study from the Western Cape province, South Africa

Risk factors for coronavirus disease 2019 (COVID-19) death in sub-Saharan Africa and the effects of human immunodeficiency virus (HIV) and tuberculosis on COVID-19 outcomes are unknown. We conducted a population cohort study using linked data from adults attending public-sector health facilities in the Western Cape, South Africa. We used Cox proportional hazards models, adjusted for age, sex, location, and comorbidities, to examine the associations between HIV, tuberculosis, and COVID-19 death from 1 March to 9 June 2020 among (1) public-sector “active patients” (≥1 visit in the 3 years before March 2020); (2) laboratory-diagnosed COVID-19 cases; and (3) hospitalized COVID-19 cases. We calculated the standardized mortality ratio (SMR) for COVID-19, comparing adults living with and without HIV using modeled population estimates.Among 3 460 932 patients (16% living with HIV), 22 308 were diagnosed with COVID-19, of whom 625 died. COVID19 death was associated with male sex, increasing age, diabetes, hypertension, and chronic kidney disease. HIV was associated with COVID-19 mortality (adjusted hazard ratio [aHR], 2.14; 95% confidence interval [CI], 1.70–2.70), with similar risks across strata of viral loads and immunosuppression. Current and previous diagnoses of tuberculosis were associated with COVID-19 death (aHR, 2.70 [95% CI, 1.81–4.04] and 1.51 [95% CI, 1.18–1.93], respectively). The SMR for COVID-19 death associated with HIV was 2.39 (95% CI, 1.96–2.86); population attributable fraction 8.5% (95% CI, 6.1–11.1)

Comparison of Two Models for Radiative Heat Transfer in High Temperature Thermal Plasmas

Numerical simulation of the arc-flow interaction in high-voltage circuit breakers requires a radiation model capable of handling high-temperature participating thermal plasmas. The modeling of the radiative transfer plays a critical role in the overall accuracy of such CFD simulations. As a result of the increase of computational power, CPU intensive methods based on the radiative transfer equation, leading to more accurate results, are now becoming attractive alternatives to current approximate models. In this paper, the predictive capabilities of the finite volume method (RTE-FVM) and the P1 model are investigated. A systematic comparison between these two models and analytical solutions are presented for a variety of relevant test cases. Two implementations of each approach are compared, and a critical evaluation is presented

Multi-disciplinary design optimization of transonic fan blade design using analytical target cascading

Analytical Target Cascading (ATC), a multilayer multidisciplinary design optimization (MDO) formulation employed on a transonic fan design problem. This paper demonstrates the ATC solution process including the specific way of initializing the problem and handling system level and discipline level targets. High-fidelity analysis tools for aerodynamics, structure and dynamics disciplines have been used. A multi-level parameterization of the fan blade is considered for reducing the number of design variables. The overall objective is the transonic fan efficiency improvement under structure and dynamics constraints. This design approach is applied to the redesign of the NASA Rotor 67. The overall study explores the key points of implementation of ATC on transonic fan design practical problem.</jats:p