Optimisation du rendement propulsif d'une aile battante par la Méthode de Surface des Réponses

Dans la présente étude, le rendement propulsif d’un profil d’aile NACA0012 en mouvement de battement est optimisé à un nombre de Reynolds de Re = 1.1 × 10^4. Il s’agit d’une étude numérique 2D réalisée caractériser l’évolution du rendement propulsif en fonction des paramètres cinématiques de aile battante. Pour résoudre les équations de Navier-Stokes autour de l'aile battantes nous avons utilisé un solver 2D instationnaire avec un couplage Pression-Vitesse SIMPLEC. Pour la discrétisation spatiale on a utilisé le schéma convectif MUSCL de 3ème ordre avec une discrétisation temporelle du premier ordre. L'amplitude du mouvement de pilonnement, l’amplitude maximale du mouvement de tangage, la fréquence de battement et l’angle de phase entre ces deux mouvements sont considérés comme variables d’optimisation. Le battement du profil d’aile est réalisé grâce à l’utilisation des fonctions UDF et du module maillage dynamique, disponible dans Ansys Fluent. La Méthode des Surfaces des Réponses (MSR) est utilisé pour l’optimisation du rendement propulsif en fonction des paramètres cinématiques de l'aile. Un plan d’expérience complet avec 5 évaluations pour chaque variable a été élaboré pour conduire les simulations et obtenir les différentes combinaisons des paramètres de contrôle. Pour la prédiction de la réponse nous avons calculé les coefficients du méta-modèle de la MSR en utilisant des fonctions polynomiale . Le processus d’optimisation du méta-modèle est piloté par la technique du recuit simulé disponible sous MATLAB. Les résultats montrent que la méthode des surfaces de réponses est suffisamment robuste et donne, approximativement, les mêmes résultats que la méthode de montée de gradient. L’erreur relative entre le rendement propulsif obtenu par approximation en utilisant la RSM et celui obtenu par simulation numérique est très petite. Cela justifie très largement le recours à cette méthode. A la lumière des résultats obtenus, en plus de sa rapidité, la méthode des surfaces de réponse présente l’avantage d’être facile à implémenter, cependant, l’approximation quadratique qu’elle utilise est limitée à un certain nombre de variables d’optimisation

Active control of the leakage flow by air injection into the rotational shroud or the fixed carter of an axial fan composed of hollow blades

In axial fan, the static pressure difference between the suction and the pressure side of the impeller produces a leakage flow through the blade and the casing. This secondary flow occurs in the opposite direction of the working flow and has a negative impact on the overall performances. It tends to reduce the pressure coefficient, the efficiency and the fan operating range while increasing the noise level. That is why many studies dealt with ways to reduce this leakage flow. In this paper, the study focusses on the control of the secondary flow by air injection. Two ways to control this flow are compared. In a first case, the air is ejected from the fixed casing and in a second case the air exit from the rotating shrouds. In both configurations, the ejected air has a direction to counter the leakage flow. To realize the second configuration, a new method to build fan with hollow blades was developed. This new kind of fan allows having internal flows which could exit by any area of the fan. The results obtained by the active controls on the fan characteristic and the efficiency are presented in this article

Taylor-Couette flow control by amplitude variation of the inner cylinder cross-section oscillation

The hydrodynamic stability of a viscous fluid flow evolving in an annular space between a rotating inner cylinder with a periodically variable radius and an outer fixed cylinder is considered. The basic flow is axis-symmetric with two counter-rotating vortices each wavelength along the whole filled system length. The numerical simulations are implemented on the commercial Fluent software package, a finite-volume CFD code. It is aimed to make investigation of the early flow transition with assessment of the flow response to radial pulsatile motion superimposed to the inner cylinder cross-section as an extension of a previous developed work in Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)] where a comparative controlling strategy is applied to the outer cylinder. The same basic system is considered with similar calculating parameters and procedure. In Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)], it is concluded that for the actuated outer cylinder and relatively to the non-controlled case, the critical Taylor number, Tac1, characterizing the first instability onset illustrated by the piled Taylor vortices along the gap, increases substantially to reach a growing rate of 70% when the deforming amplitude is ε = 15%. Interestingly, when this controlling strategy is applied to the inner cylinder cross-section with a slight modification of the actuating law, this tendency completely inverts and the critical Taylor number decreases sharply from Tac1 = 41.33 to Tac1 = 17.66 for ε = 5%, corresponding to a reduction rate of 57%. Fundamentally, this result is interesting and can be interpreted by prematurely triggering instabilities resulting in rapid development of flow turbulence. Practically, important applicative aspects can be met in several industry areas where substantial intensification of transport phenomena (mass, momentum and heat) is needed such as in chemical reactors, combustors, heat exchangers and cylindrical water filters

Automated design process of a fixed wing UAV maximizing endurance

In this study, we aim to reduce the time of the wing design and the optimization of the performances of unmanned aerial vehicles during the preliminary design through an automated framework using only open-source software (OpenVSP: VSPAERO with Parasite Drag Tool, and Python).NonPeerReviewe

Numerical Investigation of Parietal Pressure Distribution on NACA0012 Wing Controlled by Micro-cylindrical Rod Arranged in Tandem

International audienceThe aim of this study is to investigate the influence of disturbed freestream flow by a small cylinder on the laminar separated boundary layer over NACA0012 wing operating at a Reynolds number of Rec = 4.45 × 10 5. A detailed parametric investigations for the rod are performed using numerical simulations coupled with transition sensitive closure model (γ −Re θ,t) seeking for the optimal passive control parameters. Firstly, the use of such steady RANS model has been successfully accurate in capturing the separation induced transition on the baseline wing suction surface. Secondly, the rod location was scaled according to the formation length of vortices behind the micro-cylinder for which the aerodynamic loads are very sensitive. The effects of three rod diameter ratios (d/c = 0.67%, 1.33% and 2%) on the laminar separation bubble and aerodynamic performances were examined. It was observed that the qualitative analysis of the flow structures revealed the mechanisms of the control device for the aerofoil performance improvements in which the rod wake exerted considerable effects on LSB size, pressure coefficient and flow streamlines. Particularly, it contributes to eliminate the boundary layer separation with pronounced decrease of 75% by energizing the shear layer over a significant extent, resulting in a mean drag dropping of 73% at 12 • incidence, and a lift enhancement of about 23% at 15 •

Numerical Investigation of Parietal Pressure Distribution on NACA-0012 Wing Controlled by Micro-cylindrical Rod Arranged in Tandem

International audienceThe primary aim of this study is to investigate the influence of an upstream cylindrical rod on the laminar separated boundary layer that develops on a symmetrical profile wing operating at a Reynolds number of Re c = 4.45 × 10 5. To get further insight onto the aerodynamic performances of this wing at low Reynolds number, numerical simulations with a transitional turbulence model are performed with the ANSYS-Fluent software. The passive flow control technique is applied by setting up a cylindrical rod of diameter d upstream of a NACA-0012 airfoil of chord lenght c. The dimensionless rod diameter with respect to the chord length is d/c = 2/150. Simulations are carried out over a wide range of angles of attack for both the baseline case and the controlled case by the passive proposed technique. The effects of the wing incidence on the parietal pressure distributions on the suction surface of the wing are examined. The results show that the Laminar Separation Bubble that is formed on the upper surface is moving upstream toward the leading edge as the incidence is increased. Moreover, qualitative analysis of the transition zone revealed that presence of the wing in the rod wake exerted considerable effect on the pressure coefficient. Particularly, this passive turbulence generator contributes to eliminate the boundary layer separatio