19 research outputs found
High speed visualizations of the cavitating vortices of 2D mixing layer
No full textThe present study investigates experimentally vortex dynamics of a cavitating two-dimensional mixing layer at a high Reynolds number in order to determine the effect of growth and collapse of cavitation.
The dynamics and the topology of the vorticity regions corresponding to the low pressure area where cavitation effects take place are studied from the single phase state to highly cavitating conditions. LDV techniques are used in order to characterize the pattern of the turbulent single phase flow. Highspeed visualizations have been performed using a specific image processing of time series to highlight the behaviour and dynamics of the vapour phase. Visualizations, image processing and statistical analysis enable the estimation of the convective velocity and the shedding frequency of the cavitating Kelvin–Helmholtz vortices. The measured visual vapour thickness grows linearly as the Kelvin–Helmholtz instability develops and its expansion rate stays constant for the range of cavitation levels studied. The vortex pairing phenomenon is also analysed. Results show that the spatial development of the mixing area is slightly affected by the vapour phase allowing a self-similar behaviour of the mean motion
Traitement d'image utilisant la POD et la DMD pour l'étude du développement de la cavitation sur un NACA0015
No full textLe travail présenté ici concerne l’étude des instabilités de poche de cavitation se développant sur un profil bidimensionnel de type NACA0015 à haut nombre de Reynolds (Re=5 105). Les conditions expérimentales sont relatives à des poches quasistatique, périodique, transitoire et apériodique correspondant à des valeurs de s/2a de 5.75, 5, 4.3 et 3.58. Le comportement dynamique de la cavité est étudié à l’aide d’outils mathématiques de type décomposition orthogonale en modes propres (POD) et décomposition en mode dynamique (DMD) appliqués à des images issus de visualisations rapides. L’originalité de ce travail est l’application de ces méthodes pour décrire le comportement dynamique (2D et 3D) spatio-temporel de la poche en fonction des conditions de cavitation dans le but de mettre en évidence les effets 3D inhérents à l’instabilité soit de jet rentrant soit de propagation d’une onde à l’interface de la poche à l’origine du caractère pulsant de celle-ci
A Vectoring Thrust Coaxial Rotor for Micro Air Vehicle: Modeling, Design and Analysis
No full textThe growing interest of rotary wing UAVs, for military and civilian applications, has encouraged designers to consider miniaturized configurations, more efficient in terms of endurance, payload capability and maneuverability. The purpose of this paper is to study a new configuration of coaxial rotor as applied to a micro aerial vehicle (MAV) with the intention to guarantee the vehicle maneuverability while removing unnecessary control surfaces which would increase wind gust sensitivity. Coaxial rotor configurations maximize the available rotor disk surface and allow for torque cancelation. Tilting rotors may allow for the vehicle control
Lattice Boltzmann simulation and analysis of the turbulent wake of a MAV hovering near the ground
No full textPhysical analysis of the coherent motion during hysteretic static stall of Naca foil using proper orthogonal decomposition
No full textAt static stall of airfoil, an hysteretic behavior (corresponding to an abrupt loss of lift) has been observed leading to a partially detached flow (called state I, upper increasing angle branch) and massively separated flow (called state II, lower decreasing angle branch). In order to predict the type of hysteretic loop that may occur or to quantify unsteady oscillatory flow in the near wake, experiments have been performed to explore laminar separation, transition and detachment of the boundary layer (Mittal and Saxena, 2000) but the keyphysical properties of the vortex shedding establishment during hysteretic loop is not clearly understood
