SAM

Développement et validation d'un modèle de cavitation à poche sur hydrofoil et pale d'hélice

PHOEMSAPTHAWEE, Surasak — Tue, 01 Jan 2008 00:00:00 GMT

Développement et validation d'un modèle de cavitation à poche sur hydrofoil et pale d'hélice PHOEMSAPTHAWEE, Surasak; LEROUX, Jean-Baptiste; LAURENS, Jean-Marc; DENISET, François FRANCAIS Un module de cavitation à poche a été développé et implémenté sur un code potentiel hélice. La méthode pour représenter la cavitation à poche utilise les vitesses de transpiration qui permettent de dévier la condition de glissement sans modification de la géométrie. Cette modélisation permet une simulation très rapide par rapport aux différentes solutions passant par la résolution des équations de Navier-Stokes en diphasique. Le modèle est validé par comparaison avec des essais expérimentaux sur hydrofoils en 2D et en 3D. Ses performances sont également comparées à d’autres simulations numériques. ENGLISH A sheet cavitation module have been developed and applied in a BEM code for calculating propeller performance. This simulation, in order to represent the sheet cavitation, employs the transpiration velocities technique which allows the deviation of slip condition points without any modification of the geometry. The method provides a very rapid simulation compared to a two-phase Navier-Stokes simulations. The model is validated by comparison with the results of experimental trials performed on hydrofoils in 2D and 3D. Its performances are also compared with other numerical simulations.

A potential-flow based flight simulator for an underwater glider

PHOEMSAPTHAWEE, Surasak — Tue, 01 Jan 2013 00:00:00 GMT

A potential-flow based flight simulator for an underwater glider PHOEMSAPTHAWEE, Surasak; LE BOULLUEC, Marc; LAURENS, Jean-Marc; DENISET, François Underwater gliders are recent innovative types of autonomous underwater vehicles (AUVs) used in ocean exploration and observation. They adjust their buoyancy to dive and to return to the ocean surface. During the change of altitude, they use the hydrodynamic forces developed by their wings to move forward. Their flights are controlled by changing the position of their centers of gravity and their buoyancy to adjust their trim and heel angles. For better flight control, the understanding of the hydrodynamic behavior and the flight mechanics of the underwater glider is necessary. A 6-DOF motion simulator is coupled with an unsteady potential flow model for this purpose. In some specific cases, the numerical study demonstrates that an inappropriate stabilizer dimension can cause counter-steering behavior. The simulator can be used to improve the automatic flight control. It can also be used for the hydrodynamic design optimization of the devices. Keywords: underwater glider; potential flow; Newton-Euler equation; autonomous underwater vehicles (AUVs); flight simulator

Effect of the laminar separation bubble induced transition on the hydrodynamic performance of a hydrofoil

DELAFIN, Pierre-Luc — Wed, 01 Jan 2014 00:00:00 GMT

Effect of the laminar separation bubble induced transition on the hydrodynamic performance of a hydrofoil DELAFIN, Pierre-Luc; DENISET, François; ASTOLFI, Jacques Andre The present study deals with the effect of the laminar separation bubble (LSB) induced transition on the lift, drag and moment coefficients of a hydrofoil. A 2D numerical study, based on the SST γ –Reθ transition model of ANSYS-CFX⃝R , is conducted on a NACA66 hydrofoil. Angles of attack range from −4° to 14° and the chord-based Reynolds number is Re = 7.5 × 105. An experimental investigation is carried out in the French naval academy research institute’s hydrodynamic tunnel based on the measurements of lift, drag and moment. Experiments on a smooth, mirror finished, hydrofoil enable comparison with RANS calculations using the transition model. Experiments with a roughness added on the leading edge enable comparison with RANS calculations using the SST fully turbulent model. For angles of attack below 6°, the LSB triggered laminar to turbulent transition of the boundary layers of the suction and pressure sides is located near the trailing edge of the smooth NACA66. As the angle of attack reaches 6°, the LSB suddenly moves to the leading edge on the suction side while transition is located at the trailing edge on the pressure side. The smooth hydrofoil shows higher CL and CM and lower CD than the rough leading edge one from −4° to 6°. Both experiments lead to the same coefficients from 6° to 14°. The calculations show that both models are in good agreement with their corresponding experiments. Velocity profiles in the vicinity of the LSB at an angle of attack of 2° and pressure coefficients of the calculations using the transition model are compared with published experimental studies and show very good agreement. The SST γ –Reθ transition model proves to be a relevant, even essential, prediction tool for lifting bodies operating at a moderate Reynolds number. The authors thank the technical staff of IRENav for their contribution to the experimental set up.

Computational and experimental investigation of flow over a transient pitching hydrofoil

DUCOIN, Antoine — Thu, 01 Jan 2009 00:00:00 GMT

Computational and experimental investigation of flow over a transient pitching hydrofoil DUCOIN, Antoine; ASTOLFI, Jacques Andre; DENISET, François; SIGRIST, Jean-François The present study is developed within the framework of marine structure design operating in transient regimes. It deals with an experimental and numerical investigation of the time–space distribution of the wall-pressure field on a NACA66 hydrofoil undergoing a transient up-and-down pitching motion from 0 to 15 at four pitching velocities and a Reynolds number Re¼ 0.75 106. The experimental investigation is performed using an array of wall-pressure transducers located on the suction side and by means of time–frequency analysis and Empirical Modal Decomposition method. The numerical study is conducted for the same flow conditions. It is based on a 2D RANS code including mesh reconstruction and an ALE formulation in order to take into account the foil rotation and the tunnel walls. Due to the moderate Reynolds number, a laminar to turbulent transition model was also activated. For the operating flow conditions of the study, experimental and numerical flow analysis revealed that the flow experiences complex boundary layer events as leading-edge laminar separation bubble, laminar to turbulent transition, trailing-edge separation and flow detachment at stall. Although the flow is relatively complex, the calculated wall pressure shows a quite good agreement with the experiment provided that the mesh resolution and the temporal discretization are carefully selected depending on the pitching velocity. It is particularly shown that the general trend of the wall pressure (low frequency) is rather well predicted for the four pitching velocities with for instance a net inflection of the wall pressure when transition occurs. The inflection zone is reduced as the pitching velocity increases and tends to disappear for the highest pitching velocity. Conversely, high frequency wall-pressure fluctuations observed experimentally are not captured by the RANS model. Based on the good agreement with experiment, the model is then used to investigate the effects of the pitching velocity on boundary layer events and on hydrodynamic loadings. It is shown that increasing the pitching velocity tends to delay the laminar-to-turbulence transition and even to suppress it for the highest pitching velocity during the pitch-up motion. It induces also an increase of the stall angle (compared to quasi-static one) and an increase of the hysteresis effect during pitch-down motion resulting to a significant increase of the hydrodynamic loading.

Optimisation de la loi de calage d’un propulseur cycloïdal

HAUVILLE, Frederic — Mon, 01 Jan 2018 00:00:00 GMT

Optimisation de la loi de calage d’un propulseur cycloïdal HAUVILLE, Frederic; LECUYER-LE BRIS, Romain; DENISET, François; FASSE, Guillaume Les propulseurs cycloïdaux sont caractérisés par la rotation de plusieurs pales autour d’un axe vertical, associée à un mouvement de chaque pale autour de son axe propre. L’objet de cet article concerne l’étude des lois de calage d’un propulseur à axe transverse dans le domaine de la propulsion cycloïdale navale. Avec ce type de propulsion, deux modes de cinématiques sont observés : le mode épicycloïdal utilisé pour les basses vitesses d’avance de navire (<1) et le mode trochoïdal pour les hautes vitesses (>1). L’objectif final est de pouvoir établir des lois de calage, pour chacun des deux modes, maximisant l’effort propulsif. Les lois de calage sont d’abord définies cinématiquement par une approche quasi statique en utilisant la base de données SANDIA. Pour un paramètre d’avance particulier (=1,6), la loi de calage est corrigée par un processus itératif afin de prendre en compte la dynamique de l’écoulement au sein de la turbine par un calcul URANS 2D. Les lois de calage sont ensuite approchées par des fonctions paramétrables, afin de permettre leur optimisation par une méthode d’optimisation par processus Gaussiens (EGO). Dans le but de diminuer le temps d’optimisation EGO et de mieux comprendre l’influence des paramètres dans le processus d’optimisation, une périodicité et une non parité sont imposées pour ces fonctions à 2 ou 3 paramètres. Le processus d’optimisation est mis en œuvre sur l’approche quasi statique pour valider la méthode. Des essais futurs dans le bassin du centre Ifremer de Boulogne-sur-Mer avec la plateforme académique SHIVA seront mis en place pour une optimisation expérimentale des lois de calage pour les deux modes de fonctionnement. Cycloidal propulsors are characterized by the rotation of several blades around a vertical axis, associated with a movement of each blade around its own axis. The purpose of this article is to study the pitch laws of a transverse axis propulsor in the field of cycloidal marine propulsion. With this type of propulsion, two kinematic modes are observed: the epicycloidal mode used for low ship speeds (<1) and the trochoidal mode for high speeds (>1). The final aim is to be able to establish pitch laws, for each of those two modes, maximizing thrust. The pitch laws are first defined kinematically by a quasi-static approach using the SANDIA database. For a particular advance parameter (=1,6), the pitch law is corrected by an iterative process in order to take into account the flow dynamics within the turbine by a 2D URANS calculation. The pitch laws are then modeled by configurable functions, in order to allow their optimization using surrogate-model based optimization methods (EGO). In order to reduce the EGO optimization time and to better understand the influence of parameters in the optimization process, a periodicity and odd parity are imposed for these 2 or 3-parameter functions. The optimization process is implemented on the quasi-static approach to validate the method. Future tests in the facilities of the Ifremer center in Boulogne-sur-Mer with the SHIVA academic platform will be conducted for an experimental optimization of the pitch laws for the two operating modes.

Performance Improvement of a Darrieus Tidal Turbine with Active Variable Pitch

DELAFIN, Pierre-Luc — Fri, 01 Jan 2021 00:00:00 GMT

Performance Improvement of a Darrieus Tidal Turbine with Active Variable Pitch DELAFIN, Pierre-Luc; DENISET, François; ASTOLFI, Jacques Andre; HAUVILLE, Frederic Vertical axis turbines, also called Darrieus turbines, present interesting characteristics for offshore wind and tidal applications but suffer from vibrations and a lower efficiency than the more conventional horizontal axis turbines. The use of variable pitch, in order to control the angle of attack of the blades continuously during their rotation, is considered in this study to overcome these problems. 2D blade-resolved unsteady Reynolds-Averaged Navier–Stokes (RANS) simulations are employed to evaluate the performance improvement that pitching blades can bring to the optimal performance of a three-straight-blade vertical axis tidal turbine. Three pitching laws are defined and tested. They aim to reduce the angle of attack of the blades in the upstream half of the turbine. No pitching motion is used in the downstream half. The streamwise velocity, monitored at the center of the turbine, together with the measurement of the blades’ angle of attack help show the effectiveness of the proposed pitching laws. The decrease in the angle of attack in the upstream half of a revolution leads to a significant increase in the power coefficient (+40%) and to a better balance of the torque generated in the upstream and downstream halves. Both torque and thrust ripples are therefore significantly reduced.

Effects on cavitation inception of leading and trailing edge flaps on a high-performance hydrofoil

MOHAMMED ARAB, Fatiha — Fri, 22 Jul 2022 00:00:00 GMT

Effects on cavitation inception of leading and trailing edge flaps on a high-performance hydrofoil MOHAMMED ARAB, Fatiha; AUGIER, Benoit; DENISET, François; CASARI, Pascal; ASTOLFI, Jacques Andre For the high-performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. The present work investigates solutions to delay the onset of cavitation thanks to a combination of leading edge and trailing edge flaps. Both numerical studies based on a potential code and experiments in a hydrodynamic tunnel are conducted in order to assess the effect of specific geometric parameters on the hydrodynamic performance and cavitation inception. Experimentally the effect on the hydrodynamic performances and cavitation buckets of a 70% chord trailing edge flap and a 20% chord leading edge flap of NACA 0012 is investigated. The hydrofoils are manufactured using a 3D printer technique at IRENav and tested in the cavitation tunnel of the institute at an inflow velocity of 6.67 m/s (Re = 10⁶). The results show that the lift coefficient increases and the cavitation bucket gets larger with the flaps deflection. The experimental results are in good agreement with the numerical ones by highlighting the capacity of the flaps to enlarge both the operating domain and the cavitation bucket of the hydrofoil.