Vers une optimisation aéroacoustique avec méthode adjointe pour la réduction de bruit d'hélice

International audienceThe objective of the work described in this paper is to set up and validate an adjoint based method for blade shape optimisation aiming at propeller noise reduction. As a first step toward a comprehensive propeller noise optimisation, the present study focuses on the loading noise of a single propeller isolated and without incidence. In this respect, an acoustic objective function is derived, based on the Hanson-Léwy steady loading noise formulation. After defining this function, the first step is to derive its sensitivities to mesh and aerodynamic field parameters. Once implemented in the ONERA adjoint based optimisation procedure, the acoustic function predictions are compared to a classical Ffowcs Williams and Hawkings approach, and the sensitivities are validated by comparison with the finite differences method.L'objectif des travaux décrit dans ce papier est de mettre en place et valider une méthode basée sur l'adjoint pour l'optimisation de forme visant à la réduction du bruit d'hélice. En tant que première étape vers une optimisation complète du bruit d'hélice, la présente étude se concentre sur le bruit de charge d'une hélice simple isolée et sans incidence. A cet égard, une fonction objectife acoustique est développée, basée sur la formulation de bruit de charge stationnaire de Hanson-Léwy. Après avoir défini cette fonction, la première étape est de dériver ses sensibilités aux paramètres de maillage et de champ aérodynamique. Une fois implémentée dans la procédure d'optimisation par adjoint de l'ONERA, les prédictions de la fonction acoustique sont comparées à une approche classique de Ffowcs Williams et Hawkings, et les sensibilités sont validées par comparaison à la méthode des différences finies

Aeroacoustic optimization of a supersonic business jet

A multiobjective optimization has been developed for the design of the fuselage of a supersonic business jet. The attention is focused on the coupling between the CFD solver (Num3sis) developed at INRIA and the acoustic propagation code TRAPS in use at ONERA. The accuracy of the propagation prediction over the entire domain is fundamental for obtaining a valuable solution. In order to achieve this objective an iterative procedure for unstructured mesh adaptation is developed. Mesh adaptation has the potential to reduce the computational time increasing the density of the mesh only where required. After a brief introduction of the different tools required to solve the problem in analysis, the optimization is carried out in a hybrid process in which an evolutionary strategy (ES) is used first (exploration), and a gradient based method second for improve the accuracy (exploitation). The Pareto optimal curve is evaluated using the Pareto Archive Evolutionary Strategy[17] and with a classical Adapted Weighted Sum method[18] in order to compare the final results. This design methodology has the ability to generate non intuitive configuration that do not rely on the engineer's experience. Combining CAD modeling, CFD, acoustic propagation analysis and shape multicriterion optimization enhance the potential of investigation of such a complex physical phenomenon

Contribution à l'optimisation de la forme aérodynamique d'un avion de transport supersonique en vue de la réduction du bang sonique

Le travail de thèse présenté est centré autour du développement d'une boucle d'optimisation de forme aérodynamique supersonique basée sur un algorithme génétique avec comme objectif la détermination d'une forme optimisée sous contrainte de bang sonique. La contribution au développement de la boucle intervient à trois niveaux du cycle de calcul. La première partie concerne l'amélioration des performances de l'outil de calcul aérodynamique TORPEDO. Pour cela, des méthodes visant à augmenter la robustesse ainsi que la capacité à capturer des chocs est affinée y sont implémentées. Le deuxième axe de l'étude est le développement et l'implémentation d'un module de calcul de bang sonique afin qu'il constitue un critère d'optimisation de forme. Dans un dernier temps, les travaux précédents sont regroupés dans la boucle d'optimisation ainsi que l'algorithme génétique GADO auquel elle fait appel. La paramétrisation des éléments géométriques définissant les éléments de la population étudiée s'appuie sur les contraintes relatives à la physique des phénomènes, et notamment celle du bang sonique. Enfin, la boucle est utilisée pour déterminer une forme optimale pour différents cas de contraintes.The work which is presented here is focused on the development of a supersonic aircraft aerodynamic shape optimization module based on a genetic algorithm. The objective is to determine the optimized form by considering an additional constraint on the sonic boom signature. The work is related to three different levels of the computational cycle. The first part concerns the enhancement of the performance of the aerodynamic solver TORPEDO. Two methods are implemented in order to increase the robustness of the solver and improve its shock capturing capacity. The second part is devoted to the development and implementation of a sonic boom computation module in order to determine a sonic boom constraint. In the last part the works mentioned above are used to build an optimization module based on the genetic algorithm GADO. The parametrization of the geometrical elements characterizing the shape of the aircrafts are chosen in order to take into account constraints related to several physical phenomena, including the sonic boom. The module is then used to determine optimal shapes for different constraints.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Scalable Clustered Active Subspaces for Kriging in High Dimension

International audienceUseful parameterisations of shapes for engineering models often climb from many tens to a few hundreds design variables, potentially jeopardising usual optimisation techniques. Surrogate models are intractable when parameter numbers exceed a few tens, and gradient descent through adjoint computation in high-dimension is threatened by potential multimodality. Dimension reduction addresses these problems nicely. This paper aims to improve upon the Active Subspaces dimension reduction method by applying a combination of active subspaces in subregions of the design space, where their use of the objective function’s gradients will exploit useful local information to discover specific trends instead of trying to identify global trends over an entire design space. The partitioning of the input space is done through Gaussian Mixture Model clustering, where the authors assume the distribution of the joint inputs/outputs to be a mixture of Gaussians. This GMM clustering is used to drive a Support Vector Machines (SVM) based supervised classifier. The SVC classifier’s margin (the maximal separation distance between points of different clusters) is chosen using cross validation in order to set an optimal width for the overlapping zones. The use of overlapping increases prediction accuracy at the boundaries between clusters, an improvement over recombination methods typically found in the literature. The local expert of choice is Kriging, in part due to its built-in variance prediction

The TELFONA Pathfinder Model, a second look

Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim to obtain the capability of laminar flow testing of the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Pre-test numerical analysis results demonstrated that the Pathfinder wing pressure distribution was adequate to provide calibration test points. The ETW tests provided pressure distribution data and transition position obtained from images using the Cryogenic Temperature Sensitive Paint Method (cryroTSP). The evaluation of this data with several transition prediction tools was used to establish the transition Nfactor values for ETW. In this work, after test CFD solutions are obtained using numerical Navier-Stokes solutions. Stability analysis is performed using the local stability 2-N factor method. In the first part of this work, it is shown that for the range of flow conditions tested, the Pathfinder wing pressure distribution is sufficiently insensitive to different parameters like span, transition position and turbulence model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental data and numerical data. In the third part the numerical analysis and experimental data are used complementarily

High Reynolds number transition experiments in the ETW test facility with the pathfinder model

The Pathfinder model was designed in the course of the TELFONA European Research Project as a calibration tool to evaluate the transonic, cryogenic ETW facility for laminar flow testing, and assess the possibility for studies of NLF or HLF wings in ETW. The Pathfinder wing is a simplified, low taper, swept wing with an optimized profile allowing almost linear evolution of the N-factors in a wide range of flow conditions, especially designed for a precise estimation of transition N-factors. Temperature sensitive paint is used to allow optical detection of the transition location, and a series of pressure taps is used for measuring the pressure distribution. This general paper will cover model design, pre-test numerical evaluation, instrumentation and measurement methods, and will present a first set of cases selected for stability analysis and transition evaluation. Various tools for stability analysis and transition predictions will be tested, from local stability theory with the envelope methods to nonlocal theories taking into account curvature and non-local effects, based on the parabolized stability equations or on a multiple scale approach for compressible flows

Complementary Numerical and Experimental Data Analysis of the ETW Telfona Pathfinder Wing Transition Tests

Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Results of pre-test numerical analysis demonstrated that the Pathfinder wing pressure distribution was adequate for providing calibration test points. The ETW tests provided pressure distribution data while transition positions were determined from images using the Cryogenic Temperature Sensitive Paint Method (cryoTSP). The evaluation of this data with several transition prediction tools was used to establish the transition N-factor values for ETW. In this work, after-test CFD solutions are obtained using numerical Navier-Stokes solutions. In the first part of this work, numerical results are given which verify the requirements of the Pathfinder wing as a calibration model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental and numerical data. In the third part the correlation of experimental transition locations to critical N-factors is summarized for ETW Test Phases I and II. In the fourth part numerical analysis and experimental data are used complementarily